A possible mechanism for this process is proposed on the basis of previous reports and our observations (Scheme 5). The formation of Ir-H is supported by the observation of hydride signal at -14.5 ppm in the 1 H NMR control experiment study (Supplementary Figure ). Existence of sulfur is supposed to benefit the coordination of steric 1,1-disubstituted alkene with iridium center and the stability of possible intermediates C and D. The chemical shift vibrations of protons from 1a shown in Supplementary Figure could in some degree identify the interaction between sulfur and iridium. Usage of (EtO)3SiH instead of PhMe2SiH could likewise promote the formation of intermediate A and C (A and B, Supplementary Figure ). However, most of the possible proton signals for intermediate C remained unchanged with the addition of two more equivalent of (EtO)3SiH, and no information of desired hydrosilylation product was observed (Supplementary Figure ). The different electronic property of the hydrosilanes might be major factor in leading to these distinctions.