Multiligand-enabled, copper-catalyzed Hiyama coupling of arylsilanes with unactivated secondary alkyl halides: reaction development and mechanistic insights

Construction of carbon-carbon bonds is the cornerstone in organic synthesis, and Hiyama coupling is the representative synthetic approach for realizing linkages between silyl compounds and organohalides. In previous literature, such couplings are mainly utilized for the bond formations of arylsilanes with sp2-aryl halides, yet Hiyama couplings with sp3-hybridized alkyl halides still remain scarce. Copper catalysis has recently been scrutinized in several important transformations of unactivated secondary alkyl halides, whereas their conversions with organosilanes are far less developed. Herein, we leverage a multiligand catalysis to offer a solution for efficient copper-catalyzed Hiyama couplings with such unactivated alkyl halides. Detailed mechanistic studies disclosed that the incorporation of an NHC ligand with a phenanthroline-copper system would dramatically enhance the reaction efficiency, where the copper species with NHC and phenanthroline-type ligands were most likely to account for the C(sp2)-Si bond activation and C(sp2)-C(sp3) bond formation process, respectively.

Designing Cross-Coupling Reactions using Aryl(trialkyl)silanes

Organo(trialkyl)silanes have several advantages, including high stability, low toxicity, good solubility, easy handling, and ready availability compared with heteroatom-substituted silanes. However, methods for the cross-coupling of organo(trialkyl)silanes are limited, most probably because of their exceeding robustness. Thus, a practical method for the cross-coupling of organo(trialkyl)silanes has been a long-standing challenging research target. This article discusses how aryl(trialkyl)silanes can be used in cross-coupling reactions. A pioneering example is Cu^II catalytic conditions with the use of electron-accepting aryl- or heteroaryl(triethyl)silanes and aryl iodides. The reaction forms biaryls or teraryls. This design concept can be extended to Pd/Cu^II -catalyzed cross-coupling polymerization reactions between such silanes and aryl bromides or chlorides and to Cu^I -catalyzed alkylation using alkyl halides.