CONFORMATIONAL STUDIES OF TRANSITION-METAL CARBONYL-COMPLEXES OF 1,5-DITHIACYCLOOCTANE (1,5-DTCO) AND CRYSTAL-STRUCTURE OF [RECL(CO)(3),(1,5-DTCO)]

A new synthesis of the mesocyclic ligand 1,5-dithiacyclooctane (1,5-DT CO) is reported. Complexes of type [{W(CO)(5)}(n)(1,5-DTCO)] (n = 1,2) were isolated and their conformational and exchange dynamics in solut ion examined by NMR. The complex [W(CO)(4)(1,5-DTCO)], where the ligan d acts as a bidentate chelate, undergoes facile boat-chair reversible arrow chair-boat ring conformational exchange, NMR bandshape analysis of the motion yielding an activation energy, Delta G(double dagger) (2 98.15 K), of 25.1 +/- 0.2 kJ mol(-1). The complexes [ReX(CO)(3)(1,5-DT CO)] (X = Cl, Br) were isolated. An X-ray crystal structure of the X = Cl complex showed that the ligand adopts a boat-chair conformation, w ith a transannular S ... S contact distance of 3.277 Angstrom. This ri ng conformation is retained in solution.