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′= Bu^t 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′= Bu^t has been determined by X-ray diffraction. The metal–metal bond [W–Fe 2.720(2)Å] 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–CBu^t 2.14(1), and Fe–P 2.336(5)Å] but only the terminal carbons ligate the tungsten centre [W–CC₆H₄Me-4 2.18(2), W–CBu^t 2.22(1)Å]. 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′= Bu^t or Prⁱ; M = W, R′= Bu^t), 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′= Bu^t) revealed an asymmetric unit containing two crystallographically independent molecules of similar geometry. The Mo(1)–Fe(1) bond [2.710(1)Å] is bridged by a carbonyl ligand and by the C(C₆H₄Me-4)C(Bu^t)P unit. All these atoms of the CCP group are bonded to the molybdenum atom [Mo(1)–CC₆H₄Me-4 2.290(4), Mo(1)–CBu^t 2.353(5), and Mo(1)–P(1) 2.527(2)Å], 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)Å]. 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)Å]. The Fe atom is co-ordinated by two terminally bound CO groups and the PMe₃ ligand [Fe(1)–P(2) 2.246(2)Å]. The n.m.r. spectra (¹H, ¹³C-{¹H}, and ³¹P-{¹H}) of the new compounds are reported and discussed.