Strategic synthesis of FLPClusters toward catalysis

Domain: physics
Published: 2026-03-12
Editorial outcome: major_revision

Abstract
FLPClusters, which are structurally precise metal clusters incorporating Frustrated
Lewis Pairs (FLPs), represent a promising class of FLP catalysts. Although FLPClusters have
emerged only recently, their precise and strategic synthesis remains underdeveloped. Herein, we
report the approach for the strategic synthesis of FLPClusters featuring well-defined, tailorable,
and accessible FLP active sites. Our approach utilizes bis(2-(diphenylphosphino)phenyl)ether
(DPEphos) as a rigid surface ligand. The two phosphine termini of DPEphos bridge adjacent metal
atoms, while the central ether oxygen atom (Lewis base) is geometrically constrained, enabling
the formation of stable FLPs with copper atoms (Lewis acid) on the cluster surface. By modulating
the structure of ancillary thiolate ligands, we successfully synthesized three FLPClusters.
These
FLPClusters demonstrate high catalytic activity in the hydrolytic oxidation of organosilanes to
silanols. Both theoretical and experimental studies confirm that the catalysis is FLP-driven.
Crucially, their catalytic performance scales with the number of FLP sites present.

Introduction
Frustrated Lewis Pairs (FLPs) have attracted significant interest in chemical and materials
science.1-3 Comprising sterically or geometrically hindered Lewis acid (LA) and Lewis base (LB)
sites that cannot undergo classical adduct formation, FLPs exhibit a distinctive “push-pull” effect.4-
6 This enables efficient activation of diverse small molecules—including H , CO , SO , N O, NO,
2 2 2 2
and CO—leading to catalytic capabilities.7-10 A key advantage of FLPs lies in their exceptional
design flexibility: LB donors (e.g., N, O, S) and LA acceptors (e.g., B, Al, Ce, other metal centers)
offer broad tunability.11-14 Furthermore, the FLP concept extends beyond homogeneous catalysis,
proving compatible with heterogeneous systems such as zeolites, metal oxide surfaces, and
metal/covalent organic frameworks.15-17 These heterogeneous FLP catalysts demonstrate
remarkable efficiency and recyclability in small-molecule activation.18-21

The FLP concept has recently been introduced into the field of ligand-protected, atomically
precise noble metal clusters (designated as FLPClusters).22 Representing a promising class of
inorganic-organic hybrid materials, ligand-protected noble metal clusters exhibit broad
applications.23-32 Their atomically precise molecular structures, exceptional catalytic performance
across diverse chemical transformations, and structure-dependent catalytic properties establish
them as ideal model systems for investigating structure-catalysis relationships and reaction
mechanisms.33-37 Surface functionalization with tailored ligands has emerged as a strategy to create
FLP sites and enhance the catalytic performance of these metal clusters. For example,
incorporating 2-methoxybenzenethiolate ligands onto the [Cu S (RS) (PPh ) ]2+ cluster (Cu ,
34 7 18 3 4 34
RSH = 2-methoxybenzenethiol) facilitates the formation of FLPs between surface copper atoms
(acting as LAs) and the oxygen atoms of the ligands (acting as LBs).22 These precisely positioned
FLPs, stabilized by the well-defined surface coordination environment, enable efficient heterolytic
H activation. This capability leads to notable catalytic efficiency in regioselective hydrogenation
2
reactions.

Despite preliminary advances, a fundamental limitation persists in the previous Cu
34
FLPCluster system. Unlike previously reported FLP catalysts where LAs and LBs are
systematically organized via steric or electronic control, Cu exhibits significantly diminished
34
FLP formation.38,39 As illustrated in Figure 1 (previous work), most 2-methoxybenzenethiolate
ligands preferentially form thermodynamically stable O–Cu adducts instead of participating in
FLP assembly. This behavior arises from the ligands’ inherent conformational flexibility and
insufficient steric constraints, highlighting the persistent challenges in FLPCluster design. To
overcome this limitation, we focused on bis(2-diphenylphosphinophenyl)ether (DPEphos). As
widely documented, DPEphos possesses distinctive structural properties as a bidentate ligand, with
its central oxygen atom adopting an uncoordinated, pendant configuration.40,41 When assembled
on metal cluster surfaces, DPEphos exhibits optimal coordination behavior: its two phosphine
termini selectively bridge adjacent surface metal atoms, while the strategically positioned central
oxygen atom (LB) remains spatially constrained, thereby forming stable FLPs with surface metal
atoms (LAs).42 The intrinsic rigidity of the DPEphos framework ensures full participation of all
oxygen centers in FLP formation, enabling the construction of well-defined FLPClusters with
precise architectural control (Figure 1, this work). Guided by this design principle, the synthesized
triple-cluster system demonstrates that FLPClusters not only exhibit outstanding catalytic
efficiency in organic transformations but also display a near-linear correlation between catalytic
activity and the number of FLP active sites.

Results
Synthesis, structure, and characterization of well-defined FLPClusters. We employed a
facile one-pot strategy to functionalize copper clusters with the bidentate phosphine ligand,
DPEphos.43 This approach enabled the controlled assembly of structurally well-defined
FLPClusters via the co-reduction of copper(II) nitrate in the presence of DPEphos and ancillary
thiolate ligands (Figure 2). The architecture of the resulting clusters was strictly dictated by the
identity of the thiolate ligand. Specifically, the reaction system utilizing p-nitrothiophenol (R S)
1
yielded two distinct species: the tetranuclear Cu (DPEphos) (R S) (denoted Cu ) and the anionic
4 2 1 4 4
[Cu H (DPEphos) (R S) ]- (denoted Cu ). Conversely, substituting p-nitrothiophenol with p-
22 7 3 1 16 22
toluenethiol (R S) afforded the hydride-rich cluster Cu H (DPEphos) (R S) (denoted Cu ). We
2 28 9 3 2 18 28
isolated high-purity single crystals of each variant, permitting rigorous structural characterization
and catalytic evaluation. It is noteworthy that while Cu and Cu share the same ligand
4 22
components, their selective formation was controlled by DPEphos stoichiometry (100 mg for Cu
4
vs. 25 mg for Cu ). Furthermore, these two clusters exhibit pronounced morphological differences,
22
facilitating facile separation based on their distinct crystal habits.

Single-crystal X-ray diffraction (SCXRD) analysis unequivocally revealed the precise
molecular architectures of the Cu , Cu , and Cu clusters. Cu crystallizes in the triclinic space
4 22 28 4
group P1 with an asymmetric unit comprising a discrete molecule approximately 20 Å in size
(Table S1 and Figures S1–S3). This tetranuclear assembly is constructed from two
{Cu (DPEphos)(μ -RS)} motifs (hereafter {Cu }) bridged by a pair of μ -thiolate ligands (Figure
2 2 2 3
3a). Structural analysis confirms that the DPEphos ligands adopt a μ ,κ1,κ1-P,P coordination mode,
2
spanning two copper centers (Figure 3b).44 The intramolecular Cu–Cu distance of 2.63 Å is
significantly shorter than the sum of van der Waals radii (2.8 Å), indicating pronounced
cuprophilic interactions. Notably, the coordination geometry imposes significant distortion on the
DPEphos scaffold relative to its free state: the P···P distance expands to 5.29 Å (vs. 4.88 Å), while
the torsion angle (e.g., P2–C12–C2–P1) and inter-ring dihedral angle (e.g., Plane 1 and Plane 2)
increase to 84° and 87.68° (vs. 63.46° and ~67°), respectively (Table S2).45,46 The thiolate ligands
exhibit a dual role: μ -thiolates bridge Cu atoms within each {Cu } unit, putatively reinforcing Cu-
2 2
Cu interactions, whereas μ -thiolates link the two {Cu } subunits to construct the tetranuclear core.
3 2
Furthermore, an extensive network of intramolecular non-covalent interactions, including π–π
stacking (3.75 Å) and C–H···π contacts (centroid distances: 2.74–3.41 Å), further stabilizes the
solid-state conformation (Figure S4).47

Crucially, despite the well-documented hemilability of POP-type ligands,48 the steric bulk
and geometric constraints of this architecture enforce a “dangling” conformation for the ether
oxygen atom of DPEphos, precluding classical coordination to the metal centers. With O···Cu
distances of 2.98 and 3.41 Å (significantly beyond the covalent bond range), this unique steric
environment establishes a functional behavior analogous to a “frustrated Lewis pair” (FLP).49,50
The crystalline purity of the Cu cluster was unequivocally confirmed by the good agreement
4
between simulated and experimental powder X-ray diffraction (PXRD) patterns (Figure S5).
Complementary energy-dispersive X-ray spectroscopy (EDS) elemental mapping analysis
revealed homogeneous spatial distribution of all constituent elements (Cu, N, P, S, O, and C) across
the crystal surface (Figure S6). Furthermore, the purity and molecular integrity of the cluster were
verified by 1H and 13C{1H} nuclear magnetic resonance (NMR) spectroscopy (Figures S7–S8).
Solution-state characterization by 31P NMR spectroscopy (proton-decoupled) revealed a sharp
singlet at -15.47 ppm (Figure S9), indicating rapid phosphine ligand exchange dynamics on the
NMR timescale. X-ray photoelectron spectroscopy (XPS) analysis provided definitive evidence
for the oxidation state of the copper centers: (i) The characteristic Auger peak was observed at
916.1 eV, diagnostic of Cu+ species; (ii) The Cu 2p core-level spectrum exhibited well-defined
spin-orbit doublets at binding energies of 932.5 eV (2p ) and 952.1 eV (2p ), with a notable
3/2 1/2
absence of shake-up satellite features.51 These spectroscopic signatures collectively establish the
exclusive presence of monovalent copper species (Figures S10–S11), in full agreement with
SCXRD analysis. The cluster demonstrated excellent solubility in chloroform, forming stable
orange solutions that exhibited a characteristic absorption maximum at 416 nm in ultraviolet-
visible (UV–vis) spectroscopy (Figure S12). Importantly, stability studies of Cu revealed its
4
exceptional environmental robustness, with the UV–vis spectral profile remaining virtually
unaltered after 24 hours of exposure to ambient conditions, underscoring its potential for practical
application (Figure S13). The high-resolution electrospray ionization mass spectrometry (HRESI-
MS) analysis did not reveal any distinct peaks in either positive or negative mode, indicating that
the cluster possesses no charge (Figures S14–S15).

