Syntheses and crystal structures of complexes [M₂R₂][M = Cu, Ag, or Au; R = 2-C(SiMe₃)₂C₅H₄N] and [Cu₄R′₄][R′= 2-CH(SiMe₃)C₅H₄N]; electrochemical generation of [Cu₂R₂]²⁺

Abstract

Reaction of ‘LiR,’ where R = 2-C(SiMe3)2C5H4N, 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.