# Room-Temperature Rh(I)-Catalyzed P(III)-Directed C–H Bond Alkylation: Enhanced Reactivity through Ligand Acceleration

Jian Zhang, Jean-François Soulé

► To cite this version:

Jian Zhang, Jean-François Soulé. Room-Temperature Rh(I)-Catalyzed P(III)-Directed C–H Bond Alkylation: Enhanced Reactivity through Ligand Acceleration. ACS Catalysis, 2025, 15, pp.2839-2846. 10.1021/acscatal.4c05673 . hal-04926339

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# Room-Temperature Rh(I)-Catalyzed P(III)-Directed C–H Bond Alkylation: Enhanced Reactivity through Ligand Acceleration

Jian Zhang and Jean-François Soulé*

Chimie ParisTech, PSL University, CNRS, Institute of Chemistry for Life and Health Sciences, 75005 Paris, France

E-mail: jean-francois.soule@chimieparistech.psl.eu

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

**ABSTRACT:** Despite the potential of Rh(I)-catalyzed trivalent phosphorus-directed C–H functionalizations to diversify phosphorus-containing molecules, the requirement for harsh reaction conditions has limited its broader application. In this study, we introduce a ligand-accelerated catalysis approach that enables room-temperature C–H bond alkylation of biaryl phosphines using a Rh(I) catalyst. Through kinetic investigation, we identified tris(4-trifluoromethylphenyl)phosphine as a privileged ligand that significantly enhances overall processes including catalyst stability and regeneration. Our NMR mechanistic studies revealed the formation of a Rh–H intermediate, providing direct evidence for an oxidative addition pathway. This work expands the utility of Rh(I)-catalyzed C–H functionalization under mild conditions and lays the groundwork for further development of ligand-accelerated strategies in other challenging catalytic processes, particularly those involving strong σ-donor directing groups, holding significant potential to broaden the chemical space of phosphorus-based compounds, with diverse applications.

**KEYWORDS:** C–H Bond Activations; Kinetics; Mechanistic Studies; Mild Conditions; Phosphine Ligands; Rhodium.
INTRODUCTION

The exploration of transition metal-catalyzed C–H bond functionalization has become a cornerstone in the development of efficient and selective synthetic methodologies, offering a direct route to complex molecules from simple substrates.¹ However, a significant challenge in these processes is the often-harsh reaction conditions required. As a result, developing mild C–H functionalization conditions is highly desirable, as they provide the potential for improved functional group tolerance, enhanced selectivity, and broader applicability.² In transition-metal-catalyzed *ortho*-directed C–H bond functionalization, the directing group (DG) often acts as *σ*-donor ligand. While this interaction is crucial for directing the reaction, it can also lead to the formation of inactive catalytic species, necessitating harsh conditions to promote decomplexation (Figure 1A, left). An alternative strategy for performing reactions in the presence of such strongly chelating substrates is ligand-accelerated catalysis,³ where the addition of trace amounts of external ligands can promote the formation of more active catalytic species by finely tuning the electron density and coordination environment at the metal center (Figure 1A, middle).⁴ However, the ligand used in this approach must strike a delicate balance; it must not be too basic, as this could hinder ligand exchange with the substrate and lead to unreactive ligand-saturated complexes (Figure 1A, right).

<figure><img src="image_3.png" /><figcaption>**Figure 1.** Ligand-Accelerated Catalysis in C–H Bond Functionalizations</figcaption></figure>

Ligand-accelerated catalysis has been instrumental in the development of numerous ground-state Pd-catalyzed C–H functionalization reactions, utilizing a variety of ligands including but not limited to monoprotected amino acids (MPAA),⁵ pyridines,⁶ totaumeric ligands⁷, or S,O ligands.⁸ These advances have enabled new transformations and, in some cases, allowed reactions to proceed under milder conditions. However, Rh(I)-catalyzed C–H bond functionalization using ligand-accelerated catalysis remains relatively unexplored.⁹ Notable examples in this area include the use of NHC ligands for room-temperature C–H bond hydroboration¹⁰ and diphosphines for hydrosilylation under mild conditions (Figure 1B, right).¹¹