In contrast to the bulk-like crystallization habit of Cu , Cu cluster forms distinct plate-like
4 22
single crystals. Phase purity was confirmed by PXRD, which demonstrated excellent agreement
between the experimental and simulated patterns (Figure S16) and was further corroborated by 1H
and 13C{1H} NMR analysis (Figures S17–S18). Subsequent SCXRD analysis revealed that Cu
22
crystallizes in the monoclinic space group P2 /n, with each unit cell containing four discrete
1
[Cu H (DPEphos) (R S) ]⁻ structural units (Table S3 and Figures S19–S20). Structural analysis
22 7 3 1 16
(Figures 3d–3e) unveils a unique core-shell architecture: a Cu hemi-cuboctahedral metal core
10
encased within a Cu P S shell, forming the complete Cu P S framework. Crucially, the
12 6 16 22 6 16
DPEphos-type ligand maintains its μ ,κ1,κ1-P,P coordination mode. The P···P distances (5.38–5.66
2
Å), torsion angles (78.84°–87.69°), and dihedral angles (74.09°–85.18°) collectively demonstrate
its constrained geometry (Table S2). The ether oxygen atoms (LB) of the ligand, in spatial
proximity to the adjacent surface copper centers (LA), define the FLP sites. These sites are
characterized by Cu···O distances ranging from 3.21–3.54 Å, which are systematically longer than
the corresponding distances observed in the smaller Cu cluster (2.98–3.41 Å) (Figure 3f).
4
Moreover, the Cu···Cu separation at the FLP site is markedly expanded (ranging from 3.02 to 3.30
Å), significantly exceeding the Cu van der Waals radii and suggesting highly attenuated
cuprophilic interactions at this functional location (Table S2).

Negative-ion mode HRESI-MS analysis provided direct confirmation of the cluster’s
molecular composition (Figure S21). A distinct signal observed at m/z = 5486.92 was
unambiguously assigned to the single-charged species [Cu H (DPEphos) (R S) ]- (Cu -H). This
22 7 3 1 16 22
mass signature directly establishes the coordination of seven hydride atoms within the Cu
22
cluster
core. To further validate this composition, a deuterated analogue, [Cu D (DPEphos) (R S) ]-
22 7 3 1 16
(Cu -D), was synthesized via the substitution of NaBH with NaBD . Under identical HRESI-MS
22 4 4
conditions, the mass spectrum of Cu -D exhibited a predictable 7 m/z unit shift relative to its
22
hydride counterpart (Cu -H), providing robust and definitive confirmation of the cluster’s
22
structural authenticity. Cu LMM Auger and Cu 2p core-level spectra collectively confirmed
monovalent copper in Cu (Figures S22–S23), consistent with mass results. In solution, the cluster
22
exhibited excellent solubility in dichloromethane, yielding a stable yellow solution with a
maximum characteristic UV–vis absorption at 401 nm (Figure S24).

SCXRD analysis determined the molecular structure of Cu . The cluster crystallizes in the
28
trigonal system with space group R3 with each unit cell containing six discrete Cu units (Table
28
S4 and Figures S25–S26). As illustrated in Figure 3g and 3h, Cu features a Cu triangular
28 13
orthobicupola metal core, surrounded by the remaining Cu atoms that form a shell encapsulated
by thiolate and three DPEphos ligands. The DPEphos ligands coordinate in a μ ,κ1,κ1-P,P mode,
2
exhibiting a constrained geometry with P···P distances, torsion angles, and dihedral angles of 5.28
Å, 72.20°, and 75.25°, respectively (Table S2). Notably, the Cu⋯O distances between the ether
oxygen atoms and the adjacent surface copper centers are 3.20 Å and 3.61 Å, representing the
longest non-bonding interactions observed across the entire cluster series (Cu : 2.98-3.41 Å; Cu :
4 22
3.21-3.44 Å) (Figure 3i). Complementary spectroscopic techniques verified the cluster’s integrity
and composition. XPS confirmed that all copper centers maintain a +1-oxidation state (Figures
S27–S28), consistent with the structural data. The composition, purity and solution behavior of the
cluster were confirmed by HRESI-MS, EDS mapping, and NMR spectroscopy (1H, 13C{1H} and
31P{1H}, see Figures S29–S33 for details).

Identification of FLP sites in FLPClusters. To elucidate the fundamental characteristics of
surface FLPs in the three FLPClusters, we employed Cu as a model system for comprehensive
4
experimental and theoretical characterization. Mulliken charge analysis quantitatively confirmed
the Lewis acid-base character of the Cu⋯O pair. The Cu center (LA site) exhibits a partial positive
charge of +0.1 |e|, while the coordinated O atom (LB site) carries a negative charge of −0.48 |e|
(Figure 4a). This charge separation establishes the essential FLP configuration within the Cu
4
system. Complementary DFT calculations revealed the electronic structure basis for this behavior,
showing a HOMO-LUMO gap of 1.56 eV (Figure S34), which suggests substantial electronic
stability for the Cu FLPCluster. Furthermore, frontier orbital analysis demonstrated a spatial
4
separation between the HOMO, which is localized on the Cu S core, and the LUMO, which is
4 4
distributed on the -C H NO ligands. This orbital isolation further corroborates the FLP character.
6 4 2
The Lewis acidity of Cu atoms in the Cu FLPCluster was investigated through in situ NH
4 3
adsorption diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). As shown in
Figure 4b, the background spectrum of Cu showed no characteristic infrared peaks prior to NH
4 3
exposure. After 30 minutes of NH vapor exposure, characteristic vibrational modes of free
3
gaseous NH emerged. Subsequent argon purging effectively removed physically adsorbed NH ,
3 3
evidenced by the disappearance of gas-phase signals. Notably, a sharp absorption band remained
at 3333 cm-1, which is attributed to chemisorbed NH molecules on Cu(I) sites. This observation
3
provides direct experimental evidence for the accessibility and reactivity of the surface Lewis
acidic Cu centers toward basic molecular species. Correspondingly, in situ CO DRIFTS was
2
employed to analyze the Lewis basicity of O sites. As shown in Figure 4c, a distinct absorption
band at 2359 cm-1 appeared after CO exposure, assigned to the asymmetric stretching vibration
2
(ν ) of free gaseous CO . While argon purging eliminated physically adsorbed CO
3 2 2
signals, the
sharp absorption band at 2359 cm-1 persisted, indicating the chemisorption of CO
2
molecules on
O sites. These results decisively demonstrate the critical role of surface Lewis acid-base pairs in
regulating interactions with small molecules during catalysis.

Temperature-programmed desorption (TPD) measurements provided robust evidence for the
coexistence of LA and LB sites within the Cu cluster. As illustrated in Figures 4d and 4e, the
4
NH -TPD and CO -TPD profiles of Cu exhibit distinct desorption peaks, unambiguously
3 2 4
confirming the inherent acidity and basicity of these sites.52,53 Similar desorption peaks were also
observed in the Cu and Cu clusters (Figures S35–S36). This characteristic is indicative of FLP
22 28
formation, defined by sterically hindered LA and LB centers in close proximity. Such FLP systems
are well-documented for their exceptional ability to activate small molecules via synergistic
interactions between the antagonistic sites.54 Building upon our prior studies, which demonstrated
the outstanding catalytic activity of FLP systems derived from Cu clusters in the heterolytic
34
cleavage of H , we report herein the experimental evidence for the activation of H O molecules by
2 2
FLPClusters. To experimentally probe this activation process, we monitored D O adsorption on
2
the Cu cluster using deuterium NMR (2H NMR) spectroscopy, a technique ideally suited for
4
tracking the activation state of deuterated species. The observation of a distinct resonance shift in
the 2H NMR spectrum upon interaction with Cu (Figure 4f) provides compelling spectroscopic
4
evidence for the successful activation of water by the FLP sites within the Cu cluster.
4

FLPClusters-driven hydrolytic oxidation of organosilanes to silanols. Building upon the
superior water activation capability demonstrated by Cu , we investigated its catalytic utility in the
4
selective hydrolytic oxidation of organosilanes to silanols. Silanols containing Si-OH
functionalities are pivotal intermediates in organic synthesis.55 While gold and silver nanoparticles
can catalyze this transformation,56,57 the development of cost-effective, earth-abundant copper-
based nanocatalysts capable of utilizing water as a benign oxidant remains an unaddressed
challenge.55

To evaluate catalytic performance, the Cu cluster was immobilized on Vulcan XC-72 carbon
4
black via a solution impregnation method (details see METHODS SECTION). The catalytic
reaction was conducted in an air-saturated acetone/water mixture, with reaction progress
monitored in real-time by gas chromatography (GC). As envisioned, the resulting Cu /XC-72
4
catalyst (1% loading) demonstrated exceptional efficiency, achieving near-quantitative conversion
of triethylsilane within 24h at 50 oC (Figure 5a). Importantly, the catalyst exhibited excellent
cycling stability, with no appreciable decay in activity observed over six consecutive cycles (18h
each) (Figure 5b).

To confirm the structural stability of the catalysts, a suite of characterization techniques was
employed. The structural evolution of the clusters under operating conditions was probed by X-
ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure
(EXAFS) measurements at the Cu K-edge. The spectral profiles of Cu remained virtually identical
4
before and after loading onto carbon black, confirming that immobilization did not alter the
cluster’s nuclearity or geometry (Figure S37a). Crucially, the XANES and EXAFS features of the
catalyst were preserved after the reaction (Figure S37b, c). Quantitative EXAFS fitting (Figure
S38 and Table S5) revealed no significant deviations in the coordination numbers or bond lengths
of the Cu–Cu, Cu–S and Cu–P shells, proving that the cluster framework remains intact without
aggregation or fragmentation. This conclusion is corroborated by transmission electron
microscopy (TEM), which showed no formation of metal nanoparticles, and XPS and FTIR
spectroscopy, which verified the preservation of the Cu oxidation state and ligand coordination
environment (Figures S39–S42).

Comparative analysis identifies the engineered surface FLP sites as the sole origin of the
enhanced catalytic activity. The DPEphos ligand plays a dual role: it passivates the cluster to
maintain structural integrity while its central oxygen atom acts as a geometrically constrained
Lewis base, cooperating with surface copper atoms to form active FLP sites. To rigorously verify
this mechanism, we designed a series of control experiments (Figure 5c). Neither the carbon black
support nor the free DPEphos ligand exhibited significant activity (conversions < 5%). Similarly,
physical mixtures of copper salts and DPEphos showed negligible activity (5.8%). These results
collectively rule out the carbon support, free ligands, or unstructured copper species as active
contributors. Compelling evidence is provided by structurally well-defined Cu derivatives
4
stabilized by non-FLP ligands—specifically Cu (PPh Py) Cl and Cu (dpph) (PhC≡C) —which
4 2 4 2 4 2 4
exhibited only moderate activity (7.5% and 8.4% conversion, respectively) due to the absence of
accessible FLP motifs (Figures 5c and S43).58,59 Similarly, conventional copper nanoclusters
passivated by non-functional ligands (Cu (9.5%), Cu (6.2%), Cu (6.8%), Cu (6.0%), Cu
25 26 8 50 12
(6.4%), and Cu (7.3%)) showed negligible activity (Figures 5c, S44 and S45).60-64 These findings
66
collectively demonstrate that the catalytic performance is not an intrinsic property of the copper
cluster core, but originates exclusively from the geometrically well-defined FLP sites established
by the precise coordination of DPEphos to the surface copper centers. Notably, the Cu /XC-72
4
catalyst also exhibits a broad substrate scope under optimized conditions, effectively oxidizing
diverse silane substrates with equally high efficiency (Figure 5d). Impressively, the catalyst
achieves complete oxidation of both sterically hindered alkylsilanes and electronically distinct
arylsilanes without observable differences in rate attributable to steric effects.

