The reactions (CuTL + 'R -LCun-R and the mechanism of decomposition of the transient complexes LCu11-R were studied using the pulse-radiolysis technique (L1 = H2O, L* 12 = 2,5,8,ll-tetramethyl-2,5,8,ll-tetraazadodecane; 'R = 'CH3, 'CH2COOH, 'CH(CH3)COOH, •-CH2CH2COOH.) The kinetics of formation of the transient complexes obey pseudo-firstorder rate laws. The rate constants measured for these reactions are in the range (2-4) x 109 M-1 s-1 for L1 and 6 x 106 7*-1 x 10s M-1 s-1 for L2. The mechanisms of decomposition of the transient complexes depend on the nature of R and L as follows: 1. For R = CH3 ethane is the final product. The kinetics of its formation obey second-order rate laws. Free methyl radicals are not intermediates in these processes. 2. For R = CH2CH2COOH the transient complexes decompose via an analogous mechanism to that of R = CH3 for L1 and via homolysis of the copper-carbon a bond for L2. 3. For R = CH2COOH and CH(CHs)-COOH the transient complexes decompose via heterolysis of the copper-carbon a bonds forming CunL. The effect of the nature of R and L on the kinetics of these reactions is discussed.
The ligands R(2)NCH(2)CH(2)N(R)CH(2)CH(2)N(R)CH(2)CH=CH(2), where R = H, CH(3), were synthesized. The stability constants of their complexes with Cu(II) and Cu(I) in aqueous solutions were determined. Both ligands stabilize Cu(I) in aqueous solutions, though the reduction potentials of both (CuL(i)())(2+/+) couples are shifted cathodically in comparison to the Cu(2+/+)(aq) couple. These properties indicate that these complexes should be good catalysts for a variety of processes that are catalyzed by Cu(I).
The mechanism of the
reaction of Cuaq
+ with
Cl3CCOO- is reported; fumarate, which
forms a complex with Cu(I), slows down the reaction rate
considerably.
It seemed plausible that tri-and tetraamine ligands with a substituent which binds to Cu(I) but not to Cu(II), e.g., an allyl, stabilize Cu(I) in aqueous solutions and shift its redox potential cathodically relative to Cu + (aq). Therefore, the ligands N(CH 2 CH 2 NR 2 ) 2 (CH 2 CH 2 NRCH 2 CHd CH 2 ) (R ) H or CH 3 ) were synthesized. These ligands indeed stabilize Cu(I) in aqueous solutions and shift the redox potential of the Cu(II)/Cu(I) and Cu(I)/Cu(0) couples cathodically relative to Cu 2+/+ (aq) and the complexes Cu II L/Cu I L where L ) R 2 NCH 2 CH 2 NRCH 2 CH 2 NR(CH 2 CHdCH 2 ). Therefore, the copper complexes with the new ligands are expected to be better catalysts to processes in which the redox step is the rate-determining step.
octaazatetracosane has been investigated by means of potentiometric (0.1 NMe 4 Cl aqueous solution, 298.1 K) and spectrophotometric measurements. The species present in solution and their stability constants have been determined. The first five amines form only mononuclear complexes, while the last two can give both mono-and bi-nuclear complexes in aqueous solution. The thermodynamic data show that the complexes with N-methylated polyamines are tremendously less stable than their non-methylated counterparts. The UV/VIS spectra of the complexes exhibit a marked red shift of the L→M charge-transfer bands with respect to the complexes of the non-methylated ligands. As a consequence of the reduced thermodynamic stability, both mono-and bi-nuclear complexes show a particular acid-base behavior with respect to those of the non-methylated amines. Such complexes can easily bind a proton or a hydroxide anion in aqueous solution, with consequent detachment of a co-ordinated nitrogen. The crystal structures of two binuclear complexes were determined. In both the metals show distorted square-planar arrangements of the donors.
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