Iridium Pincer Catalysts for Silane Dehydrocoupling: Ligand Effects on Selectivity and Activity

Catalytic
reactions of bisphosphinite pincer-ligated iridium compounds p-XR(POCOP)­IrHCl (POCOP) [2,6-(R2PO)2C6H3, R = iPr, X = H (1); R = tBu, X = COOMe (2); = H (3); = NMe2 (4)] with primary and secondary silanes have
been performed. Complex 1 is primarily a silane redistribution
precatalyst, but dehydrocoupling catalysis is observed for sterically
demanding silane substrates or with aggressive removal of H2. The bulkier compounds (2–4) are
silane dehydrocoupling precatalysts that also undergo competitive
redistribution with less hindered substrates. Products generated from
reactions utilizing 2–4 include low
molecular weight oligosilanes with varying degrees of redistribution
present or disilanes when employing more sterically demanding silane
substrates. Selectivity for redistribution versus dehydrocoupling
depends on the steric and electronic environment of the metal but
can also be affected by reaction conditions.