Synthesis and X-ray crystal structure analysis of the triruthenium-rhodium carbonyl cluster [Ru₃Rh(μ-H)₂(CO)₁₀(η⁵-C₅H₅)]

The pyrolysis of a mixture of the labile dimer [(Rh(CO)₂Cl)₂] and the hydridocluster [Ru₄H₂(CO)₁₃] in the presence of Tl(C₅H₅), in hexane, gives the mixed metal complex [Ru₃Rh(μ-H)₂(CO)₁₀ (η⁵-C₅H₅)] as the major product. An X-ray diffraction study of this complex shows that it contains a distorted Ru₃Rh tetrahedron, two RuRu edges of which are bridged by hydrides and one RuRu edge of which is asymmetrically bridged by a carbonyl ligand. The remaining nine carbonyl ligands are terminal, with three bound to each Ru atom, while the cyclopentadienyl ligand is co-ordinated to the Rh atom. The complex crystallises in the monoclinic space group P2₁/n with a 8.186(1), b 15.061(1), c 16.302(1) Å, β 91.06(1)°, Z = 4; 2737 observed data with F > 4σ(F) were refined by blocked-cascade least squares to R = 0.040, R_w = 0.033. At low temperature, the ¹H NMR spectrum of the cluster shows two signals, in the hydride region, consistent with the inequivalent hydride positions in the ground state structure, but at higher temperatures coalescence occurs, and the activation energy for this process has been found to be 38 kJ/mol at -80° C.