# Flash Communication: Well-Defined Paramagnetic Polyhydrido-Bridged Iron–Iridium Clusters

Zachary Dubrawski, Billie Shearman, Naïme Soulé, Erwann Jeanneau, Chloé

Thieuleux, Clément Camp

► To cite this version:

Zachary Dubrawski, Billie Shearman, Naïme Soulé, Erwann Jeanneau, Chloé Thieuleux, et al. Flash Communication: Well-Defined Paramagnetic Polyhydrido-Bridged Iron–Iridium Clusters. Organometallics, 2025, 44 (19), pp.2151-2155. 10.1021/acs.organomet.5c00301. hal-05312410

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# Flash Communication: Well-Defined Paramagnetic Polyhydrido-Bridged Iron–Iridium Clusters

Zachary Dubrawski, Billie Shearman, Naïme Soulé, Erwann Jeanneau, Chloé Thieuleux, and Clément Camp*

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Cite This: *Organometallics* 2025, 44, 2151–2155

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Supporting Information

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**ABSTRACT:** Polyhydrido transition metal complexes are a constant source of interest due to their variety in bonding and reactivity. Yet, well-defined paramagnetic polyhydrido systems are relatively rare given their instability. Herein, we extend the protonolysis reactivity of the Brønsted acidic Cp\*IrH₄ polyhydride toward transition metal silylamides. Specifically, we report the synthesis and characterization of a polyhydrido diiron tetrairidium paramagnetic cluster, [Fe(Cp\*IrH₃)₂]₂, **1**, from the reaction between Fe(HMDS)₂(THF) and Cp\*IrH₄. Attempted reduction of this complex with potassium graphite yields instead an anionic species, K[Fe(Cp\*IrH₃)₂], **2**, in a proposed disproportionation mechanism. Complex **2** can be independently synthesized in good yields upon treating **1** with K[Cp\*IrH₃]. Attempts to synthesize Fe(III) analogues from the oxidation of **1** or **2** failed, with oxidation occurring at the Ir centers. Likewise, reactions between Fe(III) precursors and iridium polyhydride species consistently yield complex **1**. This highlights the unexpected driving force toward this very stable tetrairidium diiron paramagnetic polyhydride complex reported in this work.

Polyhydrido transition metal clusters continue to fascinate inorganic chemists due to their diverse bonding patterns and interesting reactivity.¹⁻⁷ The majority of polyhydrido compounds are diamagnetic. Paramagnetic counterparts remain relatively uncommon,⁸⁻¹² mostly due to the relative instability of open-shell polyhydride species, which are prone to decomposition through a variety of mechanisms.¹³⁻¹⁵ Despite growing interest in iron catalysis, paramagnetic iron hydrido clusters are especially rare, with only a few reports in the literature (Table S1).¹⁶⁻¹⁹ The latter may yet offer new avenues for reactivity, as they are implicated in a number of enzymatic processes.²⁰⁻²²

In recent years, our research group has used the protonolysis reaction between pentamethylcyclopentadienyl tetrahydrido iridium(V), Cp\*IrH₄, and a range of transition metal alkyl complexes, to prepare heterobimetallic polyhydride species.²³⁻²⁷ Herein we expand this strategy to silylamido derivatives,²⁸ and we report the synthesis, characterization, and reactivity of paramagnetic polyhydrido bridged iron–iridium clusters.

Addition of 2 equiv of Cp\*IrH₄ to bis((trimethylsilyl)-amido)iron(II) tetrahydrofuran adduct, Fe(HMDS)₂(THF), in pentane at room temperature generates complex [Fe(Cp\*IrH₃)₂]₂, **1**, isolated as a bright yellow-orange solid in

85% yield (Scheme 1). The ¹H NMR spectrum of complex **1** shows two paramagnetically shifted signals at 26.2 and 17.7 ppm (C₆D₆, 298 K, 300 MHz) appearing as two 1:~1 broad singlets, and presumably corresponding to two Cp\* ligands in different chemical environments (Figure S1). The hydride ¹H NMR resonances are not observed in a range of +4000 to -4000 ppm, as is often the case for hydride ligands located at close proximity of paramagnetic centers.²⁹⁻³²

The diffuse reflectance infrared Fourier transform (DRIFT) spectrum for **1** (Figure S15) reveals $\nu(M-H)$ signals at 2244–1789 cm⁻¹ consistent with the presence of metal hydrides in various coordination environments (see below). Complex **1** is electron paramagnetic resonance (EPR) spectroscopy silent when performed at the X band either at room temperature or at 77 K. Solution-state Evans method measurement in C₆D₆ yields a magnetic moment of 4.5 $\mu_B$ (Figure S2). Iron clusters

