(eta(6)-arene)ruthenium(II) complexes containing enantiomerically pure (beta-aminoalkyl)phosphines or a (beta-aminoalkyl) phosphinite: synthesis, stereochemical and kinetic studies

The chiral P-N* ligands [(S)-2-(dimethylamino)-3-phenylpropyl]diphenylphosp hine, (S)-phephos, 1, [(S)-2-(dimethylamino)-2-phenylethyl]diphenylphosphin e, (S)-phglyphos, 2, [(S)-2-(dimethylamino)-3-methylbutyl]diphenylphosphine , (S)-valphos, 3, and [(+)-(2S,3R)-4-(dimethylamino)-3-methyl]-2-diphenylph osphinoxy-1,2-diphenylbutane, (+)-(2S,3R)-chiraldphos, 4, reacted with [Ru( eta(6)-arene)Cl-2](2) (arene=p-cymene, benzene or hexamethylbenzene), in di chloromethane or tetrahydrofuran solution, affording the corresponding [Ru( eta(6)-arene)(P-N*)Cl-2] complexes, 5, in which the P-N* acts as a monodent ate P-bonded ligand. In methanol the same reactions easily afforded the cor responding chelate complexes [Ru(eta(6)-arene)(P-N*)Cl]Cl. Using ligands 1- 3, when the arene is p-cymene, 90:10 diastereomeric mixtures of the cationi c complexes have been obtained while only one diastereomer was formed in th e corresponding reactions when the arene is benzene or hexamethylbenzene. T he determination of the absolute configuration of the major products as R-R u,S-C diastereoisomers was made from the crystal structure and CD spectra c omparison of the complex (R-Ru,S-C)-[Ru(eta(6)-p-MeC6H4Pri)(S-phglyphos)Cl] BF4. Complexes [Ru(eta(6)-arene)(P-N*)Cl]Cl were also obtained by adding sm all amounts of methanol to solutions of [Ru(eta(6)-arene)(P-N*)Cl-2] in chl oroform. A kinetic study, in CDCl3 solution containing variable amounts of methanol, on the chelation process in the neutral species [Ru(eta(6)-arene) (P-N*)Cl-2] showed first-order behaviour of the k(obs) values with the nucl eophile (methanol) concentration. The pseudo-first-order rate constants are ascribed to replacement of Cl- by a molecule of methanol. A reaction mecha nism is proposed.