An NMR study on the ruthenium complex-catalyzed C-H/olefin coupling reaction

A dihydridoruthenium(II) complex, [RnH2(CO)(PPh3)(3)], reacts with styrene to give two species: a bis(styrene)ruthenium(0) complex, [Ru(CO)(CH2=CHPh)(2)(PPh3)(2)], and a cyclometallated hydridoruthenium(II) one, [Ru(C6H4PPh2)H(CO)(PPh3)(2)]. The complex [RuH2(CO)(PPh3)(3)] reacts with isoprene to give a piano-stool type ruthenium(0) complex [Ru(eta(4)-CH2=CMeCH=CH2)(CO)(PPh3)(2)]. In reactions among [RuH2(CO)CPPh3)(3)], styrene, and 3'-(trifluoromethyl)acetophenone, three cyclometallated hydridoruthenium(II) complexes: P,P'-cis-C,H-cis-, P,P'-trans-C,H-trans-, and P,P'-trans-C,H-cis-[Ru{C6H3(CF3)C(=O)Me}H(CO)(PPh3)(2)] are detected by NMR spectroscopy. The H-1 NMR spectra of the reaction mixture exhibit the catalytic formation of 2'-(2-phenylethyl)- and 2'-(1-phenylethyl)-5'-(trifluoromethyl)acetophenones. On the basis of these findings, a mechanism for the C-H/olefin coupling reaction is discussed. The first of the three complexes is assigned to an active intermediate in the catalytic coupling reaction, whereas the other two are assigned as quasi-stable ruthenium(II) complexes which are in equilibrium with active species.