Sulfur-nitrogen bonded metal chelates. Part 17. Reactions of alcohols with the co-ordinated nitrile in nickel(II) complexes [NiL(NCR)][ClO₄](L = a S,N,N-tridentate anion; R = Me, Et, or Ph) under different conditions

Abstract

The reactions of the nitrile complexes [NiL(NCR)][ClO₄]{HL¹= methyl 2-[(2'-aminoethyl)amino]-cyclopent-1-enedithiocarboxylate, HL²= methyl 2-[(2'-dimethylaminoethyl)amino]cyclopent-1-enedithiocarboxylate, HL³= methyl 2-[(2'-diethylaminoethyl)amino]cyclopent-1-enedithio-carboxylate; R = Me, Et, or Ph} with methanol and ethanol under different experimental conditions have been investigated. Rate constants for these reactions have been measured spectrophotometric ally at 25 °C. Dry methanol reacts with the nitrile complexes, in absence of free nitrile, to produce dinuclear µ-methoxo complexes [Ni₂L²(µ-OMe)][ClO₄] and the same reaction with wet methanol gives [Ni₂L²(µ-OH)][ClO₄]. Both methoxo- and hydroxo-bridged compounds react with imidazole to form µ-imidazolato dinuclear complexes. All the complexes have been isolated and characterized. Dry methanol adds to the co-ordinated nitrile in complexes [NiL(NCR)][ClO₄] in the presence of excess of free RCN, to produce imino-ether complexes [NiL{NH═C(OMe)R}][ClO₄]. The rate data show the following decreasing order of reactivity of the nitrile complexes: [NiL¹(NCMe)]⁺ > [NiL¹(NCEt)]⁺ > [NiL²(NCMe)]⁺ > [NiL³(NCMe)]⁺. The reaction rate with ethanol is much slower than that with methanol. The rates of formation of imino-ether complexes increase by more than four orders of magnitude when sodium alkoxide is used as a catalyst.