Evidence for the localisation of electronic charge in electrochemically reduced copper(I) complexes with electron deficient ligands: a structural and spectroelectrochemical study ‡

Abstract

The electrochemical and spectral properties of copper(I) complexes with binaphthyridine ligands, bn and tbn (where bn = 2,2′-1,8-binaphthyridine, tbn = 3,3′-trimethylene-2,2′-1,8-binaphthyridine), have been studied. The complexes are [Cu(bn)₂]⁺ 1, [Cu(tbn)₂]⁺ 2, [Cu(bn)(PPh₃)₂]⁺ 3 and [Cu(tbn)(PPh₃)₂]⁺ 4. Reduction of 1–3 results in the formation of radical anion species involving the ligands. Reduction of 4 results in decomposition. For 3^– strong near infrared absorptions (1000 nm) are observed suggesting a bn^˙– radical anion species, in which the redox MO extends across the entire ligand. For 2^– absorptions at 750 nm suggest a redox MO which is much less extensive and localised on a single naphthyridine unit of the tbn ligand. Reduction of 1 is complicated by the presence of two closely lying reduction waves. Application of a reducing potential resulted in spectral features similar to those observed for 3^–. However, further reduction showed spectral features similar to those of 2^–. The crystal structure of 3·BF₄ was determined by single-crystal X-ray diffraction.

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