First-Row Transition-Metal Chloride Complexes of the Wide Bite-Angle Diphosphine iPrDPDBFphos and Reactivity Studies of Monovalent Nickel

The diphosphine 4,6-bis(3-diisopropylphosphinophenyl)dibenzofuran (abbreviated as iPrDPDBFphos) has been metalated with transition metal dichlorides of zinc, cobalt, and nickel to yield (iPrDPDBFphos)MCl2 complexes. Within these compounds, the diphosphine iPrDPDBFphos adapts a wide range of bite angles (115 to 180°) as determined by X-ray crystallography. A three-coordinate planar Ni(I) species was isolated from the reduction of (iPrDPDBFphos)NiCl2 with KC8. Low-temperature electron paramagnetic resonance (EPR) measurements of (iPrDPDBFphos)NiCl allow the determination of g values (2.09, 2.14, 2.37) and hyperfine coupling constants to two 31P nuclei, Aiso = 46 × 10–4 cm–1, and one 37Cl/35Cl nucleus, A = (12, 0.7, 35) × 10–4 cm–1. Density functional theory (DFT) studies reveal the nature of the magnetic orbital to be dxy, which has σ-antibonding and π∥-antibonding interactions with the phosphorus and chloride atoms, respectively. The monovalent nickel complex reacts with substrates containing C–X bonds; and in the case of vinyl chloride, a Ni(II) vinyl species (iPrDPDBFphos)Ni(CHCH2)Cl is generated along with the Ni(II) dichloride complex. The monovalent Ni(I) chloride is an active catalyst in the Kumada cross-coupling reaction of vinyl chloride and phenyl Grignard reagent.