Received: August 7, 2025

Revised: September 11, 2025

Accepted: September 15, 2025

Published: September 18, 2025

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<figure><img src="image_12.png" /><figcaption>Scheme 1. Synthesis of [Fe₂Ir₄] and [FeIr₃] Polyhydrido Clustersᵃ</figcaption></figure>

ᵃThe proposed hydride bridging modes are inferred from the solid-state structures (see below).

are known for their significant ferro- or antiferromagnetic coupling properties, and so we cannot directly correlate this value to a specific spin-state configuration.³³⁻³⁵

Single crystal X-ray diffraction analysis revealed a tetrairidium diiron cluster structure, shown in Figure 1. The dimeric

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**Figure 1.** X-ray crystal structures of complexes 1 (left) and 2 (right). Thermal ellipsoids are shown at 50% probability levels, and hydrogen atoms are removed for clarity. Relevant bond lengths and angles for complex 1: Fe1–Ir1 = 2.541(2) Å (FSR = 1.04), Fe1–Ir2 = 2.671(2) Å (FSR = 1.10), Fe1–Fe2 = 2.898(3) Å (FSR = 1.24), Cp\*<sub>centroid</sub>–Ir1–Fe1 = 173.4(1)°, Cp\*<sub>centroid</sub>–Ir2–Fe<sub>1,2</sub> bond centroid = 163.3(1)°, Ir1–Fe1–Fe2 = 158.3(1)°, Ir2–Fe1–Fe2–Ir3 = 154.6(1)°, τ₄, Fe1 = 0.53. Relevant bond lengths and angles for complex 2: Ir1–Fe1 = 2.575(2) (FSR = 1.06), Ir2–Fe1 = 2.665(2) (FSR = 1.09), Ir3–Fe1 = 2.665(2) (FSR = 1.09), Ir1–K1 = 3.628(2), Ir3–K1 = 3.741(2), <Cp\*<sub>centroid</sub>–Ir1–Fe1 = 137.3(1)°, <Cp\*<sub>centroid</sub>–Ir2–Fe1 = 178.7(1)°, <Cp\*<sub>centroid</sub>–Ir3–Fe1 = 137.3(1)°. Ir2–Fe1–K1 = 144.1(1)°.

nature is not surprising given the propensity of [Cp\*IrH₃]<sup>y</sup>–moieties to bridge several metal centers, as well as the tendency of nonsolvato Fe(HMDS)₂ systems to dimerize.²³,²⁴,³⁶,³⁷ However, the majority of these di-iron, diamond core-like structures show the two Fe atoms and other coordinating atoms (N, S, O or other metals) from the bridging ligands lying along the same plane of the molecules.¹⁶,³⁷⁻⁴⁰ Here, we see a significant deflection from this plane evidenced by the Ir2–Fe1–Fe2–Ir3 dihedral angle of 156.56°, which we propose is due to a terminal hydride

deflecting the Fe center away from the butterfly cluster core (see Figure S18 for a better view of the saddle-shaped core). Unfortunately, hydrides located adjacent to very heavy elements such as Ir cannot be accurately determined from the Fourier difference map and as such have not been represented here.⁴¹ However, from the solid-state structure we can infer their locations from the Cp\*-Ir–Fe angles, as has been previously reported.⁴²,⁴³ The Cp\*<sub>centroid</sub>–Ir1–Fe1 angle of 173° is consistent with structures having three bridging hydrides between the two transition metals whereas the Cp\*<sub>centroid</sub>–Ir2–Fe<sub>1,2</sub> centroid angle of 163° tentatively confirms different bridging modes within the architecture, perhaps indicative of a terminal hydride. The Ir–Fe bond lengths are quite long (2.541(2)–2.671(2) Å) but comparable to other Fe–Ir pairs with bridging hydrido ligands.⁴⁴,⁴⁵ The Formal Shortness Ratio (FSR, defined as the ratio of interatom distance to the sum of atom radii) can be used as a qualitative guide for intermetallic bonding. With an FSR over unity (FSR = 1.04), we conclude that **1** does not exhibit any Fe–Ir bonding. Similarly, the very long Fe1–Fe2 distance (2.898(3) Å, FSR = 1.24) precludes intermetallic bonding and suggests no hydride bridges between the iron centers.¹⁷,¹⁸ Incidentally, other Fe:Ir stoichiometries (Fe₂(Cp\*IrH₃)(HMDS)₃ and Fe₂(Cp\*IrH₃)₂(HMDS)₂) could be obtained (crystal structures showing atom connectivity are located in Figures S19 and S20) which also show these dihedral deflections (suggestive that it is the bridging Cp\*IrH₃⁻ moieties causing this effect).⁴⁶ However, these partially substituted systems are not fully characterized and are not explored further in this report.