Recently, trivalent phosphorus [P(III)] has emerged as a powerful directing group, steering phosphorus-containing molecule synthesis toward late-stage diversification.¹² Several catalytic C–H bond functionalizations of phosphines have been
developed, including borylation,<sup>13</sup> arylation,<sup>14</sup> alkylation,<sup>15</sup> alkenylation,<sup>15a, 16</sup> and silylation,<sup>17</sup> with some approaches being
performed enantioselectively.<sup>18</sup> Among these, Rh(I) is commonly used as catalysts, with PhJohnPhos (2,2'-Bis(diphe-
nylphosphino)biphenyl) as the predominant substrate. However, most existing methodologies require harsh conditions, typ-
ically at temperatures around 140-160 °C, to achieve effective catalytic turnover. The strong σ-donor character of the P(III)
directing group can significantly reduce Rh reactivity and hinder catalyst regeneration. Given the potential of ligand-accel-
erated catalysis to address these challenges,<sup>19</sup> this study explores its application in the context of P(III) *ortho*-directed C–H
bond functionalizations—a context that has yet to be fully investigated. Identifying suitable ligands that can effectively
compete with substrates and products, which are themselves excellent phosphine ligands, is key to achieving this goal.
Herein, we present our findings on how ligand-accelerated catalysis enables room-temperature Rh(I)-catalyzed C–H bond
alkylation of biaryl phosphines, supported by a detailed mechanistic investigation that elucidates the reaction pathway and
the critical role of the ligand (Figure 1C).

METHODS

To investigate the ligand effect on Rh(I)-catalyzed C-H bond functionalization of phosphines, we focused on the alkylation
reaction to avoid the complexities associated with other oxidative additions, such as Ar-X or H-M (M = BPin, SiAlk₃) bond
formations (Figure 2). We selected PhJohnPhos (1a) and *tert*-butyl acrylate (2a) as model substrates in a 1:1.2 ratio. For the
catalyst, instead of using [RhCl(COD)]₂,¹⁵b we employed [RhCl(C₂H₄)]₂. The ethylene ligand in [RhCl(C₂H₄)]₂ is more
readily displaced without establishing an equilibrium in the presence of additional ligands, unlike the bidentate COD ligand.
All reactions were conducted by mixing all components *in situ* in toluene, in the presence of 3 equivalents of KOAc, at 25
°C. The progress of the reactions, specifically the formation of alkylated biarylphosphine **3a**, was monitored over 24 hours
using {¹H}³¹P NMR spectroscopy, with small aliquots taken periodically. As expected, a control reaction without a ligand
revealed that the reaction proceeded very poorly and slowly, with an initial velocity of 2.4 x 10⁻³ mol·L⁻¹·h⁻¹ and a maximum
yield of only about 13%. Subsequently, different types of “privileged” ligands in transition-metal catalysis and C-H bond
functionalization⁴ were evaluated to identify the best candidates that can compete with the phosphine starting materials and
induce ligand-accelerated catalysis. It was found that *N*-protected amino acid (**L1**), NHC (**L2**), acac (**L3**), pyridine (**L4**), and
bipyridine (**L5**) completely inhibited the reaction. The use of dppb (**L7**) and *rac*-BINAP (**L8**) definitively confirmed that
bidentate ligands inhibit the reaction.
<figure><img src="image_4.png" /><figcaption>**Figure 2.** Ligand Effect in Rh(I)-Catalyzed C–H Bond Alkylation of PhJohnPhos (1a) with tert-Butyl Acrylate (2a)</figcaption></figure>

