Nickel diarsine complexes

When the apparently penta-coordinated diarsine complexes just described are dissolved in solvents more polar than nitrobenzene, they tend to dissociate into halide ions and bivalent cations, thus becoming 2 1 electrolytes (119). The effect is most marked with the platinum compounds. It has been shown that solvation effects might be less with platinum than with palladium, and so, other things in the equilibria being equal, it can also be concluded that the bonding of further ligands by a square-planar complex is much weaker with platinum than with palladium. Square-planar nickel complexes are of course the most ready to take up further ligands. 

A large number of nickel(II) complexes with bidentate tertiary phosphines and arsines have been prepared and characterized since the initial reports on o-phenylenebisdimethylarsine and 1,2-bisdiphenylphosphinoethane (Table 64 XVIII, III) by Chatt and Mann,1267 and Wymore and Bailar126 respectively. The most common diphosphines, diarsines, distibines and mixed donor ligands are collected in Table 64 and selected nickel(II) complexes are reported in Table 65. 

Some planar complexes containing arsenic can be prepared, o-Phenylenebisdimethylarsine (diarsine) reacts with nickel carbonyl to form Ni(CO)2(diarsine) (70). Oxidation of this complex with iodine gives a red, diamagnetic, planar complex, Ni(diarsine)12. The corresponding bromides and chlorides could not be purified and appear to be much less stable (70). 

Condensing [2,3-bis(diphenylphosphino)N-methylmaleimide] nickel dichloride 86 with PhE(SiMe3)2 (E = P, As) gives the complexed diphosphene or diarsine 87 through oxidative coupling and silyl migration. Both P-P and As-As bonds are shorter than expected for single bonds (equation 80)101. 

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