SummaryThe complexation of Cu(1) and Cu(I1) by a series of 12-, 14-and 16-membered macrocyclic ligands 1 4 containing the N2S2 donor set has been studied potentiometrically, spectrophotometrically and voltammetrically.In the case of Cu(II), mononuclear complexes CuL2' with stability constants of lO'"-l OI5 are formed. In addition, partially hydrolyzed species Cu(L)OH+ are observed at pH > 10 for the 12-membered ligands. For Cu(I), beside the species CuL' with stabilities of 10'2-10'4, the unexpected formation of protonated species CuLH" was detected. In contrast to the well-known general trends in coordination chemistry, the stability of these protonated species increases relative to that of the complexes with the neutral ligand when the ring size and concomitantly the distance between neighbouring donor atoms is decreased. From the stability constants of the Cu(1)-and Cu(I1)-complexes the redox potentials have been calculated and are compared to the values of E , obtained by cyclic voltammetry. Despite the identical donor set the Cu(II)/Cu(I) redox potentials of the complexes are spanning a range of 340 mV or six orders of magnitude in relative stability, reflecting the importance of subtle differences in steric requirements.

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The macrocyclic N5 ligands (Ib) and (Ic) are prepared from the N4 macrocycle (Ia) according to the scheme shown.

The autoxidation of the Cu' complexes with a series of six 12-, 14-and 16-membered macrocycles containing the N,S, set of donor atoms has been studied with an oxygen electrode and with the stopped-flow technique. Inspite of the identical set of coordinating groups, the reactivity of the Cu' complexes towards 0, varies by more than 5 orders of magnitude, with rate constants between < 0.1 and 2. lo4 M-'s-'. Simple bimolecular rate laws are obtained from initial rates of autoxidation, but successive one-electron transfers with intermediate formation of superoxide are implied from the analysis of complete reaction curves for the complexes with the 12-membered macrocycles. The kinetic parameters are compared with the redox potentials for the corresponding CuL2'/CuL' couples. Only a rather rough correlation is found and steric factors must in addition be responsible for the observed reactivity pattern which shows a decrease of autoxidation rate with increasing size of the macrocyclic ring. No systematic effect was observed for the influence of cis-us. trans-configuration of the donor atoms.Introduction. -Because of the innate steric restrictions imposed by their structures, macrocyclic ligands would be good choices for the study of structure-reactivity relationships in the autoxidation of Cu(1) complexes. However, no such investigation seems to have been performed to this date. This finding can be rationalized on the basis that the bulk of the well-known macrocyclic ligands would not be ideal for this purpose. Tetraaza macrocycles lead to unstable Cu(1) complexes with CuL2+/CuL+ redox potentials around -400 mV [2]. Complexes with tetrathia ligands have redox potentials around f600 mV and are inert towards 0, [3]. Polyoxa ligands are preferred for the binding of main group metal ions and have been little studied with transition metals [4].Here we report on the autoxidation of Cu(1) complexes with a series of six macrocyclic ligands 1 4 containing the N,S, set of donor atoms.

279ChemInform Abstract The two pentaaza macrocyclic ligands (VI) containing an exocyclic pyrrolidinylalkyl group are prepared as shown in the scheme. The pyrrolidinylethyl derivative (VIa) reacts with (M(DMSO)6)(ClO4)2 (M: Ni, Cu) in ethanol to yield the isomorphous octahedral complexes (VII) with five-coordinated macrocycle and one coordinated perchlorate. This structure is confirmed by X-ray structural analysis of theNi complex (space group P21/c, Z=4). Both the complexes (VII) can be protonated to give the four-coordinated complexes (VIIIa) in which the pendant arm is protonated and non-coordinating. The analogous square-planar complexes (VIIIb) are formed directly by treatment of (M(DMSO6)(ClO4)2 with the pyrrolidinylpropyl macrocycle (VIb) (only for (VIIIb) (M: Ni) yield given in g; space group P21/n Z =4).