Active catalyst agent

Active catalyst agent. This is the constituent primarily accountable for the catalytic function and it includes metals, semiconductors and insulators. The type of electrical conductivity (mainly for convenience) classifies the active components. Both... 

Appaiendy a molai equivalent of catalyst (AlCl ) combines with the acyl halide, giving a 1 1 addition compound, which then acts as the active acylating agent. Reaction with aromatics gives the AlCl complex of the product ketone hberating HX ... 

Pyrrole can be reduced catalyticaHy to pyrroHdine over a variety of metal catalysts, ie, Pt, Pd, Rh, and Ni. Of these, rhodium on alumina is one of the most active. Less active reducing agents have been used to produce the intermediate 3-pyrroline (36). The 2-pyrrolines are ordinarily obtained by ring-closure reactions. Nonaromatic pyrrolines can be reduced easily with to pyrroHdines. 

Optical resolution is another method of producing (—)-mentho1 from racemic materials. (A)-Menthol is treated with optically active resolving agents to separate the (—)-mentho1 from the (+)-menthol, which is further processed by racemization over a nickel catalyst and recycled (156). 

Ethylene is an active alkylating agent. It can be used to alkylate aromatic compounds using Friedel-Crafts type catalysts. Commercially,... 

The carbonyl complex [Ru(EDTAH)(CO)] has been reported to be a very good catalyst for reactions like hydroformylation of alkenes, carbonylation of ammonia and ammines as well as a very active catalyst for the water gas shift reaction. The nitrosyl [Ru(EDTA)(NO)] is an oxygen-transfer agent for the oxidation of hex-l-ene to hexan-2-one, and cyclohexane to the corresponding epoxide. 

Asymmetric reduction with very high ee values has also been achieved with achiral reducing agents and optically active catalysts. The two most important... 

In the above cases, an optically active reducing agent or catalyst interacts with a prochiral substrate. Asymmetric reduction of ketones has also been achieved with an achiral reducing agent, if the ketone is complexed to an optically active transition metal Lewis acid. ... 

Hydroxyenones have also been used in catalytic amide formation, although 1,2,4-triazole is required as a co-catalyst. Assumed protonation of the Breslow intermediate and tautomerisation generates an acylazolium intermediate, which is trapped by triazole, releasing the NHC and generating the acyltriazole 60 that is the active acylating agent for the amine (Scheme 12.11) [16]. 

Ally 1-tin compounds are employed as more reactive allylating agents. Because of their high reactivity, less active catalysts (TX species having mild Lewis acidity) or less reactive substrates are often required (Scheme 23).88,89 In addition to carbonyl compounds as substrates, allylation reactions of imines have been also reported.90 Also, a binuclear TiIV Lewis acid has been developed (compound (C) in Scheme 23), which shows higher catalytic activity than the mononuclear analogue (D) because of bidentate coordination to the carbonyl moiety of the substrate.91... 

Although only a dozen known metal complexes were tested in this manner, proof of principle was demonstrated. The test revealed Wilkinson s catalyst to be the most active hydrosilylating agent, its use in this type of reaction being known. However, the study also led to the discovery that a palladacycle, [Pd (o-tolyl)2PC6H4 (OAc)]2, which is usually considered to be potent in Heck reactions, is also an excellent hydrosilylation catalyst.37,38 Control experiments showed that the relative order of catalyst activity is the same when conventional substrates are used in place of the dyes (8). 

Extraction of Active Catalyst Using TPPMS and Conditioning Agent. 

The reaction was carried out by addition of 1.95 equivalents of -BuLi to a THF solution of 22 at 0°C to generate the active catalyst, which was then combined with substrate (S/C about 20 1) under an inert atmosphere using phenylsilane as the stabilizing agent. Trisubstituted unfunctionalized olefins can be hydrogenated in good yield with high ee. Representative results are listed in Table 6-3. 

It is interesting to note that a Cu(II) precatalyst gives an active catalyst in the absence of reducing agent (phenylhydrazine, etc.) contrary to observations made with bis(oxazolines) as ligands and to the accepted mechanism of this reaction. This reaction occurs at temperatures as low as 0°C, and contradicts the conventional belief that slow thermal homolytic cleavage of the oxidant (tert-butyl per-benzoate) is responsible for initiation of the catalytic cycle. Clearly, further work on the mechanism of this transformation is warranted. 

Studies regarding the nature of the catalytically active species for NHC complexes in Heck-type reactions have focused on the Mizorvki—Heck reaction and have consistently revealed a palladium(O) species as the active catalyst. The induction period is shortened upon addition of a reducing agent,and postulated intermediates of the reaction were isolated and characterized as well as employed in stoichiometric and catalytic reactions. Theoretical studies using DPT calculations showed the mechanism for NHC complexes to most likely he in agreement with phosphine chemistry. ... 

An active catalyst can sometimes be made simply in situ for the target reaction, avoiding a pre-synthesis step. [Fe(NO)2Cl]2 in [BMIM]BF4 or [BMIM]PF6 was in situ treated with a reducing agent, Zn(0), (Et)2AlCl, or -butyllithium for the 1,3-butadiene cyclodimerization reaction (Scheme 22), 206). 

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