New fluxional seven-co-ordinate molybdenum(II) and tungsten(II) complexes: X-ray structure of the pyridine-2-thionato complex [W(C5H4NS)2(CO)2(PMe2Ph)]

Abstract

The reaction of [W(CO)₃(MeCN)₃] with pyridine-2-thione (pySH) at room temperature gives the tungsten(II) compound [W(pyS)₂(CO)₃](1) and the tungsten(0) compound [W(CO)₅(pySH)](2). To slow the rate of intramolecular exchange of the pyS ligands in (1), PMe₂Ph was introduced to give [W(pyS)₂(CO)₂(PMe₂Ph)](4). Crystals of (4) are monoclinic space group C2/c, a= 30.738(9), b= 9.867(2), c= 16.048(9)Å, β= 121.04(3)°, and Z= 8 and the X-ray structure was refined to R= 0.0330 and R′= 0.0335. Molecules of (4) contain two chelating pyS ligands and the tungsten is seven-co-ordinated. Approximately determined exchange rates for the diastereotopic Me groups of PMe₂Ph and of the non-equivalent pyS ligands are the same indicating that both exchanges result from the same process. The corresponding molybdenum compound is isostructural and shows similar fluxionality.