Complex **1** is remarkably stable. No detectable degradation was observed after months in an ambient glovebox atmosphere or in a benzene solution, even after heating to 70 °C for multiple days. Unfortunately, **1** is also stable toward substrates: no reaction is observed with simple small molecules such as alkenes, alkynes, azides, isocyanates, N₂, CO₂, or CO under thermal or photochemical conditions. With the interest of exploring other oxidation states of iron within this architecture, we turned to reduction with 2 equiv of potassium graphite (KC₈). The reaction can be monitored by ¹H NMR spectroscopy in THF-d₈ yielding a new compound, **2**, featuring one large signal at +33 ppm. A single crystal of product **2** could be obtained from a saturated pentane:THF solution at –40 °C, which reveals the formation of an anionic iron tris-iridate complex with a potassium countercation, K[Fe(Cp\*IrH₃)₃] (Scheme 1). The mass balance of the material isolated (24% yield) at the end of this reaction revealed a significant loss. We therefore assume some disproportionation mechanism is at play; i.e. the elusive Fe¹⁻ iridate complex falls apart into an Fe⁰ fragment and **2**. Performing this reduction under an atmosphere of dinitrogen instead of argon, in the hope of an N₂ adduct, unfortunately does not alter the outcome.

The crystal structure of **2** (Figure 1) reveals an infinite chain of potassium atoms ligated by the FeIr₃ unit. The Fe–Ir bond distances of 2.662–2.579 Å (FSR = 1.09–1.06) have not substantially changed from complex **1**. The most interesting structural difference is the dramatic change in the Cp\*<sub>centroid</sub>–Ir1–Fe1 angle, which has bent from 163° in complex **1** to 135° in **2**. This rotation of the Cp\* ligands suggests the hydrides extend out from the Ir center, in the direction of the potassium center, most likely as a result of hydride–cation bonding.¹⁷,⁴⁷,⁴⁸ Given the single signal in the ¹H NMR data (which we attribute to the Cp\* ligands), we presume some
<figure><img src="image_14.png" /><figcaption>Scheme 2. Oxidation of Complex 2</figcaption></figure>

fluxibility of this structure in solution, as already seen in other asymmetric ($Cp*IrH_3$)⁻ derived polynuclear species.²⁵,⁴²,⁴³

2 can be independently synthesized through the addition of 2 equiv of $K[Cp*IrH_3]$ to 1 in THF in 78% yield.²⁵ The paramagnetic ¹H NMR signal (+33 ppm) for the isolated complex matches that observed during ¹H NMR reaction monitoring of the $KC_8$ reduction of 1, and single crystals (grown from a saturated THF:pentane mixture) match the unit cell obtained previously. Solution state Evans' method calculations reveal a magnetic moment of 4.8 $μ_B$ corresponding to four unpaired electrons, which we assign as a high-spin Fe(II) center. Like 1, complex 2 is EPR silent. Despite the ability of $K[Cp*IrH_3]$ to break the dimeric structure of 1, the strongly coordinating N-heterocyclic carbene 1,3-bis(2,6-diisopropylphenyl)-2-imidazolidinylidene (IPr) does not react with 1 to give a monomeric species.

Given the complex reduction reactivity of 1, we turned to oxidation (Scheme 2). The reaction of 1 with $AgPF_6$ in THF proceeds readily to yield benzene insoluble paramagnetic species with two signals at 18.3 and 14.8 ppm in the ¹H NMR spectrum collected in THF-$d_8$ (Figure S8). After several attempts with different crystal growing conditions, one crystal suitable for single crystal diffraction was obtained and revealed the formation of a cationic Ag(I) adduct with complex 1 rather than an oxidation product (Figure S22). We conclude that the bulk material contains a mixture of indistinct Fe, Ir and Ag coordination polymers, and did not pursue further. Oxidation of complex 2 with 1 equivalent of $AgPF_6$ leads to the formation of 1 and the sparingly soluble, polymeric $[Ag(Cp*IrH_3)]_n$ complex previously reported by our group,⁴² presumably as a result of transmetalation from $K^+$ to $Ag^+$. The remaining ($Cp*IrH_3$)$_2$Fe fragment dimerizes in solution to yield complex 1, as confirmed by ¹H NMR reaction monitoring (see the Supporting Information (SI)). These results suggest that silver salts are not oxidizing enough, prompting us to explore stronger oxidizing agents.

