Other Cu II Complexes

Piezochromic effects have been observed in a variety of other Cu(II) complexes. In some cases it can be shown that the stmctures of a series of related complexes foUow a reaction pathway with the stmcture of one complex at, for example, 8 GPa (80 kbar) corresponding to that of a related complex at, for example, 2 GPa (20 kbar). The changes in color of the complex, of course, foUow the same sequence. 

Other Cu(II) Complexes Cu(II)-Doped Zinc Acetate Dihydrate... 

Reports of other Cu(ii) complexes include complexes with citrulline, (338) glutathione, (339) amino-acids, (340) amines such as ammonia, asparagine, and serine, (341) and dibutyl sulphide. (342)... 

Cu(I) species. This simple explanation does not explain why other species such as CuCl2° are relatively unreactl In spite of the high stability of the corresponding CuCl complex. A more complex, Inner sphere charge trasfer mechanism Is probably Involved, as suggested In previous studies with other Cu(II) complexes (17-19). 

Spectral results [180] for copper(II) complexes of 2-acetylpyridine N-dimethylthiosemicarbazone, 9, and 2-acetylpyridine 3-(4-methylpiperidine) thiosemicarbazone, 12, are included in Table 2. While the complexes of 9-H have spectral properties consistent with the other copper(II) complexes of Table 2, those of 12-H, with the exception of [Cu(12-H)F], show considerably higher values of g, and consequently higher values of k. These values indicate that there is little in-plane 7t-bonding, possibly due to the bulkiness of the 4-methylpiperidine group. 

Seven different copper(II) complexes [181] of 2-acetylpyridine iV-phenyl-thiosemicarbazone, 14, all having the general formula, [Cu(14-H)A] have been prepared and characterized. Their spectral data are included in Table 2 and g is similar to other copper(II) complexes of 2-acetylpyridine thiosemicarbazones. However, the d-d spectra all show two bands, suggesting planar stereochemistry these bands are of higher energy than the analogous complexes of the bicyclononyl derivative, 4 [128, 175]. 

Two types of FeQl) dithiocarbamates are reported. To the first type belong the complexes Fe(R2powder diffraction pattern shows the ethyl compound to be isomorphous with the five-coordinated, dimeric Cu(II) complex (18), so it is to be expected that the fifth Fe-S bond is longer than the other four. Further details about Fe(R2C fc)2 are scarce, as the compounds are air-sensitive and rapidly oxidise to Fe(III) complexes. 

By using combinations of hydrogenation and dehydrogenation reactions it has been possible to obtain nickel derivatives of the Curtis macrocycle containing from zero to four imine groups (Curtis, 1968 1974). Related reactions in the presence of a variety of other central metal ions have been described. The electrochemical oxidation of the Cu(ii) complex of the reduced Curtis ligand proceeds initially via a two-electron step to yield the monoimine complex (296) (Olson Vasilevskis, 1971). 

The utility of bis(oxazoline)-Cu(II) complexes as catalysts for the Diels-Alder reaction has been examined in a number of other systems. Aggarwal et al. (205) demonstrated that a-thioacrylates behave as effective two-point binding substrates for these catalysts. With cyclopentadiene, catalyst 271d induces the reaction at -78°C to provide the cycloadduct in 94 6 diastereoselectivity and >95% ee. Aggarwal proposes that the metal binds to the carbonyl oxygen and to the sulfur atom. The sulfur substituent is placed opposite the ligand substituent thereby shielding the bottom face of the alkene. Considerably lower selectivities are observed with 5-Me substrates. 

B. B. Hasinoff, The Interaction of the Cardioprotective Agent ICRF-187 ((+)-1,2-Bis-(3,5-dioxopiperazinyl-l-yl)propane), Its Hydrolysis Product ICRF-198, and Other Chelating Agents with the Fe(III) and Cu(II) Complexes of Adriamycin , Agents Actions 1989, 26, 378-385. 

Chemical Reviews paper. We can only discuss a small number of these here, but some important categories are (1) synthetic Fe(II)-Cu(I) complexes and their reactions with O2, (2) oxidized heme-copper models (Fe(III)-X-Cu(II) complexes, where X equals 0x0- and hydroxo-bridged complexes, cyanide-bridged complexes, or other X-bridged complexes), (3) crosslinked histidine-tyrosine residues at the heme-copper center, and (4) Cua site synthetic models. 

