Bottleable Neutral Analogues Of [B2h5](-) As Versatile And Strongly Binding Eta(2) Donor Ligands

Herein we report the discovery that two bottleable, neutral, base-stabilized diborane(5) compounds are able to bind strongly to a number of copper(I) complexes exclusively through their B-B bond. The resulting complexes represent the first known complexes containing unsupported, neutral sigma(B-B) diborane ligands. Single-crystal X-ray analyses of these complexes show that the X-Cu moiety (X=Cl, OTf, C6F5) lies opposite the bridging hydrogen atom of the diborane and is near perpendicular to the B-B bond, interacting almost equally with both boron atoms and causing a B-B bond elongation. DFT studies show that sigma donation from and pi backdonation to the pseudo-pi-like B-B bond account for their formation. Astoundingly, these copper sigma(B-B) complexes are inert to ligand exchange with pyridine under either heating or photoirradiation.