# Adaptive Rhodium Catalysis with a Lewis-Acidic Secondary Sphere for Divergent Hydrogenation of Propargylic Alcohols

Jiajun Wu, Vishal Chugh, Lachlan Sharp-Bucknall, Ibrahim Abdellah, Alexandre Vasseur, Christophe Werlé

► To cite this version:

Jiajun Wu, Vishal Chugh, Lachlan Sharp-Bucknall, Ibrahim Abdellah, Alexandre Vasseur, et al. Adaptive Rhodium Catalysis with a Lewis-Acidic Secondary Sphere for Divergent Hydrogenation of Propargylic Alcohols. Angewandte Chemie International Edition, In press, 10.1002/anie.202515903. hal-05296469

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# Adaptive Rhodium Catalysis with a Lewis–Acidic Secondary Sphere for Divergent Hydrogenation of Propargylic Alcohols

Jiajun Wu, Vishal Chugh, Lachlan Sharp-Bucknall, Ibrahim Abdellah, Alexandre Vasseur, and Christophe Werlé*

**Abstract:** Achieving chemoselective transformations of multifunctional molecules under mild and sustainable conditions remains a central challenge in catalysis. Here, we show that a rhodium complex equipped with a Lewis acidic secondary coordination sphere can mediate condition-dependent, divergent hydrogenation of propargylic alcohols. By tuning the reaction medium, the system selectively yields one of three products—retained alkynes, allylic ethers, or (E)-alkenes—from a single substrate-catalyst pair under hydrogen. Mechanical studies implicate π-allyl and rhodium hydride intermediates, with solvent polarity and nucleophilicity steering the reaction pathway. Control experiments confirm the critical roles of both molecular hydrogen and the boron Lewis acid in enabling divergent selectivity. These findings demonstrate how rational secondary-sphere design can enable adaptive catalysis and provide a platform for programmable bond transformations in multifunctional substrates.

Adaptive catalysts—systems that modulate their reactivity in response to subtle environmental cues—represent a strategic frontier in selective synthesis.[1–8] In contrast, conventional catalysts, though often effective at favoring thermodynamic products, may lack the kinetic discrimination needed to distinguish between similar reactive sites. This limitation becomes particularly evident with multifunctional substrates,

where competing pathways require careful control over chemo-, regio-, and stereoselectivity.

Molecular hydrogen ($H_2$) is a highly atom-economical and environmentally benign reductant,[9,10] and continues to attract interest for sustainable catalysis.[11–13] However, with multifunctional substrates, especially under forcing conditions (e.g., elevated pressures or temperatures), conventional hydrogenation catalysts often fail to maintain chemoselectivity due to competing pathways.

Propargylic alcohols illustrate this challenge. These readily available building blocks feature orthogonal hydroxy and alkyne groups, supporting a diverse set of transformations[14]—including substitution,[15–36] rearrangement,[37–43] and reduction (Scheme 1a1).[44–50] Although protocols have been developed to achieve specific reduction outcomes from propargylic alcohols (Scheme 1a2), each transformation generally relies on a distinct catalytic system tailored to a single pathway—such as deoxygenation or reduction of alkynes to *cis*- or *trans*-alkenes. Notably, these methods often require stoichiometric reductants (e.g., silanes or hydrides), and few offer effective chemoselectivity under hydrogen gas, highlighting a key limitation in sustainable reductive strategies. A single approach capable of selectively accessing multiple products from this functional motif—such as alkynes, allylic ethers, or alkenes—would streamline synthetic planning and facilitate access to scaffolds found in biologically active compounds (Scheme 1b).[51–55]

Inspired by this opportunity, we considered whether a catalyst combining a secondary coordination sphere for hydroxyl activation and a metal site for hydrogenation and/or alkyne binding could enable divergent reactivity (Scheme 1c). Such a system might engage the alcohol through Lewis acid-base interactions while promoting hydride formation or π-activation at the metal center. In line with this design, we turned to a rhodium complex previously developed in our group for chemoselective nitroarene hydrogenation,[4] which features a modular ligand incorporating a triazine π-acceptor, a nitrogen-tethered phosphine donor, and a proximal borane Lewis acid.[56–71] This architecture creates a polarized coordination environment capable of supporting both *inner*- and *outer*-sphere processes. We reasoned that its reactivity could be shifted from heteroatom reduction to the more challenging context of multifunctional propargylic substrates.

