Anomalous Hydroboration at a Four-Coordinate Ni(II) Diphenylvinylphosphine Complex: Geometric Impacts on Solution Equilibria

For coordination compounds, reliable control of metal geometry and spin state is of great interest, permitting control of reactivity and selectivity. As tuneable outputs, these observables are adjusted through thoughtful choice of ligand. This report examines a family of monophosphine-ligated nickel(II) dihalide compounds containing secondary coordination sphere borane groups. Interestingly, anomalous hydroboration of trans-[Ni^II(X)₂(PPh₂Vin)₂] (Vin = vinyl) was witnessed upon treatment with HBCy₂ (Cy = cyclohexyl), resulting in halide-directed Markovnikov hydroboration; these branched products were observed to be diamagnetic in solution. This outcome is in contrast with the linear ligand variants, which were prepared independently and show solution paramagnetism. Together, this report details an unusual hydroboration outcome and how this anomalous reactivity gives way to unique solution behavior of the resulting nickel(II) products simply by virtue of linear or branched secondary coordination sphere incorporation.