The reaction of tris(4-bromophenyl)ammoniumyl tetrakis(pentafluorophenyl)borate ($[Ar_3N][BArF]$, Magic Blue, MB) with 2 leads not only to the consumption of the organic radical cation but also to the production of complex 1. Here we presume that MB oxidizes one $[Cp*IrH_3]$⁻ fragment that dissociates from the Fe center. Crystals grown from this mixture confirm this hypothesis through the observation of a cationic hydrido-bridged Ir dimer, $[Cp*Ir(μ-H)_3IrCp*]BArF$ (Figure S23).⁴⁹ Analogous to the Ag case above, the liberated ($Cp*IrH_3$)$_2$Fe fragment dimerizes in solution to produce 1 without a formal Fe oxidation state change. Addition of $XeF_2$ and $[NO][PF_6]$ produce similar results (Figure S11). Unfortunately compound 2 is not stable in more coordinating

solvents such as acetonitrile, most likely due to the dissociation of $K[Cp*IrH_3]$ and formation of 1 (Figure S12), limiting choice of reaction conditions.

The inability for the hydrido-bridged Fe(II) clusters 1 and 2 to be oxidized led us to attempt the direct synthesis of Fe(III) congeners via salt metathesis between $FeCl_3$ and 3 equiv of $K[Cp*IrH_3]$. Perhaps unsurprisingly, complex 1 emerged as a major product of this reaction. We assume here that 1 equiv of $K[Cp*IrH_3]$ is acting as a reductant. Similarly, the reaction of $Fe(HMDS)_3$ with 3 equiv of $Cp*IrH_4$ proved unselective, yet again yielding complex 1 as a major product, as confirmed by ¹H NMR. It is clear from these results that the formation of the very stable diiron cluster, 1, is the driving force in all this chemistry, preventing further reactivity.

Overall, this work explores structural variations in heterometallic Ir/Fe complexes, expanding the currently limited examples of iron-containing heterometallic polyhydride clusters through a protonolysis reaction of $Cp*IrH_4$ with an iron(II) silylamide. The $[Cp*IrH_4]$ fragment, whose protonolysis reactivity was previously limited to reaction with metal alkyls, acts as a versatile weak-field ligand adopting what we propose to be one, two, or three bridging hydrido bonding modes. This flexibility can yield compounds of various nuclearities, highlighting the diversity of this heterobimetallic synthesis strategy. Given the commercial availability of transition metal (silyl)amides across the periodic table, we anticipate rapid development in hydrido-bridged heterobimetallic chemistry.

## ASSOCIATED CONTENT

### Supporting Information

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acs.organomet.5c00301.

General considerations, mono- and multimetallic iron polyhydrido complexes, synthetic procedures, and NMR, DRIFT, XRD, and ESI-MS data (PDF)

### Accession Codes

Deposition Numbers 2442205–2442209 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via the joint Cambridge Crystallographic Data Centre (CCDC) and Fachinformationszentrum Karlsruhe Access Structures service.

## AUTHOR INFORMATION

### Corresponding Author

Clément Camp – Laboratory of Catalysis, Polymerization, Processes and Materials (CP2M UMR 5128), CNRS, Université Claude Bernard Lyon 1, CPE-Lyon, Institut de Chimie de Lyon, F-69616 Villeurbanne, France;
orcid.org/0000-0001-8528-0731;
Email: clement.camp@univ-lyon1.fr

## Authors

Zachary Dubrawski - Laboratory of Catalysis, Polymerization, Processes and Materials (CP2M UMR 5128), CNRS, Université Claude Bernard Lyon 1, CPE-Lyon, Institut de Chimie de Lyon, F-69616 Villeurbanne, France

Billie Shearman - Laboratory of Catalysis, Polymerization, Processes and Materials (CP2M UMR 5128), CNRS, Université Claude Bernard Lyon 1, CPE-Lyon, Institut de Chimie de Lyon, F-69616 Villeurbanne, France;

orcid.org/0009-0002-5761-3900

Naïme Soulé - Laboratory of Catalysis, Polymerization, Processes and Materials (CP2M UMR 5128), CNRS, Université Claude Bernard Lyon 1, CPE-Lyon, Institut de Chimie de Lyon, F-69616 Villeurbanne, France

Erwann Jeanneau - Centre de Diffractométrie Henri Longchambon, Université Claude Bernard Lyon 1, 69100 Villeurbanne, France

Chloé Thieuleux - Laboratory of Catalysis, Polymerization, Processes and Materials (CP2M UMR 5128), CNRS, Université Claude Bernard Lyon 1, CPE-Lyon, Institut de Chimie de Lyon, F-69616 Villeurbanne, France;

orcid.org/0000-0002-5436-2467

Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.organomet.5c00301

## Notes

The authors declare no competing financial interest.

