Palladium-copper catalyst system

S)-(-)-CITRONELLOL from geraniol. An asymmetrically catalyzed Diels-Alder reaction is used to prepare (1 R)-1,3,4-TRIMETHYL-3-C YCLOHEXENE-1 -CARBOXALDEHYDE with an (acyloxy)borane complex derived from L-(+)-tartaric acid as the catalyst. A high-yield procedure for the rearrangement of epoxides to carbonyl compounds catalyzed by METHYLALUMINUM BIS(4-BROMO-2,6-DI-tert-BUTYLPHENOXIDE) is demonstrated with a preparation of DIPHENYL-ACETALDEHYDE from stilbene oxide. A palladium/copper catalyst system is used to prepare (Z)-2-BROMO-5-(TRIMETHYLSILYL)-2-PENTEN-4-YNOIC ACID ETHYL ESTER. The coupling of vinyl and aryl halides with acetylenes is a powerful carbon-carbon bond-forming reaction, particularly valuable for the construction of such enyne systems. 

Scope of this synthetic strategy is not limited to benzofiirans. The reaction of 2-iodo-3-hydroxypyridine and 1,1 -diethoxy-2-propync under Sonogashira coupling conditions (palladium-copper catalyst system) leads to the formation of the substituted furo[3,2-6]pyridine shown in 3.56.72... 

These processes that substitute carbon monoxide, oxygen, and an alcohol for phosgene appear to be on the verge of commercial viability. There may be questions of catalyst life and recyclability that are not mentioned in the papers and patents. Some reaction times need to be shortened through the use of improved catalysts. Aresta et. al do say that their palladium-copper catalyst system can be recycled.46 The use of supported catalysts that could be recovered by filtration could simplify workups and recycling. (Supported catalysts are described in Chap. 5.)... 

To test the selectivity of the bimetallic system, monosubstituted acetylenes (Table I) and disubstituted acetylenes (Table II) were hydrogenated with the use of the silica supported palladium-copper catalysts. The yields of the olefins at 100% conversion of the acetylene are given. However, in all cases with longer hydrogenation times it was possible to end up with the fully saturated product. 

The silica supported palladium-copper catalysts are selective in the hydrogenation of monosubstituted acetylenes giving high yields of either olefins or saturated hydrocarbons, depending on the reaction time. In addition, the catalytic system shows reasonable selectivity towards cis-olefins in the hydrogenation of disubstituted acetylenes. 

A strategy employing intramolecular amidation can also be exploited to access benzimidazolones (Scheme 24.12). The use of N,N -disubstituted ureas such as 27 was described by a process group working at Merck [60]. A palladium-based catalyst system promoted the intramolecular arylation and generated the desired heterocycles in excellent yields. Copper-catalyzed variants have also been reported [61,62]. The second reaction shown in Scheme 24.12, described by Barbero et al. illustrates such a variation where water is used as the solvent [63]. 

The Wacker process uses an aqueous solution of palladium(II) chloride, copper(II) chloride catalyst system. 

We plan to make studies on palladium-copper, iridium-copper, and platinum-copper catalysts to extend our investigation of the effect of varying miscibility of the components on the structural features of the bimetallic clusters present. With these additional systems, the whole range from complete immiscibility to total miscibility of copper with the Group VIII metal will be encompassed. 

Our new approach has proven its initial value in both palladium-(Schareina et al. 2004) and copper-catalyzed cyanations (Schareina et al. 2005) and has been adopted by other groups. Very recently, in a joint collaboration with Saltigo GmbH we developed a new and improved copper-based catalyst system, which allows for efficient cyanations of a variety of aromatic and heteroaromatic halides. Importantly, notoriously difficult substrates react in excellent yield and selectivity, making the method applicable on an industrial scale. 

The utility of a palladium catalyst in the synthesis of substituted aryl acetylenes is well established.(7,8,9,10) The end-capping agent I was produced by using a standard catalyst system, dichlorobls(triphenylphosphlne)palladlum (II)/copper (I) iodide/triphenylphosphlne mixture, which has been employed in previously developed ethynylation procedures.(10) The copper (I) iodide is believed to act as a cocatalyst, reducing the palladium (II) complex to the active palladium (0) catalyst. The scheme is shown in Figure 3 (diethylamine is the solvent).(11)... 

The adipic acid process we have developed involves butadiene oxidative carbonylation in the presence of methanol, a l, l-dimethoxycyclohexane dehydration agent, and a palladium(ll)/ copper(ll) redox catalyst system (Equation 1.). The reaction sequence includes an oxycarbonylation, hydrogenation and hydrolysis step(17-19). The net result is utilization of butadiene, the elements of synthesis gas, l, -dimethoxycyclohexane and air to give adipic acid, cyclohexanone and methanol. 

