Surface-Induced Alkene Oligomerization: Does Thermal Hydrosilylation Really Lead to Monolayer Protected Silicon Nanocrystals?

Surface functionalization of hydride-terminated silicon nanocrystals (SiNCs) with dodecene via thermal hydrosilylation has been reexamined. We observed the formation of dodecyl oligomers (n <= 4) during the reaction under an argon atmosphere at various predesigned temperatures (100-190 degrees C). In a comparative study, surface hydrosilylation and ligand oligomerization were found to be more pronounced under air (n <= 7) at the same temperatures. These observations strongly suggest that hydrogen abstraction by oxygen accelerates hydrosilylation and generates sufficient silyl radical as initiator to interact with unsaturated bonds, promote chain propagation, and generate ligand oligomers. We further propose that, to inhibit ligand oligomerization and obtain monolayer coverage on SiNC surfaces, it is feasible to apply comparatively low temperatures, inert atmosphere, and dilute ligand concentration during thermal hydrosilylation.