Reaction mechanism of silane hydrolysis catalyzed by FLPClusters. To fully elucidate
the fundamental characteristics of surface FLPs and their catalytic mechanism, we adopted an
integrated approach combining experimental characterization and density functional theory (DFT)
calculations. Initially, molecular probe-based active site blocking experiments were conducted to
investigate the active site dependence of the catalytic reaction. Previous studies have demonstrated
that exogenous LAs or LBs can competitively bind to surface FLP sites, thereby significantly
inhibiting their catalytic activity.65 As demonstrated in Figure 6a, the competitive introduction of
either LA inhibitors (pyrrole, boric acid) or LB inhibitors (pyridine, thiourea) into the reaction
system resulted in marked decreases in catalytic activity. These findings confirm the indispensable
role of bifunctional Cu⋯O FLP sites in the oxidative transformation of organosilanes, establishing
the crucial promoting effect of synergistic Lewis acid-base interactions on reaction conversion.

Our investigations conclusively identified the FLPs within the Cu cluster as the primary
4
active sites responsible for the observed catalytic transformation. This finding strongly suggests a
direct correlation between the catalytic activity of the FLPCluster system and the number of
accessible FLP sites. To rigorously verify this hypothesis, we loaded Cu and Cu clusters-each
22 28
confirmed by structural analysis to possess three well-defined FLP sites—onto carbon black
supports with an equivalent molar amount of FLP sites. Under identical reaction conditions,
catalytic test over a 6-hour period revealed significantly enhanced activity for both clusters,
reaching 1.5 and 1.5 times the benchmark activity of Cu , respectively (Figure 6b). Notably,
4
despite the differences in their overall size and structure, Cu and Cu clusters, which harbor the
22 28
identical number (three) of FLP sites, demonstrated remarkably comparable molar catalytic
activities. This key observation provides compelling evidence that the catalytic efficiency is
predominantly governed by the quantity of accessible FLP rather than the total cluster size or
structure. This conclusion is further reinforced by concentration-dependent experiments using the
Cu
4
catalyst: as the catalyst mass increased incrementally from 20 mg to 80 mg (maintaining a
constant loading ratio), the 6-hour conversion rates progressively rose from 15.6% to 32.6% and
68.4%, unambiguously demonstrating the dominant role of active site quantity in driving reaction
conversion (Figure S46). These collective results establish a critical and quantifiable relationship:
the catalytic efficiency on the surfaces of these copper clusters is intimately linked to, and primarily
determined by, the abundance of available FLP sites. This fundamental understanding provides a
robust foundation for the rational design and synthesis of next-generation, high-performance
copper cluster catalysts by strategically maximizing the density of these catalytically active FLP
centers.

To complement the experimental findings, we performed DFT calculations incorporating
Grimme’s dispersion correction to elucidate the reaction mechanism and determine accurate
adsorption energetics.66 The results reveal that water activation proceeds preferentially via
heterolytic cleavage: the hydroxyl group (OH) adsorbs on the copper center (LA site), while the
proton (H) coordinates to the oxygen atom (LB site) of the FLP (Supplementary Video 1). This
pathway is modestly endothermic (0.59 eV) with an activation barrier of 1.43 eV (Figure 6c,
IS→TS1→MS1). Although Cu and S atoms also form potential Lewis acid-base pairs, calculations
indicate they are catalytically inactive; water dissociation on these sites faces a prohibitively high
activation barrier of 2.36 eV (Figure S47), significantly higher than that of the Cu···O pathway.
Figure 6c illustrates the subsequent conversion of triethylsilane [(CH CH ) SiH] to triethylsilanol
3 2 3
mediated by the Cu⋯O FLP sites. Following exothermic silane adsorption (-0.46 eV, MS2), the
reaction proceeds through a transition state with a barrier of 0.92 eV. The subsequent formation of
the silanol product (MS4) involves dissociation of the intermediate, characterized by a barrier of
1.28 eV and a significant exothermic energy release of 1.23 eV. Desorption of the generated
(CH CH ) SiOH requires an energy input of 0.49 eV. Finally, the recombination of the proton on
3 2 3
the O site with the hydride on the Cu site generates H (FS) with a barrier of 0.75 eV and a reaction
2
energy of -1.30 eV. The catalytic cycle concludes with H desorption (0.50 eV), regenerating the
2
pristine Cu catalyst.

Methods
Materials
Sodium borohydride (NaBH , 98%), 4-nitrothiophenol (C H NO S, 99%), copper nitrate
4 6 5 2
(Cu(NO ) , 99%), bis(2-diphenyphosphinophenyl) (DPEphos, 99%), acetonitrile (CH CN, A.R.),
3 2 3
chloroform (CHCl , A.R.), tetrahydrofuran (THF, A.R.), methanol (CH OH, A.R.) and ether
3 3
(C H O, A.R.) were purchased from Sinopharm Chemical Reagent Co. Ltd. (Shanghai, China).
4 10
Deuterium oxide (D O, 99.9% D), triethylsilane (Et SiH, 99 wt%), triisopropylsilane (C H Si,
2 3 9 22
98wt%), tert-butyldimethylsilane (C H Si, 95wt%), dimethylphenylsilane (PhMe SiH, 98 wt%),
6 16 2
methyldiphenylsilane (Ph MeSiH, 98 wt%), triphenylsilane (Ph SiH, 99 wt %),
2 3
methylphenylsilane (PhMeSiH , 98 wt%), diphenylsilane (Ph SiH , 99 wt%), 1, 2-bis
2 2 2
(dimethylsilyl) benzene (C H Si , 98 wt%) and dimethylisopropylsilane (C H Si, 95 wt%) were
10 18 2 5 14
purchased from Bidepharm (Shanghai, China). All reagents require no further purification before
use. Water used in all experiments was ultrapure. [Cu HCl (PPh Py) ]+(PPh Py is diphenyl-2-
4 2 2 4 2
pyridylphosphine), Cu (dpph) (PhC≡C) (dpph is (1,6-bis(diphenylphosphino) hexane),
4 2 4
[Cu (RS) H ]3- (Cu , RSH is 2-fluorobenzenethiol), [Cu (RS) H (PPh )]2- (Cu , RSH is 2-
25 18 10 25 26 18 10 3 26
fluorobenzenethiol), [Cu (RS) (PPh ) ]2+ (Cu , RSH is dimethyldithiocarbamate),
8 6 3 4 8
Cu (CF COO) (RS) (PPh ) H (Cu , RSH is 4-fluorobenzenethiol), [Cu (NO ) (AdmS) ]-
50 3 12 18 3 4 2 50 12 3 6 6
(Cu , RSH is 1-adamantanethiol) and [Cu Cl (PPh ) (RS) H ]2+ (Cu , RSH is ethanethiol) were
12 66 8 3 8 32 24 66
prepared as shown below.58-64

Synthesis of Cu (DPEphos) (R S) 
4 2 1 4
39 mg of (Cu(NO ) ·3H O was dissolved in a mixture of 1 mL MeOH and 1 mL CH CN. A
3 2 2 3
solution of 100 mg DPEphos in 0.5 mL CHCl was then added, followed by the addition of 0.5
3
mL MeOH containing 25 mg NaSbF . After stirring for 1 min, p-nitrothiophenol (17 mg, 0.101
6
mmol) in 1 mL of CH CN was added once, followed by 50 mg of NaBH in 0.5 mL of methanol.
3 4
After stirring for one hour, the red precipitate was collected. The precipitate was then dissolved in
excess chloroform. In the final purification step, the filtered solvent was subjected to diethyl ether
vapor diffusion for crystallization over three days, resulting in the formation of red block crystals
(12.46% yield, based on Cu). 1H NMR (600 MHz, DMSO-d ) δ 7.62, 7.61, 7.50, 7.45, 7.37, 7.30,
6
7.13, 7.00, 6.96, 6.59, 6.47. 13C{1H} NMR (151 MHz, DMSO-d ) δ 133.85, 130.26, 128.79,
6
128.49, 126.01, 121.93, 121.65.

Synthesis of [Cu H (DPEphos) (R S) ]-
22 7 3 1 16
The Cu cluster was prepared with a similar procedure, except for the use of DPEphos (25 mg) as
22
the precursors. Specifically, 39 mg of (Cu(NO ) ·3H O was dissolved in a mixture of 1 mL MeOH
3 2 2
and 1 mL CH CN. A solution of 25 mg DPEphos in 0.5 mL CHCl was then added, followed by
3 3
the addition of 0.5 mL MeOH containing 25 mg NaSbF . After stirring for 1 min, p-nitrothiophenol
6
(17 mg, 0.11 mmol) in 1 mL of CH CN was added once, followed by 50 mg of NaBH in 0.5 mL
3 4
of methanol. After stirring for one hour, the red precipitate was collected. The precipitate was then
dissolved in excess chloroform. In the final purification step, the filtered solution was subjected to
diethyl ether vapor diffusion over three days, yielding orange plate crystals with a yield of 10.28%
(based on Cu). 1H NMR (600 MHz, DMSO-d ) δ 8.21, 8.19, 7.80, 7.77, 7.75, 7.73, 7.72, 7.71,
6
7.69, 7.68, 7.67, 7.64, 7.62, 7.61, 7.60, 7.55, 7.53, 7.51, 7.50, 7.49, 7.48, 7.46, 7.45, 7.43, 7.42,
7.34, 7.33, 7.29, 7.28, 7.26, 7.25, 7.14, 7.13, 7.12, 6.09, 6.08, 6.07, 6.06. 13C{1H} NMR (151 MHz,
DMSO-d ) δ 139.93, 134.01, 133.51, 132.03, 130.23, 128.78, 122.27.
6

Synthesis of Cu H (DPEphos) (R S) 
28 9 3 2 18
To prepare the compound, 39 mg of Cu(NO ) was dissolved in a mixture of 1 mL methanol and
3 2
1 mL CH CN. Then, 100 mg of DPEphos dissolved in 0.5 mL of CHCl was added to the solution.
3 3
After stirring for 1 min, p-toluenethiol (13.7 mg, 0.110 mmol) in 1 mL of CH CN was added,
3
followed by 50 mg of NaBH in 0.5 mL methanol. The mixture was stirred for one hour and then
4
centrifuged to collect the red supernatant. The supernatant was filtered through a membrane and
crystallized under diethyl ether vapor. Red block crystals were obtained after one day at room
temperature, with a yield of 8.95% (based on Cu). 1H NMR (600 MHz, THF-d ) δ 7.87, 7.39, 7.32,
8
7.29, 7.26, 7.22, 6.99, 6.90, 6.85, 6.76, 6.66, 6.64, 6.53, 6.41, 6.25, 6.03, 6.02, 6.01, 5.64,5.62,
5.58, 5.57, 5.49, 5.47, 4.95, 4.94, 2.12. 13C{1H} NMR (151 MHz, THF-d ) δ 135.07, 129.16.
8

Synthesis of [Cu HCl (PPh Py) ]+
4 2 2 4
Copper(II) nitrate hydrate (Cu(NO ) ·3H O, 39 mg, 0.161 mmol) and diphenyl-2-
3 2 2
pyridylphosphine (PPh Py, 50.2 mg, 0.191 mmol) were dissolved in a mixed solvent of MeOH
2
(1.5 mL), MeCN (1 mL) and CHCl (0.5 mL), and the mixture was stirred for 20 minutes. A freshly
3
prepared solution of NaBH (50 mg in 1 mL of MeOH) was then added dropwise under vigorous
4
stirring, and the reaction was stirred at room temperature for 1 h. The resulting mixture was
centrifuged, and the precipitate was collected. The precipitate was dissolved in CHCl (2 mL), and
3
the solution was filtered through a 0.22 μm membrane filter. The product was crystallized via
vapor diffusion of diethyl ether at room temperature over one week, yielding yellow block-like
crystals (Yield: 70%, based on Cu).

