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 [NEt 4 ][W 2 Cu(µ-CCCBu t ) 2 (CO) 4 (η 5 -C 2 B 9 H 9 Me 2 ) 2 ]·Et 2 O

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 CCBut). 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 CCBut, R′= C6H3Me2-2,6; R = CCBut, R′= But). The trimetal compounds [NEt4][W2M(µ-CR)2(CO)4(η5-C2B9H9Me2)2](M = Cu, R = C6H4Me-4 or CCBut; M = Au, R = CCBut) 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-CCCBut)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 CCCBut group [µ-C-W 1.85(1), µ-C-Cu(av.) 2.08(1)Å; W-µ-C-CCBut(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(CCCBut)(CO)2(η-C5H5)] and [Pt(nb)3](nb = norbornene = bicyclo[2.2.1] heptene) affords the compound [W2Pt(µ-CCCBut)2(CO)4(η-C5H5)2]. The 1H and 13C-{1H} NMR data for the new compounds are reported and discussed.