Chemistry of polynuclear metal complexes with bridging carbene or carbyne ligands. Part 96. Reactions with phospha-alkynes; crystal structures of [WFe{µ-C(C6H4Me-4)PC(But)(CO)5}(η-C5Me5)] and [MoFe{µ-C(C6H4Me-4)C(But)P}(µ-CO)(CO)3(PMe3)(η-C5H5)

Abstract

The electronically unsaturated dimetal compound [WFe(µ-CC6H4Me-4)(CO)5(η-C5Me5)] reacts with the phospha-alkynes R′CP (R′= But or Pri) in thf (tetrahydrofuran) below room temperature to give the complexes [WFe{µ-C(C6H4Me-4)PC(R′)}(CO)5(η-C5Me5)]. The structure of the species with R′= But has been determined by X-ray diffraction. The metal–metal bond [W–Fe 2.720(2)A] is spanned by the bridging group such that all three atoms of the CPC chain are attached to the iron atom [Fe–CC6H4Me-4 2.11 (2), Fe–CBut 2.14(1), and Fe–P 2.336(5)A] but only the terminal carbons ligate the tungsten centre [W–CC6H4Me-4 2.18(2), W–CBut 2.22(1)A]. The iron carries three CO groups, and the tungsten is co-ordinated by two CO ligands and the C5Me5 ring. Reactions between the phospha-alkynes and the dimetal compounds [MFe(µ-CC6H4Me-4)(CO)4(PMe3)(η-C5H5)](M = Mo or W) in thf afford under mild conditions the complexes [MFe{µ-C(C6H4Me-4)PC(R′)}(CO)4(PMe3)(η-C5H5)](M = Mo, R′= But or Pri; M = W, R′= But), containing a similar bridge system. The two molybdenum–iron compounds readily isomerise in solution, yielding the species [MoFe{µ-C(C6H4Me-4)C(R′)P}(µ-CO)(CO)3(PMe3)(η-C5H5)]. An X-ray diffraction study on one of the isomers (R′= But) revealed an asymmetric unit containing two crystallographically independent molecules of similar geometry. The Mo(1)–Fe(1) bond [2.710(1)A] is bridged by a carbonyl ligand and by the C(C6H4Me-4)C(But)P unit. All these atoms of the CCP group are bonded to the molybdenum atom [Mo(1)–CC6H4Me-4 2.290(4), Mo(1)–CBut 2.353(5), and Mo(1)–P(1) 2.527(2)A], but only the P and CC6H4Me-4 groups are attached to the iron [Fe(1)–CC6H4Me-4 2.017(5), Fe(1)–P(1) 2.302(2)A]. The Mo atom carries the η-C5H5 ring and a CO ligand but the latter is bent [Mo(1)–C–O 168.4(4)°] towards the µ-P atom [C ⋯ P 2.380(5)A]. The Fe atom is co-ordinated by two terminally bound CO groups and the PMe3 ligand [Fe(1)–P(2) 2.246(2)A]. The n.m.r. spectra (1H, 13C-{1H}, and 31P-{1H}) of the new compounds are reported and discussed.