Regioselective C-H activation of toluene with a 1,2-bis(N-7-azaindolyl)benzene platinum(II) complex

A new organoplatinum(II) complex, Pt(1,2-BAB)(CH3)(2) (1) (1,2-BAB = 1,2-bis(N-7azaindolyl)benzene), has been synthesized and fully characterized. Compound 1, after reacting with 1 equiv of acid [H(Et2O)(2)] [BAr'(4)], Ar' = 3,5-bis(trifluoromethyl)phenyl, has been found to be able to activate benzene and toluene C-H bonds under mild conditions. The complexes resulting from C-H activation, {Pt(1,2-BAB)(Ph)(SMe2)}[BAr'(4)] (2), {Pt(1,2-BAB)(CH2Ph)(SMe2)} [BAr'(4)] (3), and {Pt(1,2-BAB)(CH2Ph)(CH3CN)} [BAr'(4)] (4), have been isolated and structurally characterized by NMR and single-crystal X-ray diffraction analyses. The investigation by H-1 NMR on the reaction mixture of 1 with toluene in the presence of [H(Et2O)(2)] [BAX'(4)] revealed that the m-tolyl and p-tolyl C-H activation products dominate initially. However, as the reaction time increases, the benzylic C-H activation product becomes the major product (after 3 h, the yield ratio of benzyl:m-tolyl-p-tolyl is 60%:12%: 11%). The cause for the high regioselectivity in toluene C-H activation by complex 1 is not fully understood.