Synthesis of Cu (dpph) (PhC≡C) 
4 2 4
Cu (dpph) (PhC≡C) was synthesized according to a modified literature procedure. Briefly, a
4 2 4
solution of copper(II) nitrate hydrate (Cu(NO ) ·3H O, 12 mg, 0.064 mmol) in 2 mL of EtOH was
3 2 2
prepared. To this solution was added a solution of 1,6-bis(diphenylphosphino)hexane (dpph, 11.36
mg, 0.025 mmol) in 2 mL of DCM, followed by the direct addition of phenylacetylene (10 μL,
0.09 mmol). After stirring for 20 min, a freshly prepared NaBH solution (5 mg in 0.5 mL EtOH)
4
was added dropwise, shifting the color from green to dark red. The mixture was stirred for 3 h and
then aged at room temperature for 5 days until it turned bright yellow. The solvent was evaporated,
and the residue was redissolved in 2 mL DCM. After centrifugation, the supernatant was collected.
Yellow-green block crystals were obtained via vapor diffusion of n-hexane/diethyl ether (V
n-
:V = 1:1) into the DCM solution in the dark over one week (Yield: 30%,based on Cu).
hexane diethyl ether

Synthesis of [Cu (2-F-PhS) H ]3-
25 18 10
[Cu (2-F-PhS) H ]3- was synthesized according to a modified literature procedure. Briefly,
25 18 10
copper(II) nitrate hydrate (Cu(NO ) ·3H O, 39 mg, 0.161 mmol) and tetraphenylphosphonium
3 2 2
tetraphenylborate (PPh BPh , 50 mg, 0.076 mmol) were dissolved in 1 mL of MeOH. To this
4 4
solution, 2-fluorobenzenethiol (5.8 μL, 0.054 mmol) dissolved in 2 mL of DCM was added. After
stirring for 20 min, a freshly prepared aqueous solution of NaBH (50 mg in 1.5 mL of H O) was
4 2
added dropwise under vigorous stirring, and the reaction was maintained for 3 h. Upon completion,
the mixture was allowed to stand for phase separation. The upper aqueous layer was removed, and
the organic phase was washed with a MeOH/H O mixture (V :V = 4:1, 2 mL), followed
2 MeOH water
by four consecutive washes with deionized water. For each wash, the mixture was shaken and
allowed to settle for phase separation before discarding the aqueous layer to ensure thorough
removal of impurities. The final organic phase was filtered through a 0.22 μm membrane filter.
Orange-red needle-like crystals were obtained via vapor diffusion of diethyl ether into the DCM
solution at room temperature in the dark over three days (Yield: 10% based on Cu).

Synthesis of [Cu (2-F-PhS) H (PPh )]2-
26 18 10 3
[Cu (2-F-PhS) H (PPh )]2- was synthesized according to a modified literature procedure.
26 18 10 3
Briefly, copper(I) thiocyanate (CuSCN, 12.16 mg, 0.100 mmol), triphenylphosphine (PPh , 25 mg,
3
0.095 mmol), and tetraphenylphosphonium chloride (PPh Cl, 10 mg, 0.027 mmol) were dissolved
4
in 1 mL MeOH. To this solution, 2-fluorobenzenethiol (11.7 μL, 0.107 mmol) dissolved in 2 mL
DCM was added. The mixture was stirred at room temperature for 20 minutes. Subsequently, a
freshly prepared aqueous solution of NaBH (30 mg in 1.5 mL of H O) was added dropwise under
4 2
vigorous stirring. The reaction was allowed to proceed with stirring at room temperature for 3 h.
The subsequent workup and washing procedure followed that described for Cu . The final organic
25
phase was filtered through a 0.22 μm membrane filter. Red needle-like crystals were obtained by
vapor diffusion of diethyl ether into the DCM solution at room temperature in the dark over three
days (Yield: 5% based on Cu).

Synthesis of [Cu (S CN(CH ) ) (PPh ) ]2+
8 2 3 2 6 3 4
[Cu (S CN(CH ) ) (PPh ) ]2+ was synthesized according to a modified literature procedure.
8 2 3 2 6 3 4
Briefly, copper dimethyldithiocarbamate (31 mg, 0.1 mmol) and 3,5-bis(trifluoromethyl)-1H-
pyrazole (10 mg, 0.049 mmol) were dissolved in a mixture of DCM (2 mL) and MeOH (1 mL)
and stirred for 20 minutes. Subsequently, a DCM solution (2 mL) of
bis(triphenylphosphine)copper(I) borohydride ((PPh ) CuBH , 80 mg, 0.133 mmol) was then
3 2 4
added. Within minutes, the solution color changed from reddish-brown to bright yellow, and
stirring was continued for 3 h. Upon completion, the mixture was centrifuged to obtain the
supernatant. The supernatant was subjected to crystallization via vapor diffusion of diethyl ether
at room temperature in the dark. Orange block-shaped crystals were obtained after two weeks
(Yield: 25% based on Cu).

Synthesis of Cu (CF COO) (3,5-diMe-PhS) (PPh ) H
50 3 12 18 3 4 2
Cu (CF COO) (3,5-diMe-PhS) (PPh ) H was synthesized according to a modified literature
50 3 12 18 3 4 2
procedure. Briefly, copper(II) trifluoroacetate (Cu(CF COO) , 30 mg, 0.153 mmol) and sodium
3 2
hexafluoroantimonate (NaSbF ,10 mg, 0.039 mmol) were dissolved in MeOH (1 mL). To this
6
solution, 4-fluorobenzenethiol (2.75 μL, 0.025 mmol) dissolved in DCM (1 mL) was added, and
the mixture was stirred for 20 minutes. Subsequently, a DCM solution (2 mL) of
bis(triphenylphosphine)copper(I) borohydride ((PPh ) CuBH , 40 mg, 0.066 mmol) was added,
3 2 4
and stirring was continued for 3 h. Upon completion, the mixture was centrifuged to obtain the
supernatant. The supernatant was subjected to crystallization via vapor diffusion of diethyl ether
at room temperature in the dark. After two weeks, red block-shaped crystals were obtained (Yield:
3% based on Cu).

Synthesis of [Cu (NO ) (AdmS) ]-
12 3 6 6
[Cu (NO ) (AdmS) ]- was synthesized according to a modified literature procedure. Briefly,
12 3 6 6
copper(II) nitrate hydrate (Cu(NO ) ·3H O, 24 mg, 0.099 mmol) and tetraphenylphosphonium
3 2 2
tetraphenylborate (PPh BPh , 20 mg, 0.030 mmol) were dissolved in MeOH (1 mL). To this
4 4
solution, 1-adamantanethiol (AdmSH, 4.2 mg, 0.025 mmol) dissolved in DCM (1 mL) was added,
and the mixture was stirred for 20 minutes. Subsequently, a DCM solution (2 mL) of
bis(triphenylphosphine)copper(I) borohydride ((PPh ) CuBH , 40 mg, 0.066 mmol) was added,
3 2 4
and stirring was continued for 3 h. Upon completion, the mixture was centrifuged to obtain the
supernatant. The supernatant was then subjected to crystallization via vapor diffusion of diethyl
ether at room temperature in the dark. After two weeks, yellow block-shaped crystals were
obtained (Yield: 50% based on Cu).

Synthesis of [Cu Cl (PPh ) (SC H ) H ]2+
66 8 3 8 2 5 32 24
[Cu Cl (PPh ) (SC H ) H ]2+ was synthesized according to a modified literature procedure.
66 8 3 8 2 5 32 24
Briefly, copper(II) trifluoroacetate (Cu(CF COO) , 48 mg, 0.245 mmol), sodium
3 2
hexafluoroantimonate (NaSbF , 25 mg, 0.097 mmol), and triphenylphosphine (PPh , 50 mg, 0.191
6 3
mmol) were dissolved in a mixed solvent of MeOH (1.5 mL), MeCN (1 mL), and CHCl (0.5 mL).
3
To this solution, diethyl disulfide (13.5 μL, 0.100 mmol) dissolved in MeCN (1 mL) was added,
and the mixture was stirred for 20 minutes. A freshly prepared solution of NaBH (50 mg in 1 mL
4
of MeOH) was then added dropwise under vigorous stirring, and the reaction was stirred at room
temperature for 1 h. The resulting mixture was centrifuged, and the precipitate was collected. The
precipitate was dissolved in CHCl (2 mL), and the solution was filtered through a 0.22 μm
3
membrane filter. The product was crystallized via vapor diffusion of diethyl ether at room
temperature over one week, yielding dark red block-like crystals (Yield: 20%, based on Cu).

Catalytic experiment
Preparation of Cu /XC-72.
4
The Cu NCs were supported on carbon black (Vulcan XC-72) by stirring a carbon black
4
dispersion (200 mg in 1 mL of methanol) along with the cluster solution (2.0 mg in 2 mL of CHCl )
3
for 4 h at room temperature. The supported clusters were separated by centrifugation and dried
under vacuum.

Catalytic oxidation of silane to silanol.
0.08% catalyst, 0.25 mmol silane and 1 mL of Milli-Q water were mixed in 5 mL of acetone. After
stirring in air at 50 °C for given time, the solution was analyzed using gas chromatography (GC).

