B(C₆F₅)₃‐Catalyzed Selective Chlorination of Hydrosilanes

Abstract

The chlorination of Si-H bonds often requires stoichiometric amounts of metal salts in conjunction with hazardous reagents, such as tin chlorides, Cl , and CCl . The catalytic chlorination of silanes often involves the use of expensive transition-metal catalysts. By a new simple, selective, and highly efficient catalytic metal-free method for the chlorination of Si-H bonds, mono-, di-, and trihydrosilanes were selectively chlorinated in the presence of a catalytic amount of B(C F ) or Et O⋅B(C F ) and HCl with the release of H as a by-product. The hydrides in di- and trihydrosilanes could be selectively chlorinated by HCl in a stepwise manner when Et O⋅B(C F ) was used as the catalyst. A mechanism is proposed for these catalytic chlorination reactions on the basis of competition experiments and density functional theory (DFT) calculations.

Lewis Base Catalyzed Selective Chlorination of Monosilanes

“…Other notorious drawbacks are low yields, use of expensive or toxic reagents and solvents, formation of waste products in large quantities, long reaction times, harsh reaction conditions or tedious workup processes . Very recently, Chulsky and Dobrovetsky reported the selective chlorination of di‐ and trihydridosilanes with HCl in the presence of catalytic amounts of B(C 6 F 5 ) 3 or Et 2 O⋅B(C 6 F 5 ) 3 . In case of B(C 6 F 5 ) 3 , the proposed reaction mechanism involves preactivation of the Si−H bond by the borane, followed by concerted HCl addition across the Si−H bond in the [Si]−H−B(C 6 F 5 ) 3 intermediate.…”

“…The stabilizing role of ether in ts2 is mechanistically intriguing, as it reveals the possibility to assist the chlorination reaction by intermediate coordination of a Lewis base as an alternative to Lewis acid catalysis exploited by Chulsky and Dobrovetsky . This hypothesis was validated by further experiments using additional amounts of Lewis bases (Table ).…”

“…The substrate scope of the selective chlorination of hydridomonosilanes R 2 SiH 2 and RSiH 3 in different HCl/ether solutions is broad and the degree of chlorination is readily controlled by temperature and reaction time. The theoretical assessment provides detailed rationalizations of the experimental findings and establishes a new mode of Si−H bond activation assisted by Lewis bases such as ethers, amines, phosphines and chloride ions as an alternative to Lewis acid assistance reported in earlier work . Furthermore, we have shown that alcohol assistance through hydrogen‐bond networks is equally efficient and selective, effectively bypassing side reactions like siloxane formation.…”

“…[8,12] Very recently,C hulskya nd Dobrovetsky reported the selective chlorination of di-and trihydridosilanes with HCl in the presence of catalytic amounts of B(C 6 F 5 ) 3 or Et 2 O·B(C 6 F 5 ) 3 . [13] In case of B(C 6 F 5 ) 3 ,t he proposed reactionm echanismi nvolves preactivationo ft he SiÀHb ondb yt he borane, followed by concerted HCl addition across the SiÀHb ond in the [Si]ÀHÀB(C 6 F 5 ) 3 intermediate. For Et 2 O·B(C 6 F 5 ) 3 ,t ransformation into an ethanol borane adduct Et(H)O·B(C 6 F 5 ) 3 as actual catalytically actives pecies is suggested, which undergoes dehydrocoupling with further silane equivalents to ethoxysilane intermediates.…”

B(C6F5)3 catalysis accelerates the hydrosilane chlorination by Ph3CCl

“…Similarly, an efficient (yields 60–90%) chlorination of Si‐H of tertiary, secondary and primary silanes by dry HCl in the presence of catalytic amounts of B(C 6 F 5 ) 3 or Et 2 O·B(C 6 F 5 ) 3 was reported. The utilization of etherate was found advantageous for a selective stepwise chlorination …”