Coordination of cyclo-Octasulfur and cyclo-Heptaselenium to Dinuclear Rhenium(I) Systems

By substitution reactions of the coordinated THF ligands of Re2(μ-X)2(CO)6(THF)2 by elemental chalcogens (S8 and red selenium), the complexes Re2(μ-X)2(CO)6(S8) (X = Br, 1; I, 2), and Re2(μ-X)2(CO)6(Se7), (X = I, 3; Br, 4) have been prepared. Binuclear compound 3 was crystallographically established to be a coordination compound of cyclo-heptaselenium, two adjacent selenium atoms of the Se7 ligand [Se−Se distance, 2.558(3) Å] being bonded to rhenium(I), at an average Re−Se distance of 2.586(3) Å, and the nonbonding Re···Re distance being 4.077(3) Å. Spectroscopic evidence of the existence of these chalcogen complexes in solution is reported. The Re2(μ-X)2(CO)6(S8) complexes undergo S8 displacement by THF, while the coordinated Se7 moiety is less readily displaced from 3.