Synthesis and Spectroscopic Characterization of Dinuclear Mono(μ-hydrido) Arene Complexes of Divalent Ruthenium

Abstract

Dinuclear mono(μ-hydrido) arene complexes {RuX(η-arene)}2(μ-H)(μ-X) (X = Cl, Br, arene = C6Me6, 1,2,4,5-C6H2Me4, l,3,5-C6H3Me3; X = Cl, arene = C6H4-1-Me-4-CHMe2, C6H6) containing one bridging and two terminal halide groups are formed from the reaction of [RuX2(η-arene)]2 with hydrogen (4 atm) at room temperature in the presence of triethylamine. The tendency for one chloride ion to dissociate in nitromethane is enhanced by increasing the degree of alkyl substitution on the arene, the hexamethylbenzene chloro complex being a 1:1 electrolyte in this solvent. The cations [{Ru(η-arene)}2(μ-H)(μ-X)2]+ containing two bridging halide groups can be isolated as PF6 salts. Heating of acetato complexes Ru(O2CMe)2(η-arene) with 2-propanol gives mono(μ-hydrido) bis (μ-acetato) complexes containing the cations [{Ru(η-arene)}2-(μ-H)(μ-O2CMe)2]+, which can be isolated as solid hydrogenbis(acetate) salts for arene = C6Me6 or 1,2,4,5-C6H2Me4 and as PF6 salts for all the arenes studied. The corresponding trifluoroacetato complexes could not be isolated in a pure state but were identified spectroscopically. Reaction of Ru(O2CR)X(η-arene) with hot 2-propanol gives hydrido complexes of empirical formula {Ru(η-arene)}2H(O2CR)X2 (X = Cl, Br; R = CH3, CF3) except when arene = C6H6; in this case {Ru(η-C6H6)}2HCl3 is formed. These complexes readily give PF6 salts of the cations [{Ru(η-arene)}2(μ-H)(μ-O2CR)(μ-X)]+ that have three different bridging groups. In solution, the parent compounds (arene = C6Me6, l,2,4,5-C6H2Me4) behave as the halide salts of these cations but when arene = p-cymene (C6H4-1-Me-4-CHMe2) and R = CH3, the halide salt and a neutral dimer {RuX(η-arene)}2(μ-H)(μ-O2CR) coexist. Complexes of p-cymene in which three different groups are attached to ruthenium exhibit diastereotopic aromatic protons and isopropyl methyl groups in their 1H NMR spectra; those of durene (l,2,4,5-C6H2Me4) have diastereotopic methyl groups. The hydride protons of all the carboxylato complexes become progressively more shielded with increasing alkyl substitution on the arene. The formation and structure of the hydrido(arene)ruthenium(II) complexes are compared with those of the corresponding (η-pentamethylcyclopentadienyl)rhodium(III) and-iridium(III) compounds. Show more