Iron-Catalyzed Regiodivergent Alkyne Hydrosilylation

Abstract

Although tremendous effort has been devoted to the development of methods for iron catalysis, few of the catalysts reported to date exhibit clear superiority to other metal catalysts, and the mechanisms of most iron catalysis remain unclear. Herein, we report that iron complexes bearing 2,9-diaryl-1,10-phenanthroline ligands exhibit not only unprecedented catalytic activity but also unusual ligand-controlled divergent regioselectivity in hydrosilylation reactions of various alkynes. The hydrosilylation protocol described herein provides a highly efficient method for preparing useful di- and trisubstituted olefins on a relatively large scale under mild conditions, and its use markedly improved the synthetic efficiency of a number of bioactive compounds. Mechanistic studies based on control experiments and density functional theory calculations were performed to understand the catalytic pathway and the observed regioselectivity.

Transition-Metal-Catalyzed Stereo- and Regioselective Hydrosilylation of Unsymmetrical Alkynes

“…By using 1 or 2 equiv silanes, alkenyl silanes or geminal bis(silanes) (through twice hydrosilylation) were obtained, respectively (Table 2, entries 12). [68][69] This catalyst system exhibited extremely high activity (up to 35.5 s -1 TOF and 35,500 TONs) in the alkyne hydrosilylation and could be performed at 20 g-scale with well retained outcomes. In addition, catalysts based on Ti, Sc and Cu were also reported to achieve β-E selective in alkyne hydrosilylation.…”

“…114 The 2,9diaryl-1,10-phenanthroline modified Fe exhibited excellent αselectivity in the hydrosilylation of various terminal alkynes with high activity (TON up to 4500, Table 5, entry 16). 68 Interestingly, when the 2,9-diaryls of phenanthroline ligand were 3,5-disubstituted aryls, the Fe catalyst gave α-selectivity; when the 2,9-diaryls of phenanthroline ligand were 2,4,6trisubstituted aryls, the Fe catalyst gave β-selectivity (Table 2, entry 12). NHC-Ni complex was used for the α-selective hydrosilylation of 1-octyne and triethoxysilane, with moderate yield and selectivity (Table 5, entry 17).…”

“…65 Table 6 Transition-metal-catalyzed α-selective hydrosilylation of aryl-alkyl acetylenes. 68 1 mol% H3SiR aryl alkenyl Me Et α-syn/ up to >98 up to 99…”

Recent Advances in Catalytic Hydrosilylations: Developments beyond Traditional Platinum Catalysts

“…[28][29][30][31][32] Notably,i twas estimated that consumption of platinum accounts for up to 30 %o ft he cost of silicones. [33] Hence,f rom an industrial point of view,t he high price of platinum strongly motivates researchers to develop recyclable and less expensive catalysts to reduce the precious metal consumption.…”

Recent Advances in Catalytic Hydrosilylations: Developments beyond Traditional Platinum Catalysts

“…For example, platinum complexes can be easily trapped in the product and it is difficult to recover them due to the viscous properties of the resulting products [28–32] . Notably, it was estimated that consumption of platinum accounts for up to 30 % of the cost of silicones [33] . Hence, from an industrial point of view, the high price of platinum strongly motivates researchers to develop recyclable and less expensive catalysts to reduce the precious metal consumption.…”