Cobalt-Catalyzed Regio- and Stereoselective Hydrosilylation of Alk-2-ynes with Tertiary Silanes

Abstract

Selectivity control in the addition reactions of internal alkynes that bear two similar substituents presents a big challenge in modern organic synthesis. Herein we report that β-(E)-selective hydrosilylation of alk-2-ynes with tertiary silanes can be achieved by using Co 2 (CO) 8 as the catalyst. Under the catalytic reaction conditions, a wide range of alk-2-ynes can be converted into vinylsilanes with the β-(E) isomers as the major or sole hydrosilylation products. Mechanistic studies suggest that alkynebridged dicobalt species are the likely intermediates. Steric repulsion between substituents in alkenyl-bridged dicobalt silyl intermediates is proposed as the key factor inducing the observed regioselectivity.

Co‐catalyzed Selective syn‐Hydrosilylation of Internal Alkynes

“…Interestingly, for Co-catalyzed hydrosilylation of alkynes, the phenomenon of an extraordinary ligand control over the reaction pathway offers to receive all of the plausible regio-and/or stereoisomers, e. g., β-(E)-, [26,[41][42][43][44] β-(Z)-, [45] and α-vinylsilanes. [33,[35][36][37][38][39][40][41][42][43][44] However, to the best of our knowledge, there were no protocols describing the use of the triazine-based PNP-Co catalysts in the hydrosilylation of alkynes. Please take note that these specific complexes exhibit extraordinary catalytic activity in several processes, thereby providing access to a variety of important organic molecules.…”

“…Given our recent success in incorporating readily available and cost‐effective cobalt complexes into organometallic synthesis, we hypothesized that an appropriate catalytic system could serve as a sustainable platform for producing diverse libraries of vinylsilanes [51–53] . Significantly, the subject of Co‐catalyzed hydrosilylation for internal alkynes, especially symmetrical ones, was limited to a few examples up until now [32,33,38–46] . As far as we know, only four research groups have reported satisfactory results to date, specifically regarding diaryl and bis‐aliphatic symmetrical internal alkynes [34–37,39,43] .…”

“…[51][52][53] Significantly, the subject of Cocatalyzed hydrosilylation for internal alkynes, especially symmetrical ones, was limited to a few examples up until now. [32,33,[38][39][40][41][42][43][44][45][46] As far as we know, only four research groups have reported satisfactory results to date, specifically regarding diaryl and bis-aliphatic symmetrical internal alkynes. [34][35][36][37]39,43] Herein, we report a first example of catalytic hydrosilylation of internal alkynes triggered by the combination of PNP-Co catalyst and hydrosilanes.…”

“…However, due to the low availability of noble metals and rising prices of such catalysts, more and more researchers try to develop sustainable alternatives. Thus, the complexes of Ni, [19–21] Mn,, [22] Fe, [23–26] and Co [26–46] were recently intensively studied. Interestingly, for Co‐catalyzed hydrosilylation of alkynes, the phenomenon of an extraordinary ligand control over the reaction pathway offers to receive all of the plausible regio‐ and/or stereoisomers, e. g ., β‐( E )‐, [26,41–44] β‐( Z )‐, [45] and α‐vinylsilanes [33,35–44] .…”

“…Thus, the complexes of Ni, [19–21] Mn,, [22] Fe, [23–26] and Co [26–46] were recently intensively studied. Interestingly, for Co‐catalyzed hydrosilylation of alkynes, the phenomenon of an extraordinary ligand control over the reaction pathway offers to receive all of the plausible regio‐ and/or stereoisomers, e. g ., β‐( E )‐, [26,41–44] β‐( Z )‐, [45] and α‐vinylsilanes [33,35–44] . However, to the best of our knowledge, there were no protocols describing the use of the triazine‐based PNP‐Co catalysts in the hydrosilylation of alkynes.…”