However, the use of 8 mol% of PPh₃ (L6) allowed the reaction to proceed faster than the background reaction, with an initial velocity of 10.0 x 10⁻³ mol·L⁻¹·h⁻¹ and an overall ligand-acceleration effect of 4.17. Although the overall yield remained moderate (above 50%), these results encouraged us to evaluate other monophosphines with different electronic and steric features. Electron-rich tricyclohexylphosphine (L9) and tri(o-tolyl)phosphine (L10) also improved the kinetics of the reaction, but with lower overall ligand-acceleration effects of 2.71 and 2.50, respectively. The reaction performed in the presence of bulky tris-(2-naphthyl)phosphine (L11) showed a moderate initial velocity of 5.5 x 10⁻³ mol·L⁻¹·h⁻¹. In contrast, bulkier phosphines such as QPhos (L12) and BrettPhos (L13) resulted in ligand deceleration. However, the discovery of the strong accelerating effect of electron-poor tris(4-trifluoromethylphenyl)phosphine (L14) was remarkable. L14 enables the reaction to proceed with a significant initial velocity of 29.2 x 10⁻³ mol·L⁻¹·h⁻¹ and an overall ligand-acceleration effect of 12.17. Furthermore, the catalyst remained stable throughout the reaction, yielding 3a in an excellent 93%. This discovery highlights the crucial role of electron-poor phosphines in enhancing catalytic performance. It should be noted that a similar acceleration effect of this phosphine was also observed with Rh catalysts in the C(sp²)–H bond alkylation directed by a ketone group.²⁰ In comparison, more electron-poor phosphines such as L15 and L16 showed lower overall ligand-acceleration effects of 4.17 and 4.36, respectively. In addition, electron-rich aryl phosphines such as tri-p-tolylphosphine, or tris(4-methoxyphenyl)phosphine exhibited similar performance than thiphenyl phosphines (Table S9). This suggests that a balanced combination of σ-donation and π-back donation is required to maintain the stability of the catalytic active species and intermediate stabilization.
The insights gained from ligand-accelerated catalysis have enabled the development of a room-temperature Rh(I)-catalyzed biarylphosphine C–H bond alkylation reaction that accommodates diverse functional groups with varying electronic, steric, and binding characteristics, facilitated by the addition of 8 mol% of L14. Using PhJohnPhos as the substrate, a variety of alkenes were evaluated as coupling partners (Scheme 1). With tert-butyl acrylate as the coupling partner, we demonstrated that the reaction is reproducible on a 1 g scale of PhJohnPhos, affording the alkylated phosphine 3a in a slightly lower yield of 86% (1.19 g). Relatively low boiling point alkyl acrylates, such as methyl (80 °C) and ethyl (100 °C), reacted smoothly to yield the corresponding alkylated biarylphosphines 3b and 3c with excellent yields. Aryl containing acrylates, including benzyl and biphenyl, exhibited slightly lower reactivity, producing compounds 3d and 3e in 81% and 69% yields, respectively. Interestingly, sterically hindered 2,3,6-trimethylphenyl acrylate successfully coupled with PhJohnPhos, resulting in a 68% yield of 3f. Additionally, chiral L-menthyl acrylate was employed to synthesize chiral phosphine 3g, achieving an excellent 95% yield. This phosphine 3g is obtained as a 50% mixture of diastereoatropisomers, as shown by the two peaks in the ¹H{{³¹P} NMR (δ = -13.7, -13.9), attributed to the combination of an axial and a central chirality (see ³¹P NMR-VT experiments in Figure S13). Chelating alkenes, such as dimethylacrylamide, also proved to be suitable coupling partners, although the reaction required a temperature of 60 °C to yield the phosphino-amide hybrid ligand 3h in 94% yield. Finally, non-activated alkenes such as styrene derivatives were tested. Using PhJohnPhos and methyl 4-vinylbenzoate, phosphine 3i was obtained in 35% yield at room temperature without decarboxylation of the ester moieties. This yield was subsequently improved to 83% by increasing the reaction temperature to 60 °C.

<figure><img src="image_5.png" /><figcaption>**Scheme 1.** Scope of Alkenes in Rh(I)-Catalyzed C–H Bond Alkylation of PhJohnPhos.</figcaption></figure>

Next, we explored the scope of biarylphosphines using the same catalytic system: 2 mol% of [RhCl(C₂H₄)]₂ associated with 8 mol% of L14, in the presence of 3 equivalents of KOAc in toluene at 25 °C (Scheme 2). Initially, we tested different PhJohnPhos derivatives substituted at the *para'*-position to study the effect of electronic nature. The observed reactivity trends were OMe (3j, 97%), F (3k, 61%), Cl (3l, 82%), and CO₂Me (3m, 50%), indicating that electron-rich substituents on the aryl group, which undergo C–H bond activation, facilitate the reaction. In contrast, when the biarylphosphine bears an *ortho'*-substituent, the yield dropped significantly, as exemplified by compounds 3n and 3o, obtained in only 12% and 15%
yield, respectively. This lack of reactivity can be explained by the combination of steric hindrance during the formation of the cyclometalated species and the electron-donating character of the methyl substituent. Notably, the yields increased to 86% and 90% when the reaction was carried out at 60 °C. N-o-tolylindole-based phosphine was also alkylated in the presence of methyl acrylate at 60 °C, affording **3p** in 41% yield. The efficiency of ligand acceleration is not significantly affected by the nature of the aryl group attached to the PPh₂ directing group. For example, a pyrrolyl-derived phosphine reacted efficiently under the optimized conditions, yielding **3q** in 87% at room temperature. Importantly, the reaction is not limited to substrates undergoing transformations *via* 6-membered rhodacycles. 1-naphthyl-type phosphines, forming a 5-membered rhodacycle intermediates, underwent alkylation at 60 °C to afford **3r** and **3s** in 67% and 69% yield, respectively. Notably, one of these examples features a PPh₂ group attached to a quinonyl moiety rather than an aryl group again demonstrating that the elect. Finally, we demonstrated that these conditions, in combination with ligand **L14**, can also be applied to functionalize phosphines *via* a 7-membered rhodacycle intermediate, delivering the desired alkylated phosphine **3t** in 45% yield.