## ACKNOWLEDGMENTS

Funded by the European Union (ERC, DUO, 101041762). Views and opinions expressed are however those of the authors only and do not necessarily reflect those of the European Union or the European Research Council. Neither the European Union nor the granting authority can be held responsible for them. Dr. David Gajan is acknowledged for his assistance with paramagnetic NMR analysis.

## REFERENCES

(1) Babón, J. C.; Esteruelas, M. A.; López, A. M. Homogeneous Catalysis with Polyhydride Complexes. *Chem. Soc. Rev.* **2022**, *51* (23), 9717–9758.

(2) Yu, H.; Li, X.; Zheng, J. Beyond Hydrogen Storage: Metal Hydrides for Catalysis. *ACS Catal.* **2024**, *14* (5), 3139–3157.

(3) Takenaka, Y.; Shima, T.; Baldamus, J.; Hou, Z. Reduction of Transition-Metal-Coordinated Carbon Monoxide by a Rare-Earth Hydride Cluster: Isolation of Well-Defined Heteromultimetallic Oxycarbene, Oxymethyl, Carbene, and Methyl Complexes. *Angew. Chem., Int. Ed.* **2009**, *48* (42), 7888–7891.

(4) Shima, T.; Hou, Z. Rare Earth/d-Transition Metal Heteromultimetallic Polyhydride Complexes Based on Half-Sandwich Rare Earth Moieties. *Organometallics* **2009**, *28* (7), 2244–2252.

(5) Sun, C.; Teo, B. K.; Deng, C.; Lin, J.; Luo, G.-G.; Tung, C.-H.; Sun, D. Hydrido-Coinage-Metal Clusters: Rational Design, Synthetic Protocols and Structural Characteristics. *Coord. Chem. Rev.* **2021**, *427*, No. 213576.

(6) Ye, C. Z.; Del Rosal, I.; Kelly, S. N.; Ouellette, E. T.; Maron, L.; Camp, C.; Arnold, J. Synthesis, Structure, and Bonding of Actinide–Rhenium Polyhydrides. *Inorg. Chem.* **2024**, *63* (44), 21167–21176.

(7) Esteruelas, M. A.; López, A. M.; Oliván, M. Polyhydrides of Platinum Group Metals: Nonclassical Interactions and σ-Bond Activation Reactions. *Chem. Rev.* **2016**, *116* (15), 8770–8847.

(8) Plois, M.; Hujo, W.; Grimme, S.; Schwickert, C.; Bill, E.; de Bruin, B.; Pöttgen, R.; Wolf, R. Open-Shell First-Row Transition-Metal Polyhydride Complexes Based on the Fac-[RuH3(PR3)3]–Building Block. *Angew. Chem., Int. Ed.* **2013**, *52* (4), 1314–1318.

(9) Baya, M.; Houghton, J.; Daran, J.-C.; Poli, R. Formation and Structure of a Sterically Protected Molybdenum Hydride Complex with a 15-Electron Configuration: [(1,2,4-C5H2tBu3)Mo(PMe3)-2H]+. *Angew. Chem.* **2007**, *119* (3), 433–436.

(10) Poli, R. Chapter 6 - Paramagnetic Mono- and Polyhydrides of the Transition Metals. In *Recent Advances in Hydride Chemistry*; Peruzzini, M., Poli, R., Eds.; Elsevier: 2001; pp 139–188. DOI: 10.1016/B978-044450733-4/50006-1.

(11) Calvo-Molina, A.; Jover, J.; Pérez-Redondo, A.; Yélamos, C. Revisiting the Structure and Properties of Mid-Valent Monopentamethylcyclopentadienylchromium Complexes. *Dalton Trans.* **2025**, *54* (20), 8190–8203.

(12) Smythe, N. C.; Mondal, J.; Duque, J. G.; Feller, R. K.; Flores, M.; Gordon, J. C.; Henson, N. J.; Paz-Pasternak, M.; Rein, F. N.; Scott, B. L.; Taylor, R. D.; Trovitch, R. J. Historical Account of Dinitrogen-Bridged Diiron Complex Synthesis Using a Commercial Tripodal Ligand. *Chem. Commun.* **2025**, *61* (54), 9908–9911.

(13) Ryan, O. B.; Tilset, M.; Parker, V. D. Chemical and Electrochemical Oxidation of Group 6 Cyclopentadienylmetal Hydrides. First Estimates of 17-Electron Metal-Hydride Cation-Radical Thermodynamic Acidities and Their Decomposition of 17-Electron Neutral Radicals. *J. Am. Chem. Soc.* **1990**, *112* (7), 2618–2626.