Here, we report that this boron-assisted rhodium complex enables condition-dependent hydrogenation of propargylic alcohols to yield three distinct products under mild conditions

<footnote>[*] J. Wu, V. Chugh, L. Sharp-Bucknall, C. Werlé
Max Planck Institute for Chemical Energy Conversion, Stiftstr. 34–36
45470, Mülheim an der Ruhr, Germany
E-mail: christophe.werle@cec.mpg.de
christophe.werle@univ-lorraine.fr</footnote>

<footnote>I. Abdellah
Université de Lorraine, CNRS, L2CM, Metz F-57000, France</footnote>

<footnote>A. Vasseur, C. Werlé
Université de Lorraine, CNRS, L2CM, Nancy F-54000, France</footnote>
a) Current Strategies

a) Functionalization of Propargylic Alcohols

<figure><img src="image_2.png" /></figure>

<figure><img src="image_3.png" /></figure>

a2) Selective Reduction of Propargylic Alcohols

<figure><img src="image_4.png" /></figure>

For Deoxygenation

[Ru] / Et₃SiH

□ Ca(NTf)₂ / Et₃SiH

□ B(C₆F₅)₃ / PhSiH₃

For cis-Reduction

□ Lindlar Catalyst / H₂

For trans-Reduction

□ Vitride

□ NHC / Ph₂SiH₂

□ [Cp*Ru(cod)Cl] / H₂

<figure><img src="image_5.png" /></figure>

<figure><img src="image_6.png" /><figcaption>Vitride</figcaption></figure>

<figure><img src="image_7.png" /><figcaption>NHC</figcaption></figure>

b) Construction of Bioactive Molecules from Propargylic Alcohols

<figure><img src="image_8.png" /><figcaption>Tumor Necrosis
Factor-α
Inhibitor Candidate</figcaption></figure>

<figure><img src="image_9.png" /><figcaption>Docetaxel
(Clinically Approved Anticancer
Chemotherapeutic)</figcaption></figure>

<figure><img src="image_10.png" /><figcaption>Synthetic Retinoid
(Retinoic Acid
Receptor Agonist)</figcaption></figure>

c) Motivation and Design Principles

<figure><img src="image_11.png" /></figure>

d) This Work: Adaptive, Condition-Controlled Chemoselectivity

<figure><img src="image_12.png" /><figcaption>**Scheme 1.** Conceptual overview and design framework for controlled hydrogenation of propargylic alcohols.</figcaption></figure>

(Scheme 1d). By modulating the reaction medium, the catalyst can be directed to favor the formation of retained alkynes, allylic ethers, or alkenes. These findings expand the scope of adaptive catalysis beyond heteroatom reduction, demonstrating that secondary-sphere interactions and hydrogen activation can be orchestrated to direct divergent reactivity from a single scaffold—a hallmark of adaptive catalysis.

With the mechanistic hypothesis in hand, we first assessed
whether rhodium complex C1 could mediate condition-

dependent transformations of propargylic alcohols. We
selected 1,3-diphenylprop-2-yn-1-ol (1a) as a benchmark
substrate. Under initial conditions (1 mol% C1 in dioxane,
80 °C, 2 bar H₂, 5 h), hydrodeoxygenation to alkyne 2a was
the predominant outcome, forming in 65% yield alongside
minor amounts of allylic alcohol 3aa and (E)-alkene 4a
(Table 1, entry 1). This outcome indicated that C1 can engage
and discriminate between both the hydroxyl and alkyne
functionalities under a single catalytic platform, enabling
multiple distinct reductive pathways. Systematic variation of
<figure><img src="image_13.png" /><figcaption>**Table 1:** Optimization of reaction conditions for divergent hydrogenation of propargylic alcohol **1a**.</figcaption></figure>

a) Conversions (%) and yields (%) are determined by ¹H NMR using mesitylene (0.25 mmol) as the internal standard.

reaction parameters revealed strong condition-dependence in product distribution. Lowering the hydrogen pressure to 1 bar and reducing the temperature to 70 °C increased the yield of alkyne **2a** to 76%, indicating that milder conditions favor hydrodeoxygenation (Table 1, entry 7). In contrast, the choice of solvent had a marked effect on selectivity. When the reaction was conducted in isopropanol, alkene **4a** was obtained as the major product in 92% yield (Table 1, entry 4), whereas methanol under milder conditions (40 °C) favored the formation of allylic ether **3a** in 90% yield (Table 1, entry 8). These outcomes suggest that both the polarity and nucleophilicity of the medium influence the course of the reaction. Control experiments confirmed the homogeneous nature of the catalysis.[72,73] Neither mercury nor thiourea poisoning significantly affected the reactivity (Table 1, entries 9–11). In contrast, omission of H₂ completely suppressed product formation, confirming the requirement of molecular hydrogen as the terminal reductant.

