Chiral ruthenium complexes with sulfur ligands; X-ray structure of (R)Ru-Ru(NmCp)(CO)(PPh3)SCN (NmCp=neomenthylcyclopentadienyl)

The reaction of Ru(NmCp)(CO)(PPh3)I (NmCp=neomenthylcyclopenta-dienyl) with AgSCN occurs with retention of configuration at the ruthenium to give the S-bonded Ru(NmCp)(CO)(PPh3)SCN. This was confirmed by determining the X-ray structure of (R)Ru-Ru(NmCp)(CO)(PPh3)SCN. The reaction of (S)Ru-Ru(NmCp)(CO)(PPh3)I with AgBF4 in CH2Cl2 followed by treatment with MeSR gave the following sulfide complexes [(RS)Ru-Ru(NmCp)(CO)(PPh3){S(Me)R}]BF4 (R=CH2Ph, Ph and tBu). NMR studies have shown that for R=CH2Ph the chiral sulfur centre binds to the chiral ruthenium centre with a 33% d.e. and the free energy for inversion of the S-centre is 49±1 kJ mol−1. In contrast, with the bulky phenyl and tert-butyl substituents the chiral ruthenium centre shows an overwhelming preference (≥99%) for binding to one enantiomer of the sulfide ligand. Despite this, arguments are presented to show that this ruthenium system is not a suitable chiral auxiliary for use in synthesizing chiral sulfoxides from complexed sulphides.