Schiff base complexes of copper

The conformation of Schiff-base complexes of copper(IT) a stereo-electronic view. H. S. Maslen and T. N. Waters, Coord. Chem. Rev., 1975,17,137-176 (127). 

While there are no crystal structures of mononuclear Schiff base complexes of copper(I) (N—O ligands) available, these do occur as in the dimeric structure of... 

Clark, G. R., Waters, J. M., Waters, T. N. and Williams, G. J. (1977). Polymorphism in Schiff base complexes of copper(II) the crystal and molecular structure of a second brown form of bis(N-methyl-2-hydroxy-l-naphthaldiminato)copper(II). J. Inorg. Nucl. Chem., 39, 1971-5. [163]... 

Schiff base complexes of copper with Q,b,c atoms/ring coordination... 

The potentials of this and other similar chiral Schiff base complexes of copper were originally explored for the manufacture of synthetic pyre-throids, a class of highly active pesticides. Cyclopropane rings with asymmetric centers are an integral part of the molecular structures of synthetic pyrethroids. Synthetic pyrethroids were made because the natural product chrysanthemic acid, 7.69, and its derivatives have insecticidal properties. 

Although the term dynamical combinatorial chemistry has only been coined at the end of the last century, the template effect has been used for a much longer time. Some of the best known macrocyclic ligands such as cyclam probably would not have been known so well if their synthesis had not implied the template effect. Probably the first example of a metal ion template for the formation of imino-macrocycles N. F. Curtis, D. A. House, Structure of some aliphatic Schiff-base complexes of nickel (II) and copper (II), Chem. and End., 1961, 42, 1708-1709. 

The oxidation of Ti " by Fe" and the reaction between TF" and Sn" have been studied using flow and potential-time dependences. An investigation has also been made of the Ag -Ce " reaction. Polarographic studies of planar Schiff base complexes of Co , Ni", and Cu have shown well-defined oxidation waves and in some chelates the two-electron oxidation Co" Co " is postulated. Kinetic studies have also been made on the oxidation of cobalt(ii) dipyridyl complexes by copper(n) and iron(m) perchlorates in anhydrous acetonitrile. Solvent effects have also been investigated in redox reactions of tetrahalogenoplatinum(iv) complexes of the type PtLaX4. ... 

The polymerization of diacrylate monomers functionalized with Schiff base complexes of Cu(IT), Pd(n), and Zn(ll) has been investigated. Thermal polymerizations of monomer 17 (M=Pd and Zn) were successful however, polymers were not obtained when flie copper analog was subjected to tiie same conditions. Photopolymerization of these monomers in the presence of a titanium initiator and their copolymerization with monoacrylate organic monomers were also examined. In aU cases, the copper complexes inhibited the polymerization reaction. The palladium-containing polymers exhibited liquid crystalline properties. ... 

Mixed 6),Af-donor ligands such as Schiff bases are of interest in that they provide examples not only of square-planar coordination but also, in the solid state, examples of square-pyramidal coordination by dimerization (Fig. 28.6(b)). A similar situation occurs in the bis-dimethylglyoximato complex, which dimerizes by sharing oxygen atoms, though the 4 coplanar donor atoms are all nitrogen atoms. Copper(II) carboxylates are easily obtained by crystallization from aqueous solution or, in the case of the higher carboxylates, by precipitation with the appropriate acid from ethanolic solutions... 

In 1966, Nozaki et al. reported that the decomposition of o-diazo-esters by a copper chiral Schiff base complex in the presence of olefins gave optically active cyclopropanes (Scheme 58).220 221 Following this seminal discovery, Aratani et al. commenced an extensive study of the chiral salicylaldimine ligand and developed highly enantioselective and industrially useful cyclopropanation.222-224 Since then, various complexes have been prepared and applied to asymmetric cyclo-propanation. In this section, however, only selected examples of cyclopropanations using diazo compounds are discussed. For a more detailed discussion of asymmetric cyclopropanation and related reactions, see reviews and books.17-21,225... 

A number of structurally very different copper complexes were employed as catalysts. The copper complex of binaphthol-derived phosphoramidite 32 and the Schiff base complex 53 (derived from salicylaldehyde and phenylglycine) gave promising results in a screening reaction between 52 and MeMgBr, and 53 was chosen as the candidate for optimization. The effect of solvent (THF or Et20),... 

The catalytic asymmetric Henry reaction has been reviewed.42 Mild and efficient enantioselective nitroaldol reactions of nitromethane with various aldehydes have been catalysed by chiral copper Schiff-base complexes yielding the corresponding adducts with high yields and good enantiometric excess.43,44... 

