Theoretical study on the mechanism of the carbonylation cyclization of 1,5-diynes with hydrosilanes

Abstract

The carbonylation cyclization of unstaturated hydrocarbons with hydrosilanes is an appealing strategy for the construction of valuable silicon-containing carbonyl compounds. Despite significant advances, the detailed mechanistic investigations on these reactions are still scarce. Herein, density functional theory (DFT) calculations are carried out to provide mechanistic insights into Rh-catalyzed carbonylative cyclization of 1,5-diyne with triethylsilane. The calculated results indicate that (1) In the silylrhodation process, distinguished from the classical Chalk−Harrod mechanism and the modified Chalk−Harrod mechanism, H atom on the Rh center first transfers to CO ligand to yield a aldehyde group. Then the terminal alkyne of 1,5-diyne inserts into Rh−Si bond to form C−Si bond. With the subsequent H atom retransfer to Rh center, β-(E)-silyl-substituted enyne can be obtained. (2) In the CO insertion process, internal alkyne prior to CO ligand coordinates to the Rh center. (3) The yielded metallacyclohexanone intermediate undergoes H-transfer and C−C cyclization steps rather than direct C−C cyclization forming the η3-binding intermediate. Finally, after the reductive elimination, the product (1E,3Z)-1-pentylidene-3-[(triethylsilyl)methylidene]indan-2-one is formed. The computational results demonstrate that H-transfer is the rate-determining step.