Palladium/copper halide

If palladium/copper halide catalysts are used, C—C coupling occurs and dimethyl oxalate is formed. The by product water can be trapped by addition of orthoformates and, instead of oxygen, quinones can also be used as the oxidizing agent. Typical conditions are 70 bar of CO and temperatures of 125 C. Based on results of Rivetti et aL, product formation can be envisioned via alkoxycarbonyl species [73] ... 

The reaction on unactivated halides can also be done with copper halide catalysts (the Hurtley reaction), and with palladium complex catalysts. 

Tributylstannyl)-3-cyclobutene-1,2-diones and 4-methyl-3-(tributylstan-nyl)-3-cyclobutene-l,2-dione 2-ethylene acetals undergo the palladium/copper-catalyzed cross coupling with acyl halides, and palladium-catalyzed carbon-ylative cross coupling with aryl/heteroaryl iodides [45]. The coupling reaction of alkenyl (phenyl )iodonium triflates is also performed by a palladium/copper catalyst [46],... 

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. 

Diazasilacyclopent-4-ene derivatives complexed with palladium and copper halides (Section 4.24.1.3.4.) (cf. (27)) possess UV absorption at 436-655 nm range <86ZN(B)1230>. 

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]. 

Diaryl tellurium dichlorides react with olefins in the presence of palladium(II) chloride to give arylated olefins in moderate yields. The reactions are catalytic with respect to palladium chloride when copper halides are added as oxidants. An aryl palladium compound was postulated as the intermediate5 ... 

Nickel, palladium and copper catalysts can effect a variety of C — C bond-forming reactions P to the ester carbonyl via j8-zinc esters. These include 1,4-addition to a,jS-unsaturated carbonyl compounds (copper), arylation with aryl halides (palladium, nickel), allylation with allyl chloride (copper), and acylation with acyl chlorides (palladium, copper). " ... 

The DMC productivity increases by addition of palladium salts to copper salts supported on active carbon. It is worth pointing out that, although copper salts without halides are practically inactive in the reaction, the use of halogen-free palladium/copper salts supported on active carbon reportedly gives high DMC productivity and CO selectivity. ... 

The above DMC synthesis using MN was discovered at UBE, and a plant based on this technology has recently gone onstream with a capacity of about 6000ton/yr. Reaction (7) is catalyzed by supported palladium(II) halide complexes, which allow high (90-95%) CO selectivity. The addition of a cocatalyst such as copper chloride is required to prevent the reduction of Pd(II) to Pd(0) because Pd(0) tends to accelerate the formation of DM0. 

The mechanism of palladium/aryl halide amination is very closely related to that of cross coupling, with displacement of the halide on palladium (or copper or nickel) by an amine or A-anion instead of the trans-metallation step. In the case of Cu and Ni catalysis, it may proceed through M(0)-M(11) or M(l)-M(lll) cycles. 

The palladium-copper-catalyzed cross-coupling of acetylenic systems with aryl halide has been used successfully to homopolymerize p-bromoethynylbenzene (eq 4) [8]. The poly-p-ethynylbenzene was isolated as a white pol3nmer of relatively low molecular weight. The coupling of acetylenic reagents with aryl halides has been noted to lead to explosions and therefore due care should be exercised. 

Although the majority of direct arylations have been catalyzed by palladium, rhodium, and ruthenium, some additional studies have also focused on direct arylations catalyzed by first-row metals, such as iron and copper. For example, an iron-catalyzed direct arylation reaction between arylzinc reagents and 2-arylpyridine derivatives has been reported (Equation 19.146). Several direct couplings of heteroarenes with aryl halides (Equation 19.147) or hypervalent iodine reagents ° catalyzed by copper halides have also been reported. 

The first pol5unetallaynes contained nickel, palladium, or platinum atoms in the main chain and were isolated in 1977 as yellow, film forming materials (203-205). These were prepared by efficient copper halide-catalyzed coupling processes (eg, eq. 36) and possessed estimated molecular weights (Mw) from 13,000 to 120,000. 

The key point in divalent Pd-catalyzed cyclization of allylic alkynoates is the method of quenching of the carbon-paUadium bond formed after cyclization. In order to develop a divalent Pd-catalyzed reaction, a divalent palladium species must be regenerated in the quenching of the carbon-paUadium bond. Lu and co-workers developed different quenching methods for the carbon-palladium bonds, for example, /3-heteroatom elimination, copper halide mediated oxidative cleavage, and carbonylation and protonolysis of... 

Oxidative addition of alkenyl halides, triflates, and other esters to zerovalent palladium compounds has been long known as a viable route to palladium(ii)-alkenyl complexes. Stereospecific coupling reactions involving mono- and (E)- or (Z)-dihalo-alkenes with palladium-copper catalysis under modified Sonogashira conditions are quite versatile and useful. These proceed through oxidative addition of the alkenyl halide via palladium(ii) alkenyl complexes, followed by coupling with a nucleophile (usually an alkynylcopper reagent obtained in situ with co-catalytic copper(i) from terminal alkynes in the presence of, in this case, a base like piperidine instead of diethylamine). ... 

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