Enantioselective Addition of Secondary Phosphines to Methacrylonitrile:  Catalysis and Mechanism SadowAaron D. TogniAntonio 2005 A highly enantioselective intermolecular hydrophosphination reaction is described. The (Pigiphos)nickel(II)-catalyzed reaction of secondary phosphines and methacrylonitrile gives chiral 2-cyanopropylphosphines in good yield and high enantiomeric excess (ee's up to 94%; (<i>R</i>)-(<i>S</i>)-Pigiphos = bis{(<i>R</i>)-1-[(<i>S</i>)-2-(diphenylphosphino)ferrocenyl]ethyl}cyclohexylphos phine). We propose a mechanism involving coordination of methacrylonitrile to the dicationic nickel catalyst followed by 1,4-addition of the phosphine, and then, rate-determining proton transfer. This mechanism is supported by (a) the experimentally determined rate law (rate = <i>k</i>‘[Ni][methacrylonitrile][<i>t</i>-Bu<sub>2</sub>PH]), (b) a large primary deuterium isotope effect <i>k</i><sub>H</sub>/<i>k</i><sub>D</sub> = 4.6(1) for the addition of <i>t-</i>Bu<sub>2</sub>PH(D) at 28.3 °C in toluene-<i>d</i><sub>8</sub>, (c) the isolation and characterization of the species [Ni(κ<sup>3</sup>-Pigiphos)(κ<i>N</i>-methacrylonitrile)]<sup>2+</sup>, and (d) DFT calculations of model compounds.