Reactions of the co-ordinatively unsaturated µ3-alkylidyne cluster [WFe2(µ3-CC6H4Me-4)(µ-H)(µ-PPh2)(CO)6(η-C5H5)] with PMe2Ph

Abstract

Treatment of the co-ordinatively unsaturated complex [WFe₂H (µ₃-CR)(µ- PPh₂)(CO)₆(η-C₅H₅)](3b; R = C₆H₄Me-4) with 1 equivalent of PMe₂Ph at 20 °C affords the thermally unstable kinetic derivative [WFe₂(µ₃-CR)(µ-H)(µ-PPh₂)(CO)₆(PMe₂Ph)(η-C₅H₅)](4). N.m.r. spectroscopy reveals that at –40 °C compound (4) exists as an equilibrium mixture of two isomers [(4a) : (4b)= 4:3]. The core structures of all the PMe₂Ph derivatives described have features in common, and consist of a WFe₂ triangle of metal atoms which is capped by a µ₃-CR moiety. One W–Fe bond is bridged by a µ-PPh₂ligand and the W atom carries a CO ligand and a cyclopentadienyl ring. In addition, for (4a) and (4b), the Fe–Fe bond is bridged by an hydride ligand and the iron atom remote from the µ-PPh₂ group carries three terminal CO ligands. The Fe atom which is ligated by the µ-PPh₂ group carries two CO ligands and the PMe₂Ph ligand. In isomer (4a) one of the latter CO ligands is pseudo trans to the µ-PPh₂ group, whereas the PMe₂Ph ligand adopts this site in (4b). At ambient temperature rotation of the Fe(CO)₂(PMe₂Ph) group leads to interconversion of (4a) and (4b), but at this temperature (4) also isomerises to the thermodynamically favoured isomer [WFe₂(µ₃-CR)(µ-H)(µ-PPh₂)(µ-CO)(CO)₅(PMe₂Ph)(η-C₅H₅)](5). In compound (5) the hydride ligand bridges a W–Fe bond and the Fe–Fe bond is bridged by a CO ligand. The iron atom ligated by the µ-PPh₂ group carries two terminal CO ligands, whilst the remaining iron centre now carries the PMe₂Ph ligand and two terminal CO ligands. Thermal decarbonylation of (5) gives two new co-ordinatively unsaturated isomers [WFe₂H(µ₃-CR)(µ-PPh₂)(CO)₅(PMe₂Ph)(η-C₅H₅)](7) and (8) which do not interconvert at room temperature. The structure of (7) is closely related to that of compound (4) except that an FeH(CO)(PMe₂Ph) group is now ligated by the µ-PPh₂ ligand. The structure of (8) is similarly related to that of (5), but the Fe–Fe bond is no longer bridged by a CO ligand and the hydride occupies a terminal site on the Fe atom remote from the µ-PPh₂ group. Compound (7) does not react with CO, but (8) with CO readily gives the saturated precursor (5). Compounds (7) and (8) do not react with PMe₅Ph at ambient temperatures but both react with this ligand in refluxing toluene to give good yields of the co-ordinatively unsaturated bis-PMe₂Ph complex [WFe₂H(µ₃-CR)(µ-PPh₂)(CO)₄(PMe₂Ph)₂(η-C₅H₅)](9). In compound (9) the iron centre remote from the µ-PPh₂ group carries two CO ligands and a PMe₂Ph ligand, whilst an FeH (CO)(PMe₂Ph) group is ligated by the µ-PPh₂ ligand.