Mechanism of the Hydrosilylation Reaction of Alkenes at Porous Silicon: Experimental and Computational Deuterium Labeling Studies

The mechanism of the formation of Si−C bonded monolayers on silicon by reaction of 1-alkenes with hydrogen-terminated porous silicon surfaces has been studied by both experimental and computational means. We propose that monolayer formation occurs via the same radical chain process as at single-crystal surfaces:1 a silyl radical attacks the 1-alkene to form both the Si−C bond and a radical center on the β-carbon atom. This carbon radical may then abstract a hydrogen atom from a neighboring Si−H bond to propagate the chain. Highly deuterated porous silicon and FTIR spectroscopy were used to provide evidence for this mechanism by identifying the IR bands associated with the C−D bond formed in the proposed propagation step. Deuterated porous silicon surfaces formed by galvanostatic etching in 48% DF/D2O:EtOD (1:1) electrolytes showed a 30% greater density of Si−D sites on the surface than Si−H sites on hydrogen-terminated porous silicon surfaces prepared in the equivalent H-electrolyte. The thermal reaction ...