| Abstract |
Nickel(II) complexes of azine diphosphine ligands, PR2CH2C(Bu-t)NNC(Bu-t)CH2PR2 (R = Ph, Bu-t, Pr-i, C6H11), were prepared for the first time by reactions of anhydrous NiX2 (X = Cl, Br, I) with ligands. Complexes are cationic, the counterion being either simple halide anion or, in two cases, 1/2[NiCl4](2-). The azine diphosphines are coordinated terdentately in (E,Z) configuration forming thereby a bicyclic ligand frame (five and six-membered ring) with diphosphine bite angles 160-165degrees. A balance of stereoelectronic factors governing square planar versus tetrahedral coordination of the ligands is suggested. Structures of four of the complexes with bulky ligands (R = Bu-t, X- = Cl-, Br-, I-; R = C6H11, X- = 1/2[NiCl](2-)) were determined by X-ray diffraction and qualitative Huckel MO calculations on model undistorted square planar [trans-NiX(NH2)(PH3)(2)](+) were carried out to elucidate the contributions of steric and electronic factors. Two reduction and two oxidation processes depending on the substituent R and the halide were identified from cyclic voltammetry data on the complexes. (C) 2002 Elsevier Science B.V. All rights reserved. |