A quantitative treatment of the Jahn-Teller effect is more challenging (46). A major issue is that many theoretical models explicitly or implicitly assume the Bom—Oppenheimer approximation which, for octahedral Cu(II) systems in the vibronic coupling regime, cannot be correct (46,51). Hitchman and co-workers solved the vibronic Hamiltonian in order to model the temperature dependence of the molecular structure and the attendant spectroscopic properties, notably EPR spectra (52). Others, including us, take a more simphstic approach (53,54) but, in either case, a similar Mexican hat potential energy description of the principal features of the Jahn-Teller effect in homoleptic Cu(II) complexes emerges (Fig. 13). 

In the case of other derivatives of dap and acylhydrazones (Table II), it was impossible to isolate Cu(II) complexes with a neutral form of these ligands. Syntheses with Cu(II) chloride or nitrate did not afford defined products and only those with Cu(II) acetate produced stoichio-metrically defined substances. The complexes produced have a PBP structure and contain a doubly-deprotonated polydentate ligand. Their more precise characterization has not been performed so far and only on the basis of IR spectra of [Cu(dapb)] (46). [Cu(daps)] (52), and [Cu(dapab)] (54), a dimeric or polymeric structure was suggested, whereas there are no data available on the coordination number. [Cu2(dappc)(H20)3]2[Cu2(dappc)(H20)2(C104)]2(C104)6 2H20... 

Reported rate constants for the reaction of 02 with GSH have varied from 102 to > 105 M 1 s. A re-examination of this reaction by spin trapping with DMPO established that earlier studies had been confounded by the direct reduction of the DMPO/ OOH adduct to DMPO/ OH by GSH. Taking account of this reaction, the revised rate constant was reported to be 200 M-1 g-i.25i.2S2 other workers have examined, for example, the effects of GSH and N-acetyl-L-cysteine on lipid peroxidation 253 and the role of GS in the toxicity of the diabetogenic agent alloxan.254 Direct EPR has been used to detect binuclear Cu(II) complexes of homocysteine. The interactions of such complexes with blood-vessel linings may account for the link between elevated homocysteine and atherosclerosis.255... 

Substituent effects in 1,10-phenanthrolines have been comprehensively investigated201,202 from their pA s, stability constants in Fe(III) and Cu(II) complexes, and redox potentials the Ni(II) complexes have also been examined,203 as have other metal complexes.204 p- Values have been obtained for the three successive proton losses (1, 2, 3, respectively) from 4-substituted dications of 10-hydroxy- 1,7-phenanthrolines (23).205... 

When the carbinol substituents (R) were the bulky 5-ler -butyl-2-(n-octyloxy)phenyl group, optimum enantioselectivities were achieved with the catalytic use of the corresponding Cu(II) complex (2) in both enantiomeric forms. Specific applications of the Aratani catalysts have included the synthesis of chrysanthemic acid esters (Eq. 5.6) and a precursor to permethrinic acid, both potent units of pyrethroid insecticides, and for the commercial preparation of ethyl (S)-2,2-dimethylcyclopropanecarboxylate (Eq. 5.2), which is used for constructing cilastatin. Several other uses of these catalysts and their derivatives for cyclopropanation reactions have been reported albeit, in most cases, with only moderate enantioselectivities [26-29],... 

The salen-Ni(II) complex 39a derived from (lR,2R)-[N,N -bis(2 -hydroxybenzyl-idene)]-l,2-diaminocyclohexane was also equally effective (Table 7.3, entry 4). In contrast to earlier reports on salen-metal complexes, where the introduction of a bulky tert- butyl substituent increased enantioselectivity [31], the use of complex 39b exhibited a significant decrease in enantioselectivity (entry 5). The presence of a bulky tert-butyl group obstructed the chelation of alkali metal ions by phenolic oxygen atoms. A dramatic increase in selectivity could be achieved when nickel was replaced with copper, and a salen-Cu(II) complex 39c afforded 85% ee (entry 6). Although screening of other bases or 50% NaOH were not advantageous, the use of 3 equiv. NaOH improved the enantiomeric excess to 92% (entry 9) and after recrystallization of a-methylphenylalanine optical purity was increased to 98% ee. 

An ion-pair derived from the substrate and solid NaOH forms a cation-assisted dimeric hydrophobic complex with catalyst 39c, and the deprotonated substrate occupies the apical coordination site of one of the Cu(II) ions of the complexes. Alkylation proceeds preferentially on the re-face of the enolate to produce amino acid derivatives with high enantioselectivity. However, amino ester enolates derived from amino acids other than glycine and alanine with R1 side chains are likely to hinder the re-face of enolate, resulting in a diminishing reaction rate and enantioselectivity (Table 7.5). The salen-Cu(II) complex helps to transfer the ion-pair in organic solvents, and at the same time fixes the orientation of the coordinated carbanion in the transition state which, on alkylation, releases the catalyst to continue the cycle. 

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