Early Metal Metallocenium Hydridoborate Catalysts for Carbon Dioxide Hydrosilation

Abstract

A series of permethylmetallocenium(III) hydridotris(pentafluorophenyl)borate complexes was synthesized and investigated as CO2 hydrosilation catalysts in tandem with a B(C6F5)3 co-catalyst. The increasing d electron count across the series of metals studied (ScIII: d0, TiIII: d1, VIII: d2) gave rise to contrasting kinetic behaviours as catalysts. The Sc- and Ti-based systems demonstrated sigmoidal hydrosilane consumption characteristic of two operative catalytic pathways. In particular, the activation of the secondary, more active catalytic pathway was attributed to the build-up of the hydrosilation intermediate, bis(triethylsiloxy)methane in the initial stages of the reaction. This acetal species is capable of binding to the ScIII and TiIII centers, resulting in the observed reactivity. In the VIII system, the electronic configuration precludes coordination of this acetal intermediate, resulting in the operation of only the initial pathway. In addition, carbonyl poisoning of the VIII center allowed for insights to the role of the metal catalyst in the dual catalyst system.