The heteronuclear cluster chemistry of the Group 1B metals. Part 3. Synthesis, structures, and chemical properties of the trimetallic hexanuclear Group 1B metal cluster compounds [MM′Ru4(µ3-H)2(CO)12(PPh3)2](M = Cu, M′= Ag or Au; M = Ag, M′= Au). X-Ray crystal structure of the complex [AgCuRu4(µ3-H)2(CO)12(PPh3)2]·CH2Cl2

Abstract

Treatment of dichloromethane solutions of the salt [N(PPh₃)₂]₂[Ru₄(µ-H)₂(CO)₁₂] with dichloromethane solutions containing one equivalent of [MX(PPh₃)] and one equivalent of [M′X(PPh₃)](M ≠ M′; M,M′= Cu or Au, X = Cl; M,M′= Ag, X = I), in the presence of TlPF₆, affords the novel trimetallic clusters [MM′Ru₄(µ₃-H)₂(CO)₁₂(PPh₃)₂][M = Cu, M′= Ag (1) or Au (2); M = Ag, M′= Au (3)] in ca. 35–45% yield. A single-crystal X-ray diffraction study on (1) reveals that the metal skeleton consists of a tetrahedron of ruthenium atoms [Ru–Ru 2.793(1)–2.968(1)Å] capped by a Cu(PPh₃) moiety [Group 1B metal site M(2)], with one of the CuRu₂ faces of the CuRu₃ tetrahedron so formed further capped by a Ag(PPh₃) unit [Group 1B metal site M(1)] to give a capped trigonal bipyramidal metal core geometry [Ag–Cu 2.764(1), Ag–Ru 2.819(1) and 2.825(1), Cu–Ru 2.683(2)–2.796(2)Å]. The other two CuRu₂ faces of the cluster are both capped by triply bridging hydrido ligands and each ruthenium atom carries three terminal CO groups. Spectroscopic data demonstrate that (2) and (3) adopt similar structures to that of (1), with the heavier of the pair of Group 1B metals in each cluster again occupying the position M (1). This coinage metal site preference allows Group 1B metal exchange reactions to be used as an alternative synthetic route to (1)–(3) in good yield (ca. 70–80%).