Phosphine, Phosphite, and Arsine Compounds

The kinetics of the reaction of Ni(Pp3)4 and of PtCPFg) with cyclohexyl isocyanide have been followed, by i.r. spectroscopy, in toluene, n-hexane, and n-heptane solution. The rate law is first-order. This, and the determined activation entropies (Table 4), indicate a dissociative mechanism 

When Ni(LL)(Me4-l,4-benzoquinone), where LL = a bidentate cyclic alkene such as cot, cod, nor, or en /o-dicyclopentadiene, reacts with trimethyl phosphite, it is the alkene LL which is replaced first, en route to the product Ni(P OMe 3)4. This first step is bimolecular, producing an intermediate containing unidentate alkene. Some kinetic parameters are reported, particularly for LL = cyclo-octa-1,5-diene. The formation of the cation [NiH(P OEt 3)4]+ in perchloric acid-methanol solution appears to involve direct protonation of the nickel. Activation parameters for this are = 13 1 kcalmoL and AS = — 2 3 cal deg mol . 

A paper on the reaction of tetra-arsine complexes of nickel(o) with hexafluorobutadiene contains the suggestion that the mechanism of these reactions may involve the intermediacy of an ionic intermediate, for example (14).  

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