With three condition sets identified—*Condition A* (hydrodeoxygenation to alkynes), *Condition B* (allylic ether formation), and *Condition C* (alkene formation)—we next evaluated the generality of the rhodium complex across a series of propargylic alcohols (Scheme 2).

Under *Condition A*, substrates bearing electron-donating substituents (Me, *t*-Bu, OMe, and OH) on the aryl ring afforded alkynes **2b–2d** and **2m–2p** in good yields. Halogenated substrates (*p*-F, *p*-Cl) were similarly well tolerated, furnishing **2e**, **2h**, **2q**, and **2r**. In contrast, electron-deficient motifs such as CF₃, CO₂Me, and *m*-F led to diminished reactivity, with only trace to moderate yields of **2f** and **2s–2t**. Notably, amide-substituted alcohol **1u** gave alkyne **2u** in 84% yield, suggesting good chemoselectivity toward reductive deoxygenation in the presence of polar functional

groups.[74] Heterocyclic, biphenyl, and naphthyl substrates (**2i**, **2j**, **2v**, **2w**) were also compatible. However, purely aliphatic substrate **1y** showed low conversion, yielding only 25% of **2y**, consistent with a preference for π-rich aryl systems under these conditions.

Applying *Conditions B* and *C* to the same substrate pool enabled divergent access to allylic ethers (**3b–3j**) and alkenes (**4b–4j**), maintaining broad compatibility. Aryl substrates with electron-donating or halogen substituents underwent smooth conversion under both conditions, with representative yields up to 99%. Biphenyl and naphthyl derivatives also performed well, affording **3i–3j** and **4i–4j** in high yields. In contrast, substrates bearing strongly electron-withdrawing groups (e.g., CF₃, CO₂Me) required increased temperature and catalyst loading to achieve moderate yields of **3k–3l** and **4k–4l**. For the cyclohexyl-substituted substrate **1x**, *Condition B* afforded ether **3x** (90%), while *Condition C* yielded alkene **4x** (83%) with retained isopropyl ether functionality—an exception to the typical full deoxygenation observed under these conditions. For unsymmetrical substrates bearing electronically distinct aryl groups, reactions under *Conditions B* and *C* generally afforded near 1:1 mixtures of regioisomeric ethers and alkenes. These outcomes likely reflect similar accessibility of both aryl termini during the transformation (see the Supporting Information, Scheme S1, for full product distributions and yields).

To evaluate the operational practicality of the system, representative substrates were subjected to *gram-scale* reactions. Substrates **1a** (4.75 mmol), **1c** (3.5 mmol), and **1n** (4.5 mmol) were subjected to the reaction conditions appropriate for each target product, affording alkyne **2n** (75%, 0.75 g), ether **3a** (87%, 0.93 g), and alkene **4c** (88%, 0.94 g) without loss of efficiency or selectivity. These results demonstrate that the
### Scope of Selective Deoxygenation, Hydrogenation and Deoxygenation-Hydrogenation<sup>a</sup>

<figure><img src="image_14.png" /></figure>

<figure><img src="image_15.png" /></figure>

#### Scope of Selective Deoxygenation (Condition A)

<figure><img src="image_16.png" /></figure>

2a 76(69)

2b (R = Me) 68(67)

2c (R = t-Bu) 63(54)

2d (R = OMe) 70(62)

2e 81(77)

<figure><img src="image_17.png" /></figure>

<figure><img src="image_18.png" /></figure>

2i 83(74)<sup>d</sup>

2j 50(41)

<figure><img src="image_19.png" /></figure>

<figure><img src="image_20.png" /></figure>

2s (R = CF<sub>3</sub>) 10<sup>f</sup>

2t (R = CO<sub>2</sub>Me) 19<sup>c</sup>

2u 84(73)

<figure><img src="image_21.png" /></figure>

2m (R = Me) 79(73)

