Chemistry of di- and tri-metal complexes with bridging carbene or carbyne ligands. Part 8. Synthesis of the trimetal compounds [M{W(µ-CC6H4Me-4)(CO)2(η-C5H5)}2](M = Ni, Pd, or Pt) and crystal structures of the platinum and nickel complexes

Abstract

The alkylidyne complex [W(CC₆H₄Me-4)(CO)₂(η-C₅H₅)] reacts in 1 : 2 mol ratio with the compounds [Pt-(C₂H₄)₃], [Pd(C₇H₁₀)₃], and [Ni(cod)₂](cod = cyclo-octa-1,5-diene) to give the trimetalla species [MW₂(µ-CC₆H₄Me-4)₂(CO)₄(η-C₅H₅)₂](M = Pt, Pd, or Ni), characterised spectroscopically. Additionally, the structures of the platinum and nickel compounds have been established by single-crystal X-ray diffraction studies. Crystals of the platinum compound are monoclinic, space group P2₁/c, with Z= 4 in a unit cell of dimensions a= 12.187(6), b= 13.404(7), c= 16.938(9)Å, and β= 96.42(4)°. The structure has been solved by heavy-atom methods and refined by least squares to R 0.047 (R′ 0.048) for 4 369 independent diffracted intensities measured at 200 K. For the nickel compound the crystals are monoclinic, space group P2₁/n, with Z= 4, in a unit cell of dimensions a= 7.980(2), b= 22.080(6), c= 16.025(3)Å, and β= 103.45(2)°. Intensities were measured at room temperature to 2θ= 65° and the structure has been refined to R 0.053 (R′ 0.063) for 5 246 unique reflections. The two molecules have similar structures with a metal atom sequence W–Pt(Ni)–W in which the Pt–W or Ni–W bonds are bridged by alkylidyne ligands, CC₆H₄Me-4, affording two three-membered orthogonal ring systems sharing a common vertex (Pt or Ni). In the nickel compound the W–Ni–W sequence is nearly linear (175°), whereas in the platinum complex the angle W–Pt–W is 165°. The W–µ-C bond lengths in both compounds are very similar [1.91(1) and 1.89(1)Å], and suggest a bond order of ca. 2 between the tungsten atom and the bridging carbon atom. The metal–metal distances [mean Ni–W 2.584(1), mean Pt–W 2.713(1)Å] also imply multiple bonding within the dimetallacyclopropene rings. Each tungsten atom carries two carbonyl groups, one of which is semi-bridging to the Pt(Ni) atom and lies in the plane of the corresponding cyclopropene ring, while the other is orthogonal to this plane. The dihedral angle between the two dimetallacyclopropene rings is ca. 97°. A fascinating difference between these two molecules is that, whereas in the nickel compound the terminal carbonyl groups on the tungsten atoms each lie trans to the tolyl group of the second metallacyclopropene ring, in the platinum compound the corresponding carbonyl ligands lie one cis and one trans.