Chemistry of di- and tri-metal complexes with bridging carbene or carbyne ligands. Part 27. Studies on the compounds [MW{µ-σ:η3-CH(C6H4Me-4)}(CO)2Ln(η-C5H5)][BF4][MLn= Pt(PR3)2 or Co(CO)(η-C5Me5)]; X-ray crystal structures of [CoW{µ-σ:η3-C-(C6H4Me-4)C(Me)C(Me)H}(µ-CO)(CO)(η-C5H5)(η-C5Me5)][BF4] and [PtW{µ-CH(C6H4Me-4)}(µ-CO)(PMe3)2(η-MeC2Me)(η-C5H5)][BF4]

Abstract

The compound [CoW{µ-σ:η³-CH(C₆H₄Me-4)}(CO)₃(ηC₅H₅)(η-C₅Me₅)][BF₄] reacts with PMe₂Ph to form [CoW{µ-CH(C₆H₄Me-4)}(CO)₃(PMe₂Ph)(η-C₅H₅)(η-C₅Me₅)][BF₄], as a mixture of diastereoisomers, and with MeCCMe to give the complex [CoW{µ-σ:η³-C(C₆H₄Me-4)C(Me)C-(Me)H}(µ-CO)(CO)(η-C₅H₅)(η-C₅Me₅)][BF⁴]. The structure of the latter has been established by an X-ray diffraction study. The Co–W bond [2.552(1)Å] is asymmetrically bridged by a CO ligand [W–C–O 150.7(6), Co–C–O 130.1 (6)°] and is also spanned by the C(C₆H₄Me-4)C(Me)C(Me)H group via what may be regarded as an η³-allylic attachment to the tungsten and a σ bond of the C(C₆H₄Me-4) end of the chain to the cobalt. The tungsten atom carries a terminal CO ligand and the η-C₅H₅ group, and the cobalt atom the η-C₅Me₅ ring. Crystals are monoclinic (P2₁/C); the structure has been refined to R= 0.037 for 3 678 reflections measured to 2θ= 50° at 298 K. In contrast with the facile reaction at 0–25 °C between [CoW{ησ:η³-CH(C₆H₄Me-4)}(CO)₃(µ-C₅H₅)(η-C₅Me₅)]-[BF₄] and MeCCMe, the alkyne only slowly reacts with the platinurrv–tungsten salt [PtW{µ-σ:η³-CH(C₆H₄Me-4)}(CO)₂(PMe₃)₂(η-C₅H₅)][BF₄] to give [PtW{µ-CH(C₆H₄Me-4)}(µ-CO)(PMe₃)₂(η-MeC₂Me)(η-C₅H₅)][BF₄], a compound in which the but-2-yne molecule is η²co-ordinated to the tungsten centre. This was confirmed by an X-ray diffraction study. The Pt–W bond [2.771 (1)Å] is asymmetrically bridged by the CO ligand [W–C–0 151.9(15), Pt–C–0 124.3(13)°] and symmetrically bridged by the tolylmethylene group [µ-C–W 2.101 (18), µC–Pt 2.110(15)Å]. In addition to the MeC₂Me ligand, the tungsten atom is bonded to the η-C₅H₅ ring, while the platinum atom is in an essentially planar environment ligated by the two PMe₃ groups, the tungsten, the asymmetrically bridging CO, and the carbon atom of the tolylmethylene ligand. Crystals are monoclinic (P2₁/n); the structure has been refined to R= 0.063 for 3 798 reflections measured to 2θ= 50° at 298 K. The alkyne complexes [PtW{µ-CH(C₆H₄Me-4)}(µ-CO)(PR₃)₂(η-R′C₂R′)(η-C₅H₅)][BF₄](PR₃= PMe₂Ph, R′= Me; PR₃= PMe₂Ph or PMePh₂, R′= Ph) have also been prepared. The n.m.r. spectra of the new tungsten–cobalt and –platinum compounds are reported and discussed in relation to their structures, and the dynamic behaviour of some of the species in solution.