Rhodium complexes of the binucleating ligands pyridine-2-thiolate and benzothiazole-2-thiolate. Crystal structures of [{Rh(µ-SC5H4N)(CO)2}2] and [{Rh(µ-SC5H4N)(tfbb)}2]·Me2CO (tfbb = tetrafluorobenzobarrelene)

Abstract

The binuclear complexes [(Rh)µ-SC₅H₄N)(diolefin)}₂][SC₅H₄N = pyridine-2thiolate, diolefin = cycle-octa-1,5-diene (cod)(1), norborna-2,5-diene (nbd)(2), or tetrafluorobenzobarrelene (tetrafluorobenzo[5,6] bicyclo[2.2.2]octa-2,5,7-triene)(tfbb)(3)] are prepared by reaction of LiSC₅H₄N with the appropriate complex [{Rh(µ-Cl)(diolefin)}₂] and show fluxional behaviour in solution associated with the bridging ligands. The related compounds [{Rh(µ-C₇H₄NS₂)(diolefin)}₂][C₇H₄NS₂= benzothiazole-2-thiolate, diolefin = cod(5), nbd(6), or tfbb(7)] are prepared by a similar route. Carbonylation reactions of (1) and (5) give the tetracarbonyl complexes [{Rh(µ-L)(CO)₂}₂][L = SC₅H₄N (4) or C₇H₄NS₂(8) respectively]. Triphenylphosphine replaces carbon monoxide stepwise in compound (4) yielding the mono-(10) and di-substituted (11) complexes whilst the disubstituted complex [{Rh(µ-C₇H₄NS₂)(CO)(PPh₃)}₂](9) is obtained from compound (8). Methyl iodide adds to complexes (4) and (10) affording respectively the diacetyl complexes [{Rh(µ-SC₅H₄N)(COMe)I(CO)}₂](12) and [{Rh)(µ-SC₅H₄N)(COMe)l}₂(CO)(PPh₃)](13). The molecular structures of (3) and (4) have been determined by X-ray analyses. Crystals of (3) are triclinic, space group P, with a= 13.772(7), b= 14.184(8), c= 9.738(4)Å, α= 108.99(2), β= 75.65(3), γ= 106.04(3)°, and Z= 2. Crystals of (4) are orthorhombic, space group P2₁2₁2 (no, 18), with a= 14.637(6), b= 6.734(4), c= 8.852(5)Å, and Z= 2. Both complexes are binuclear with two pyridine-2-thiolate groups acting as bridges. In (4) both ligands, having a head-to-tail disposition, bridge the metal centres through the N and S atoms whereas in (3) one of the pyridine-2-thiolate ligands bridges through the S atom only. The square-planar environments of the Rh atoms are completed by two tfbb ligands [(3)] or four CO groups [(4)], with metal–metal separations of 3.028(2) and 2.941 (2)Å respectively.