<figure><img src="image_6.png" /><figcaption>**Scheme 2.** Scope of Biarylphosphines in Rh(I)-Catalyzed C–H Bond Alkylation with Methyl or *tert*-Butyl Acrylates</figcaption></figure>

We further investigated the potential of employing this ligand-accelerated catalysis strategy to achieve the *bis*-alkylation of PhJohnPhos (1a) at room temperature. By using 3 equivalents of acrylates instead of 1.2, we successfully prepared the *bis*-alkylated phosphines 4a-4c in yields ranging from 40% to 95% (Scheme 3, top). Notably, this catalytic system enabled a multicomponent approach, allowing the one-pot, two-step synthesis of a non-symmetrical *bis*-alkylated biaryl phosphine 5a in 65% yield using two different acrylates. The alkenes were added sequentially, with a 12-hour interval between additions (Scheme 3, bottom).
<figure><img src="image_7.png" /><figcaption>**Scheme 3.** Rh(I)-Catalyzed C–H Bond *Bis*-Alkylation of PhJohnPhos</figcaption></figure>

The mechanism of Rh(I)-catalyzed C–H functionalization reactions has not been thoroughly explored to date. Although low-valent Rh(I) complexes are known to undergo alkyl or aryl C–H bond oxidative addition,²¹ alternative proposals suggest that aryl C–H bond cleavage occurs *via* concerted metalation-deprotonation (CMD).²² In order to delineate this mechanism using phosphine-based substrates, we have designed a series of mechanistic experiments. The H/D kinetic isotope effect (KIE) was measured based on the reactions of **1a** or its deuterated counterpart **1a-d<sub>5</sub>** with *tert*-butyl acrylate (**2a**) using [RhCl(C<sub>2</sub>H<sub>4</sub>)]<sub>2</sub> in conjunction with 8 mol% of **L14** as the catalytic system (Figure 3A). The *k*<sub>H</sub>/<k*<sub>D</sub>* value of 0.84 with **L14**, (0.30 without **L14**, see ESI) obtained from independently measured rate constants in parallel experiments— suggest that the C–H activation of biarylphosphines is not the rate-limiting step. Similar inverse KIEs have been observed by Bergman and others in the case of the reversible C–H bond oxidative addition of C(sp<sup>3</sup> )–H bonds, which were explained by a pre-equilib- rium involving a σ-complex (or π-complex) intermediate.²³ This observation suggests a similar pathway, potentially involv- ing a reversible oxidative addition through a comparable two-step mechanism. Moreover, we conducted a competitive reac- tion between electron-rich and electron-poor aryl C–H substrates (Figure 3B). The reaction occurred preferentially on the electron-rich substrate (3j/3m = 0.6), ruling out the possibility of C–H bond cleavage related to the pKa, as in CMD (or σ- BM, a related mechanism). These findings are consistent with an oxidative C–H bond addition pathway involving a pre- association σ-complex intermediate. In addition, ¹H NMR analysis revealed 40-48% deuterium incorporation at the β posi- tion, with no incorporation (0%) observed at the α position after 3 to 6 hours (Figure S2), suggesting a classical 1,2-alkene insertion mechanism following the oxidative addition of the aryl C–D bond. Our mechanistic investigations continue with the identification of catalytically active Rh species and intermediates (Figure 1C). Theoretically, the dynamic nature of this system poses a challenge in identifying these species due to the presence of various possible ligands [starting material (**1a**), product (**3a**), and **L14**], leading to the expected formation of multiple Rh-complexes. Therefore, we decided to proceed step by step using stoichiometric reactions, independent ligands, and varying ratios to control and identify the species involved, monitored by {¹H}³¹P NMR. Using a young NMR tube in toluene-*d*<sub>8</sub>, when the **1a**/[Rh] ratio was set to 1:1, the dominant dimeric mix-ligand species was [RhCl(**1a**)(C<sub>2</sub>H<sub>4</sub>)]<sub>2</sub>. This