Hydrophenylation of ethylene using a cationic Ru(ii) catalyst: comparison to a neutral Ru(ii) catalystElectronic supplementary information (ESI) available: Crystallographic data (CIF), 1H NMR spectral data and representative kinetic plot. See DOI 10.1039/c4sc01665c

Charge neutral Ru( ii ) complexes of the type TpRu(L)(NCMe)Ph [Tp = hydridotris(pyrazolyl)borate; L = CO, PMe 3 , P(OCH 2 ) 3 CEt or P(O&z.ub1s;CH 2 ) 2 (OC&z.ub1e;CH 3 )] have been previously reported to catalyze the hydrophenylation of ethylene ( Organometallics , 2012, 31 , 6851-6860). However, catalyst longevity for the TpRu(L)(NCMe)Ph complexes is inhibited by competitive ethylene C-H activation. For example, ethylene C-H activation limits catalysis using TpRu(P(OCH 2 ) 3 CEt)(NCMe)Ph to a maximum of 20 turnover numbers for conversion of benzene and ethylene to ethylbenzene. In contrast, reaction of the cationic Ru( ii ) complex [(HC(pz 5 ) 3 )Ru(P(OCH 2 ) 3 CEt)(NCMe)Ph][BAr ′ 4 ] [HC(pz 5 ) 3 = tris(5-methyl-pyrazolyl)methane; BAr ′ 4 = tetrakis[3,5-bis(trifluoromethyl)phenyl]borate] (0.025 mol% relative to benzene) in benzene with C 2 H 4 (15 psi) at 90 °C gives 565 turnover numbers of ethylbenzene after 131 hours. The production of 565 turnovers of ethylbenzene corresponds to an approximate one-pass 95% yield with ethylene is the limiting reagent and is a 28-fold improvement compared to the charge neutral catalyst TpRu(P(OCH 2 ) 3 CEt)(NCMe)Ph. Under identical conditions, the activity of [(HC(pz 5 ) 3 )Ru(P(OCH 2 ) 3 CEt)(NCMe)Ph][BAr ′ 4 ] is only 1.3 times less than TpRu(P(OCH 2 ) 3 CEt)(NCMe)Ph, but the increased stability of the cationic Ru( ii ) catalyst allows reactivity at much higher temperatures (up to 175 °C) and significantly enhanced rates. The cationic Ru( ii ) complex [(HC(pz 5 ) 3 )Ru(P(OCH 2 ) 3 CEt)(NCMe)Ph] + (HC(pz 5 ) 3 = tris(5-methyl-pyrazolyl)methane) is an efficient catalyst for hydrophenylation of ethylene and provides a substantial improvement in catalyst longevity compared to the charge neutral variant TpRu(P(OCH 2 ) 3 CEt)(NCMe)Ph (Tp = hydridotris(pyrazolyl)borate).