Regioselective C−H Activation of Toluene with a 1,2-Bis(<i>N-</i>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-7-azaindolyl)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 1H NMR on the reaction mixture of 1 with toluene in the presence of [H(Et2O)2][BAr‘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.