Synthesis and absolute configuration of a series of chiral ruthenium complexes; Crystal structure of (R)-[Ru(η5-C5H 4R*)(CO)(PPh3)I] (R* = neomenthyl)

The syntheses of [Ru(η5-C5H4R*) (CO)22] and [Ru(η5-C5H 4R*)(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-C5H 4R*)(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.