Copper(II) complexes of hydrolysis products of the anticancer bis(3,5-dioxopiperazin-1-yl)alkanes. Displacement of co-ordinated carboxylate ligands by deprotonated amide groups in basic solution
- 1 January 1991
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in J. Chem. Soc., Dalton Trans.
- No. 9,p. 2301-2304
- https://doi.org/10.1039/dt9910002301
Abstract
The copper(II) complexes of the diacid diamide –O2CCH2(H2NOCCH2)NCH2CHRN(CH2CONH2)-CH2CO2 –(R = H, L3; Me, L4) which have in-plane 2Namine′ 2 Ocarboxylate ligands at pH 6 undergo amide group deprotonation in basic solution to give CuN(amine)2N–(amide)2 chromophores resulting from the displacement of the in-plane carboxylate ligands by the superior σ-donating, deprotonated, amide nitrogens. The concentration pKa values for the deprotonations at 25 °C, I= 0.1 mol dm–3 are 9.19 ± 0.02 and 9.87 ± 0.02 for [CuL3], and 8.60 ± 0.02 and 9.81 ± 0.02 for [CuL4]. The unexpectedly large differences in the first pKa values is attributed to a steric interaction between the methyl substituent and an axially co-ordinated CH2CONH2 group, in the complex of L4 which is relieved as a result of the first ionisation step.Keywords
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