Chemistry of polynuclear metal complexes with bridging carbene or carbyne ligands. Part 63. Synthesis of eight-membered-ring metallacycles: X-ray crystal structures of [Pt4W4(µ-CR)(µ3-CR)3(µ-CO)(CO)7(η-C5H5)4]·CH2Cl2, [Ni2Pt2W4(µ-CR)(µ3-CR)3(µ-CO)(CO)7(η-C5H5)4]·CH2Cl2(R = C6H4Me-4), and [Ni2Pt2W4(µ3-CPh)4(CO)8(η-C5H5)4

Abstract

The reaction between [Pt3W4(µ-CC6H4Me-4)2(µ3-CC6H4Me-4)2(CO)8(η-C5H5)4] and [Pt(cod)2](cod = cyclo-octa-1,5-diene) in tetrahydrofuran (thf) affords the compound [Pt4W4(µ-CC6H4Me-4)(µ3-CC6H4Me-4)3(µ-CO)(CO)7(η-C5H5)4]. The latter may also be obtained from the reaction between the tetranuclear metal cluster [Pt2W2(µ-CC6H4Me-4)(µ3-CC6H4Me-4)(CO)4(cod)(η-C5H5)2] and ethylene under pressure. The structure of [Pt4W4(µ-CC6H4Me-4)(µ3-CC6H4Me-4)3(µ-CO)(CO)7(η-C5H5)4] has been established by X-ray diffraction. The molecule has a ring of eight metal atoms with the four platinum and four tungsten atoms in alternating positions, such that the tungsten atoms form the four points of a ‘star’, and the platinum atoms lie in an essentially square arrangement (mean Pt ⋯ Pt 2.954, mean Pt–W 2.754 A). Three of the tolylmethylidyne groups triply bridge Pt2W triangles, while the fourth edge-bridges a Pt–W bond. Two of the µ3-CC6H4Me-4 groups lie on one side of the Pt4W4 ring, while the third is on the other side. On this side also a CO ligand asymmetrically bridges the Pt2W triangle which in a symmetrical isomer would have been occupied by a µ3-CC6H4Me-4 fragment. One CO group bridges the Pt–W bond adjacent to that spanned by the edge-bridging tolylmethylidyne ligand. The remaining six carbonyl groups semi-bridge the other six Pt–W bonds. The reaction between the trimetal compound [PtW2(µ-CC6H4Me-4)2(CO)4(η-C5H5)2] and an excess of [Ni(cod)2] affords the compound [Ni2Pt2W4(µ-CC6H4Me-4)(µ3-CC6H4Me-4)3(µ-CO)(CO)7(η-C5H5)4]. The latter is formed as a mixture of two isomers by interchange of the platinum and nickel sites. In one isomer a tolylmethylidyne ligand edge-bridges a Ni–W bond, and in the other a Pt–W bond. An X-ray diffraction study showed that in the crystal both isomers are present, leading to disorder at the nickel and platinum sites. In the Ni2Pt2W4 rings there is a trans-Ni ⋯ Ni and a trans-Pt ⋯ Pt arrangement, as expected from the mode of synthesis. Treatment of [PtW2(µ-CPh)2(CO)4(η-C5H5)2] with an excess of [Ni(cod)2] yields an octanuclear Ni2Pt2W4 metal complex formed as a separable mixture of three isomers: [Ni2Pt2W4(µ-CPh)(µ3-CPh)3(µ-CO)(CO)7(η-C5H5)4](two isomers) and [Ni2Pt2W4(µ3-CPh)4(CO)8(η-C5H5)4]. An X-ray diffraction study on the latter species confirmed the presence of the eight-membered metal ring in which four tungsten atoms are at the points of a ‘star’ and there is a central Ni ⋯ Pt ⋯ Ni ⋯ Pt fragment. Four CPh ligands triply bridge the NiPtW triangles, two lying above the mean plane through the eight metal atoms, and two below this plane. The structure has a crystallographic two-fold axis through the centre of the ring. A cluster compound [NiPt3W4(µ-CC6H4Me-4)(µ3-CC6H4Me-4)3(µ-CO)(CO)7(η-C5H5)4](two isomers) has been prepared by addition of [Ni(cod)2] to the seven-metal-atom chain complex [Pt3W4(µ-CC6H4Me-4)2(µ3-CC6H4Me-4)2(CO)8(η-C5H5)4]. In thf at reflux temperatures, the species [Pt4W4(µ-CC6H4Me-4)(µ3-CC6H4Me-4)3(µ-CO)(CO)7(η-C5H5)4] and [Ni2Pt2W4(µ-CR)(µ3-CR)3(µ-CO)(CO)7(η-C5H5)4](R = Ph or C6H4Me-4) readily isomerise to their respective symmetrical forms with four triply bridging alkylidyne groups. The 13C-{1H} and 195Pt-{1H} n.m.r. data for the various compounds are reported, and are discussed in relation to the molecular structures.