Origins of Selective C(sp2)-H Activation Using Transition Metal Complexes with N,N-Bidentate Directing Groups: A Combined Theoretical-Experimental Study

The strategy using N,N-bidentate directing groups is a promising way to achieve selective C(sp(2))-H activation inaccessible by that of monodentate directing groups. Herein, through theoretical calculations, we present a rationale behind this strategy, which deciphers its key roles in C-H activation promoted by Ni, Pd, Ru, and Cu. The calculations reveal two key points: (a) Between the two coordination sites of the N,N-bidentate directing group, the proximal one influences more the C-H activation barrier Delta G(double dagger), whereas the distal site affects more the free energy change Delta G relevant to the substrate coordination. (b) Enlarging/shrinking the chelation ring can exert different effects on the reactivity, depending on the metal identity and the ring size. Importantly, our computational results are in full agreement with previous experimental findings concerning reactivity. Furthermore, a prediction about the unprecedented reactivity from our theory is confirmed by our experiments, lending more credence to the rationale and insights gained in this study.