Computation Revealed Mechanistic Complexity of Low-Valent Cobalt-Catalyzed Markovnikov Hydrosilylation

Abstract

We explored the mechanism of Markovnikov-selective hydrosilylation of phenylacetylene catalyzed by N–N–N Pincer–cobalt complex with density functional theory (DFT) calculations. In contrast to the previously proposed Co­(I) mechanism, computational results suggest a Co(0) pathway, which is further supported by experimental studies. At the same time, our study reveals unexpected complexity in terms of the origin of regioselectivity. First, different orientations between the phenyl group in the substrate and the ligand plane lead to two possible transition states responsible for the branched product. However, the favored one varies according to ligand substitution pattern. Second, both entropy and solvation effects (rather than the conventional approach that considers electronic energies) have to be considered to explain regioselectivity, where the dominant factor also varies from case to case. Despite this complexity, computations predict a general overall ligand structure–regioselectivity relationship. In addition to increasing steric hindrance, introduction of an electron-withdrawing group to the ligands will also increase regioselectivity, which unveils a new dimension of ligand design.

Decoding Key Transient Inter-Catalyst Interactions in a Reductive Metallaphotoredox-Catalyzed Allylation Reaction

“…Interest in such processes was initially focused on the combination of nickel or copper catalysis with photoredox catalysis, but recently cobalt has emerged as a potent, alternative metal in dual catalytic procedures. − While mechanistic studies for cobalt catalysis have been thoroughly probed under reductive conditions using chemical reductants − or via electrochemistry, it remains uncertain whether dual metal/photoredox approaches proceed through the occurrence of similar intermediates. Several features of Co catalysis under reductive conditions remain open for debate, including the intermediacy of either Co I or Co 0 -species ,, and in dual Co/photoredox catalysis, particularly, how the effectiveness of different catalyst components and additives can be rationally optimized.…”

Sustainable Synthesis of Silicon Precursors Coupled with Hydrogen Delivery Based on Circular Economy via Molecular Cobalt-Based Catalysts

“…For low-valent metals, the oxidative cleavage of the Si−H bond is feasible. 43,44 However, for our Co(II) complex, all attempts to find such a process were unsuccessful. 24 Instead, we propose the participation of five-coordinate MeO−[Si] − transition states that activate the Si−H bond.…”

External Electric Field—Phenyl interaction boosts hydrosilylation of substituted alkynes to α‐vinylsilane

“…Vinylsilanes are valuable building blocks in organic synthesis and material chemistry because of their versatile characters, such as low toxicity, high stability, facile manipulations, and a variety of transformations . Accordingly, methods for the preparation of vinylsilanes have gained increased attentions from synthetic chemists, in which the hydrosilylation of alkynes was considered as a simple and straightforward method . This hydrosilylation reaction involves the addition of a Si − H bond across a C − C triple bond, bringing an atom‐economical result with 100% atom efficiency.…”

“…However, control of stereo-and regioselectivity is the major issue hampering the widespread use of this method, largely because three possible hydrosilylation products, namely α-, β-(Z)-, and β-(E)-vinylsilanes, can be generated in the hydrosilylation reaction of terminal alkynes, with the former being rarely obtained selectively. [65][66][67] By now, some works about the formation of α-vinylsilane had been published by theorists [39,40] and experimenters. [41][42][43][44][45][46][47][48][49] By inspection of these researches, we found that the metal-catalysts were mainly introduced for catalyzing this hydrosilylation of alkynes, such as Co, [41][42][43][44][45][46] Pt, [47] and Ru.…”