Preparation and resolution of chiral arene-ruthenium (II) complexes

The synthesis of the chiral complexes [{RuCl2(eta(6)-C(6)H(5)CHMeR)}(2)], (R = Et, 1, (t)Bu, 2), is reported. 1 was prepared from RuCl3.3H(2)O and 1-(2-butyl)-1,4-cyclohexadiene, whereas 2 was obtained starting from [Ru(eta(6)-naphthalene)(eta(4)-COD)] (COD = 1,5-cyclooctadiene) and 2,2-dimethyl-3-phenylbutane, which gives [Ru(eta(6)-C(6)H(5)CHMe(t)BU)(eta(4)-COD)] and subsequent reaction with HCl. Complexes 1 and 2 react with (+)-neomenthyldiphenylphosphine (NMDPP) to give monomeric. diastereomers [RuCl2(eta(6)-C(6)H(5)CHMeEt)(NMDPP)] (3a, 3b), and [RuCl2(eta(6)-C(6)H(5)CHMe(t)Bu)(NMDPP)], (4a, 4b), which were separated by HPLC. The structure of compound 3a was solved by Patterson and Fourier techniques and refined by full-matrix least-squares analysis to R = 0.053, R(w) = 0.061. The arene is eta(6)-bonded to the ruthenium with the phosphorus and the two chlorine atoms arranged as a three legs piano stool. The absolute configuration of the chiral centre of the aromatic ligand in 3a is R. The monomeric diastereomers 3a, 3b, 4a and 4b, were reconverted into their dimeric precursors (R,R)-1a, (S,S)-1b, (R,R)-2a and(S,S)-2b as pure enantiomers. The CD spectra of (R,R)-1a and (S,S)-2b are also reported.