Contrasting pathways for the reactions of triruthenaborane cluster anions with [{M(η5– C5Me5)Cl2}2](M = Rh or Ir). Molecular structures of [RhRu3(η5– C5Me5)H2(CO)8(PPh3)BH] and [IrRu3(η5– C5Me5)H(CO)10BH2]

Abstract

The reactions of [N(PPh₃)₂][Ru₃(CO)₉BH₄] and [N(PPh₃)₂][Ru₃(CO)₉(B₂H₅)] with [{M(η₅C₅Me₅)Cl₂}₂](M = Rh or Ir) follow two different, but related, pathways. For M = Rh, the products in each case are the 62-electron butterfly borido-cluster [RhRu₃(η⁵– C₅Me₅)H(CO)₉BH₂]1 and the tetrahedral cluster [RhRu₃(η⁵– C₅Me₅)H₂(CO)₁₀]. In contrast, the reaction of [{Ir(η⁵– C₅Me₅)Cl₂}₂] with [N(PPh₃)₂][Ru₃(CO)₉BH₄] leads to the 64-electron cluster [IrRu₃(η⁵– C₅Me₅)H(CO)₁₀BH₂]4 and tetrahedral [IrRu₃(η⁵– C₅Me₅)H₄(CO)₉]3 but when the starting cluster is [Ru₃(CO)₉(B₂H₅)]^–, only 4 is formed. A single-crystal X-ray diffraction analysis of compound 4 has been carried out: triclinic, space group Pa= 8.780(1), b= 12.304(3), c= 12.432(3)Å, α= 105.78(2), β= 93.55(2), γ= 91.44(2)°Z= 2, R= 0.0483. The Ru₃Ir cluster core in 4 can be described either as an open-butterfly or a spiked triangle which is supported by a µ₄-boron atom [Ir–B 2.04(1)Å and Ru–B(av.) 2.28(1)Å]. In solution, two isomers of [IrRu₃(η⁵– C₅Me₅)H(CO)₁₀BH₂], which differ in the positions of cluster hydrogen atoms, are observed. Compound 1 reacts with PPh₃ to give [RhRu₃(η⁵– C₅Me₅)H₂(CO)₈(PPh₃)BH]5. The crystal structure of compound 5 has been determined and the results confirm the presence of a heterometallic butterfly core: monoclinic, space group P2₁/n, a= 11.538(1), b= 18.141(2), c= 19.089(3)Å, β= 102.98(1)°, Z= 4, R= 0.0368. A comparison of the ¹¹B and ¹H NMR spectroscopic data for 1 and 5 indicates that a redistribution of cluster hydrogen atoms occurs during the substitution of a phosphine for carbonyl ligand; one Ru–H–B and two Ru–H–Ru bridging hydrogen atoms have been located directly in 5 by X-ray diffraction.