Complex catalyst, zinc

Gif family chemistry" originally provided an alkane hydroxylation system by using an iron complex catalyst, zinc powder, acetic acid and pyridine under dioxygen as shown in eq. (8) [91]. 

The cationic aqua complexes prepared from traws-chelating tridentate ligand, R,R-DBFOX/Ph, and various transition metal(II) perchlorates induce absolute enantio-selectivity in the Diels-Alder reactions of cyclopentadiene with 3-alkenoyl-2-oxazoli-dinone dienophiles. Unlike other bisoxazoline type complex catalysts [38, 43-54], the J ,J -DBFOX/Ph complex of Ni(C104)2-6H20, which has an octahedral structure with three aqua ligands, is isolable and can be stored in air for months without loss of catalytic activity. Iron(II), cobalt(II), copper(II), and zinc(II) complexes are similarly active. 

Although the aqua nickel(II) complex A was confirmed to be the active catalyst in the Diels-Alder reaction, no information was available about the structure of complex catalyst in solution because of the paramagnetic character of the nickel(II) ion. Either isolation or characterization of the substrate complex, formed by the further complexation of 3-acryloyl-2-oxazolidinone on to the l ,J -DBFOX/ Ph-Ni(C104)2 complex catalyst, was unsuccessful. One possible solution to this problem could be the NMR study by use of the J ,J -DBFOX/Ph-zinc(II) complex (G and H, Scheme 7.9) [57]. 

Vinylic copper reagents react with CICN to give vinyl cyanides, though BrCN and ICN give the vinylic halide instead." Vinylic cyanides have also been prepared by the reaction between vinylic lithium compounds and phenyl cyanate PhOCN." Alkyl cyanides (RCN) have been prepared, in varying yields, by treatment of sodium trialkylcyanoborates with NaCN and lead tetraacetate." Vinyl bromides reacted with KCN, in the presence of a nickel complex and zinc metal to give the vinyl nitrile. Vinyl triflates react with LiCN, in the presence of a palladium catalyst, to give the vinyl nitrile." ... 

Lewis-Acid Catalyzed. Recently, various Lewis acids have been examined as catalyst for the aldol reaction. In the presence of complexes of zinc with aminoesters or aminoalcohols, the dehydration can be avoided and the aldol addition becomes essentially quantitative (Eq. 8.97).245 A microporous coordination polymer obtained by treating anthracene- is (resorcinol) with La(0/Pr)3 possesses catalytic activity for ketone enolization and aldol reactions in pure water at neutral pH.246 The La network is stable against hydrolysis and maintains microporosity and reversible substrate binding that mimicked an enzyme. Zn complexes of proline, lysine, and arginine were found to be efficient catalysts for the aldol addition of p-nitrobenzaldehyde and acetone in an aqueous medium to give quantitative yields and the enantiomeric excesses were up to 56% with 5 mol% of the catalysts at room temperature.247... 

The trigonal planar zinc phenoxide complex [K(THF)6][Zn(0-2,6-tBu2C6H3)3] is formed by the reaction of a zinc amide complex, via a bis phenoxide, which is then further reacted with potassium phenoxide. TheoX-ray structure shows a nearly perfect planar arrangement of the three ligands with zinc only 0.04 A out of the least squares plane defined by the three oxygen atoms.15 Unlike the bisphenoxide complexes of zinc with coordinated THF molecules, these complexes are not cataly-tically active in the copolymerization of epoxides with C02. The bisphenoxide complex has also been structurally characterized and shown to be an effective polymerization catalyst. 43... 

Furthermore, 2,2-difluoro-3-hydroxyesters are readily obtained from ClCF2COOMe and carbonyl compounds by electrolysis in a one-compartment cell using a sacrificial zinc anode and a nickel-complex catalyst [26], The catalytic cycle is shown in Scheme 3.11 and nickel zinc exchange is a key step. 

Darensbourg DJ, Wildeson JR, Yarbrough JC (2002) Solid-state structures of zinc(II) benzoate complexes. Catalyst precursors for the coupling of carbon dioxide and epoxides. Inorg Chem 41(4) 973-980... 

