Chemistry of di- and tri-metal complexes with bridging carbene or carbyne ligands. Part 28. Synthesis and X-ray crystal structures of the compounds [MoW2(µ-CR)2(µ-CO)2(CO)4(η-C5H5)2] and [AuW2(µ-CR)2(CO)4(η-C5H5)2][PF6](R = C6H4Me-4)

Abstract

The compound [W(CR)(CO)₂(η-C₅H₅)](R = C₆H₄Me-4) reacts readily with the complexes [M(CO)₃(NCMe)₃](M = Mo or W) in hexane at reflux to afford the trimetal compounds [MW₂(µ-CR)₂(µ-σ:η²-CO)₂(CO)₄(η-C₅H₅)₂], n.m.r. and i.r. data for which are reported. The molybdenum–ditungsten compound was fully characterised structurally by a single-crystal X-ray diffraction study. It comprises a bent W–Mo–W spine [148.2(2)°] with the Mo–W bonds [2.938(1)Å] bridged by CC₆H₄Me-4 groups. The Mo atom carries two terminal carbonyl ligands; the bisector of the angle between these is an approximate axis of two-fold symmetry for the molecule as a whole. The two molybdenum–tungsten–carbene ring systems are not coplanar, but are twisted relative to one another so that the two planes are nearly orthogonal. The Mo–W and Mo–C(carbene) bonds do not form a pseudo-tetrahedral group, however, because of the presence of two cis carbonyl ligands on the central Mo atom. An especially interesting feature is that, of the two terminal carbonyl ligands on each tungsten atom, one is η²-bonded to the central molybdenum atom. The significance of this is discussed. Crystals are triclinic, space group P(no. 2), and the structure has been refined to R= 0.038 for 3 711 intensities measured to 2θ= 55° at 210 K. Treatment of chloro(tetrahydrothiophene)gold(I) with [W(CR)(CO)₂(η-C₅H₅)] in tetrahydrofuran in the presence of TIPF₆ affords the salt [AuW₂(µ-CR)₂(CO)₄(η-C₅H₅)₂][PF₆], while [Ag(NCMe)₄][BF₄] and [W(CR)(CO)₂(η-C₅H₅)] give [AgW₂(µ-CR)₂(CO)₄(η-C₅H₅)₂][BF₄]. The spectroscopic data (i.r. and n.m.r.) for these gold and silver compounds are discussed, and the structure of the former has been established by X-ray diffraction. The cation has a bent W–Au–W spine [162.8(1)°] with the Au–W bonds [2.752(1)Å] bridged by the CC₆H₄Me-4 groups. The dihedral angle between the two dimetallacyclopropene rings is 62°. The tungsten atoms carry η-C₅H₅ groups and two terminally bound CO ligands. Crystals are orthorhombic, space group Pnna(no. 52), and the structure has been refined to R= 0.050 for 1 654 reflections measured to 2θ= 50° at 200 K.