Characterizations
Ultraviolet–visible spectroscopy. UV–vis spectra were obtained using the JascoV-680
spectrophotometer at room temperature. The absorption spectrum was measured with a 1 mm
quartz colorimetric tube, and the spectra were recorded in a CHCl or CH Cl solution with the
3 2 2
subtraction of the blank solvent signal. High-resolution electrospray ionization mass
spectrometry (HRESI-MS). The HRESI-MS data were recorded on an Agilent 6224 time-of-
flight mass spectrometer in the positive mode. Initially, the cluster sample was dissolved in a mixed
solvent of CH Cl and filtered. A slight amount of HCOOH was added into the solution for
2 2
promoting ionization. Subsequently, the solution was directly infused into the spectrometer at a
flow rate of 1.2 mL/h via an injection pump. Measurement parameters were as follows: capillary
voltage: 4.0 kV; dry gas temperature: 150 oC; dry gas flow rate: 4 L/min; atomizer pressure: 20
psi. Single-crysal X-ray diffraction (SCXRD) measurement. The single crystal diffraction data
of the Cu , Cu and Cu cluster was collected at 100 K using an Agilent Technologies Super
4 22 28
Nova System X-ray diffractometer. The data was collected at Cu K
α
(λ= 1.54184 Å) and processed
using CrysAlisPro after testing. The structure was solved and refined using the full matrix least
squares method based on F2 in ShelXT67, and ShelXL68 within Olex269. The geometric shape and
displacement parameters of the atoms in the cluster were properly restricted and constrained. The
thermal ellipsoid in the ORTEP diagram was completed with a 50% probability. Detailed crystal
data and structure refinements for this compound can be found in Table S1, Table S3 and Table
S4. Nuclear magnetic resonance (NMR) characterization. 1H NMR, 13C{1H}, 31P{1H} and 2H
NMR spectra were recorded on a Bruker AV-600 MHz NMR spectrometer at room temperature.
All NMR data were processed on MestReNova software. X-ray photoelectron spectroscopy
(XPS). XPS data were recorded using an X-ray photoelectron spectrometer (ESCALAB XI+)
equipped with a monochromatic Al Ka X-ray source. Prior to analysis, charge correction was
performed by setting the adventitious C1s peak to 284.5 eV. Peak fitting was subsequently carried
out using a Shirley-type background correction. After achieving a satisfactory baseline, the desired
peaks were added and optimized through multiple iterations, followed by manual refinement of
the peak parameters to ensure the fitted data closely matched the original spectra. Powder X-ray
diffraction (PXRD). X-ray diffraction patterns were conducted on Bruker D8 ADVANCE using
Cu Kα radiation. The operation voltage and current were 40 kV and 40 mA, respectively. The
scanning speed was set as 11 degree∙min-1. Transmission electron microscopy (TEM). TEM
analysis was conducted on a TECNAI F30 transmission electron microscope at a working voltage
of 300 kV. The samples were prepared by dropping ethanol dispersion of samples onto 300-mesh
carbon-coated copper grids and immediately evaporating the solvent. In-situ diffuse reflectance
infrared Fourier transform spectroscopy (DRIFTS). In-situ DRIFTS was performed on a
Thermo Fisher IS50 Fourier transform infrared spectrometer equipped with an MCT detector. To
perform in-situ CO /NH adsorption DRIFTS analysis, the sample of Cu was loaded into an in-
2 3 4
situ chamber (Harrick) and purged with Ar (10 mL·min-1) for 30 min. Following this, a background
spectrum was collected. Next, 5 vol% CO /NH /Ar was charged to the sample for 10 min and then
2 3
flushed with Ar before the spectra were recorded. X-ray absorption spectroscopic. In this
investigation, static X-ray absorption fine structure (XAFS) analyses of the Cu K-edge were
conducted utilizing a commercial Laboratory-Based XAFS spectrometer (RapidXAFS HE, Anhui
Absorption Spectroscopy Analysis Instrument Co., Ltd.). X-rays were generated via a Mo target
X-ray source operated at 20 kV and 20 mA. A Si (553) spherically bent crystal analyzer (SBCA)
with a radius of curvature of 500 mm served as the monochromator, thereby ensuring a diffraction
geometry approaching a 90-degree backscatter angle at the absorption edge. After
monochromatization, the X-rays pass through the sample and were collected using a high-energy-
resolution silicon drift detector (SDD) to obtain the X-ray intensity. The XAFS data were acquired
in transmission mode. During the XAFS measurements, the position of the absorption edge (E0)
was calibrated using a standard Cu foil sample, and all data collection occurred within a single
time period. Temperature programmed desorption (TPD). NH and CO TPD analysis was
3 2
conducted using the Micromeritics AutoChem II 2920 instrument. Sample was analyzed under a
constant flow rate of 50.20 cm3 STP/min. Signal inversion was enabled, and no baseline offset was
applied.