2n (R = OMe) 89(87)

Gram-scale: 80(75)

2o (R = OH) 66(60)<sup>e</sup>

<figure><img src="image_22.png" /></figure>

2v 77(76)

2f 13<sup>b,c</sup>

<figure><img src="image_23.png" /></figure>

2p 85(81)

<figure><img src="image_24.png" /></figure>

2w 48(48)

2h 55(53)<sup>c</sup>

<figure><img src="image_25.png" /></figure>

2q (X = F) 71(66)

2r (X = Cl) 54(50)<sup>c</sup>

<figure><img src="image_26.png" /></figure>

2y 25

#### Scope of Selective Hydrogenation (Condition B)

<figure><img src="image_27.png" /></figure>

3a 90(81)
Gram-scale: 92(87)

3b 77(65)<sup>g</sup>

3c 47<sup>g</sup>

3e 92(89)

<figure><img src="image_28.png" /></figure>

3f 97(90)<sup>c</sup>

3g 86(80)<sup>c</sup>

3h 81(77)

3i 75(71)<sup>d</sup>

<figure><img src="image_29.png" /></figure>

<figure><img src="image_30.png" /></figure>

3j 86(80)<sup>g</sup>

3k 65(60)<sup>c,d,h</sup>

<figure><img src="image_31.png" /></figure>

3l 69(65)<sup>b,c,d</sup>

<figure><img src="image_32.png" /></figure>

3x 90(86)<sup>c</sup>

#### Scope of Deoxygenation and Hydrogenation (Condition C)

<figure><img src="image_33.png" /></figure>

4a 92(91)

4b 95(86)

4c 99(98)

Gram-scale: 92(88)

4d 45<sup>f</sup>

4e 87(85)

<figure><img src="image_34.png" /></figure>

<figure><img src="image_35.png" /></figure>

<figure><img src="image_36.png" /></figure>

<figure><img src="image_37.png" /></figure>

4f 57(49)<sup>d,h,j</sup>

4g 69(61)<sup>d,h,j</sup>

4h 91(84)<sup>d,j</sup>

4i 80(75)<sup>d,j</sup>

<figure><img src="image_38.png" /></figure>

<figure><img src="image_39.png" /></figure>

<figure><img src="image_40.png" /></figure>

<figure><img src="image_41.png" /></figure>

4j 91(85)

4k 26<sup>d,k</sup>

4l 70(62)<sup>d,k</sup>

4x 58(50) (from 1x)
83(75) (from 1y)

**Scheme 2.** Scope of substrates under optimized conditions. <sup>a)</sup> Condition A: **1** (0.5 mmol), **C1** (1 mol%), dioxane (2 mL), **H<sub>2</sub>** (1 bar), 70 °C, 3 h; Condition B: **1** (0.5 mmol), **C1** (1 mol%), MeOH (2 mL), **H<sub>2</sub>** (2 bar), 40 °C, 5 h; Condition C: **1** (0.5 mmol), **C1** (1 mol%), i-PrOH (2 mL), **H<sub>2</sub>** (2 bar), 80 °C, 5 h; yields were determined by ¹H NMR using mesitylene (0.5 mmol) as an internal standard; isolated yields are given in parentheses. <sup>b)</sup> **C1** (2 mol%). <sup>c)</sup> 80 °C. <sup>d)</sup> Substrate in 0.25 mmol scale. <sup>e)</sup> i-PrOH, 2 bar, 60 °C, 5 h. <sup>f)</sup> 16 h. <sup>g)</sup> 3 h. <sup>h)</sup> **C1** (3 mol%). <sup>i)</sup> MeOH, 40 °C. <sup>j)</sup> 100 °C. <sup>k)</sup> **C1** (5 mol%), 120 °C.
Catalyst Evaluation under Optimized Conditions

<figure><img src="image_42.png" /><figcaption>Target Products:</figcaption></figure>

<figure><img src="image_43.png" /></figure>

<figure><img src="image_44.png" /><figcaption>Side Products:</figcaption></figure>

<figure><img src="image_45.png" /></figure>

<figure><img src="image_46.png" /></figure>

5a-2 (R = Me)

5a-3 (R = i-Pr)

6a-1 (R = H)

6a-2 (R = i-Pr)

<figure><img src="image_47.png" /><figcaption>Catalyst Performance Under Condition A</figcaption></figure>

