Chemistry of di- and tri-metal complexes with bridging carbene or carbyne ligands. Part 47. Synthesis of tri-, tetra-, and penta-heteronuclear metal cluster compounds involving tungsten with platinum or nickel: crystal structures of the compounds [Pt3W2(µ3-CR)2(CO)4(cod)2(η-C5H5)2] and [Pt2W3(µ-CR)2(µ3-CR)(CO)6(η-C5H5)3](R = C6H4Me-4, cod = cyclo-octa-1,5-diene)

Abstract

Tris(ethylene)platinum, prepared in situ from [Pt(cod)₂](cod = cyclo-octa-1,5-diene), reacts with the compounds [W(CR)(CO)₂L] to give the complexes [PtW₂(µ-CR)₂(CO)₄L₂](R = Me or Ph, L =η-C₅H₅; R = Me, Ph, or C₆H₄Me-4, L =η-C₅Me₅). The analogous nickel compounds [NiW₂(µ-CR)₂(CO)₄L₂] have also been prepared using [Ni(cod)₂]. Treatment of the trinuclear metal species [MW₂(µ-CR)₂(CO)₄L₂] with one equivalent of [Pt(cod)₂] affords the tetranuclear metal compounds [MPtW₂(µ-CR)(µ₃-CR)(CO)₄(cod)L₂](M = Ni or Pt, R = C₆H₄Me-4, L =η-C₅H₅ or η-C₅Me₅; M = Pt, R = Me, L =η-C₅Me₅), while with two equivalents of [Pt(cod)₂] the pentanuclear metal complexes [Pt₃W₂(µ₃-CR)₂(CO)₄(cod)₂L₂](R = C₆H₄Me-4, L =η-C₅H₅; R = Me, L =η-C₅Me₅) are obtained. These tetra- and penta-nuclear metal compounds were generally isolated as isomeric mixtures, as revealed by n.m.r. measurements (¹H, ¹³C-{₁H}, and ¹⁹⁵Pt-{¹H}). An X-ray diffraction study structurally characterised a symmetrical isomer of [Pt₃W₂(µ₃-CC₆H₄Me-4)₂(CO)₄(cod)₂(η-C₅H₅)₂], a molecule having a crystallographic two-fold rotation axis. The structure comprises two ‘butterfly’µ₃-CPt₂W fragments sharing a wing-tip platinum vertex, with isosceles metal triangles [Pt–W 2.751(1) and 2.748(1), Pt ⋯ Pt 3.089(1)Å] capped by the CC₆H₄Me-4 groups. The terminal Pt atoms each carry a cod ligand, and the four CO groups semi-bridge Pt–W bonds. The pentanuclear metal compounds [Pt₂W₃(µ-CR)₂(µ₃-CR)(CO)₆L₃](R = C₆H₄Me-4, L =η-C₅H₅; R = Me or C₆H₄Me-4, L =η-C₅Me₅), [Pt₂W₃(µ-CMe)(µ-CC₆H₄Me-4)(µ3-CMe)(CO)₆(η-C₅H₅)(η-C₅Me₅)₂], and [Pt₂W₃(µ-CC₆H₄Me-4)₂(µ₃-CC₆H₄Me-4)(CO)₆(η-C₅H₅)(η-C₅Me₅)₂] have also been prepared by treating the appropriate tetranuclear metal compound [Pt₂W₂(µ-CR)(µ₃-CR)(CO)₄(cod)L₂] with an alkylidynetungsten complex so as to displace the cod ligand. Again isomeric mixtures were produced, and identified by n.m.r. spectroscopy. An X-ray diffraction study established the molecular structure of one of the three isomers of [Pt₂W₃(µ-CC₆H₄Me-4)₂(µ₃-CC₆H₄Me-4)(CO)₆(η-C₅H₅)₃]. The molecule has an essentially planar five-metal atom framework, with two edge-bridging and one triply bridging tolylmethylidyne groups. Four of the six CO ligands semi-bridge W–Pt bonds [W–C–O 163–168(2)Å] and each tungsten carries an η-C₅H₅ group, with each terminal W atom having one linearly bound CO. The Pt ⋯ Pt separation [2.949(2)Å] implies little direct metal-metal bonding between these atoms. Bond lengths to the central µ₃-CC₆H₄Me-4 ligand are µ₃-C–Pt 2.02(3) and 2.09(2), µ₃-C–W 1.99(3)Å, while those to the edge-bridging CC₆H₄Me-4 groups are µ-C–W 1.96(2)(mean) and µ-C–Pt 2.03(2)Å(mean).