Steric influences on sulphur inversion barriers in group 6a tetracarbonyl complexes of dithioethers

The complexes cis-M(CO)₄(RSCH₂CH₂SR)] (M = Cr, Mo, W, R =^t Bu; M = W, R = Me, Et, ⁱPr, ^tBu) and cis-M(CO)₄(cis-RSCHCHSR)] (M = Cr, Mo, W; R = Me, ^tBu) have been synthesised, and sulphur inversion studied using variable temperature ¹H and ¹³C {¹H} NMR techniques. For complexes of the saturated ligands, signals due to both DL and meso invertomers were observed at −90°C, with the relative populations of these invertomers being dependent on the steric bulk of the alkyl groups attached to sulphur. Sulphur inversion barriers, which have been calculated via total bandshape analysis of the variable temperature NMR spectra of these complexes, show a marked dependence on the steric requirements of the dithioether ligand. For the complexes of the unsaturated ligands, only the meso-invertomers were observed at limiting low temperatures (ca. −90°C), and sulphur inversion barriers were therefore not able to be calculated in these cases.