<figure><img src="image_48.png" /><figcaption>Catalyst Performance Under Condition B</figcaption></figure>

<figure><img src="image_49.png" /><figcaption>Catalyst Performance Under Condition C</figcaption></figure>

<figure><img src="image_50.png" /><figcaption>**Scheme 3.** Comparative catalyst screening under standard conditions. Black bars indicate the remaining unreacted starting material **1a**.</figcaption></figure>
a) Control Experiments in the Absence of H₂

<figure><img src="image_51.png" /></figure>

<table><thead><tr><th>Entry</th><th>Conditions</th><th>Conv.(%)</th><th>Yield of 5a-1(%)</th><th>Yield of 5a-2(%)</th><th>Yield of 5a-3(%)</th></tr></thead><tbody><tr><td>1</td><td>Dioxane, 70 °C</td><td>85</td><td>83</td><td>-</td><td>-</td></tr><tr><td>2</td><td>MeOH, 40 °C</td><td>82</td><td>53</td><td>24</td><td>-</td></tr><tr><td>3</td><td>i-PrOH, 80 °C</td><td>&gt;99</td><td>-</td><td>-</td><td>&gt;99</td></tr></tbody></table>

b) Control Experiment: Formation of 2a from 5a-1

<figure><img src="image_52.png" /></figure>

c) Deuterium-Labeling Experiment under Condition A

<figure><img src="image_53.png" /></figure>

d) Deuterium-Labeling Experiment with 3a as Starting Material

<figure><img src="image_54.png" /></figure>

e) Deuterium-Labeling Experiment under Condition B

<figure><img src="image_55.png" /></figure>

e) Formation of 2a with [Rh–H]

<figure><img src="image_56.png" /><figcaption>Proposed Structure of the
Rhodium Hydride Species</figcaption></figure>

<figure><img src="image_57.png" /></figure>

f) Formation of 4a with [Rh–H]

<figure><img src="image_58.png" /></figure>

Inferred from NMR (Angew. Chem. Int. Ed. 2022, 61, e202205515) and XRD of a boron-free analogue (Chem Catal. 2024, 4, 101078).

g) Control Experiments with 3m

<figure><img src="image_59.png" /></figure>

h) Proposed Mechanistic Pathway

<figure><img src="image_60.png" /><figcaption>**Scheme 4.** Empirical mechanistic studies and tentative catalytic cycle. a) Yields were determined by ¹H NMR using an internal standard, as detailed in the Supporting Information; isolated yields are provided in parentheses.</figcaption></figure>
method is readily scalable without compromising efficiency or selectivity, supporting its potential application in synthetic campaigns.

To elucidate the origins of selectivity and the role of
catalyst design in governing divergent reactivity, we compared
rhodium complex C1 to a series of structurally related
analogues under representative conditions (Scheme 3). The
boron-free complex C2, previously shown to catalyze the
semihydrogenation of internal alkynes,[8] displayed dimin-
ished activity and selectivity, affording only 30% of alkyne 2a
under Condition A and 70% of alkene 4a under Condition C.
Supplementing C2 with a boron-based additive (C3) partially
restored activity, suggesting that boron-mediated secondary-
sphere interactions contribute critically to both reactivity and
selectivity, particularly during deoxygenation.[75] In contrast,
benchmark hydrogenation catalysts (C4–C9) failed to yield
the target products under any of the tested conditions, instead
producing mixtures of side products, highlighting the distinct
reactivity of C1.

Further mechanistic studies with C1 revealed a condition-
responsive, stepwise network (Scheme 4). In the absence of
hydrogen, propargylic alcohol 1a underwent etherification to
yield a mixture of propargylic ethers (5a-1, 5a-2, 5a-3), with
the product distribution dependent on solvent (Scheme 4a).
Under hydrogenative conditions, 5a-1 was selectively con-
verted to alkyne 2a (Scheme 4b), supporting the role of ether
intermediates in the hydrodeoxygenation pathway.[76]

