C-H Bond Activation by an Imido Cobalt(III) and the Resulting Amido Cobalt(II) Complex

Abstract

The 3d-metal mediated nitrene transfer is under intense scrutiny due to its potential as an atom economic and ecologically benign way for the directed amination of (un)functionalised C-H bonds. Here we present the isolation and characterisation of a rare, trigonal imido cobalt(III) complex, which bears a rather long cobalt-imido bond. It can cleanly cleave strong C-H bonds with a bond dissociation energy of up to 92 kcal mol^-1 in an intermolecular fashion, unprecedented for imido cobalt complexes. This resulted in the amido cobalt(II) complex [Co(hmds)₂ (NH^t Bu)]^- . Kinetic studies on this reaction revealed an H atom transfer mechanism. Remarkably, the cobalt(II) amide itself is capable of mediating H atom abstraction or stepwise proton/electron transfer depending on the substrate. A cobalt-mediated catalytic application for substrate dehydrogenation using an organo azide is presented.

Keywords: C−H activation; H atom transfer; amido cobalt complex; catalysis; imido cobalt complex.