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

Abstract

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 tert-butoxide complexes of phosphine ligands allows the isolation of the dimeric μ-boryl-bridged Cu(I) complexes [(iPr3P)Cu–Bdmab]2 (4) and [(C6H4(Ph2P)2)Cu–Bpin]2 (6) with Cu···Cu distances of 2.24–2.27 A (dmab = (NMe)2C6H4, pin = (OCMe2)2)). A slightly more sterically demanding boryl ligand furnishes the unprecedented multinuclear copper boryl complex [(iPr3P)2Cu8(B(iPrEn))3(OtBu)3] (5), a potential intermediate of the decomposition of an initial Cu(I) boryl complex (iPrEn = (NiPr)2C2H4). 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.