Metal-Schiff base salen

Finally, innovative bimetallic complexes as dissymmetric ligands can easily be built, giving birth to an unprecedented class of metal Schiff base salen complexes that can be successfully electropolymerized concomitantly with an overoxidation process. The electrooxidation of 8-(3-acetylimino-6-methyl-2,... 

Sigman and Jacobsen reported the first example of a metal-catalyzed enantioselective Strecker-type reaction using a chiral Alnl-salen complex (salen = N,N -bis(salicyhdene)-ethylenediamine dianion) [4]. A variety of N-allylimines 4 were evaluated in the reaction catalyzed by complex 5 to give products 6, which were isolated as trifluoroacetamides in good yields and moderate-to-excellent enantioselectivities (Scheme 3). Substituted arylimines 4 were the best substrates, while alkyl-substituted imines afforded products with considerably lower ee values. Jacobsen and co-workers also reported that non-metal Schiff base catalysts 8 and 9 proved to be effective in the Strecker reaction of imines 7 with hydrogen cyanide to afford trifluoroacetamides 10 after reaction with trifluoroacetic anhydride, since the free amines were not stable to chromatography (Scheme 4) [5]. 

Palladium, rhodium and ruthenium complexes of the Schiff base salen are synthesized in the supercages of zeolite Y. The existence of intracrystalline transition metal-salen complexes is verified by a detailed physicochemical characterization. The catalytic properties of the prepared host/guest inclusion compounds are explored in the hydrogenation of hexene-(l) or an equimolar mixture of hexene-(l) and 2,4,4-trimethylpentene-(l). 

The assymetric Strecker reaction of diverse imines, including aldimines as well as ketoimines, with HCN or TMSCN provides a direct access to various unnatural and natural amino acids in high enantiomeric excesses, using soluble or resin-linked non-metal Schiff bases the corresponding chiral catalysts are obtained and optimized by parallel combinatorial library synthesis [93]. A rather general asymmetric Strecker-type synthesis of various imines and a, 9-unsaturated derivatives is catalyzed by chiral bifunctional Lewis acid-Lewis base aluminum-containing complexes [94]. When chiral (salen)Al(III) complexes are employed for the hydrocyanation of aromatic substituted imines, excellent yields and enatio-selectivities are obtained [94]. 

As already shown in Scheme 8, carpanone (44) has been synthesized by an electrochemical method. More efficient synthesis of 44 was effected with O2 catalyzed by metal-Schiff base complexes. Of the four complexes, Co(II)(salpr), Co(ll)(salen), Fe(II)(salen) and Mn(ll)(salen), Co(ll)(salen) provides the best results its solution with 4,5-methylenedioxy-... 

Much work has been devoted to the study of Schiff base complexes, in particular M(salen), where M = metal, has been the subject of extensive work 114). The early work by Calvin et al. (section 111(A)) suggested that the 2 1 (M O2) dioxygen adduct, type I, formed by Co(salen) in the solid state, contains a peroxo linkage. An X-ray analysis 115, 116) of the complex (Co Salen)202(DMF)2 supports this hypothesis see Fig. 5 for the pertinent results of this study. 

As alluded to earlier, an important advancement in catalyst design for the copolymerization of epoxides and carbon dioxide involves the use of Schiff base metal complexes where the ligand is in a cis configuration, as depicted in Fig. 9. For example, Chen and coworkers have recently reported a (salen)Co... 

Mitchell and Valero (1982, 1983) studied VO-phthalocyanine (VO-PC) and a Schiff base complex, VO-salen, as model vanadium compounds. The VO-PC provides a metal coordination environment comprised of four nitrogens, similar to the porphyrin. The benzo rings at the /3-pyrrolic positions contribute to enhanced aromaticity in the metal ligand. 

Many other projects in the past dealt with the immobilization of the famous chelating salen ligand or salen metal complexes, respectively—the Mnm salen Schiff base complex is also known as Jacobsen s catalyst, and it is used, among others, in asymmetric epoxidation of olefinstttt—mainly onto the surface of MCM-41 and SBA-15. 

The most comprehensively studied Mn" Schiff base compounds are those of the quadridentate hybrid O—N—N—O donor set ligands of structure (161) the ligand salenH2 (161) where Y = H and X = (CH2)2) being the object of a number of different studies.389,418 The orange-yellow, crystalline, air-stable compound [Mn(salen)(en)J was isolated in 1933 and shown to rapidly oxidize in solution.419 The compound [Mn(salen)] has been prepared by the four main methods used to prepare metal compounds of ligands derived from the interaction of salicylaldehydes and primary amines,420 these are ... 

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