Efficient C–H bond activations via O(2) 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.