(14) Smith, K. T.; Roemming, C.; Tilset, M. Unexpected Disproportionation Mechanism for Proton-Transfer Reactions between 17-Electron Metal Hydride Cation Radicals and Neutral 18-Electron Metal Hydrides. *J. Am. Chem. Soc.* **1993**, *115* (19), 8681–8689.

(15) Pleune, B.; Morales, D.; Meunier-Prest, R.; Richard, P.; Collange, E.; Fettinger, J. C.; Poli, R. Stable Paramagnetic Half-Sandwich Mo(V) and W(V) Polyhydride Complexes. Structural, Spectroscopic, Electrochemical, Theoretical, and Decomposition Mechanism Studies of [Cp\*MH3(Dppe)]+ (M = Mo, W). *J. Am. Chem. Soc.* **1999**, *121* (10), 2209–2225.

(16) Araake, R.; Sakadani, K.; Tada, M.; Sakai, Y.; Ohki, Y. [Fe4] and [Fe6] Hydride Clusters Supported by Phosphines: Synthesis, Characterization, and Application in N2 Reduction. *J. Am. Chem. Soc.* **2017**, *139* (15), 5596–5606.

(17) Tseng, C.-C.; Ding, Y.-W.; Chen, Z.-Y.; Lan, H.-Y.; Li, H.-J.; Cheng, Y.-S.; Kuo, T.-S.; Chen, P.-L.; Wu, W.-C.; Shi, F.-K.; Yang, T.; Liu, H.-J. A Bis-Cyclopentadienyl Ligand-Supported Di-Iron Trihydride Motif as a Synthon for Access to Heterobimetallic Trinuclear Complexes. *Inorg. Chem.* **2024**, *63* (24), 11361–11368.

(18) Reiners, M.; Maekawa, M.; Baabe, D.; Zaretzke, M.-K.; Schweyen, P.; Daniliuc, C. G.; Freytag, M.; Raeder, J.; Hohenberger, J.; Sutter, J.; Meyer, K.; Walter, M. D. Monomeric Fe(III) Half-Sandwich Complexes [Cp\*FeX2] – Synthesis, Properties and Electronic Structure. *Dalton Trans.* **2018**, *47* (31), 10517–10526.

(19) Ott, J. C.; Blasius, C. K.; Wadepohl, H.; Gade, L. H. Synthesis, Characterization, and Reactivity of a High-Spin Iron(II) Hydrido Complex Supported by a PNP Pincer Ligand and Its Application as a Homogeneous Catalyst for the Hydrogenation of Alkenes. *Inorg. Chem.* **2018**, *57* (6), 3183–3191.

(20) Foerster, S.; Stein, M.; Brecht, M.; Ogata, H.; Higuchi, Y.; Lubitz, W. Single Crystal EPR Studies of the Reduced Active Site of [NiFe] Hydrogenase from Desulfovibrio Vulgaris Miyazaki F. *J. Am. Chem. Soc.* **2003**, *125* (1), 83–93.

(21) Igarashi, R. Y.; Laryukhin, M.; Dos Santos, P. C.; Lee, H.-I.; Dean, D. R.; Seefeldt, L. C.; Hoffman, B. M. Trapping H-Bound to the Nitrogenase FeMo-Cofactor Active Site during H2 Evolution: Characterization by ENDOR Spectroscopy. *J. Am. Chem. Soc.* **2005**, *127* (17), 6231–6241.

(22) Gloaguen, F.; Lawrence, J. D.; Rauchfuss, T. B. Biomimetic Hydrogen Evolution Catalyzed by an Iron Carbonyl Thiolate. *J. Am. Chem. Soc.* **2001**, *123* (38), 9476–9477.
(23) Escomel, L.; Del Rosal, I.; Maron, L.; Jeanneau, E.; Veyre, L.; Thieuleux, C.; Camp, C. Strongly Polarized Iridiumδ--Aluminumδ+ Pairs: Unconventional Reactivity Patterns Including CO2 Cooperative Reductive Cleavage. *J. Am. Chem. Soc.* **2021**, *143* (12), 4844–4856.

(24) Lassalle, S.; Jabbour, R.; Schiltz, P.; Berruyer, P.; Todorova, T. K.; Veyre, L.; Gajan, D.; Lesage, A.; Thieuleux, C.; Camp, C. Metal–Metal Synergy in Well-Defined Surface Tantalum–Iridium Heterobimetallic Catalysts for H/D Exchange Reactions. *J. Am. Chem. Soc.* **2019**, *141* (49), 19321–19335.

(25) Ye, C. Z.; Rosal, I. D.; Boreen, M. A.; Ouellette, E. T.; Russo, D. R.; Maron, L.; Arnold, J.; Camp, C. A Versatile Strategy for the Formation of Hydride-Bridged Actinide–Iridium Multimetals. *Chem. Sci.* **2023**, *14* (4), 861–868.

