Cross-Electrophile Silylation of Aryl Carboxylic Esters with Hydrochlorosilanes by SiH-Directed and Cr-Catalyzed Couplings

Abstract

The formation of silicon–carbon bonds through the selective coupling of two strong electrophilic bonds has been less developed. We report here silylation reactions that proceed by coupling of strong Si–Cl/C–O bonds in a process that is promoted by chromium catalysis via α-agostic SiH → Cr interactions, allowing the formation of Si–C bonds under ambient conditions. The reactions occur by coupling of inexpensive hydrochlorosilanes with unactivated aryl carboxylic esters to give arylated hydrosilanes, while suppressing the side hydride-mediated reduction of aryl carboxylic esters in achieving high chemoselectivity. In addition to monosilylation, both geminal Si–Cl bonds of hydrodichlorosilanes couple with aryl C–O bonds smoothly to afford two Si–C bonds and achieve double silylations. The formation of disilanes by coupling of hydrochlorosilanes with two C–O bonds of diesters is also described. Experimental and theoretical studies suggest that silylation initiates by reaction of hydrochlorosilane with Cr, in which the α-agostic SiH interaction of the SiH group to Cr stabilizes the related intermediate and transition state, leading to cleavage of the Si–Cl bond by Cr with a low barrier to give silachromate. Further breaking of an unactivated C–O bond with Cr occurs along with the agostic interaction, which may serve as the rate-determining step in silylation. The observation of a normal second-order kinetic isotope effect indicates the effect of the agostic SiH → Cr interaction on the rates of coupling. Because reactive SiH groups of hydrochlorosilanes are retained in silylation, the approach provides a viable strategy to access tetraorganosilane motifs through late-stage hydrofunctionalization.

Cobalt-catalyzed cross-electrophile coupling of alkynyl sulfides with unactivated chlorosilanes

“…Different Co(II) precursors were tested, CoCl 2 , CoBr 2 and Co(acac) 2 gave the product 3a in high yields but with less efficiency (entries 2-3). Meanwhile, the cross-selectivity decreased dramatically and a certain amount of 1,3-diyne was obtained when NiI 2 or CrCl 2 was utilized instead of CoI 2 as the catalyst (entry 4) 24 , 28 , 31 . The alkynyl sulfide 1a was fully recovered in the presence of iron salt precatalyst (entry 5) 30 .…”

“…1a ) 24 – 29 . Subsequently, Fe- and Cr-catalyzed XEC of activated chlorosilanes had also been developed using different catalytic systems 30 , 31 . Despite formidable advances, no examples of XEC of alkynyl electrophiles with silyl electrophiles by transition-metal catalysis to form Csp-Si bond, have been reported until now.…”

Organophotocatalyzed Cross Coupling of C- and Si-Radical to Access Dibenzylic Silanes from para-Quinone Methides and Silanecarboxylic Acids

“…4 Moreover, organosilicon reagents represent a type of outstanding synthon for a variety of coupling reactions in organic synthesis. 5 Hence, methodologies for synthesizing this class of compounds hold substantial importance in contemporary organic synthesis and are continuously pursued. 6 Traditional approaches for forming C−Si bonds are predominantly limited to polar reactions (Scheme 1a).…”

Aliphatic Hydrosilanes via Nickel-Catalyzed Reductive Csp3–Si Coupling of Primary Alkyl Bromides and Chlorohydrosilanes

“…In 2022, our group reported a nickel-catalyzed reductive C–Si coupling between R 2 Si­(H)Cl and Ar/Vinyl–X, where the Si–Cl bond was selectively cleaved (Scheme b-1, Shu 2022) . The carbon coupling partners were later expanded to Ar–OCO t Bu and bromostyrenes by Zeng and Ye groups using chromium and iron catalysts, respectively (Scheme b-1). However, these reactions have predominantly focused on Csp 2 –Si couplings.…”