Salicylaldimine copper complexes

In 1966 Nozaki et al. [14] reported the first examples of enantioselective metal-catalyzed cyclopropanation reactions of diazo compounds. Although the enantiomeric excesses induced by chiral copper-salicylaldimine complexes were low (Scheme 2), this work proved to be seminal as it demonstrated the principle... 

Based on Hitosi Nozakis and Ryoji Noyori s seminal work, Tadatoshi Aratani developed in 1975 at Sumitomo in Osaka a copper-salicylaldimine complex, with which it was possible for the first time to prepare menthyl (lR)-tra s-chry-santhemate with high ( /Z)-selectivity and optical purity. [74,75] This synthesis provided the foundation for the industrial manufacturing process at Sumitomo. 

In fact, several reports have appeared on the spectroscopic features of complexes of zinc and cadmium with Schiff bases. The electronic absorption spectra of various salicylaldimine complexes of zinc have been determined335 to clarify assignments made previously for similar copper(II) complexes. A band at ca. 41000 cm-1 has been reassigned as an n-n transition of the oxygen lone pair, rather than the o-3d transition proposed earlier. 

The initial reactions of this type were used to produce copper(II) complexes of salicylaldimines, where additional coordination support is provided by the phenolic oxygen atoms (equation l).10 11 Similar use can be made of pyridine-2-carbaldehyde in the formation of imine chelates. For example, the combination of pyridine-2-carbaldehyde and 2-aminobenzenethiol in the presence of metal ions yields tridentate complexes (Scheme l).12 If the reaction is carried out in the absence of the metal ion, the benzothiazolidine (1) is isolated. Thus the metal ion is essential for the formation of the imine product in this case. Metal complexes of the related tridentate ligands (2),13 (3),14 (4)li and (5)16 can be prepared similarly. 

Several reports have appeared on complexes of zinc and cadmium with Schiff bases. The electronic absorption spectra of various salicylaldimine complexes of zinc have been determined54 to clarify assignments made previously for similar copper(n)... 

SlOO proteins, 577 structure, 573 Saccharomyces cerevLsiae cation transport, 559 manganese transport, 570 Salicylaldimine copper(II) complexes, 156 Salicylaldoximes adsorption minerals, 782... 

Table 3. Structures, susceptibility anisotropies and alignment of salicylaldimine complexes of copper [7, 8]. N-Y...

Most of the paramagnetic salicylaldimine copper(II) complexes, first reported by Ovchinnikov et al. in 1984, showed smectic mesophases [94]. However, nematic behavior was observed by Galyametdinov et al. for 41 [95]. They were the first examples of materials with a paramagnetic nematic phase. 

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... 

Effects of Different Metal Salicylaldimine Chelates. Varying the central metal profoundly affected catalytic and inhibitory properties. There were only small quantitative variations, however, between N-phenyl- and V-butylsalicylaldimines having the same central metal atom. The only other salicylaldimines where catalyst-inhibitor conversion could be demonstrated were those of copper (II). With copper (II) both the catalytic and the inhibitory effects are much less pronounced than for cobalt (II). Surprisingly nickel (II) complexes behaved like conventional catalysts for hydrocarbon autoxidation—i.e., the rate is proportional to... 

The IR spectra of 15N-labelled complexes of A-p-tolylsalicylaldimines with zinc, copper and cobalt have yielded assignments of the metal-ligand stretching frequency and certain ligand vibrations.336 The v(M—N) values are metal-ion dependent in the order CoZn as expected from crystal field theory. Substituent-induced shifts are related to the residual polar effects of salicylaldimine substitution and to the inductive effects of N-aryl substitutents. 

Even before Aratani introduced his chiral salicylaldimine copper catalysts, Nakamura and Otsuka reported in 1974 that chiral bis(a-camphorquinonedioximato)cobalt(II) (29) and related complexes were effective enantioselective cyclopropanation catalysts [76], and they more fully described the preparation, characteristics, and uses of these catalysts in 1978 [77], Optical yields as high as 88% were achieved for the cyclopropanation of styrene with neopentyl diazoacetate, and chemical yields greater than 90% were obtained in several cases. 

A variety of mixed ligand complexes of copper(II) are known which contain bipyridine and phenanthroline. Examples of the other ligands are 8-diketones (479), salicylaldehyde and salicylaldimines (552), and nitrate (721). The use of some mixed ligand copper(II) phenanthroline complexes as absorbents for gas chromatography has been considered (14). 

Enantioselection can be controlled much more effectively with the appropriate chiral copper, rhodium, and cobalt catalyst.The first major breakthrough in this area was achieved by copper complexes with chiral salicylaldimine ligands that were obtained from salicylaldehyde and amino alcohols derived from a-amino acids (Aratani catalysts ). With bulky diazo esters, both the diastereoselectivity (transicis ratio) and the enantioselectivity can be increased. These facts have been used, inter alia, for the diastereo- and enantioselective synthesis of chrysan-themic and permethrinic acids which are components of pyrethroid insecticides (Table 10). 0-Trimethylsilyl enols can also be cyclopropanated enantioselectively with alkyl diazoacetates in the presence of Aratani catalysts. In detailed studies,the influence of various parameters, such as metal ligands in the catalyst, catalyst concentration, solvent, and alkene structure, on the enantioselectivity has been recorded. Enantiomeric excesses of up to 88% were obtained with catalyst 7 (R = Bz = 2-MeOCgH4). 

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