期刊
HELVETICA CHIMICA ACTA
卷 88, 期 4, 页码 782-795出版社
WILEY-V C H VERLAG GMBH
DOI: 10.1002/hlca.200590055
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The stopped-flow technique was used to measure the rates of formation and dissociation of tetrahedral [ML2] complexes (M2+ = Ni2+ or Co2+) of four bidentate S-2-donor 'dithioimidodiphosphato' ligands L- (HL = [(RR2)-R-1 P(= S)]NH[P(= S)(RR4)-R-3], R-1 to R-4 = alkyl) at 25.0 degrees in MeOH/H2O 95:5 (v/v) solution and in the presence of either MOPS (= 3-(morpholin-4-yl)propanc-1-sulfonic acid) or 2,6-lutidine (= 2,6-dimethylpyridine) buffers. ne kinetically determined equilibrium formation constants for [ML](+) ions (M = Ni or Co) are 10(-5) K = 0.50 +/- 0.01 or 1.64 +/- 0.071 mol(-1) for L = L-3 (R-1 = R-2 = Me(CH2)(2)CH(Me), R-3 = R-4 = Mc(2)CH), 1.27 +/- 0.02 or 7.93 +/- 0.091 mol(-1) for L = L-7 (R-1 to R-4 = Me2CHCH2), 0.88 +/- 0.04 or 3.84 +/- 0.131 mol(-1) for L = L-8 (R-1 to R-4 = Me2CH), and in case of Ni2+ 1.88 +/- 0.04 1 mol(-1) for L = L-6 (R-1 = R-3 = Bu, R-2 = R-4 = 'Bu) (see Table 3; for L-3 and L-6 - L-8, see Table 1). Whereas the tetrahedral Ni2+ complexes dissociate more slowly than the analogous Co2+ species, in all cases, the Co2+ complexes arc more stable than those of Ni2+ due to their larger formation rate constants (Table 3). Reactions of Cu2+ with eight ligands HL (R-1 to R-4 = alkyl, alkoxy, aryl, and aryloxy) show that formation of intensely colored tetrahedral [(CuL2)-L-II] species is too fast be measured with the available stopped-flow apparatus (t(1/2) < 2 ms), but the subsequent rates of reduction of [(CuL2)-L-II] to give trinuclear products [(CU3L3)-L-1] are measurable. An X-ray analysis establishes the structure of one of the [Cu3L3] complexes, where R-1 = R-2 = Me2CHO and R-3 = R-4 = 2-(tert-butyl)phenyl (L = L-5), and a multiwavelength stopped-flow kinetic experiment establishes the spectrum of a tetrahedral [(CuL2)-L-II] species prior to the reduction reactions. The redox reactions proceed at 25.0 degrees with first-order rate constants in the range 0.285 s(-1) (R-1 to R-4 = PhO; L = L-11) to 2.58 10(-4) s(-1) (R-1 to R-4 = Me2CHCH2; L = L-7) (Table 4).
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