Arene ruthenium(II) complexes formed by dehydrogenation of cyclohexadienes with ruthenium(III) trichloride

Abstract

Arenedi-µ-chloro-ruthenium complexes [RuCl₂(arene)]₂ have been prepared by dehydrogenation of the appropriate cyclohexa-1,3-diene or cyclohexa-1,4-diene with ethanolic ruthenium(III) trichloride. They react with ligands (L) such as pyridine, tertiary phosphines, or tertiary arsines to give monomeric complexes [RuCl₂(arene)L], which are formally analogous to the arenetricarbonylchromium complexes. Analogous dibromo-, di-iodo-, halogeno-(methyl), and dimethyl derivatives have also been prepared; the latter are thermally unstable and air-sensitive. Reaction of the complexes [RuCl₂(arene)]₂(arene = benzene or p-cymene) with water gives binuclear tri-µ-chloro-cationic species [Ru₂C1₃(arene)₂]⁺, and reaction with silver(I) tetrafluoroborate in acetonitrile gives monomeric [Ru(arene)(MeCN)₃]²⁺. I.r. and n.m.r. data for the new complexes are given. The complexes [RuCl₂(arene)L](L = PBuⁿ ₃ or PPh₃) undergo partial or complete arene exchange on heating or on u.v. irradiation in an aromatic solvent, co-ordinated p-cymene being the most easily displaced. The exchange method can be used to prepare hexamethylbenzene complexes, e.g.[RuCl₂(C₆Me₆)(PBuⁿ ₃)]. The results are compared with available data on arene exchange in arenetricarbonylchromium complexes and discussed in terms of electronic and steric effects on metal–arene bonding.