Elusive Phosphine Copper(l) Boryl Complexes: Synthesis, Structures, and Reactivity

We report the first isolation of phosphine copper boryl complexes-species pivotal to numerous copper-catalyzed borylation reactions. The reaction of diboron(4) derivatives with copper terf-butoxide complexes of phosphine ligands allows the isolation of the dimeric mu-boryl-bridged Cu(l) complexes [(iPr(3)P)Cu-Bdmab](2)(4) and [(C6H4(Ph2P)(2))Cu-Bpin](2) (6) with Cu center dot center dot center dot Cu distances of 2.24-2.27 A (dmab = (NMe)(2)C6H4, pin = (OCMe2)(2))). A slightly more sterically demanding boryl ligand furnishes the unprecedented multinuclear copper boryl complex [(iPr(3)P)(2)Cu-8(B(iPrEn))(3)(OrBu)(3)] (5), a potential intermediate of the decomposition of an initial Cu(l) boryl complex (iPrEn = (NiPr)(2)C2H4). All complexes were characterized by single-crystal X-ray diffraction, NMR spectroscopy; and elemental analysis. DFT computations support the nature of these unique complexes and give insight into their electronic structures.