Conformational studies of transition metal carbonyl complexes of 1,5-dithiacyclooctane (1,5-DTCO) and crystal structure of [ReCl(CO) 3(1,5-DTCO)

Abstract

A new synthesis of the mesocyclic ligand 1,5-dithiacyclooctane (1,5-DTCO) is reported. Complexes of type [{W(CO) 5} n (1,5-DTCO)] ( n= 1,2) were isolated and their conformational and exchange dynamics in solution examined by NMR. The complex [W(CO) 4(1,5-DTCO)], where the ligand acts as a bidentate chelate, undergoes facile boat-chair⇌chair-boat ring conformational exchange, NMR bandshape analysis of the motion yielding an activation energy, ΔG ‡ (298.15 K), of 25.1 ± 0.2 kJ mol −1 . The complexes [ReX(CO) 3(1,5-DTCO)] (X = Cl, Br) were isolated. An X-ray crystal structure of the X = Cl complex showed that the ligand adopts a boat-chair conformation, with a trans-annular S…S contact distance of 3.277 Å. This ring conformation is retained in solution.