Tetranuclear group 7/8 mixed-metal and open trinuclear group 7 metal carbonyl clusters bearing bridging 2-mercapto-1-methylimidazole ligands

Abstract

The reactivity of group 7 metal dinuclear carbonyl complexes [M₂(CO)₆(μ-SN₂C₄H₅)₂] (1, M = Re; 2, M = Mn) toward group 8 metal trinuclear carbonyl clusters were examined. Reactions of 1 and 2 with [Os₃(CO)₁₀(NCMe)₂] in refluxing benzene furnished the tetranuclear mixed-metal clusters [Os₃Re(CO)₁₃(μ₃-SN₂C₄H₅)] (3) and [Os₃Mn(CO)₁₃(μ₃-SN₂C₄H₅)] (4), respectively. Similar treatment of 1 and 2 with Ru₃(CO)₁₂ yielded the ruthenium analogs [Ru₃Re(CO)₁₃(μ₃-SN₂C₄H₅)] (5), and [Ru₃Mn(CO)₁₃(μ₃-SN₂C₄H₅)] (6), but in the case of 2 a secondary product [Mn₃(CO)₁₀(μ-Cl)(μ₃-SN₂C₄H₅)₂] (7) was also formed. Compounds 3–6 have a butterfly core of four metal atoms with the M (Mn or Re) at a wingtip of the butterfly and containing a noncrystallographic mirror plane of symmetry. This result provides a potential method for the synthesis of a series of new group 7/8 mixed metal complexes containing a bifunctional heterocyclic ligand. Compound 7 is a unique example of a 54-electron trimanganese complex having bridging 2-mercapto-1-methylimidazolate and chloride ligands. Interestingly, the reaction of 1 with Fe₃(CO)₁₂ at 70–75 °C furnished the tri- and dirhenium complexes [Re₃(CO)₁₀(μ-H)(μ₃-SN₂C₄H₅)₂] (8) and [Re₂(CO)₆(N₂C₄H₅)(μ-SN₂C₄H₅)₂] (9), respectively instead of the expected formation of the mixed-metal clusters. The former is an interesting example of a 52-electron trirhenium-hydridic complex containing bridging 2-mercapto-1-methylimidazolate ligand, while the latter can be viewed as a 1-methylimidazole adduct of 1. No mixed Fe–Re complexes were produced in this reaction. The molecular structures of the new compounds 3–5 and 7–9 were established by single-crystal X-ray diffraction analyses and the DFT studies of compounds 5, 7 and 8 are reported.