Aliphatic and aromatic C–H activation of benzo[h]quinolines by Rh(I). Unique precursor dependent formation of mono-, di- and trinuclear complexes

Treatment of 7,8-benzo[h]quinoline (bhq-H, 1) and 10-methyl benzo[h]quinoline (bhq-Me, 3) with [Rh(C2H4)2(THF)2][BF4] resulted in double C–H activation of aliphatic and aromatic C–H bonds, yielding the Rh(III) complexes 4 and 5, respectively. The structures of 4 and 5 were revealed by X-ray diffraction. The reaction of 1 with two other slightly different rhodium precursors, [Rh(olefin)n(THF)2][BF4] (COE (n = 2), COD (n = 1)), led to completely different products, a dinuclear complex 7 and a trinuclear complex 6, respectively, which were characterized by X-ray diffraction. Complex 6 exhibits a rare linear Rh–Rh–Rh structure. Utilizing excess of 1 with [Rh(COD)(THF)2][BF4] led to the formation of a new product 8 with no C–H bond activation taking place. Additional C–H activation products of 1, cationic and neutral, in the presence of PiPr3 (9a, 9b and 10) are also presented.