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)]

Abstract

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)Å] is spanned by a PPh₂ group [Fe–P 2.21 0(3), W–P 2.406(3)Å]. 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)Å], 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.