Dihydrofuran reacts with /3,7-unsaturated a-keto esters with copper or zinc complex catalysts to generate furo[2,3-/ ]pyran derivatives in good yields with high stereoselectivity. The synthesis proceeds via an inverse electron demand hetero-Diels-Alder reaction <2000CC459>. 

O-isopropylidene-a-D-glucofuranose by zinc methoxypropanol complex catalyst, J. Polym. Sci., Part A Polym. Chem., 22 (1984) 3593-3598. 

Fig. 18 Representative examples of homogeneous catalysts for CO epoxide copolymerization Inoue s tetraphenylporphyrin aluminium chloride complex (a), zinc hw-2,6-fluorophenoxide complex (b), zinc (3-diiminate complex (c) and chromium-salen complex (d)...

Additives are also used to improve the solubility of halide donors [382, 383]. Metal(II) halides such as magnesium chloride, calcium chloride, barium chloride, manganese chloride, zinc chloride and copper chloride etc. are used as halide sources. In order to increase the solubility of the halides they are reacted with electron donors which have been previously described for the increase of solubility of Nd-components [338,339]. The number of catalyst components is further increased if two Al-compounds (alumoxane + aluminum (hydrido) alkyl) are used. In addition, a small amount of diene can also be present during the preformation of the different catalyst components as described by JSR. In some catalyst systems the total number of components reaches up to eight [338,339]. Such complex catalyst systems are also referred to in other JSR patents [384,385] (Sect. 2.2.6). 

Organozinc reagents have been coupled with halides in the synthesis of dienes and other conjugated systems to form new carbon-carbon bonds such reactions have been reviewed477-479. In particular, the reaction of alkynyl zinc reagents with vinyl halides has been used in natural product synthesis, usually catalyzed by palladium complex catalysts. 

Formation of the 1 1 complexes with zinc and cadmium has been studied in aqueous solution, and the complexes are more stable than the corresponding 1 1 adducts with bipy 245). Ternary mercury(II)-hydroxo-terpy complexes are active catalysts for hydrolysis of esters and amides 477). 

Complexes of various metal salts and chiral hw-oxazolines have also been examined as catalysts for allylations of aldehydes (Eq. 21) [38], The most effective salts were ZnCl2, ZnBr2, Znl2, Sn(OTf)2, and InCl3. Octanal and cyclohexanecarboxaldehyde afford adducts of 40 5% ee with complexes of zinc salts. 

A classical example of the dehydrogenative formation of a carbon-carbon double bond conjugated with an aromatic ring is the dehydrogenation of ethylbenzene to styrene at 500-600 °C over a complex catalyst containing oxides of zinc and chromium [1090] or at 625 °C over vanadium pentoxide on alumina [478]. 

Other suitable catalysts for the carboxymethylation of aromatic amines are zinc or copper carbamates. In 1997 it was patented a process " for the preparation of carbamates Ifom an aromatic amine and DMC in the presence of N,N-substituted carbamate complexes of zinc and copper. Table 6 summarises results reported in some of the patent examples, high selectivity was reported with aniline, while with MDA a considerable amount of N-methyl derivatives was foimd. 

Inoue et al. ( ) found that a porphyrin-Zn alkyl catalyst polymerized methyloxirane to form a polymer having syndio-rich tacticity. The relative population of the triad tacticities suggests that the stereochemistry of the placement of incoming monomer is controlled by the chirality of the terminal and penultimate units in the growing chain. There is no chirality around the Zn-porphyrin complex. Achiral zinc complex forms syndio-rich poly(methyloxirane), while chiral zinc complex, as stated above, forms isotactic-rich poly(methyloxirane). The situation is just the same as that for propylene polymerizations. Achiral vanadium catalyst produces syndiotactic polypropylene, while chiral titanium catalyst produces isotactic polypropylene. 

Pd-catalyzed metallation of carbon electrophiles is also applicable to carbon-transition metal bond formation. Beletskaya and colleagues have reported that, in the presence of a Pd(II) catalyst, zinc salts of metal (Fe, Re, W, and Mn) carbonylates smoothly react with aryl and vinyl halides to afford the corresponding rj -aryl and Tj -vinyl complexes (Table 7 and Scheme 16). " The metallation of vinyl halides proceeds with stereochemical retention as in the case with other metal nucleophiles. The use of alkali salts of the metal carbonylates considerably reduces the yields of coupling products. 

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