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

Article abstract of DOI:10.1246/bcsj.73.2099

A dihydridoruthenium(II) complex, [RuH₂(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(η⁴-CH₂CMeCH=CH₂)(CO)(PPh₃)₂]. In reactions among [RuH₂(CO)(PPh₃)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 ¹H 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.