(26) Lassalle, S.; Petit, J.; Falconer, R. L.; Hérault, V.; Jeanneau, E.; Thieuleux, C.; Camp, C. Reactivity of Tantalum/Iridium and Hafnium/Iridium Alkyl Hydrides with Alkyl Lithium Reagents: Nucleophilic Addition, Alpha-H Abstraction, or Hydride Deprotonation? *Organometallics* **2022**, *41* (13), 1675–1687.

(27) Dubrawski, Z.; Rosal, I. D.; Jeanneau, E.; Maron, L.; Thieuleux, C.; Camp, C. Synergistic C–H Bond Activation across Molybdenum–Iridium Multiply Bonded Complexes: A Cascade of Transformations. *Chem. Sci.* **2025**, *16* (32), 14564–14577.

(28) Saint-Denis, T. G.; Zhang, B.; Settineri, N. S.; Handford, R. C.; Hall, M. B.; Tilley, T. D. Dimetalloylene (M-E-M) Complexes of Heavier Main Group Elements Ge, Sn, Pb, Bi via Cleavage of E-X Bonds (X = N(SiMe3)2, OtBu) with an Iridium Hydride. *Chemistry-A European Journal* **2023**, *29* (49), No. e202301863.

(29) Ye, C. Z.; Rosal, I. D.; Kelly, S. N.; Brackbill, I. J.; Maron, L.; Camp, C.; Arnold, J. Photolysis-Driven Bond Activation by Thorium and Uranium Tetraosmate Polyhydride Complexes. *Chem. Sci.* **2024**, *15* (25), 9784–9792.

(30) Ishihara, K.; Araki, Y.; Tada, M.; Takayama, T.; Sakai, Y.; Sameera, W. M. C.; Ohki, Y. Synthesis of Dinuclear Mo–Fe Hydride Complexes and Catalytic Silylation of N2. *Chemistry-A European Journal* **2020**, *26* (43), 9537–9546.

(31) Ott, J. C.; Wadepohl, H.; Enders, M.; Gade, L. H. Taking Solution Proton NMR to Its Extreme: Prediction and Detection of a Hydride Resonance in an Intermediate-Spin Iron Complex. *J. Am. Chem. Soc.* **2018**, *140* (50), 17413–17417.

(32) Higaki, T.; Tanaka, K.; Izu, H.; Oishi, S.; Kawamoto, K.; Tada, M.; Sameera, W. M. C.; Takahata, R.; Teranishi, T.; Kikkawa, S.; Yamazoe, S.; Shiga, T.; Nihei, M.; Kato, T.; Cramer, R. E.; Zhang, Z.; Meyer, K.; Ohki, Y. An Icosahedral 55-Atom Iron Hydride Cluster Protected by Tri-Tert-Butylphosphines. *J. Am. Chem. Soc.* **2025**, *147* (4), 3215–3222.

(33) Timmer, G. H.; Berry, J. F. Jahn-Teller Distortion, Ferromagnetic Coupling, and Electron Delocalization in a High-Spin Fe–Fe Bonded Dimer. *Comptes Rendus Chimie* **2012**, *15* (2), 192–201.

(34) Hernández Sánchez, R.; Betley, T. A. Meta-Atom Behavior in Clusters Revealing Large Spin Ground States. *J. Am. Chem. Soc.* **2015**, *137* (43), 13949–13956.

(35) Hernández Sánchez, R.; Bartholomew, A. K.; Powers, T. M.; Ménard, G.; Betley, T. A. Maximizing Electron Exchange in a [Fe3] Cluster. *J. Am. Chem. Soc.* **2016**, *138* (7), 2235–2243.

(36) Olmstead, M. M.; Power, P. P.; Shoner, S. C. Three-Coordinate Iron Complexes: X-Ray Structural Characterization of the Iron Amide-Bridged Dimers [Fe(NR2)2]2 (R = SiMe3, C6H5) and the Adduct Fe[N(SiMe3)2]2(THF) and Determination of the Association Energy of the Monomer Fe{N(SiMe3)2}2 in Solution. *Inorg. Chem.* **1991**, *30* (11), 2547–2551.

(37) Chacon-Teran, M. A.; Creutz, S. E.; Rodriguez-Lugo, R. E.; Demeshko, S.; Meyer, F.; Kajetanowicz, A.; Grela, K. Construction of Diiron Diamond-Core Complexes Influenced by a Fluoroalkoxide Ligand. *Organometallics* **2024**, *43* (4), 564–572.

