Bimetallic Ru–Cu tellurido complexes: controlled synthesis and electrochemical studies of copper halide–TeRu₅ and Te₂Ru₄ clusters

When [TeRu₅(CO)₁₄]²⁻ (1) was treated with 1 equiv. of CuX (X = Cl, Br, I) in THF, mono-CuX–TeRu₅ clusters [TeRu₅(CO)₁₄CuX]²⁻ (X = Cl, 2a; Br, 2b; I, 2c) were obtained. Clusters 2a–2c consist of an octahedral TeRu₅ core, in which one triangular Ru₃ plane is capped by a μ₃-CuX fragment. For CuX (X = Cl, Br), the reaction of complex 1 with 2 equiv. of CuX in THF at room temperature formed Cu₄X₂-linked di-TeRu₅ clusters [{TeRu₅(CO)₁₄}₂Cu₄X₂]²⁻ (X = Cl, 3a; Br, 3b), while the same reaction in MeCN at −35 °C produced bis-CuX–TeRu₅ complexes [TeRu₅(CO)₁₄(CuX)₂]²⁻ (X = Cl, 4a; Br, 4b). X-Ray analysis showed that 4b displays a TeRu₅ core with two adjacent Ru₃ triangles each capped by a μ₃-CuBr ligand while 3b has two TeRu₅ cores that are linked by a μ₆-Cu₄Br₂ moiety. Clusters 4a and 4b underwent coupling reactions in THF to yield clusters 3a and 3b, and easily transformed to bis-CuX–Te₂Ru₄ clusters [Te₂Ru₄(CO)₁₀(CuX)₂]²⁻ (X = Cl, 5a; X = Br, 5b) in MeCN. On the other hand, the reaction of 1 with 2 equiv. of CuI in THF directly produced the bis-CuI–Te₂Ru₄ cluster [Te₂Ru₄(CO)₁₀(CuI)₂]²⁻ (5c). The nature, stability, stepwise cluster transformation, and electrochemistry of these CuX-incorporated TeRu₅- and Te₂Ru₄-based complexes are discussed systematically. In particular, the effects of CuX and the metal cores (TeRu₅vs. Te₂Ru₄) on the resultant Te–Ru–Cu clusters are further elucidated by molecular orbital calculations at the B3LYP level of the density functional theory.