Efficient C-H bond activations via O2 cleavage by a dianionic cobalt(II) complex

A dianionic, square planar cobalt(II) complex reacts with O-2 in the presence of acetonitrile to give a cyanomethylcobalt(III) complex formed by C-H bond cleavage. Interestingly, PhIO and p-tolyl azide 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 pK(a) of the C-H bond, rather than on the C- H bond dissociation energy. Kinetic isotope experiments reveal a moderate KIE value of ca. 3.5 using either O-2 or PhIO. The possible involvement of a cobalt(IV) oxo species in this chemistry is discussed.