Chemistry of di- and tri-metal complexes with bridging carbene or carbyne ligands. Part 44. Formation of unsaturated dimetal compounds with elimination of alkylidyne groups; X-ray crystal structures of [FeW(µ-PPh2)(CO)5{HB(pz)3}][HB(pz)3= tris(pyrazol-1-yl)borate] and [RhW(µ-CO)2(CO)(PPh3)2(η-C5H5)]

Treatment of the complexes[FeW(µ-CR)(CO)5{HB(pz)3}][R = C6H4Me-4 or Me; HB(pz)3= tris(pyrazol-1-yl)borate] with diphenylphosphine in dichloromethane at room temperature gives the compounds [FeW(µ-CR)(CO)4(PHPh2){HB(pz)3}]. On heating in toluene, the p-tolylmethylidyne derivative affords the complex [FeW{µ-σ,η3-CH(C6H4Me-4)}(µ-PPh2)(µ-CO)-(CO)3{HB(pz)3}]. In contrast, the ethylidyne analogue under similar conditions yields the compound [FeW(µ-PPh2)(CO)5{HB(pz)3}]. The latter was structurally characterised by X-ray diffraction. A short Fe–W bond [2.658(2)A] is spanned by a PPh2 group [Fe–P 2.21 0(3), W–P 2.406(3)A]. The iron atom is ligated by three CO groups and the tungsten atom by two such groups. One CO ligand on tungsten semi-bridges the Fe–W bond [W–C–0168(1)°]. The tungsten atom carries the HB(pz)3 ligand which functions as a tridentate group in the usual manner. The ethylidyne tungsten compound [W(CMe)(CO)2(η-C5H5)] reacts with the complexes [RhH(L)(PPh3)3](L = CO or PPh3) to give a mixture of the dimetal compounds [RhW(µ-CO)2(CO)(PPh3)2(η-C5H5)] and [RhW(µ-CO)2(PPh3)2(η-C2H4)(η-C5H5)]. The former species was identified by a single-crystal X-ray diffraction study [Rh–W 2.587(1)A], the latter could only be identified by 1H and 13C-{1H} n.m.r. spectroscopy. Spectroscopic data for all the new compounds are reported and discussed.