Syntheses and crystal structures of complexes [M₂R₂] [M = Cu, Ag, or Au; R = 2-C(SiMe₃)₂C₅H ₄N] and [cu₄R′₄] [r′ = 2-CH(SiMe₃)C₅H₄N]; Electrochemical generation of [cu₂R₂]²⁺

Reaction of 'LiR,' where R = 2-C(SiMe₃)₂C ₅H₄N, with CuCl, AgBF₄ or [Au(CO)Cl] in tetrahydrofuran-hexane yields binuclear complexes [M₂R₂] [M = Cu, (1); Ag, (2); Au, (3)] of relative thermal stabilities (1) > (3) > (2), the copper complex being sublimable in vacuo. In the same solvents, 'Li[2-CH(SiMe₃)C₅H₄N]' yields a tetranuclear species [Cu₄{2-CH(SiMe₃)C₅H₄N} ₄], (4), which rapidly decomposes in solution at ambient temperature to elemental copper. Electrochemistry reveals that (1) is reversibly oxidized to the formally copper(II) alkyl species [Cu₂R₂] ²⁺. The structures of complexes (1)-(4) have been established from single-crystal X-ray diffraction data. Molecules of (1)-(3) are centrosymmetric with each ligand bridging the two metal centres which are in close proximity [M ⋯ M 2.412(1) in (1), 2.654(1) in (2), and 2.672(1) Å in (3)]. In (4) the ligands bridge successive metal centres, alternating above and below a Cu₄ square, M ⋯ M 2.668(2) Å.