Homo- and Heterobinuclear Cu and Pd Complexes with a Bridging Redox-Active Bisguanidino-Substituted Dioxolene Ligand: Electronic Structure and Metal–Ligand Electron-Transfer

5 years ago

Homo- and Heterobinuclear Cu and Pd Complexes with a Bridging Redox-Active Bisguanidino-Substituted Dioxolene Ligand: Electronic Structure and Metal–Ligand Electron-Transfer

Hans-Jörg Himmel, Hubert Wadepohl, David Fridolin Schrempp, Elisabeth Kaifer, Elisa Schneider

A new redox-active 4,5-bisguanidino-substituted o-benzoquinone ligand L is synthesized, which allows rational access to heterobinuclear complexes through the sequential coordination of two metals. In the examples discussed in this work, mononuclear Cu and Pd complexes are prepared in a first coordination step, and these complexes are then used as precursors to homobinuclear [CuII-L0-CuII] and heterobinuclear [PdII-L0-CuII] complexes. In the heterobinuclear complex, the PdII is coordinated by the softer bisguanidine side of L and the CuII by the harder dioxolene side (in line with the HSAB concept). The heterobinuclear complex is in a temperature-dependent equilibrium with its dimer, with two unsymmetrical Cu-Cl-Cu bridges. The redox-chemistry of the [CuII-L-CuII] and [PdII-L-CuII] complexes is studied. One-electron oxidation of both complexes was found to be quasi-reversible in CV experiments, and chemical one-electron oxidation was achieved with NO+(SbF6−). In the case of the homobinuclear complex [L(CuCl2)2]+, intramolecular ligand–metal electron-transfer, triggered by coordination of a CH3CN solvent molecule, leads to a temperature-dependent equilibrium between the form [CuII-L0-CuIII] at low temperatures (with CH3CN coordinated to the CuIII atom) and [CuII-L⋅+-CuII] at higher temperatures (without CH3CN). We′re guana have a good time: The new 4,5-bisguanidino-substituted o-benzoquinone ligand L allows rational access to homo- and heterobinuclear complexes by the sequential coordination of two metals. Upon one-electron oxidation of the Cu2 complex, an intramolecular electron-transfer triggered by coordination is observed.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/chem.201702053