Elusive Phosphine Copper(I) 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 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
Å (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.