Free-energy relationships between the proton and hydride donor abilities of [HNi(diphosphine)2]+ complexes and the half-wave potentials of their conjugate bases

A linear free-energy relationship exists between the half-wave potentials of the (II/I) couples of Ni(diphosphine)(2) complexes and the hydride donor ability (DeltaG(H)(o)(-)) of the corresponding [HNi(diphosphine)(2)](+) complexes. A similar correlation is observed between the half-wave potentials of the (I/O) couples of Ni(diphosphine)(2) complexes and the pK(a) values (or DeltaG(H)(o)(+)) of the corresponding [HNi(diphosphine)(2)](+) complexes. As a result, it is possible to use the potentials of these two couples to predict the free energies of all three Ni-H bond cleavage reactions, DeltaG(H)(o)(+), DeltaG(H)(o)(.), and DeltaG(H)(o)(-), for this class of nickel complexes. The molecular structures of Ni(Et2PCH2CH2PPh2)(2) and Ni(Ph2PCHCHPPh2)(2) were determined by single-crystal Ii-ray diffraction studies.