Mechanistic Studies on Programmed C?O/C?H Activation with Valence-Adjusted Ti-Complexes

Comprehensive SummaryTwo-electron reduction of [N2NBn](TiCl2)-Cl-IV (3) gave a highly reactive [N2N]Ti-II species, which underwent C-O bond activation of THF (tetrahydrofuran) to generate [N2NBn]Ti-IV[O(CH2)(4)] (4) through oxidative addition. The resulted Ti-IV-Csp(3) bond in oxametallacyclohexane was tantamount to the elaborately-designed Ti-alkyl complexes, competent to activate intramolecular Csp(2)-H bond, forming ortho-cyclometalated complex [N2NCH2C6H4]Ti-IV((OBu)-Bu-n) (5). Key intermediates were isolated and fully characterized by X-ray crystallography. Mechanistic studies revealed that the oxidative addition of C-O bond took place at Ti-II-center via a radical intermediate, while a Csp(2)-H bond activation proceeded by sigma-bond metathesis with a kitelike four-centered Ti-IV-transition state.