Syntheses and structures of (Et(4)N)(2)[Re(CO)(3)(NCS)(3)] and (Et(4)N)[Re(CO)(2)Br4]

Rhenium(I) and rhenium(III) carbonyl complexes can easily be prepared by ligand exchange reactions starting from (Et(4)N)(2)[Re(CO)(3)Br-3]. Using nonoxidizing reagents the facial Re-1(CO)3 unit remains and only the bromo ligands are exchanged. Following this procedure, (Et(4)N)(2)[Re(CO)(3)(NCS)(3)] can be obtained in high yield and purity using trimethylsilylisothiocyanate. The compound crystallizes in the monoclinic space group P2(1)/n, a = 18.442(5), b = 17.724(3), c = 18.668(5) Angstrom, beta = 92.54(1)degrees, Z = 8. The NCS- ligands are coordinated via nitrogen. The reaction of [Re(CO)(3)Br-3](2-) with Br-2 yields the rhenium(III) anion [Re(CO)(2)Br-4](-). The tetraethylammonium salt of this complex crystallizes in the noncentrosymmetric, orthorhombic space group Cmc2(1), a = 8.311(1), b = 25.480(6), c = 8.624(1) Angstrom, Z = 4. The carbonyl ligands are positioned in a cis arrangement. Their strong trans influence causes a lengthening of the Re-Br bond distances by at least 0.05 Angstrom.