Computational Details
Density functional theory (DFT) calculations were performed using Perdew-Burke-Ernzerhof
(PBE) functional70 as implemented in DMol3 code71,72. All electron potential, double-numeric
quality with a polarization function (DNP basis set)71 on all atoms, and dispersion correction with
the Grimme term66 were employed for calculations. During optimization, all atoms were relaxed
until the self-consistent field (SCF) tolerance was no larger than 10−4 au on the total energy, and
the orbital cutoff was set to be 4.2 Å. The Mulliken method73 was utilized for charge analysis. The
complete synchronous LST/QST method74 was adopted for locating transition state with 20 frames
for each reaction pathway. Spin-unrestriction with multiplicity of auto finding was set through the
all calculations. The adsorption energy (E ) was defined as E = E – E – E , where E , E
ad ad tot * sorbate tot * 
and E are the energies of complex after and before adsorption, the energy of a free sorbate,
sorbate
respectively. According to the definition, a negative E indicates an energetically favorable
ad
adsorption process.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "The manuscript by Zheng and coworkers reported the synthesis and characterization of three distinct copper-based sila (FLP) clusters. This is a highly robust and compelling study. The well-defined structures demonstrate exceptional catalytic performance and outstanding stability in the hydrolytic oxidation of organosilanes. This work is suitable for publication in Nature Communications after major revisions.\n1. The authors employed Cu(II) nitrate as the sole copper precursor in the synthesis of FLP clusters for catalysis. How about the reactivity of other copper sources? Was there any particular consideration for not using Cu(I) species? How about the use of Cu(I) affect the formation and catalytic performance of the resulting clusters? If possible, please provide more information for the synthesis of FLPClusters.\n2.The synthesis of FLP clusters in this work appears to rely exclusively on DPPOE as the best ligand. What was the basis for not screening other bisphosphine ligands? Were other ligands incompatible with the cluster formation process? If possible, please provide more information for the difference of other phosphine ligands.\n3.The application of the synthesized catalysts in the hydrolytic oxidation of silanes is interesting. However, it was found that chlorosilanes (e.g., 2c, 2f) can also be applied in this reaction. It is difficult to understand the experiment results because chlorosilanes are highly sensitive to hydrolysis in air and might be occurred with polymerization, it is a serious question that how to determine the formation of such products?", "reviewer_2": "The manuscript reports the synthesis of FLPClusters—structurally defined metal clusters incorporating frustrated Lewis pairs (FLPs), and their application in catalysis. While the study presents interesting results and the topic is timely, the novelty appears limited, as the work seems to be a direct continuation of the group’s earlier publication from last year. More importantly, there are several inconsistencies and missing controls, particularly in the catalytic evaluation and stability studies, that prevent the work from meeting the standards for publication in Nature Communications.\n1)The clusters are deposited on carbon black, yet no blank catalytic tests are presented with carbon black alone or with carbon black + ligand. Such controls are essential to rule out contributions from the support or ligand alone.\n2)The manuscript claims recyclability and stability, but there is no convincing evidence that the cluster structure and ligand shell remain intact after deposition and catalytic runs. No characterization of the supported clusters is shown. The interaction between the cluster and ligands, which is central to the proposed mechanism, is not experimentally validated.\n3)The comparison with non-functionalized clusters is vague. The manuscript simply mentions them without details or quantitative data, which weakens the claim of superior performance.\n4)The catalytic activity is reported to persist or even improve over 6 hours, but no mechanistic explanation is provided. This raises the possibility of cluster modification, leaching, or restructuring under reaction conditions, which should be addressed with appropriate post-reaction characterization. Additional details are needed to confirm the structural integrity of the clusters after deposition and catalysis.\n5) Atomically precise clusters are known to display size-dependent catalytic properties, sometimes even with single-atom differences. Surprisingly, the authors report no differences across clusters of different sizes. This contradiction requires explanation. If the activity is solely attributed to the ligands, then one must also consider testing the ligands alone on the support.", "reviewer_3": "This manuscript presents a well-designed study on the development of three distinct copper FLPClusters: Cu4(DPPOE)2(R1S)4, [Cu22H7(DPPOE)3(R1S)16]- and Cu28H9(DPPOE)3(R2S)18. These clusters exhibit good catalytic activity and stability in the hydrolytic oxidation of organosilanes. A detailed molecular structural analysis reveals that the bulky nature of the DPPOE ligand sterically encumbers the central oxygen atom, acting as a Lewis base, while Cu(I) serves as a Lewis acid. This work is innovative, methodologically sound, and addresses a significant gap in the field of FLPClusters. The results are scientifically significant, with promising yields and recyclability.\nDuring revision, the authors might consider the following comments:\n1. Only Cu4 clusters have been characterised for Lewis acidity and basicity using theoretical and experimental methods, such as DRIFT. Similar analyses should be conducted on other clusters, like Cu28 and Cu22, to identify the optimal LA-LB pair.\n2. The authors link catalytic activity to the number of FLP sites, but only two types were studied, which is insufficient to support this claim. Additional experiments, such as varying catalyst concentration, are recommended to clarify this point.\n3. The authors noted that changing DPPOE amounts produced different types of FLPClusters, with a possibility of mixed clusters. What is their perspective on this?\n4. On page 17, the authors note that Cu22 and Cu28 both have three FLP active sites, yet Cu28 shows higher catalytic activity. Is there another factor besides FLP active sites?\n5. It appears that the stability of the FLP clusters increases with greater ligand bulkiness. Have the authors considered utilising alternative bulky ligands or derivatives of DPPOE in similar experiments?\n6. For the catalytic comparison study, the author should consider selecting copper clusters with similar atomic numbers rather than using random clusters. Using Cu4 with different ligands may be more appropriate for comparison in this study.\n7. Ligand-protected nanoclusters typically exhibit a core-shell structure, with the metal in the core as M(0) and in the shell as M(I). However, the authors state that all copper sites in Cu28 (Figures S20-S21) are in the +1 oxidation state. This raises the question: what drives the stability of these nanoclusters, particularly during catalysis?\n8. Since hydrogen, a reductant, is produced as a side product during catalysis, the copper site may be reduced. To confirm its oxidation state, the author should perform XPS or Auger analysis."}, "author_response": "Reply to Reviewer #1\nComment: The manuscript by Zheng and coworkers reported the synthesis and characterization of three\ndistinct copper-based sila (FLP) clusters. This is a highly robust and compelling study. The well-defined\nstructures demonstrate exceptional catalytic performance and outstanding stability in the hydrolytic oxidation\nof organosilanes. This work is suitable for publication in Nature Communications after major revisions.\nResponse: We sincerely thank the reviewer for the positive evaluation and valuable suggestions, which have\nbeen instrumental in improving our manuscript. We have carefully addressed all the comments in the revised\nversion. The key revisions are summarized below:\nComment 1: The authors employed Cu(II) nitrate as the sole copper precursor in the synthesis of FLPClusters\nfor catalysis. How about the reactivity of other copper sources? Was there any particular consideration for not\nusing Cu(I) species? How about the use of Cu(I) affect the formation and catalytic performance of the resulting\nclusters? If possible, please provide more information for the synthesis of FLPClusters.\nResponse: We thank the reviewer for raising this important question. Our selection of Cu(II) nitrate as the\nprecursor was based on systematic optimization during method development. We did evaluate various copper\nsources, including Cu(CF COO) , Cu(L-Valine) , and Cu(MeCN) BF , Cu O、CuCl among others.\n3 2 2 4 4 2\nEvaluation of various copper sources indicated that, in addition to Cu(NO ) , Cu(CF COO) (a Cu(II)\n3 2 3 2\nprecursor) also exhibited good reactivity. Utilizing this copper source, we successfully isolated another Cu\n25\nand Cu cluster, which will be subjected to further investigation. Conversely, the use of Cu(I) precursors did\n28\nnot yield additional FLPClusters, suggesting that the probability of constructing FLPClusters using Cu(I) is\nrelatively lows. Nevertheless, we do not exclude that Cu(I)species remain viable for FLPCluster development.\nComment 2: The synthesis of FLPClusters in this work appears to rely exclusively on DPEphos as the best\nligand. What was the basis for not screening other bisphosphine ligands? Were other ligands incompatible\nwith the cluster formation process? If possible, please provide more information for the difference of other\nphosphine ligands.\nResponse: We thank the reviewer for this insightful and constructive feedback.\nIndeed, beyond DPEphos, we have systematically explored other bidentate\nphosphine ligands bearing potential basic sites, notably including\nbis(diphenylphosphino)amine (DPPA). Encouragingly, employing DPPA also\nsuccessfully led to the synthesis of a novel FLPCluster—Cu —thereby\n35\ndemonstrating the robustness and generality of our FLPCluster construction\nstrategy.\nHowever, as the comprehensive structural characterization and functional investigation of Cu constitute\n35\nan independent and in-depth research project, the complete study will be presented in a subsequent dedicated\npublication.\nComment 3: The application of the synthesized catalysts in the hydrolytic oxidation of silanes is interesting.\nHowever, it was found that chlorosilanes (e.g., 2c, 2f) can also be applied in this reaction. It is difficult to\nunderstand the experiment results because chlorosilanes are highly sensitive to hydrolysis in air and might be\noccurred with polymerization, it is a serious question that how to determine the formation of such products?\nResponse: We really thank the reviewer for this insightful comment. The concern regarding potential\nspontaneous hydrolysis of chlorosilanes is indeed crucial for accurately evaluating the true performance of\nour catalytic system. To address this, we redesigned controlled experiments comparing a no-catalyst group\nwith the Cu /XC-72 group. The results revealed that the two chlorosilane substrates (2c, 2f) indeed underwent\n4\nsignificant spontaneous hydrolysis under catalyst-free conditions (as shown in Figure R1-R2), whereas the\nother eight non-chlorosilane substrates showed noticeable conversion only when the catalyst was used.\nThis outcome fully confirms the reviewer's assessment. From a mechanistic perspective, this can be\nattributed to the highly polarized Si–Cl bond in chlorosilanes, which exhibits extreme susceptibility to water\nmolecules. Their propensity for spontaneous hydrolysis far exceeds that of the Si–H bonds, which require\ncatalytic activation. Therefore, chlorosilanes are unsuitable for evaluating the genuine performance of our\ncatalytic system.\nIn response, we have replaced the original diisopropylchlorosilane and diphenylchlorosilane with tert-\nbutyldimethylsilane and triisopropylsilane in Figure 5. To ensure accurate product identification, all silanol\nproducts were rigorously re-analyzed by gas chromatography and compared with corresponding authentic\nsilanol standards. This revision not only eliminates interference from background reactions but also robustly\ndemonstrates the versatility of our catalyst in the hydrolytic oxidation of silanes.\nThe reviewer's valuable input has prompted us to explore the catalytic system more deeply, significantly\nenhancing the scientific rigor and persuasiveness of our study. We express our sincere gratitude for this\ncontribution.\nFigure 5. FLPs-functionalized Cu for hydrolytic oxidation of organosilanes. (a) Time-dependent\n4\nconversion of Cu /XC-72 for catalyzing the oxidation of triethylsilane. Error bars represent the standard\n4\ndeviation from at least three independent measurements. (b) Recyclability activity of Cu /XC-72 (18 h). (c)\n4\nhydrolytic oxidation of organosilanes. Reaction conditions: 0.25 mmol silane, 0.08 mol % catalyst and 1 mL\nof Milli-Q water were mixed in 5 mL of acetone, 50 oC, 24 hours.\nFigure R1. GC spectra of diisopropylchlorosilane (a) and the mixture of diisopropylchlorosilane and\nH O (b, catalyst-free). When diisopropylchlorosilane was used as the reaction substrate, its retention time\n2\nin gas chromatography was approximately 4.98 minutes. A high conversion rate was observed under catalyst-\nfree conditions while keeping all other parameters unchanged. Note: the highest peak in all gas\nchromatography analyses corresponds to acetone, the reaction solvent.\nFigure R2. GC spectra of diphenylchlorosilane (a) and the mixture of diphenylchlorosilane and H O (b,\n2\ncatalyst-free). When diphenylchlorosilane was used as the reaction substrate, its retention time in gas\nchromatography was approximately 3.1 minutes. A certain degree of conversion was observed under catalyst-\nfree conditions while keeping all other parameters unchanged. Note: the highest peak in all gas\nchromatography analyses corresponds to acetone, the reaction solvent.