Vanadyl and copper(n) ions catalyse the /J-elimination reaction of O-phospho-threonine in the presence of pyridoxal.429 Equilibrium spectroscopic studies of the threonine-metal ion-pyridoxal system have identified a metal-ion complex of the amino-acid-pyridoxal Schiff base. The catalytic effect of the metal is ascribed to its electron-with drawing effecCIt was suggested that the specific catalytic effect of Cu2 + and V02+ arises from their reluctance to co-ordinate the phosphate in an axial position. Other metal ions such as nickel can also form the Schiff base complex but probably stabilize the phosphothreonine system by chelate formation. 

The aerobic oxidation of phenols in the presence of cobalt-Schiffs base complexes as catalysts is facilitated by (electron-donating) alkyl substituents in the ring and affords the corresponding p-quinones, e.g. the Vitamin E intermediate drawn in Fig. 4.87. When the para-position is occupied the reaction may be directed to the ortho-position [252, 253]. Copper compounds also mediate this type of oxidation, e.g. the Mitsubishi Gas process for the Vitamin E intermediate... 

Abe S, Ueno T, Reddy PAN, Okazaki S, Hikage T, Suzuki A, Yamane T, Nakajima H, Watanabe Y. Design and structure analysis of artificial metalloproteins selective coordination of His64 to copper complexes with square-planar structure in the apo-myoglobin scaffold. Inorg. Chem. 2007 46 5137-5139. Ohashi M, Koshiyama T, Ueno T, Yanase M, Fuji H, Watanabe Y. Preparation of artificial metalloenzymes by insertion of chromium Schiff base complexes into apomyoglobin mutants. Angew. Chem Int. Ed. 2003 42 1005-1008. 

More recently, similar reactions have been used extensively in the formation of macrocyclic compounds. Imine or Schiff base complexes (R j N=CHR2) have been extensively studied. In this case, the compounds can be formed without complexation, but the reaction is much faster in the presence of metal ions. An example is shown in Figure 12-17. In the absence of copper, benzothiazoline is favored in the final step rather than the imine very little of the Schiff base is present at equilibrium. 

The amino alcohol, i -2-amino-l,l-di-(2-octyoxy-5-ferf-butyl-phenyl)-propa-nol, was prepared by the reaction of a Grignard reagent from 2-bromo-4-ferf-butylphenyl octyl ether [35] with D-alanine ethyl ester. The copper complex was prepared in the similar manner as above. In this case, neither the amino alcohol, the Schiff base, nor the copper complex was crystalline. 

The in situ Schiff base condensation of 2,6-diacetylp3Tddine with AT,A7 A, iV -tetrakis(3-aminopropyl)-l,2-diaminoethane in the presence of copper(II) chloride was demonstrated to 3neld the dinuclear cation 50 (n = 2 R = CH3) as its perchlorate salt (83). The corresponding single-ring, mononuclear copper(II) complex 51 (R = CH3) had been reported previously (84). Both this and the dinuclear species 3neld similar visible spectra, suggesting that similar copper coordination... 

In situ photoacoustic spectroscopy has been used to study the redox process on the surface of an electrode using copper metal in alkaline solution. The values of copper(II) Schiff base complexes " absorbed on optically transparent thin-layer electrodes (OTTLE) have been... 

Complexes of metal + ligand + protein or DNA can also catalyze the Diels Alder cycloaddition or oxidations with hydrogen peroxide. Copper complexes bound to DNA catalyzed the Diels-Alder cycloaddition with up to 99% ee [15, 16], Cu(phthalocyanine) complexed to serum albumin also catalyzed the enantioselective (98% ee) Diels-Alder reaction, but only with very high catalyst loading (10 mol%) and only with pyridine-bearing dienophiles (presumably to complex the copper) [17]. Achiral Cr(III) complexes or Mn(Schiff-base) complexes inserted into the active site of apomyoglobin variants catalyzed the sulfoxidation of thio-anisole with up to 13 and 51% ee, respectively [18, 19]. A copper phenanthroline complex attached to the adipocyte lipid-binding protein catalyzed the enantioselective hydrolysis of esters and amides [20]. 

Homogeneous catalyst systems include transition metals, for example, Schiff base complexes with cobalt [59]. Unfortunately, there is no protocol known to recover and recycle the expensive Schiff base. Many copper complexes have been employed for the oxidation of phenols to 1,4-benzoquinones [60]. Copper salts such as CUCI2 and CuBr2 are widely used for the oxidation of trimethylphenol with molecular oxygen at larger scale [61]. In addition, applications of the halides of Cr, Mn, Fe, Ni, and Zn as catalysts have been described [58]. Copper halides have also been combined with earth metal halides, for example, MgCl2 [62] or LiCl, in the presence of a phase transfer catalyst [63]. 

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