Dissociative and Nondissociative Pathways in the endo to exo Isomerization of Tetramethyl-o-xylylene Complexes of Ruthenium and Osmium, ML3{η4-o-C6Me4(CH2)2} (M = Ru, L = PMe3; M = Os, L = PMe3, PMe2Ph). Formation of Hexamethylbenzene-1,2-diyl Complexes by Ligand Addition to the exo-Osmium Complexes

Abstract

Treatment of the (η6-hexamethylbenzene)ruthenium(II) and -osmium(II) salts [M(O2CCF3)L2(η6-C6Me6)]PF6 (M = Ru, L = PMe3; M = Os, L = PMe3, PMe2Ph) in the presence of L with KO-t-Bu gives exclusively the endo- (tetramethyl-o-xylylene)metal(0) complexes ML3{η4-endo-o-C6Me4(CH2)2}, endo-1, -2, and -3, respectively, in high yield; these are protonated by an excess of triflic acid (CF3SO3H, TfOH) to give the (η6-hexamethylbenzene)metal(II) salts [ML3(η6-C6Me6)](OTf)2 [M = Ru, L = PMe3 (4); M = Os, L = PMe3 (5); M = Os, L = PMe2Ph (6)). Complexes 4−6 revert to endo-1−3 on treatment with KO-t-Bu, whereas for M=Ru, L=PMe2Ph the complexes [ML3(η6-C6Me6)]2+ and [M(O2CCF3)L2(η6-C6Me6)]+/L react with KO-t-Bu to give exclusively the exo isomer, Ru(PMe2Ph)3{η4-exo-o-(CH2)2C6Me4} (exo-7). The endo complexes 1−3 are converted quantitatively into the corresponding exo isomers in toluene in the temperature range 65−106 °C, the process being first order in endo complex. Kinetics studies in the presence of PMe3 (for 1 and 2)...