Activation of Inert sp3 C-H, C-O and C-Si Bonds at Cationic Iridium Complexes

Abstract

The intermolecular activation and functionalization of inert sp3 bonds using transition-metal complexes has remained a challenging area of research. Cationic dihydrido bis(phosphine) iridium complexes are found to activate ethereal sp3 C-H and C-O bonds upon dehydrogenation with tert-butylethylene (TBE). Investigation of these processes has resulted in the observation that reversible intramolecular phosphine cyclometalation can precede intermolecular C-O bond cleavage of methy tert-butyl ether (MTBE) and is a competing kinetic pathway in the first example of alkane dehydrogenation. Related studies using a cationic PNP pincer-supported iridium complex have shown the facile formation of an alkoxycarbene derived from α,α-dehydrogenation of cyclopentyl methyl ether (CPME) and demonstrate its reactivity in atom- and group-transfer reactions. In this system, metoxytrimethyl silane does not undergo α,α-dehydrogenation to give the corresponding siloxymethylidene, instead reacting by Si-CH3 oxidative addition. The generality of this transformation across a family of organosilanes has allowed an in-depth analysis of the kinetic and thermodynamic effects at play in sp3 Si-C oxidative addition and reductive elimination.