To probe the origin of hydrogen incorporation during
reduction, deuterium-labeling experiments were conducted
under *Conditions A* and *C*. Exposure of *1a* to *D*₂ (1 bar) under
*Condition A* led to *d*₁-2*a* in 60% yield (Scheme 4c), while
treatment of *3a* under *Condition C* afforded *d*₁-4*a* in 58%
yield (Scheme 4d). In both cases, deuterium incorporation
occurred at the propargylic or allylic position, consistent with
reduction mediated by a metal hydride species. To directly
evaluate the involvement of rhodium hydride intermediates,
a stoichiometric [Rh–H] complex was generated in situ from
C1 via a reported protocol.[8] This species converted *1a* and
3a into 2a (47%) and 4a (72%), respectively (Scheme 4e.f),
supporting its role as a common reductive intermediate in
both transformations.[77]

To gain further insight into the ether formation pathway
under *Condition B*, additional deuterium-labeling experi-
ments were carried out. Reaction of *1a* with *D*₂ (2 bar) gave
a near 1:1 mixture of *trans*-d₂-3*a* and *d*₂-3*a'* (Scheme 4g),
while transformation of *3m* in *d*₄-methanol afforded the
corresponding labeled ethers *d*₃-3*m* and *d*₃-3*m'* in 97%
combined yield (Scheme 4h, left). These results indicate
that methanol acts as a nucleophile, displacing the methoxy
group in a substitution process. Upon further hydrogenation,
*3m* was converted to alkenes *4m* and *4m'* in 91% yield
(Scheme 4h, right). The formation of regioisomeric and
isotope-labeled products from both ether and olefin precur-
sors supports a common intermediate accessible via C–O
bond activation, consistent with the involvement of a π-allyl-
type species,[78–93] likely formed through rhodium-catalyzed
activation of propargylic ethers.

Taken together, these findings support a unified mech-
anistic model for the condition-dependent transformation

of propargylic alcohols (Scheme 4i). Under nonreductive
conditions, initial etherification leads to propargylic ethers
(5), which serve as common intermediates. In aprotic solvents
such as dioxane, these ethers undergo deoxygenation via
rhodium hydride species to afford alkynes (2). In contrast,
protic solvents like methanol or isopropanol promote C–O
bond activation, enabling substitution to form allylic ethers
(3/3') at lower temperatures, or further reduction to alkenes
(4/4') at elevated temperatures via sequential hydrogenation.
This condition-responsive divergence highlights how subtle
changes in the reaction environment can steer product
selectivity through a shared intermediate pathway.

In summary, we have developed a condition-responsive
method for the divergent hydrogenation of propargylic
alcohols using a boron-assisted rhodium complex. By tuning
the reaction medium, a single substrate–catalyst combination
can selectively yield alkynes, allylic ethers, or alkenes with
high selectivity. Mechanistic studies support the involvement
of rhodium hydride and allylic-type intermediates, with
molecular hydrogen playing a central role in both reductive
pathways.

These findings illustrate how secondary-sphere design can
enable adaptive reactivity through modulation of reaction
conditions. More broadly, the ability to steer divergent
product outcomes from a common intermediate platform
suggests a powerful approach to programmable catalysis. This
strategy may ultimately be extended to enable chemo-, regio-,
or even enantioselective control in other transformation
classes—including C–C bond formation or multistep cascade
processes—using a single, tunable catalytic architecture. Such
adaptive systems challenge the traditional notion of “one
catalyst, one transformation” and open new directions for
reactivity control in complex molecular settings.

Author Contributions

J.W. performed the experiments, carried out analytical char-
acterizations, and prepared the initial manuscript draft. J.W.,
V.C., and L.S.B. jointly evaluated the substrate scope. I.A. and
A.V. contributed technical support in experiment execution
and data analysis. C.W. conceived and supervised the project
and led the manuscript revision with input from all authors.
All authors reviewed and approved the final version of the
manuscript.

Acknowledgements

The authors gratefully acknowledge the Max Planck Society for its generous financial support. This research was conducted under the auspices of the “Fuel Science Center” funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany’s Excellence Strategy–Exzellenzcluster 2186, the Fuel Science Center “ID: 90919832.” This work was supported partly by the French France 2030 program “Initiative d’Excellence Lorraine (LUE)”, reference ANR-15-IDEX-04-LUE. The authors thank D. Dodin for the design and construction of custom
devices. The authors are especially indebted to Prof. Dr. Walter Leitner for his unwavering and long-standing support.

Open access funding enabled and organized by Projekt DEAL.

## Conflict of Interests

The authors declare no conflict of interest.

**Keywords:** Adaptive catalysis • Divergent hydrogenation • Propargylic alcohols • Rhodium • Secondary-sphere interactions

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