Chemistry of polynuclear metal complexes with bridging carbene or carbyne ligands. Part 110. Synthesis of compounds with tungsten–copper or –gold bonds; crystal structure of [NEt4][W2Cu(µ-CCCBut)2(CO)4(η5-C2B9H9Me2)2]·Et2O

Abstract

Treatment of the reagents [NEt₄][W(CR)(CO)₂(η⁵-C₂B₉H₉Me₂)] in CH₂Cl₂ with 1 equivalent of CuCl or [AuCl(tht)](tht = tetrahydrothiophene) affords the labile complexes [NEt₄][WMCl(µ-CR)(CO)₂(η⁵-C₂B₉H₉Me₂)](M = Cu or Au, R = C₆H₄Me-4 or CCBu^t). Use of 2 equivalents of CuCl yields the stable tungstendicopper species [NEt₄][WCu₂Cl₂(µ-CR)(CO)₂(η⁵-C₂B₉H₉Me₂)], which may also be obtained by adding 1 equivalent of CuCl to the tungsten-copper dimetal compounds in CH₂Cl₂. Reactions of the salts [NEt₄][WCuCl(µ-CR)(CO)₂(η⁵-C₂B₉H₉Me₂)] with CNR′ in CH₂Cl₂ in the presence of TIBF₄ yields the neutral complexes [WCu(µ-CR)(CO)₂(CNR′)(η⁵-C₂B₉H₉Me₂)](R = C₆H₄Me-4 or CCBu^t, R′= C₆H₃Me₂-2,6; R = CCBu^t, R′= Bu^t). The trimetal compounds [NEt₄][W₂M(µ-CR)₂(CO)₄(η⁵-C₂B₉H₉Me₂)₂](M = Cu, R = C₆H₄Me-4 or CCBu^t; M = Au, R = CCBu^t) have been prepared by treating, in CH₂Cl₂, 2 equivalents of the reagents [NEt₄][W(CR)(CO)₂(η⁵-C₂B₉H₉Me₂)] with 1 equivalent of CuCl or [AuCl(tht)] in the presence of TIBF₄. An X-ray diffraction study of the salt [NEt₄][W₂Cu(µ-CCCBu^t)₂(CO)₄(η⁵-C₂B₉H₉Me₂)₂] revealed a novel structure in the crystal. The anion has a W₂Cu spine [W–Cu 2.602(1) and 2.764(1)Å, W–Cu–W 152.7(1)°] with each metal–metal bond asymmetrically bridged by a CCCBu^t group [µ-C-W 1.85(1), µ-C-Cu(av.) 2.08(1)Å; W-µ-C-CCBu^t(av.) 169.5(1)°]. The shorter of the two W–Cu separations is also spanned by a C₂B₉H₉Me₂ cage. As expected the latter is η⁵ co-ordinated to the tungsten atom, but it also forms an exopolyhedral B–H ⇀ Cu three-centre two-electron bridge bond employing the boron atom β to the carbon atoms in the pentagonal CCBBB face of the cage [µ-B–W 2.36(1), µ-B–Cu 2.33(1)Å]. The other tungsten atom is ligated by a C₂B₉H₉Me₂ group in the normal η⁵ bonding mode, and both tungstens carry two terminally bound CO groups. The reaction between [W(CCCBu^t)(CO)₂(η-C₅H₅)] and [Pt(nb)₃](nb = norbornene = bicyclo[2.2.1] heptene) affords the compound [W₂Pt(µ-CCCBu^t)₂(CO)₄(η-C₅H₅)₂]. The ¹H and ¹³C-{¹H} NMR data for the new compounds are reported and discussed.