complex corresponded to the doublet peaks at δ 49.4 ppm (*J*<sub>Rh–P</sub> = 202.8 Hz) (Figure 3D top). When the **1a**/[Rh] ratio was switched to 2:1, the dark brown precipitate started to appear along with **1a**-oxide (δ 24.6 ppm). This precipitate was filtered off but was found to be insoluble in most common organic solvents (e.g., DMF, DMSO, CH<sub>2</sub>Cl<sub>2</sub>, and acetone), believing that **1a** provoked the degradation of Rh(I) to black rhodium. Moreover, this solid was found to be catalytically inactive. Similar experiments were carried out using **L14** instead of **1a**, and the
scenario was slightly different. When the L14/[Rh] ratio was set to 1:1, the major signal at δ 54.2 ppm (d, J<sub>Rh-P</sub> = 189.1 Hz) was attributed to the dominant dimeric mix-ligand species [RhCl(L14)(C<sub>2</sub>H<sub>4</sub>)]<sub>2</sub>. However, using a 2:1 ratio resulted in the observation of an orange precipitate that was soluble in THF-d<sub>8</sub>, corresponding to the doublet peaks at δ 52.3 ppm (d, J<sub>Rh-P</sub> = 194.7 Hz) (Figure 3D, middle). This complex corresponded to [RhCl(L14)<sub>2</sub>]<sub>2</sub>, and its structure was confirmed by X-ray analysis. Interestingly, from [RhCl(L14)<sub>2</sub>]<sub>2</sub>, the addition of 1 equivalent of L14 broke down the Rh dimer core structure with the di-μ-Cl bridge, resulting in a monomeric Rh-Wilkinson-type complex [RhCl(L14)<sub>3</sub>]. This was supported by two sets of peaks at δ 49.1 ppm (dt, J<sub>Rh-P</sub> = 186.6, Hz and J<sub>P,P</sub> = 37.3 Hz) for the phosphine in *trans* of the Cl atom and δ 33.2 ppm (dd, J<sub>Rh-P</sub> = 143.7Hz and J<sub>P,P</sub> = 37.3 Hz) for the two equivalent phosphines in *trans* of each other, which integrated for 1 and 2 phosphorus atoms respectively. Next, from RhCl(L14)<sub>2</sub> we added 1 equivalent of **1a**. Surprisingly, we observed the exchange of phosphine L14 with **1a**, resulting in the exclusive formation of the *cis*-isomer [RhCl(L14)<sub>2</sub>(**1a**)]. This was supported by {<sup>1</sup>H}<sup>31</sup>P NMR analysis, which showed three signals, each integrating for one phosphorus atom: δ 45.5 (ddd, J<sub>P',P</sub> = 301.0 Hz, J<sub>Rh-P</sub> = 181.8 Hz, and J<sub>P,P</sub> = 27.7 Hz, **1a**), δ 38.8 (dt, J<sub>Rh-P</sub> = 132.4 Hz and J<sub>P,P</sub> = 26.7 Hz), and δ 27.2 (ddd, J<sub>P',P</sub> = 301.1 Hz, J<sub>Rh-P</sub> = 174.5 Hz, and J<sub>P,P</sub> = 25.4 Hz, L14 in *trans* of **1a**), which are characteristic of *cis*-isomers.<sup>24</sup> This regioselectivity might be explained by the stronger *trans*-effect of the electron-deficient phosphine L14 compared to Cl. Interestingly, when **3a** was used instead of **1a**, no coordination of **3a** onto [RhCl(L14)<sub>3</sub>] was observed, suggesting that following functionalization, **3a** is consistently released to complete the turnover, likely due to steric hindrance. After 72 hours at 25 °C, the *cis*-[RhCl(L14)<sub>2</sub>(**1a**)] complex underwent transformation, leading to the formation of a small amount of the cyclometalated intermediate *trans*-[Rh ClH(P^C)(L14)<sub>2</sub>] through oxidative addition of the C-H bond of the coordinated PhJohnPhos ligand. Although other signals are challenging to identify, the Rh-H signal was distinctly observed at δ -19.9 (ddd, J<sub>H,P</sub> = 25.0 Hz, J<sub>Rh-H</sub> = 21.1 Hz, and J<sub>H,P</sub> = 15.7 Hz). The small J<sub>P,H</sub> coupling constants, ranging from 15 to 25 Hz, are consistent with a configuration where the hydrido ligand is *cis* to the phosphorus atoms.<sup>25</sup> These findings provide compelling evidence that the Rh(I)-catalyzed C-H bond alkylation of biarylphosphine operates through a genuine C-H bond activation mechanism.
A. Determination of Kinetic Isotope Effect (KIE) & Deuterium Labeling Experiments

