Synthesis of monohydridohexamethylbenzeneruthenium(II) complexes containing group V donor ligands. Isomerism arising from cyclometallation of a tertiary phosphine at aliphatic and aromatic carbon atoms

Abstract

The η-hexamethylbenzenehydridoruthenium(II) complexes RuHCl(η-C 6Me 6)L (L = PPh 3 ( 11), AsPh 3 ( 12), P(C 6H 4- p-F) 3 ( 14), P(C 6H 4- p-Me) 3 ( 15), P(C 6H 4- p-OMe) 3 ( 16), P-t-BuPh 2 ( 17), P-i-PrPh 2 ( 18), P-i-Pr 3 ( 19), PCy 3 ( 20) and P-t-BuMe 2 ( 21)) have been made by heating [RuCl 2(η-C 6Me 6)] 2, the ligand and sodium carbonate in propan-2-ol. The triarylphosphine complexes 11, 14 and 15 react with methyllithium to give aryl ortho-metallated hydridoruthenium(II) complexes such as RuH( o-C 6H 4P Ph 2)(η-C 6Me 6) ( 22) and 19 similarly gives the isopropyl cyclometallated complex RuH(CH 2CHMeP -i-Pr 2(η-C 6Me 6) ( 29) as a mixture of diastereomers. Reaction of 17 with methyllithium gives initially the t-butyl cyclometallated complex RuH(CH 2CMe 2P Ph 2)(η-C 6Me 6) ( 25) which isomerizes by a first order process ( k 0 ̃ .2 h −1 in C 6D 6 or THF- d 8 at 50°C) to the aryl ortho-metallated complex RuH( o-C 6H 4P -t-BuPh)(η-C 6Me 6) ( 26). The similarly generated isopropyl cyclometallated complex RuH(CH 2CHMeP Ph 2)(η-C 6Me 6) ( 27) has not been isolated in a pure state owing to rapid isomerization to RuH( o-C 6H 4P -i-PrPh)(η-C 6Me 6) ( 28); both 27 and 28 exist as a pair of diastereomers. The formation of the cyclometallated complexes and the isomerizations are thought to involve intermediate 16-electron ruthenium(O) complexes Ru(η-C 6Me 6)L.