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.