KINETICS AND MECHANISM OF METAL SUBSTITUTION AND THE IRVING-WILLIAMS SERIES - ANION-CATALYZED SUBSTITUTION OF NICKEL FOR COPPER IN CU(AMBEN) [= ,N'-ETHYLENEBIS(2-AMINOBENZALDIMINATO))COPPER(II)]

Visible spectrophotometry was used to study the kinetics of metal subs titution in the system Cu(amben)/Ni(DMF)(6)(ClO4)(2)/R4NX in DMF at 29 8 K and I = 0.2 M (Bu4NPF6) (H(2)amben = N,N'-ethylenebis(2-aminobenza ldimine); X = Br-, SCN-, Cl-: DMF = N,N-dimethylformamide). The rate o f nickel for copper substitution is markedly affected by the nature of the anion X, the order of reactivity being ClO4- < Br- < SCN- much le ss than Cl-. For X = Cl- and under excess conditions [(Cu(amben)] much less than [Ni(DMF)(6)(ClO4)(2)], [BzEt(3)NCl]), the overall process i s triphasic and multiwavelength analysis in the range 350-900 pm yield s the experimental rate constants k(obsd)(1), k(obsd)(2), and k(obsd)( 3) Rate constant k(obsd)(1) is nickel and chloride dependent, whereas k(obsd)(2) and k(obsd)(3) are not. For the rate of disappearance of Cu (amben), v = -d[Cu(amben)]/dt, it is found that v proportional to [Cl] (tot)(2) at [Ni(DMF)(6)(ClO4)(2)](0) = constant and v proportional to [Ni](tot)(3) at [nickel]:[chloride] = 1:2 ([Cl](tot) and [Ni](tot) ref er to the total concentration of chloride and nickel, respectively). T hese dependencies suggest a second-order rate law, v = k(1)[Cu(amben)] [''NiCl2''], for the first step, with k(1) = 64 +/- 8 M-1 s(-1) at 29 8 K. In view of the ligand properties of Cu(amben) it is concluded tha t the species ''NiCl2'' is tetrahedral Ni(DMF)(2)Cl-2 which reacts wit h Cu(amben) as ligand to form a binuclear adduct in the first step. It is suggested that the observed rate effects of the anions X are linke d with their ability to favor the formation of nickel species with red uced coordination number, such as four-coordinate Ni(DMF)(2)X-2. The m echanism of the overall process of nickel for copper substitution in C u(amben) is discussed. The results of the analysis of the visible spec tra of Cu(amben) and Ni(amben) and of MO calculations on the charge di stribution in these complexes are reported.