Transition metal complexes sulfoxides

Figure 12. Supramolecular porphyrins obtained by coordination of transition metal complexes to the periphery of the macrocyclic ring (a similar scheme can be extended to the 3-TPyP and analogous porphyrazine species), [dmso = dimethyl sulfoxide (ligand), form = A,A-9-di- -tolyformamidinate, and TFA = trifluoroacetate.l...

As chiral ligands for transition metal complex-catalyzed asymmetric reactions, a variety of novel chiral ferrocenylchalcogen compounds, which possess a planar chirality due to the 1,2-unsymmetrically disubstituted ferrocene structure, have been prepared from chiral ferrocenes (Scheme 1). Thus, chiral diferrocenyl dichalcogenides bearing an optically active dimethylaminoethyl or p-tolyl-sulfoxide moiety 1-10 were prepared by lithiation of the corresponding chiral ferrocenes, highly diastereoselectively, in moderate to high chemical yields. 

High-valent d transition metal complexes, e.g. complexes of Mo , V and Ti, catalyze numerous oxidations of organic substrates by alkyl hydroperoxides, such as epoxidation of alkenes, oxidation of tertiary amines to the corresponding N-oxides, of sulfides to sulfoxides. 

Perfluorodecalin has been used in aerial oxidations catalyzed by transition metal complexes," e.g., aromatic aldehydes to aroic acids, sulfides to sulfoxides, alkenes to epoxides. The mild conditions for oxidation of alkanes to ethers with the (Ph,P),PdBr,-NaOMe-0, are valuable. 

The most efficient way to generate optically active sulfoxides is via enantiose-lective catalysis [10,11]. For this purpose enzymes and metal catalysts can be used. In this chapter, the various approaches to metal-catalyzed formation of sulfoxides based on oxidation chemistry are described. All of these methods rely on chiral transition metal complexes and, therefore, special focus will be given to a discussion of the structures of these metal-containing compounds. 

This asymmetric oxidation of sulfides has been achieved successfully using bio-transformations. However, a detailed discussion of these reactions is beyond the scope of the present book. A number of enatiomerically pure transition metal complexes in combination with terminal oxidants have been used to effect the asymmetric oxidations of sulfides to sulfoxides. ... 

The oxidation of OH by [Fe(CN)6] in solution has been examined. Application of an electrical potential drives the reaction electrochemically, rather than merely generating a local concentration of OH at the anode, as has been suggested previously, to produce both O and [Fe(CN)6] in the vicinity of the same electrode. With high [OH ] or [Fe(CN)6] /[Fe(CN)6] ratio, the reaction proceeds spontaneously with a second-order rate constant of 2.2 x 10 M s at 25 °C. Under anaerobic conditions, iron(III) porphyrin complexes in dimethyl sulfoxide solution are reduced to the iron(II) state by addition of hydroxide ion or alkoxide ions. Excess hydroxide ion serves to generate the hydroxoiron(II) complex. The oxidation of hydroxide and phenoxide ions in acetonitrile has been characterized electrochemically " in the presence of transition metal complexes [Mn(II)L] [M = Fe,Mn,Co,Ni L = (OPPh2)4,(bipy)3] and metalloporphyrins, M(por) [M = Mn(III), Fe(III), Co(II) por = 5,10,15,20-tetraphenylpor-phinato(2-), 5,10,15,20-tetrakis(2,6-dichlorophenyl)porphinato(2-)]. Shifts to less positive potentials for OH and PhO are suggested to be due to the stabilization of the oxy radical products (OH and PhO ) via a covalent bond. Oxidation is facilitated by an ECE mechanism when OH is in excess. 

