σ-BH activation of NHC → BH ₃ fragments in dinuclear Cu complexes

We explored herein the coordination properties of the bis(phosphine)NHC → BH₃ ligand toward cationic and neutral Cu centres. The synthesis of three dinuclear Cu complexes featuring σ-BH interactions is reported. Noticeably, in each Cu complex, a BH moiety bridges two Cu centres <i>via</i> two σ-BH interactions in a μ₂-η¹η¹ BH coordination mode. NMR, IR, deuterium incorporation and X-ray diffraction analyses, supported by DFT investigation, enabled us to finely measure the level of activation of the B-H bond depending on the coordination environment. The study shows a gradual increase of activation whether the BH fragment is involved in none, one or two σ-BH interactions with Cu centres.