Efficient C–H bond activations via O₂cleavage by a dianionic cobalt(<scp>ii</scp>) complex

A dianionic, square planar cobalt(II) complex reacts with O₂ in the presence of acetonitrile to give a cyanomethylcobalt(III) complex formed by C-H bond cleavage. Interestingly, PhIO and <i>p</i>-tolylazide react similarly to give the same cyanomethylcobalt(III) complex. Competition studies with various hydrocarbon substrates indicate that the rate of C-H bond cleavage greatly depends on the <i>p</i> Ka of the C-H bond, rather than on the C-H bond dissociation energy. Kinetic isotope experiments reveal a moderate KIE value of <i>ca.</i> 3.5 using either O₂ or PhIO. The possible involvement of a cobalt(IV) oxo species in this chemistry is discussed.