Synthesis and absolute configuration of a series of chiral ruthenium complexes; crystal structure of (R)-[Ru(η5-C5H4R*)(CO)(PPh3)I](R*= neomenthyl)

Abstract

The syntheses of [{Ru(η⁵-C₅H₄R*)(CO)₂}₂] and [Ru(η⁵-C₅H₄R*)(CO)₂X](R*= menthyl or neomenthyl; X = Cl, Br, or I) are reported. Phosphines and phosphites react with the halide complexes to give the diastereoisomers [Ru(η⁵-C₅H₄R*)(CO)LX][R*= menthyl, X = Cl, L = PPh₂Me or PPh₂(CH₂OMe); X = Br, L = PBuⁿ₃ or P(OPh)₃; R*= neomenthyl, X = I, L = PPh₃] containing a chiral ruthenium atom. These diastereoisomers have been resolved and their circular dichroism (c.d.) spectra are reported. An X-ray analysis of c.d.(–)₃₂₅[Ru(η⁵-C₅H₄R*)(CO)(PPh₃)I](R*= neomenthyl) has been carried out which established the absolute configuration of the ruthenium centre to be R. The crystals are monoclinic, space group P2₁(no. 4) with a= 12.833(6), b= 15.186(6), c= 7.972(5)Å, β= 101.50(4)°, and Z= 2. On the basis of 1 773 observed reflections, the structure was refined to R= 0.054. It is proposed that the c.d. spectrum in the region 300–400 nm can be used to establish the configuration of the ruthenium atom in complexes of the type [Ru(η⁵-C₅H₄R*)(CO)LX] described.