SYNTHESIS, SPECTROSCOPIC, AND STRUCTURAL STUDIES OF DIARSINE COMPLEXES OF NICKEL(III) IODIDE

The formation of nickel(III) and nickel(IV) complexes [Ni-(L-L)(2)X(2)](+/2+) (X = Cl or Br) with alkyl-substituted diphosphine and diarsine ligands including o-C6H4(AsMe(2))(2), o-C6H4(PMe(2))(2), o-C6F4(AsMe(2))2, and o-C6F4(PMe(2))(2) has long been known, and more recently detailed spectroscopic and structural studies have confirmed the high oxidation states of nickel present. While the stabilities appear to vary little between the corresponding chloro and bromo complexes, no iodo analogues have been reported, and the combination of strongly oxidising metal centers with soft reducing iodide ligands seems unfavorable. Indeed we demonstrated that reaction of [Ni(L-L)(2)-Cl-2](+/2+) with I- or of [Ni(L-L)(2)I-2] with I-2 afforded nickel(II) polyiodides such as [Ni(L-L)(2)](I-3)(2) or [Ni{o-C6H4(PMe(2))(2)}(2)]-I-10. However two nickel(mj iodo complexes with tertiary phosphines have been obtained, which contain the only known examples of nickel(III))-iodine bonds. [Ni(PMe(3))(2)I-3] which was crystallographically characterized, was made by reaction of [{Ni(mu-Bu(2)As)(PMe(3))}(2)] With I-2, and both it and [Ni(PMe(2)Ph)(2)I-3] are formed from the appropriate R(3)PI(2) and nickel powder. In view of this we have re-examined the oxidation of some iodonickel(II) diarsine and diphosphine complexes. and report the results below.