Copper Complexes Bearing a Dianionic Diborane(4) Ligand: Synthesis and Evaluation of the Donor Property

A series of mono- and dinuclear copper complexes 2–4 bearing a η2-dianionic diborane(4) ligand was synthesized and characterized. The strong donating ability of the dianionic diborane(4) ligand was evaluated by IR spectrum, structural parameters in the crystal, XANES spectra, and DFT calculations. The NBO calculations revealed that the π-backdonation to dianionic diborane(4) ligand is weaker than that to the ethylene ligand due to the dianionic charges on the boron atoms.