Hydroxymethylfurfural. 2,5-Di(hydroxymethyl)furan can be synthesized from 5-HMF via hydrogenation (Scheme 16). Under a hydrogen pressure of 7 MPa at 140 °C in the presence of platinum or copper catalysts, practically quantitative yields of 2,5-di(hydroxymethyl)furan can be obtained.However, under similar conditions but with palladium or nickel as catalyst, hydrogenation of the ring system occurs so that 2,5-di(hydroxymethyl)-tetrahydrofuran is obtained as the predominant product. 

A variety of palladium(O) or palladium(ii)/phosphine systems have been used as catalyst precursors (Figure 9). Triphenylphosphine was usually the ligand of choice until Farina showed in 1991 that the use tri-(2-furyl)phosphine enhanced reaction rates. The positive effects of additives such as copper salts and diethylamine ... 

Copper was also effective in the creation of carbon-nitrogen bonds. N-(o-halophenyl)-guanidines gave 2-aminobenzimidazoles in the presence of a copper-1,10-phenantroline catalyst system. While the iodo and bromo derivatives in the presence of the copper catalyst gave the cyclized product in 83% and 96% yields respectively, the analogous palladium catalysed transformation showed similar efficiency in both cases, resulting in 88% and 86% yields.52... 

The Sonogashira coupling of haloazoles and terminal acetylenes in the presence of a palladium(0)-copper(l) catalyst system usually proceeds readily. Its application has, in the beginning, been limited to iodoazoles, while recent examples frequently utilise bromo-heterocycles too. 

In certain cases, when the palladium or nickel catalyzed coupling is not efficient or fails completely, an alternate solution is provided by the use of copper based catalyst systems. The 5-iodouracil derivative shown in 7.77. was unreactive towards imidazole using either the Buchwald-Hartwig conditions or the copper(I) triflate promoted the carbon-nitrogen bond formation reported by Buchwald98 These latter conditions, however, were effective in coupling the iodouracil with a series of other amines (7.77.), The optimal catalyst system consisted of copper(I) triflate, phenantroline and dibenzylideneacetone (dba).99... 

When either an alcohol or an amine function is present in the alkene, the possibility for lactone or lactam formation exists. Cobalt or rhodium catalysts convert 2,2-dimethyl-3-buten-l-ol to 2,3,3-trimethyl- y-butyrolactone, with minor amounts of the 8-lactone being formed (equation 51).2 In this case, isomerization of the double bond is not possible. The reaction of allyl alcohols catalyzed by cobalt or rhodium is carried out under reaction conditions that are severe, so isomerization to propanal occurs rapidly. Running the reaction in acetonitrile provides a 60% yield of lactone, while a rhodium carbonyl catalyst in the presence of an amine gives butane-1,4-diol in 60-70% (equation 52).8 A mild method of converting allyl and homoallyl alcohols to lactones utilizes the palladium chloride/copper chloride catalyst system (Table 6).79,82 83... 

Generally, the Sonogashira coupling reaction is achieved by a palladium-copper catalyzed reaction of aryl or vinyl halide and terminal alkyne [70-72], The presence of the copper co-catalyst is an obstacle, however, towards the metallodendritic approach of the system. In this context, only a few examples of copper-free procedures have been reported [73-77], involving for instance, in situ Pd(0) complex formation with bulky phosphines [78]. 

Following the development of sponge-metal nickel catalysts by alkali leaching of Ni-Al alloys by Raney, other alloy systems were considered. These include iron [4], cobalt [5], copper [6], platinum [7], ruthenium [8], and palladium [9]. Small amounts of a third metal such as chromium [10], molybdenum [11], or zinc [12] have been added to the binary alloy to promote catalyst activity. The two most common skeletal metal catalysts currently in use are nickel and copper in unpromoted or promoted forms. Skeletal copper is less active and more selective than skeletal nickel in hydrogenation reactions. It also finds use in the selective hydrolysis of nitriles [13]. This chapter is therefore mainly concerned with the preparation, properties and applications of promoted and unpromoted skeletal nickel and skeletal copper catalysts which are produced by the selective leaching of aluminum from binary or ternary alloys. 

In the search for more efficient catalyst systems for diazoester additions several groups" "" have employed rhodium(II) acetate. Transition metal complexes have been widely used in cyclopropane synthesis but copper(I) triflate and palladium(II) acetate are ineffective for substituted ethenes. Rhodium(II) carboxylates have been shown" to... 

The copper and palladium transition metal catalysts noted in Table 18 proved to be superior to nickel, ruthenium and rhodium catalysts. The nature of the reacting species has not been unequivocally defined, but the following experimental observations may provide some insight (i) tetrahydrofuran solvent is essential for the palladium-mediated reactions, since complex reaction mixtures (presumably containing carbinols) were observed when the reactions were performed in either benzene or methylene chloride (ii) the reaction is truly catalytic with respect to palladium (2 mmol alkylaluminum, 0.05 mmol of Pd(PPh3)4), whereas the copper catdyst is stoichiometric and (iii) in the case where a direct comparison may be made (entries 1-8, Table 18), the copper-based system is superior to palladium catalysis with regard to overall yield. 

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