Coordination of a Phosphine-Tethered Aminoborane to Group 10 Metals

While π-complexes of C=C bonds are ubiquitous in organometallic chemistry, analogous complexes of the isoelectronic but strongly polarized B=N double bond of aminoboranes are extremely scarce. To address this gap, a diphosphine-aminoborane ligand (^PhDPBA^iPr) is introduced and its coordination with group 10 metals is investigated. The B=N bond does not coordinate to the metal in Pt(0) and Pd(II) complexes. In contrast, side-on coordination of the B=N bond is observed in the Ni(0) complex (^PhDPBA^iPr)Ni(NCPh), and the X-ray crystal structure reveals B-N bond elongation compared to the free ligand. The choice of co-ligand strongly influences the presence or absence of side-on coordination at Ni(0) as evidenced by NMR spectroscopy. While the B=N π-complex is geometrically similar to C=C analogues, a bonding analysis reveals that the interaction of the B=N motif with the electron-rich Ni(0) center is best described as 3c4e hyperbond, in which Ni and N are competing for the empty orbital on B.