Coordination of cyclo-octasulfur and cyclo-heptaselenium to dinuclear rhenium(I) systems

By substitution reactions of the coordinated THF ligands of Re-2(mu-X)(2)(CO)(6)(THF)(2) by elemental chalcogens (S-8 and red selenium), the complexes Re-2(mu-X)(2)(CO)(6)(S-8) (X = Br, 1; I, 2), and Re-2(mu-X)(2)(CO)(6)(Se-7), (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 Se-7 ligand [Se-Se distance, 2.558(3) Angstrom] being bonded to rhenium(I), at an average Re-Se distance of 2.586(3) Angstrom, and the nonbonding (ReRe)-Re-... distance being 4.077(3) Angstrom. Spectroscopic evidence of the existence of these chalcogen complexes in solution is reported. The Re-2(mu-X)(2)(CO)(6)(S-8) complexes undergo S-8 displacement by THF, while the coordinated Se-7 moiety is less readily displaced from 3.