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)(CH 3 ) 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(Et 2 O) 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)(SMe 2 )}[BAr‘ 4 ] ( 2 ), {Pt(1,2-BAB)(CH 2 Ph)(SMe 2 )}[BAr‘ 4 ] ( 3 ), and {Pt(1,2-BAB)(CH 2 Ph)(CH 3 CN)}[BAr‘ 4 ] ( 4 ), have been isolated and structurally characterized by NMR and single-crystal X-ray diffraction analyses. The investigation by 1 H NMR on the reaction mixture of 1 with toluene in the presence of [H(Et 2 O) 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.