Ethanol catalysts, palladium complexes

The kinetic modeling study of l-(4-isobutylphenyl)ethanol (IBPE) carbonylation nsing a homogeneous palladium complex has been reported by Chaudhari. The three key steps (formation of the active substrate formation of the active catalyst catalytic carbonylation of active substrate) were studied in detail. The average carbonylation rate depends on several factors, so a dynamic analysis, where the concentrations of both the catalyst species and the intermediates were varied, was carried out. 

Moreover, the reaction between cinnamyl acetate and cyclohexylamine or dipropylamine, which is catalyzed by a palladium complex with this ligand, shows that the catalyst can be reused even when the product is soluble in the water-ethanol phase. After saturation of this phase with the product in the first catalytic cycle, in the second and subsequent cycles, almost no product is lost. To cari7 out this reaction in a system composed of 85% aqueous ethanol and heptane, it is necessary for the polymer catalyst to form a single phase at a temperature of 80 °C. 

PNIPAM-modified polymers were used as ligands to synthesize catalysts that are soluble in the nonpolar phase (e.g. alkane) at low temperatures and are miscible with the polar phase (90% aqueous ethanol) owing to the introduction of octadecyl groups into the amide group of the polymer (PNODAM polymers). Rhodium and palladium complexes of polymers modified with diphenylphosphines were active in hydrogenation and Heck reactions, respectively. In Heck reactions, a palladium complex with a PNODAM polymer modified with chelating ligands was used [98]. 

The selective hydrogenation of alkynes to alkenes may he achieved with polymer-bound palladium(n) complexes, particularly in solvents such as dimethyl formamide, dimethyl sulphoxide, and ethanol. The catalytic activity appears to depend on the acidity of the alkyne rather than steric factors. This polymer-bound palladium complex is siniilar in selectivity to cationic rhodium and the lindlar catalysts. ... 

Examples of sohd-bound Pd-catalyzed carbonylation of aryl and alkenyl halide, allyl alcohol, and derivatives are abundant in the literature. Polyketones have been obtained via carbonylation of ethylene and carbon monoxide catalyzed by palladium complexes of polysiloxane-bound phosphinet t or Pd(dppp) absorbed on alumina.f f Similar processes can also be carried out by catalyst formed simply by absorbing Pd(02CNEt2)2(NHEt2)2 onto silica geL Polyphosphine-bound palladium has been used to prepare ethyl hexanoate from 1-pentene, CO, and ethanol. Similar esterification of styrene has been achieved using a bimetallic system involving palladium and nickel immobilized on poly(Af-vinyl-2-pyrrolidone).f ... 

In these cases, NFSI was preferred to Selectfluor and the reactions were performed either in alcohol or in ionic liquids in which the palladium complexes can be immobilized and reused with excellent reproducibility even after 10 consecutive cycles. For example, the enantioselective electrophilic fluorination of 2-methyl-3-oxo-3-phenylpro-pionic acid tert-butyl ester in [hmim] [BF4] gives the corresponding fluorinated product in 93% yield with 92% ee, and still in 67% yield with 91% ee after 10 cycles. The fluorination of various cyclic and acyclic (3-keto esters was carried out with NFSI in ethanol in the presence of 2.5 mol% of catalyst, leading to excellent ee-values up to 94%. The reaction is not sensitive to water, can be run on a 1-g scale, and proceeds via a palladium enolate complex as for the titanium-4,5-bis(diphenylhydroxymethyl)-2,2-dimethyl-dioxolane (TADDOL) catalyst. The reaction was extended to tert-butoxycarbonyl lactones and lactams. Reactions with lactones proceeded smoothly in an alcoholic solvent with 2.5 mol% of catalyst and NFSI, while the less acidic lactam substrates required concurrent use of the Pd complex and 2,6-lutidine as a co-catalyst. Under the reaction conditions, the fluorinated lactones and lactams were obtained in good yields with excellent enantioselectivities (up to 99%... 

Rhodium(III) complexes [e.g. (i-Pr,P)2Rh(H)Cl2] in the presence of quaternary ammonium salts are excellent catalysts for the hydrogenolysis of chloroarenes under mild conditions [5] other labile substituents are unaffected. Hydrodehalogenation of haloaryl ketones over a palladium catalyst to give acylbenzenes is also aided by the addition of Aliquat [6]. In the absence of the phase-transfer catalyst, or when the hydrogenation is conducted in ethanol, the major product is the corresponding alkyl-benzene, which is also produced by hydrodehalogenation of the halobenzyl alcohols. 

In addition to the successful reductive carbonylation systems utilizing the rhodium or palladium catalysts described above, a nonnoble metal system has been developed (27). When methyl acetate or dimethyl ether was treated with carbon monoxide and hydrogen in the presence of an iodide compound, a trivalent phosphorous or nitrogen promoter, and a nickel-molybdenum or nickel-tungsten catalyst, EDA was formed. The catalytst is generated in the reaction mixture by addition of appropriate metallic complexes, such as 5 1 combination of bis(triphenylphosphine)-nickel dicarbonyl to molybdenum carbonyl. These same catalyst systems have proven effective as a rhodium replacement in methyl acetate carbonylations (28). Though the rates of EDA formation are slower than with the noble metals, the major advantage is the relative inexpense of catalytic materials. Chemistry virtually identical to noble-metal catalysis probably occurs since reaction profiles are very similar by products include acetic anhydride, acetaldehyde, and methane, with ethanol in trace quantities. 

Complexes 11, 1010, after line 3 from bottom]. When a partly epoxidized fatty ester or glyceride carrying residual unsaturation is hydrogenated to the corresponding monohydroxy product at a low pressure over palladium-on-carbon catalyst in ethanol, the presence of silver nitrate in the solution provides complete protection to the ethenoid linkages, probably by7r-complex formation.173... 

The transition metal-catalyzed reductive carbonylation of o-substituted nitrobenzenes is a useful method for the synthesis of nitrogen heterocycles. Application of this methodology to the preparation of l,4-dihydro-2/f-3,l-benzoxazin-2-one derivatives and to the synthesis of the 3,1-benzox-azepin-2-one (42) has been reported <93JOM(451)157>. Reaction of 2-(2-nitrophenyl)ethanol (41) (100% conversion) with carbon monoxide in the presence of a palladium(Il) catalyst gave (42) in 60% yield, together with some of the macrocyclic dimer (43) ( nation (2)). It is suggested that a nitrene complex may not be involved with the palladium catalyst in view of the reaction path selectivity observed <93JOM(45i)l57>. 

Recently, Wang [64] prepared by radieal copolymerization a cinchona alkaloid copolymer the methyl acrylate-co-quinine (PMA-QN (71)) (Scheme 34). Complexed with palladium(II), its catalytic activity in the heterogeneous catalytic reduction of aromatic ketones by sodium borohydride was studied. High yields in their corresponding alcohols are obtained but it is found that the efficiency of the catalyst depended on the nature of the solvent and the ketone which related to the accessibility of the catalytic active site. The optical yields in methanol and ethanol 95% were lower than in ethanol. This ability was attributed to a bad coordination between PMA-QN-PdCl2 and sodium borohydride and a reaction rate which was very rapid. The stability of the chiral copolymer catalyst was studied... 

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