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

Abstract

Catalytic reactions of bisphosphinite pincer-ligated iridium compounds <i>p</i>-X^<i>R</i>(POCOP)­IrHCl (POCOP) [2,6-(R₂PO)₂C₆H₃, R = ^<i>i</i>Pr, X = H (<b>1</b>); R = ^<i>t</i>Bu, X = COOMe (<b>2</b>); = H (<b>3</b>); = NMe₂ (<b>4</b>)] with primary and secondary silanes have been performed. Complex <b>1</b> 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 (<b>2</b>–<b>4</b>) are silane dehydrocoupling precatalysts that also undergo competitive redistribution with less hindered substrates. Products generated from reactions utilizing <b>2</b>–<b>4</b> 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