<figure><img src="image_8.png" /></figure>

B. Competitive Reaction

<figure><img src="image_9.png" /></figure>

C. Proposed Equilibrium of Various Rh-Complexes with L = 1a or L14 and [Rh]/L Ratios

<figure><img src="image_10.png" /></figure>

D. ³¹P NMR Spectra of Mixtures of Rh-Precursors with L = 1a or L14 and [Rh]/L Ratios

<figure><img src="image_11.png" /><figcaption>**Figure 3.** Mechanistic Investigations</figcaption></figure>

Based on the collected data and relevant literature,²⁶ we propose a catalytic cycle in which L14 plays three critical roles: (i) increasing the catalyst stability and (ii) facilitating catalyst regeneration (product decoordination) through its *trans*-effect and facilitate reductive elimination (Figure 4). Initially, [RhCl(C₂H₄)]₂ reacts with L14 to form the Wilkinson-type complex A, which serves as the resting-state catalyst. In the presence of PhJohnPhos (1a), ligand exchange occurs, leading to the formation of the intermediate B in *cis*-conformation. This intermediate undergoes reversible oxidative addition of the *ortho*-C–H bond of the coordinated PhJohnPhos through a σ-complex C, yielding the rhodium hydride complex D, where the Cl and H substituents are in a *trans* configuration, as confirmed by NMR analysis. Subsequent ligand exchange between L14 and the alkene facilitates the previously observed 1,2-insertion of the alkene into the Rh–H bond, forming E.²⁷ After reductive elimination, which is the rate-determining step and can be facilitated by an electron-withdrawing phosphine ligand,²⁸ the complex G is produced. Finally, a ligand exchange regenerates the catalyst, yielding the desired alkylated phosphine 3a. However, we cannot completely rule out the possibility that, due to the dynamic nature of the catalytic system and equilibrium processes, other catalytic intermediates bearing different phosphine ligands, such as the starting materials (1a)
may also be present. However, catalysis surronded by **3a** can be denied based on our <sup>31</sup>P NMR analysis, which confirmed that A did not react with **3a**.

<figure><img src="image_12.png" /><figcaption>**Figure 4.** Proposed Mechanism for Rh(I)-Catalyzed C–H Bond Alkylation of Biarylphosphines.</figcaption></figure>

## CONCLUSION

This study demonstrates the successful development of a ligand-accelerated Rh(I)-catalyzed C–H bond alkylation of biaryl phosphines, allowing the reaction to occur at room temperature, compared to the previously required 140-160 °C. By addressing the challenges posed by the strong σ-donor character of the P(III) directing group, we identified the electron-poor phosphine **L14**, tris(4-trifluoromethylphenyl)phosphine, as a privileged ligand that enhances both catalyst stability and the rate of reductive elimination. Our mechanistic investigation revealed that this ligand not only accelerates the reaction but also stabilizes key catalytic intermediates, enabling efficient turnover at room temperature. This work expands the scope of Rh(I)-catalyzed C–H functionalization by demonstrating its applicability to a diverse range of biaryl phosphines and challenging alkenes, styrenes, which exhibit superior reactivity under these conditions. The room-temperature protocol not only enhances the compatibility with sensitive functional groups but also opens the door to enantioselective transformations, providing a promising avenue for the synthesis of chiroptical materials with potential applications in advanced materials science and pharmaceuticals. Importantly, the observation of the Rh–H intermediate in our study provides compelling evidence that the reaction proceeds through an oxidative addition of the C–H bond, further validating the proposed mechanistic pathway. The mechanistic insights gained from this study lay the groundwork for further exploration of ligand-accelerated strategies in other transition metal-catalyzed processes, particularly those involving strong σ-donor directing groups.

## ACKNOWLEDGMENT

We thank the Agence Nationale de la Recherche (Grant No. ANR-20-CE07-0019-01) for providing financial support. The NMR service of Chimie ParisTech (Dr. Marie-Noelle Rager) are thanked for VT-NMR analyses. Ms. Lise-Marie Chamoireau Sorbonne Universités, IPCM, UMR 8232) is thanked for X-ray crystallography analyse.
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