\nReply to Reviewer #2\nComment: The manuscript reports the synthesis of FLPClusters—structurally defined metal clusters\nincorporating frustrated Lewis pairs (FLPs), and their application in catalysis. While the study presents\ninteresting results and the topic is timely, the novelty appears limited, as the work seems to be a direct\ncontinuation of the group’s earlier publication from last year. More importantly, there are several\ninconsistencies and missing controls, particularly in the catalytic evaluation and stability studies, that prevent\nthe work from meeting the standards for publication in Nature Communications.\nResponse: We sincerely thank you for your evaluation of our work and the insightful and constructive feedback\nyou provided. We fully understand and accept the high standards of rigor required for high-impact\npublications in Nature Communications. In light of your important suggestions, we have made comprehensive\nand substantive revisions to the manuscript, supplementing it with a large number of new control experiments\nand in-depth structural characterization data to enhance the scientific rigor and persuasiveness of this\nresearch.\nThe reviewer pointed out that this work seems to be a direct continuation of our group’s previous research\nwith limited novelty. We understand this concern but wish to emphasize the significant innovations and\nessential distinctions of this study in design principle, synthetic strategy and mechanistic investigation:\n(1) In our previous work, FLP sites were serendipitously discovered during cluster synthesis—an importance\nlying in introducing the FLP concept into the cluster field. However, the construction of these FLP sites\nfrom 2-methoxybenzenethiol ligand was highly random. As illustrated in Figure 1 (previous work), most\n2-methoxybenzenethiolate ligands preferentially form thermodynamically stable O–Cu adducts instead\nof participating in FLP assembly. This behavior arises from the ligands’ inherent conformational\nflexibility and insufficient steric constraints, highlighting the persistent challenges in FLPCluster design.\nClearly, the strategy of randomly constructing FLP sites in clusters is unfavorable for synthesizing high-\nperformance catalytic clusters and studying synergistic catalytic mechanisms on cluster surfaces.\n(2) This study demonstrates the first approach for the strategic synthesis of FLPClusters featuring well-\ndefined, tailorable, and accessible FLP active sites. In other words, the novelty of this work lies in\nensuring the inevitability of FLP site construction by designing a unique bidentate phosphine ligand\n(DPEphos). Thanks to the rigid framework of DPEphos, the distance between the O atom in the ligand\nand Cu in the cluster is kept too far to form a bond yet not too distant—roughly controlled within 2.9-3.5\nÅ. This distance exactly achieves a state where it is neither close enough to form a bond nor too far to\nallow a certain weak interaction between Cu and O. For FLP site construction, the distance between the\nLewis acid and Lewis base is crucial, and the subtle control of the Cu-O distance benefits entirely from\nthe ingenious design of the phosphine ligand. Through the FLPCluster synthesis strategy presented here,\nwe can significantly improve the success rate of FLPCluster synthesis and further design and synthesize\nFLPClusters with higher catalytic performance.\n(3) We claim that while FLP-functionalized metal nanoclusters were reported in our earlier work, the concept\nof “FLPClusters”-central to this field-is introduced here for the first time. Moreover, this study\nestablishes a quantitative correlation between the number of FLP sites in the clusters and their catalytic\nactivity, which is also unprecedented.\nFurthermore, we have comprehensively supplemented the missing control experiments and structural\nintegrity characterizations in accordance with all your specific suggestions to ensure the rigor of the\nexperimental results. The details are as follows:\nFigure 1. The strategies for the construction of FLPClusters in previous and this work.\nComment 1: The clusters are deposited on carbon black, yet no blank catalytic tests are presented with carbon\nblack alone or with carbon black + ligand. Such controls are essential to rule out contributions from the support\nor ligand alone.\nResponse: We thank the reviewer for this important suggestion. To accurately identify the origin of the\ncatalytic activity, we have performed systematic control experiments as recommended. We designed and\ncompleted the following control experiments:\n(1) The carbon black support (Vulcan XC-72) alone.\n(2) The carbon black loaded with the free DPEphos ligand (DPEphos/XC-72).\n(3) Carbon black loaded with a mixture of copper nitrate and DPEphos (Cu(NO ) +DPEphos/XC-72).\n3 2\nThe results indicate that none of these three systems exhibited significant catalytic activity for the hydrolytic\noxidation of triethylsilane, with conversion rates of only 4.4%, 4.9%, and 5.8%, respectively. These systematic\ncontrol experiments demonstrate that:\n(1) The catalytic activity does not originate from the support, free ligand, or unstructured copper species.\n(2) The genuine catalytic activity must arise from the FLP active sites, which are constructed through\nprecise coordination between the DPEphos ligand and copper centers on the cluster surface, featuring\nspecific geometric configurations. Mechanically mixed Lewis acid (Cu) and base (O) sites, lacking\nprecise spatial arrangement and electronic coupling, cannot form effective FLPs and therefore do not\nyield catalytic activity.\nThese findings demonstrate the crucial role of constructing FLP sites through precise molecular\nengineering in achieving highly efficient catalysis. We have incorporated the complete experimental data and\ncorresponding discussion into Figure 5 and the main text of the revised manuscript.\nFigure 5. FLPs-functionalized Cu for hydrolytic oxidation of organosilanes. (a) Time-dependent\n4\nconversion of Cu /XC-72 for catalyzing the oxidation of triethylsilane. Error bars represent the standard\n4\ndeviation from at least three independent measurements. (b) Recyclability activity of Cu /XC-72 (18 h). (c)\n4\nhydrolytic oxidation of organosilanes. Reaction conditions: 0.25 mmol silane, 0.08 mol % catalyst and 1 mL\nof Milli-Q water were mixed in 5 mL of acetone, 50 oC, 24 hours.\nComment 2: The manuscript claims recyclability and stability, but there is no convincing evidence that the\ncluster structure and ligand shell remain intact after deposition and catalytic runs. No characterization of the\nsupported clusters is shown. The interaction between the cluster and ligands, which is central to the proposed\nmechanism, is not experimentally validated.\nResponse: We are very grateful to the reviewer for raising these critical questions regarding the structural\nintegrity and mechanistic verification of our FLPClusters. We fully recognize the importance of these\nexperiments for a reliable catalytic study and are pleased to provide additional experimental evidence to\naddress these inquiries.\nTo confirm that the cluster structure and ligand shell remain intact following loading and catalysis, we\nconducted a systematic characterization of the local atomic structures of the samples using X-ray absorption\nfine structure (XAFS) spectroscopy. Comparison of the pristine Cu cluster, the freshly prepared Cu /XC-72\n4 4\ncatalyst, and the recovered post-reaction catalyst revealed that the line shapes of their Cu K-edge XANES\nspectra are identical, and the Cu–Cu, Cu–S, and Cu–P coordination bond lengths and coordination numbers\nobtained from EXAFS fitting remain unchanged within the error margin (Figure S29, S30 and Table S5). This\ndirect structural evidence strongly indicates that the Cu FLPCluster maintains its structural integrity under\n4\ncatalytic conditions, ruling out significant decomposition, leaching, or restructuring of the cluster.\nTo further verify the weak interaction between Cu and O, we performed Raman spectroscopy analysis on\nfree DPEphos ligand and Cu . For the C–O bond, an increase or decrease in the electron cloud density of O\n4\nwill cause the Raman peak position of the C–O bond to shift to higher and lower wavenumbers, respectively\n(DOI: 10.1038/s41467-024-47319-z). As shown in Figure R3, a strong sharp peak appears at 1000-1033 cm-\n1, corresponding to the C–O–C groups in the free DPEphos ligand. In the spectra of Cu , the peak of the C–\nshift is an important indicator for the formation of FLP sites.\nFigure S29. Comparison of Cu K-edge X-ray absorption spectra. (a) Normalized XAS, (b) first-\nderivative XANES, and (c) k2-weighted EXAFS spectra for the unsupported Cu cluster (black), the\n4\ncluster loaded on carbon black (Cu /XC-72, red), and the catalyst after reaction (blue). The minimal\n4\nspectral changes indicate that the cluster’s nuclearity and geometry are preserved upon immobilization\nand throughout catalysis.\nFigure S30. R-space EXAFS fitting curves. Experimental data (black circles) and corresponding fits\n(red lines) for (a) unsupported Cu , (b) freshly prepared Cu /XC-72, and (c) post-catalysis Cu /XC-72.\n4 4 4\nThe fitting range was 1.0-3.0 Å. Quantitative fitting results (see Table S5) confirm the stability of the\nCu–Cu, Cu–S, and Cu–P coordination shells.\nTable S5. EXAFS fitting parameters at the Cu K-edge various samples (Ѕ02=0.80).\nSample Path C.N. R (Å) σ2×10-3 (Å2) ∆E (eV) R factor\nunsupported Cu-S/P 4.0±0.5 2.28±0.01 12.2±1.6 4.9±1.0 0.018\nbefore Cu-S/P 4.1±0.5 2.27±0.01 11.0±1.9 5.2±1.2 0.020\nafter Cu-S/P 4.3±0.4 2.29±0.01 12.9±1.4 5.4±0.4 0.013\nC.N.: coordination numbers; R: bond distance; σ2: Debye-Waller factors; ΔE : the inner potential correction.\nFigure R3. Raman spectra of the Cu and free DPEphos.\nthem without details or quantitative data, which weakens the claim of superior performance.\nResponse: We thank the reviewer for this valuable comment. Following the suggestion, we have supplemented\nthe following:\n(1) The well-defined structures of the clusters are shown in Supplementary Figure S36.\n(2) Quantitative catalytic conversion data for all reference samples under identical reaction conditions\nhave been added to the relevant section of the revised manuscript.\nWe believe these supplementary data enhance the persuasiveness of the performance comparison.\nFigure S36. The overall structure of copper nanoclusters passivated by non-functional ligands. Atomic\ncolor: blue, Cu; yellow, S; purple, P; gray, C; dark blue, N; green, F; dark green, Cl; red, O. All\nhydrogen atoms are omitted for clarity. The strcutrues of the clusters were redrawn from the literatures\n(10.26599/POM.2024.9140072; 10.26599/POM.2024.9140080; 10.1021/acsmaterialslett.3c01305;\n10.1021/acs.inorgchem.4c03203; 10.1002/agt2.651).\nComment 4: The catalytic activity is reported to persist or even improve over 6 hours, but no mechanistic\nexplanation is provided. This raises the possibility of cluster modification, leaching, or restructuring under\nreaction conditions, which should be addressed with appropriate post-reaction characterization. Additional\ndetails are needed to confirm the structural integrity of the clusters after deposition and catalysis.\nResponse: We thank the reviewer for raising this important issue. We have systematically addressed this\nconcern through additional experiments and characterization data.\nFirst, we re-measured the catalytic performance and performed six parallel experiments to obtain\nstatistical errors (Figure 5a). The updated data show that the catalytic activity increases steadily throughout\nthe reaction process, with no significant changes in rate. The previously apparent slope increase between 6–\n12 hours has been confirmed to be an artifact caused by the larger sampling interval and experimental errors.\nFigure 5. FLPs-functionalized Cu for hydrolytic oxidation of organosilanes. (a) Time-dependent\n4\nconversion of Cu /XC-72 for catalyzing the oxidation of triethylsilane. Error bars represent the standard\n4\ndeviation from at least three independent measurements. (b) Recyclability activity of Cu /XC-72 (18 h). (c)\n4\nhydrolytic oxidation of organosilanes. Reaction conditions: 0.25 mmol silane, 0.08 mol % catalyst and 1 mL\nof Milli-Q water were mixed in 5 mL of acetone, 50 oC, 24 hours.\nMore importantly, we conducted a systematic characterization of the local atomic structures of the\nsamples before and after catalysis using X-ray absorption fine structure (XAFS) spectroscopy. This direct\nstructural evidence strongly indicates that the Cu FLPCluster maintains its structural integrity under\n4\ncatalytic conditions, ruling out significant decomposition, leaching, or restructuring of the cluster (see\nresponse to Comment 2).\nOverall, we confirm that the observed sustained and stable catalytic activity originates from the\nstructurally stable FLPCluster itself, rather than from derived species or leached entities. We have\nincorporated the complete characterization data and discussion into the relevant sections of the revised\nmanuscript.\nComment 5: Atomically precise clusters are known to display size-dependent catalytic properties, sometimes\neven with single-atom differences. Surprisingly, the authors report no differences across clusters of different\nsizes. This contradiction requires explanation. If the activity is solely attributed to the ligands, then one must\nalso consider testing the ligands alone on the support.\nResponse: We thank the reviewer for this insightful perspective. We fully recognize the importance of size\neffects in metal cluster catalysis and are pleased to provide further clarification.\nThis study emphasizes that for the specific silane hydrolytic oxidation reaction examined, the presence\nand number of surface FLP sites—rather than cluster size effects—are the key catalytic determinants.\nIn principle, a Cu (DPEphos) L structure would provide an ideal reference. However, the DPEphos ligand\n4 3 x\nfeatures two phenyl-attached phosphine centers linked by a rigid diphenyl ether backbone, imposing distinct\nspatial and electronic constraints. Introducing a third such ligand into the limited configurational space of a\ntetranuclear copper cluster would likely cause significant steric repulsion, potentially compromising the\nelectronic stability and structural coherence of the cluster. Although we attempted its synthesis, the target\nstructure has not been obtained. A systematic search of the CCDC also confirms that no Cu (DPEphos) L -\n4 3 x\ntype structures exist. These experimental and literature observations support our interpretation and\nunderscore the inherent challenges in the precise control of FLP number in the same cluster core.