A Combined Computational and Experimental Study of Rh-Catalyzed C–H Silylation with Silacyclobutanes: Insights Leading to a More Efficient Catalyst System

Abstract

The study of new C−H silylation reagents and reactions remains an important topic. We reported that under Rh catalysis, silacyclobutanes (SCBs) for the first time were able to react with C(sp 2 )−H and C(sp 3 )−H bonds, however the underlying reasons for such a new reactivity were not understood. Through this combined computational and experimental study on C−H silylation with SCBs, we not only depict a reaction pathway that fully accounts for the reactivity and all the experimental findings but also streamline a more efficient catalyst that significantly improves the reaction rates and yields. Our key findings include: (1) the active catalytic species is a [Rh]−H as opposed to the previously proposed [Rh]−Cl; (2) the [Rh]−H is generated via a reductive elimination/β-hydride (β-H) elimination sequence, as opposed to previously proposed endocyclic β-H elimination; (3) the regio-and enantio-determining steps are identified; (4) and of the same importance, the discretely synthesized [Rh]−H is shown to be a more efficient catalyst. This work suggests that the [Rh]−H/diphosphine system should find further applications in C−H silylations involving SCBs.

Rhodium hydride enabled enantioselective intermolecular C–H silylation to access acyclic stereogenic Si–H

“…Similar results were also obtained in the reaction of diphenylsilacyclobutane (Supplementary Fig. 13), which underscored the different reactivities between the current work with our previous report 67,68 . Significantly, when a possible intramolecular silylation site of SCB substrate was available, as opposed to the cases of 1 h and 1i wherein the sites were blocked, intramolecular C-H silylation prevailed as seen in the cases of 1 v and 1w.…”

“…We thus turned our attention to [Rh]-H catalyst based on our earlier findings that it was the true catalyst for the intramolecular C-H silylation of SCB with aryl C-H bonds 68 . To this end, we prepared a number of pre-formed [Rh]-H catalysts (Supplementary Figs.…”

“…First, we choose silacyclobutanes (SCBs) as the prochiral silanes based on our earlier findings 54,67 . Second, we employ [Rh]-H as the catalyst, since our combined computational and experimental study 68 have identified it as the true and more reactive catalyst for C-H silylation. Third, we uncover that a blocking group (but not a directing group) on the aryl substituent effectively prevents the oligomerization of SCBs.…”

Enantioselective C–H Functionalization toward Silicon-Stereogenic Silanes

“…In 2021, W. He and co-workers reported a detailed mechanism for this Rh-catalyzed C−H silylation with silacyclobutane (SCB) via combined computational and experimental studies (Scheme 5). 13…”

Construction of Si‐Stereogenic Silanes through C−H Activation Approach

“…In addition, this process is also suitable for the access of ferrocene‐based benzosilole bearing both a stereogenic silicon center and planar chirality with high diastereoselectivity and enantioselectivity. Mechanistic studies disclosed that this reaction may proceed through Rh(I)−H enabled the silacyclobutanes opening/intramolecular C−H silylation process, followed by Si−H/C−H dehydrogenative arylation with simple arenes [26c] …”