(38) Stennett, C. R.; Wagner, C. L.; Fettinger, J. C.; Vasko, P.; Power, P. P. Reductions of M{N(SiMe3)2}3 (M = V, Cr, Fe): Terminal and Bridging Low-Valent First-Row Transition Metal

Hydrido Complexes and “Metallo-Transamination.” *Inorg. Chem.* **2021**, *60* (15), 11401–11411.

(39) Ohta, S.; Yokozawa, S.; Ohki, Y.; Tatsumi, K. Oxido-Bridged Di-, Tri-, and Tetra-Nuclear Iron Complexes Bearing Bis-(Trimethylsilyl)Amide and Thiolate Ligands. *Inorg. Chem.* **2012**, *51* (4), 2645–2651.

(40) Gieshoff, T. N.; Chakraborty, U.; Villa, M.; Jacobi von Wangelin, A. Alkene Hydrogenations by Soluble Iron Nanocluster Catalysts. *Angew. Chem., Int. Ed.* **2017**, *56* (13), 3585–3589.

(41) Stevens, R. C.; Mclean, M. R.; Wen, T.; Carpenter, J. D.; Bau, R.; Koetzle, T. F. An X-Ray and Neutron Diffraction Structure Analysis of a Triply-Bridged Binuclear Iridium Complex, [[C5-(CH3)5Ir)2](μ-H)3]+ [ClO4]⁻·2C6H6]. *Inorg. Chim. Acta* **1989**, *161* (2), 223–231.

(42) Escomel, L.; Soulé, N.; Robin, E.; Del Rosal, I.; Maron, L.; Jeanneau, E.; Thieuleux, C.; Camp, C. Rational Preparation of Well-Defined Multinuclear Iridium–Aluminum Polyhydride Clusters and Comparative Reactivity. *Inorg. Chem.* **2022**, *61* (15), 5715–5730.

(43) Lassalle, S.; Jabbour, R.; Del Rosal, I.; Maron, L.; Fonda, E.; Veyre, L.; Gajan, D.; Lesage, A.; Thieuleux, C.; Camp, C. Stepwise Construction of Silica-Supported Tantalum/Iridium Heteropolymeric Catalysts Using Surface Organometallic Chemistry. *J. Catal.* **2020**, *392*, 287–301.

(44) Bortoluzzi, M.; Ciabatti, I.; Femoni, C.; Hayatifar, M.; lapalucci, M. C.; Zacchini, S. [H3-NFe4(CO)12(IrCOD)]N⁻ (n = 1, 2) and [H2Fe3(CO)10(IrCOD)]⁻–Bimetallic Fe–Ir Hydride Carbonyl Clusters. *Organometallics* **2015**, *34* (1), 189–197.

(45) Berti, B.; Bortoluzzi, M.; Cesari, C.; Femoni, C.; Hayatifar, M.; lapalucci, M. C.; Zacchini, S. Bimetallic Fe–Ir and Trimetallic Fe–Ir–Au Carbonyl Clusters Containing Hydride and/or Phosphine Ligands: Syntheses, Structures and DFT Studies. *J. Clust Sci.* **2021**, *32* (3), 743–753.

(46) Ohki, Y.; Araki, Y.; Tada, M.; Sakai, Y. Synthesis and Characterization of Bioinspired [Mo2Fe2]–Hydride Cluster Complexes and Their Application in the Catalytic Silylation of N2. *Chemistry-A European Journal* **2017**, *23* (53), 13240–13248.

(47) Abdur-Rashid, K.; Gusev, D. G.; Landau, S. E.; Lough, A. J.; Morris, R. H. Organizing Chain Structures by Use of Proton–Hydride Bonding. The Single-Crystal X-Ray Diffraction Structures of [K(Q)][Os(H)5(PiPr3)2] and [K(Q)][Ir(H)4(PiPr3)2], Q = 18-Crown-6 and 1,10-Diaza-18-Crown-6. *J. Am. Chem. Soc.* **1998**, *120* (45), 11826–11827.

(48) Pérez-Jiménez, M.; Campos, J.; Jover, J.; Álvarez, S.; Carmona, E. Supported σ-Complexes of Li–C Bonds from Coordination of Monomeric Molecules of LiCH3, LiCH2CH3 and LiC6H5 to Mo≡Mo Bonds. *Angew. Chem., Int. Ed.* **2022**, *61* (8), No. e202116009.

(49) Gilbert, T. M.; Bergman, R. G. Synthesis of Trimethylphosphine-Substituted (Pentamethylcyclopentadienyl)Iridium Hydride Complexes; Protonation and Deprotonation of (Pentamethylcyclopentadienyl)(Trimethylphosphine)Iridium Hydride. *J. Am. Chem. Soc.* **1985**, *107* (12), 3502–3507.