\nTo further assess the role of FLP sites in the catalytic reaction, we prepared two Cu clusters as control\n4\nsamples (Figure S35):\nCu (PPh Py) Cl (DOI: 10.1039/D5NR03478G)\n4 2 4 2\nCu (dpph) (PhC≡C) (DOI: 10.1002/cjoc.202000613)\n4 2 4\nThe ligands used in these clusters lack functional groups that can serve as Lewis bases, thus preventing\nthe formation of effective FLP active sites on the cluster surfaces. Catalytic performance tests show that these\nCu clusters without FLP sites exhibit significantly lower activity (with conversions of 7.5% and 8.4%,\n4\nrespectively) compared to Cu (DPEphos) (R S) . This comparison strongly demonstrates the critical role of\n4 2 1 4\nFLP sites in the catalytic reaction.\nRegarding the verification of the ligand's individual role, we have already included rigorous control\nexperiments (detailed in our response to Comment 2), which rule out the free ligand as an independent\ncatalytic component.\nFigure S35. Molecular structures of the non-FLP Cu derivatives. (a) Cu (PPh py) Cl and (b)\n4 4 2 4 2\nCu (dpph) (PhC≡C) . Atomic color: blue, Cu; purple, P; gray, C; dark blue, N; green, Cl. All hydrogen\n4 2 4\natoms are omitted for clarity. The strcutrues of the clusters were redrawn from the literatures\n(10.1039/D5NR03478G; 10.1002/cjoc.202000613).\nReply to Reviewer #3\nComment: This manuscript presents a well-designed study on the development of three distinct copper\nFLPClusters: Cu (DPEphos) (R S) , [Cu H (DPEphos) (R S) ]- and Cu H (DPEphos) (R S) . These\n4 2 1 4 22 7 3 1 16 28 9 3 2 18\nclusters exhibit good catalytic activity and stability in the hydrolytic oxidation of organosilanes. A detailed\nmolecular structural analysis reveals that the bulky nature of the DPEphos ligand sterically encumbers the\ncentral oxygen atom, acting as a Lewis base, while Cu(I) serves as a Lewis acid. This work is innovative,\nmethodologically sound, and addresses a significant gap in the field of FLPClusters. The results are\nscientifically significant, with promising yields and recyclability. During revision, the authors might consider\nthe following comments:\nResponse: We sincerely thank the reviewer for the thorough evaluation and insightful comments on our work,\nwhich have significantly enhanced the scientific rigor of this study. We have carefully addressed all the\nsuggestions through supplementary experiments and detailed explanations. Key improvements include\nproviding more comprehensive characterization of the FLP sites in the three clusters, reinforcing the central\nrole of FLP site quantity in catalysis through a series of additional catalytic experiments, and offering\nrigorous characterization of the stability of the FLPClusters during the catalytic process. All revisions are\nsupported by newly added experimental data and figures and have been incorporated into the manuscript. We\nbelieve these enhancements have substantially improved the logical coherence and academic value of the\nstudy, and we are truly grateful for the reviewer's expert guidance.\nComment 1: Only Cu clusters have been characterised for Lewis acidity and basicity using theoretical and\n4\nexperimental methods, such as DRIFT. Similar analyses should be conducted on other clusters, like Cu and\nbasicity of clusters of different sizes is essential for understanding the structure-activity relationship of FLP\nsites. As observed from the supplementary temperature-programmed desorption (TPD) characterization, the\nCu and Cu clusters also exhibit NH and CO desorption feature peaks, confirming the existence of surface\n22 28 3 2\nLewis acid and base sites on the Cu and Cu cluster surfaces as well.\n22 28\nFigure S27. NH -TPD (a) and CO -TPD (b) profiles of Cu .\n3 2 22\nFigure S28. NH -TPD (a) and CO -TPD (b) profiles of Cu .\n3 2 28\nComment 2: The authors link catalytic activity to the number of FLP sites, but only two types were studied,\nwhich is insufficient to support this claim. Additional experiments, such as varying catalyst concentration,\nare recommended to clarify this point.\nResponse: We thank the reviewer for this valuable suggestion. To more rigorously establish the correlation\nbetween catalytic activity and the number of FLP sites, we have conducted systematic concentration-\ndependent experiments as recommended.\nWhile maintaining the same catalyst loading, we examined the catalytic conversion at three different\ncatalyst amounts (20, 40, and 80 mg) after six hours of reaction, with five independent replicates performed\nfor each condition and the results averaged. The experimental data show that the average conversion rates\ncorresponding to the three catalyst amounts were 15.6%, 32.6%, and 68.4%, respectively. This series of\nresults demonstrates a clear positive correlation between the catalytic conversion and the catalyst amount\n(i.e., the total number of FLP sites present in the system) within the same reaction duration.\nThis concentration-dependent study provides strong support for the proposed structure-activity\nrelationship. We have incorporated the complete dataset from these experiments into the relevant section of\nthe revised manuscript (see Figure S37).\nFigure S37. The 6-hour conversion rates achieved with 20, 40, and 80 mg of the Cu /XC-72 catalyst\n4\n(Error bars represent the standard deviation from at least three independent measurements).\nComment 3: The authors noted that changing DPEphos amounts produced different types of FLPClusters,\nwith a possibility of mixed clusters. What is their perspective on this?\nResponse: We fully agree that the feed ratio of the ligands plays a critical role in determining the final\nstructure of the FLPClusters. Our experimental results demonstrate that the molar ratio between DPEphos\nand the thiolate ligand is a key factor governing the structural selectivity of the clusters. Specifically, with the\namount of thiol fixed at 17 mg (0.11 mmol):\n(1) When a higher amount of DPEphos (100 mg, 0.19 mmol) is used, corresponding to a ligand molar ratio\nof n :n ≈1.7:1, the reaction system selectively produces the Cu cluster.\nDPPOE RSH 4\n(2) When the amount of DPEphos is reduced to 25 mg (0.05 mmol), yielding a ligand molar ratio of\n≈0.42:1, the product shifts exclusively to the Cu cluster.\n22\n(3) At intermediate ligand molar ratios, such as n :n =1:1, the reaction yields a mixture of Cu\nDPPOE RSH 22\nand Cu , with Cu as the major product and Cu as the minor one.\n4 22 4\nThis systematic variation clearly indicates that the DPEphos-to-thiol ratio modulates the nucleation\npathway of the copper precursors and the thermodynamic stability of the resulting clusters. The formation of\nmixtures under specific ratios further confirms the existence of competitive nucleation pathways leading to\ndifferent cluster structures in the system. We have incorporated the above discussion into the revised\nmanuscript to more clearly elucidate the structure-directing role of ligand stoichiometry in the synthesis of\nFLPClusters.\nComment 4: On page 17, the authors note that Cu and Cu both have three FLP active sites, yet Cu shows\n22 28 28\nhigher catalytic activity. Is there another factor besides FLP active sites?\nResponse: We thank the reviewer for this insightful question. We have reevaluated the catalytic performance\nthrough rigorous assessment, conducting five parallel experiments with error analysis to ensure data\nreliability. The updated experimental results show that the average conversion rates for Cu , Cu , and Cu\n4 22 28\nat 6 hours of reaction time are 28.6%, 42.7%, and 43.9%, respectively. Statistical analysis shows that, under\nidentical conditions, the catalytic performance of both Cu and Cu is approximately 1.5 times that of the\n22 28\nCu catalyst, and the difference between them is not statistically significant within the margin of error (Figure\n4\n6). These findings further support our central thesis that the number of FLP sites is the primary determinant\nof catalytic activity.\nFigure 6. Mechanistic studies on FLPCluster-driven hydrolytic oxidation of organosilanes to silanols.\n(a) Influence of molecular Lewis acids or Lewis bases on the catalytic activity of Cu . (b) Catalytic activity\n4\ncomparison of Cu , Cu , and Cu at 6 h: correlation between FLP site density and performance. Error bars\n4 22 28\nrepresent the standard deviation from at least three independent measurements (c) Computed free energy\nprofile for triethylsilane hydrolytic oxidation catalyzed by Cu . Color scheme: Cu, orange; S, yellow; C, grey;\nComment 5: It appears that the stability of the FLPClusters increases with greater ligand bulkiness. Have\nthe authors considered utilising alternative bulky ligands or derivatives of DPEphos in similar experiments?\nResponse: We thank the reviewer for this insightful suggestion. We fully agree that ligand steric bulk plays\nan important role in stabilizing FLPClusters. Indeed, beyond the DPEphos ligand focused on in this study, we\nhave conducted preliminary explorations using other bidentate phosphine ligands with different backbone\nstructures. For example, by employing bis(diphenylphosphino)amine (DPPA) as a surface ligand, we\nsuccessfully constructed a structurally novel FLPCluster—Cu . This result strongly indicates that our\n35\nproposed synthetic strategy of \"utilizing bidentate phosphine ligands to construct FLPClusters\" possesses a\nrobust generality and is not limited to the DPEphos system.\nHowever, given that the cluster systems based on DPPA and similar ligands exhibit considerable\nstructural complexity, their full structural elucidation and property characterization constitute a separate\nresearch project. We therefore plan to systematically and thoroughly investigate these novel clusters in a\nsubsequent study.\nComment 6: For the catalytic comparison study, the author should consider selecting copper clusters with\nsimilar atomic numbers rather than using random clusters. Using Cu with different ligands may be more\n4\nappropriate for comparison in this study.\nResponse: We thank the reviewer for this valuable suggestion. As detailed in our response to Reviewer 2-\nComment 5, we have designed and synthesized two nanoclusters with Cu cores but different ligand structures\n4\nas reference systems:\nCu (PPh Py) Cl (DOI: 10.1039/D5NR03478G)\n4 2 4 2\nCu (dpph) (PhC≡C) (DOI: 10.1002/cjoc.202000613)\n4 2 4\nThe ligands used in these clusters lack functional groups that can serve as Lewis bases, thus preventing\nthe formation of effective FLP active sites on the cluster surfaces. Catalytic performance tests show that these\nCu clusters without FLP sites exhibit significantly lower activity (with conversions of 7.5% and 8.4%,\n4\nrespectively) compared to Cu (DPEphos) (R S) . This comparison strongly demonstrates the critical role of\n4 2 1 4\nFLP sites in the catalytic reaction.\nFigure S35. Molecular structures of the non-FLP Cu derivatives. (a) Cu (PPh py) Cl and (b)\n4 4 2 4 2\nCu (dpph) (PhC≡C) . Atomic color: blue, Cu; purple, P; gray, C; dark blue, N; green, Cl. All hydrogen atoms\n4 2 4\nare omitted for clarity.\nComment 7: Ligand-protected nanoclusters typically exhibit a core-shell structure, with the metal in the core\nas M(0) and in the shell as M(I). However, the authors state that all copper sites in Cu (Figures S20-S21) are\n28\nin the +1 oxidation state. This raises the question: what drives the stability of these nanoclusters, particularly\nduring catalysis?\nReponse: The Cu cluster maintains high stability with its all-Cu(I) structure probably due to three key\n28\nfactors: First, the 1.9 eV electrochemical band gap measured by cyclic voltammetry (Figure R4) demonstrates\nits high electronic stability. Second, the network of noncovalent interactions in the system - including C–H···π\n(2.64-3.01 Å) and π–π stacking (3.99 Å) (Figure R5) - works synergistically with strong coordination bonds\nto enhance structural integrity. Last, particularly noteworthy is that its catalytic mechanism operates through\nsurface FLP sites without involving changes in metal oxidation states, thereby preventing structural\nreconstruction during catalysis. These combined characteristics ensure the persistent stability of the all-Cu(I)\nclusters under catalytic conditions.\nFigure R4. Cyclic voltammogram of the Cu cluster.\n28\nrepresent the π-π and C-H···π interactions, respectively. Atomic color: blue, Cu; yellow, S; purple, P;\nred, O; gray, C; dark blue, N; white, H.\nComment 8: Since hydrogen, a reductant, is produced as a side product during catalysis, the copper site may\nbe reduced. To confirm its oxidation state, the author should perform XPS or Auger analysis.\nResponse: We thank the reviewer for this important suggestion. We have performed X-ray photoelectron\nspectroscopy (XPS) analysis on the Cu /XC-72 catalyst before and after the reaction. The characterization\n4\nresults show no observable shifts in either the Cu 2p binding energies or the Cu LMM Auger spectra after\ncatalysis. Specifically, the Cu 2p and Cu 2p binding energy remain stable at 952.2eV and 932.4 eV with\n3/2 1/2\nno detectable satellite features characteristic of Cu2+ species, while the Auger kinetic energy is maintained at\n916.1 eV. All these features represent characteristic signatures of Cu+ species.\nFigure S32. Cu LMM Auger spectra of the Cu /XC-72 catalyst before and after catalysis.\n4"}, {"round": 2, "reviewer_comments": {"reviewer_1": "The revised version could be accepted for publication on Nature Communications.", "reviewer_2": "The authors have done an excellent job addressing and clarifying all of my comments through substantial additional work. I therefore recommend publication of the manuscript in its current form.", "reviewer_3": "The authors diligently reviewed my comments during the revision process, and I am now convinced that the revised version is suitable for publication."}, "author_response": ""}]

Decision letter