Poraij-Koshits MA (1978) Structural effects of mutual influence of ligands in transition- and non-transition-metal complexes. Koordinatsionnaya Khimiya 4 842-866 (in Russian) Hartley FR (1973) The cis- and trans-effects of ligands. Chem SocRev 2 163-179 Russell DR, Mazid MA, Tucker PA (1980) Crystal structures of hydrido-tris(triethyl-phosphine)platinum(II), fluoro-tris(triethylphosphine)platinum(lD, and chloro-tris(trieth-ylphosphine)platinum(II) salts. J Chem Soc Dalton Trans 1737-1742 Blau R, Espenson J (1986) Correlations of platinum-195-phosphorus-31 coupling constants with platinum-hgand and platinum-platinum bond lengths. Inotg Chem 25 878-880 Belsky VK, Konovalov 1, Kukushkin VYu (1991) Structure of cis-dichloro-(dimethyl-sulfoxide)-(pyridine)platinum(II). Acta Cryst C47 292-294... 

Asymmetric synthesis has emerged as a major preparative method, widely used in organic chemistry and in the total synthesis of natural products, and which is also of interest for industrial chemistry. The importance of enantiomerically pure compounds is connected with the applications in pharmaceutical industries, since very often the biological activity is strongly linked to the absolute configuration. In this article the historical developments of asymmetric synthesis will be briefly presented, as well as the main methods to prepare enantiomerically enriched compounds. Then recent asymmetric synthesis of two classes of compounds will be discussed i) Sulfoxides, chiral at sulfur ii) Ferrocenes with planar chirality. The last part of the article will be devoted to asymmetric catalysis with transition-metal complexes. The cases of asymmetric oxidation of sulfides to sulfoxides and nonlinear effects in asymmetric catalysis will be mainly considered. 

This particular thiourea used by Russo for sulfoxidation, gives a catalytic turnover that competes well with transition metal complexes generally used for sulfoxidation reactions. The effectiveness of the TBHP activation could be rationalised according to a donble hydrogen-bonding interaction of the thiourea with the proximal oxygen of TBHP, which should enhance the elctrophilic character of the distal oxygen attacked by a snlfide. Formation of the TBHP and thiourea complex (Fig. 1.11) was confirmed by H NMR spectroscopic analysis, where the chemical shift of H moves downfield from 7.88 to 7.91 ppm, and the proton in the TBHP also shifts downfield from 7.14 to 7.42 ppm. 

Colona and coworkers oxidized a variety of alkyl aryl and heterocyclic sulfides to the sulfoxides using t-butyl hydroperoxide and a catalytic amount of a complex (97) derived from a transition metal and the imines of L-amino acids. Of the metals (M = TiO, Mo02, VO, Cu, Co, Fe), titanium gave the highest e.e. (21%), but molybdenum was the most efficient catalyst. The sulfoxides were accompanied by considerable sulfone125. 

This review is intended as an account of the coordination chemistry of both dimethyl sulfoxide and the higher sulfoxides, with particular reference to the mode of bonding and the extent to which this affects the chemistry of transition-metal sulfoxide complexes. No attempt has been made to provide an exhaustive listing of all known sulfoxide complexes, many of which contain coordinated sulfoxide moieties only coincidentally to their other important functions. 

In order to understand the bonding in transition-metal sulfoxide complexes, it is necessary to summarize the physical data available in the literature and so determine what constraints are necessary in any bonding model. An understanding of the factors affecting the bonding in these complexes is essential if further developments are to be made in the chemistry of transition-metal sulfoxide complexes. 

An excellent review article (460) has covered much of the literature concerning Me2SO complexes of the transition metals up to 1969. In consequence, only the major points prior to this period will be discussed, together with more recent developments and comments on complexes of the higher sulfoxides. 

Oxidation reactions are not limited to those that occur at a carbon centre. The perfluorinated Ni(F-acac)2-benzene-CgFi7Br system described above was also active for the oxidation of sulfides to sulfoxides and sulfones [28], A sacrificial aldehyde is required as co-reductant, but the reaction may be tuned by changing the quantity of this aldehyde. If 1.6 equivalents of aldehyde are used, the sulfoxide is obtained, whereas higher quantities (5 equivalents) lead to sulfones. Fluorous-soluble transition metal porphyrin complexes also catalyse the oxidation of sulfides in the presence of oxygen and 2,2-dimethylpropanal [29],... 

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