Pd , as catalyst

The oxidation reaction is generally described with Pt or Pd as catalyst, eventually on active coal, in aqueous alkaline solutions at temperature from 40°C to 100°C. The oxidation reaction is mostly carried out with oxygen or with an oxygen-containing gas such as air [17,18]. 

Hydrostannation, applied to alkynes with Pd as catalyst, produces vinylstannanes129,131 as mixtures of two regioisomers, a and b ... 

Several alkyne-linked bis-2H-indazoles have been synthesized by the double cycliza-tion of butadiyne-linked (167) phenyltriazenes or phenyldiazenes, in turn obtained by Cu(OAc)2-mediated homocoupling of ethynylphenyltriazenes (Scheme 46).144 The reactions proceed rapidly under neutral conditions with mild heating, affording the heterocycles in excellent yields. By using Pd as catalyst under oxidative conditions, bis-2//-indazoles (170) were obtained directly from ethyne-linked phenyltriazenes (169). DFT calculations revealed for these reactions low barriers to cyclization that... 

This cannot be relied upon though The same reaction with Pd as catalyst gives mainly the trans isomer, because of the reversibility of the hydrogenation process. This intermediate can easily escape from the catalyst as an isomeric alkene, which can be re-hydrogenated from the other face. Isomerizations of this sort somatimes accompany hydrogenations. 

The dibenzo- 1,5-oxazocine 540 was obtained, in nearly quantitative yield, via intramolecular carbonylation of ortho-substituted aniline 539 with 100 psi CO in the presence of recyclable palladium-complexed dendrimer on silica (Gl-Pd) as catalyst and diisopropylethylamine (DIPEA) (Equation 23) <2005JA14776>. 

Oxidation of methanol to C02 and H20 on a supported Pd as catalyst exhibits oscillations. Jaeger et al. (1981) measured the temperature of the catalyst corresponding to various frequencies and reported periodic and complex oscillations in temperature. 

Fig. 21. Variation of [NH3], with the composition of the initial nitrogen-hydrogen mixture for clean glass and palladized Pd as catalyst ...

Despite the general superiority of Zn over Mg, it is important to retain Mg as an option, especially in those cases where arylzincs are generated via arylmagnesium derivatives, and the use of Zn as the second metal countercation must be experimentally justified. It is also important to consider both Ni and Pd as catalyst components. Despite its shortcomings, Ni is significantly less expensive than Pd. So, it is very desirable to experimentally justily the use of Pd in preference to Ni. ... 

Cross-coupling reactions were carried out in direct aqueous miniemulsions with 1,2,4-tribromobenzene as crosslinker, and Pd as catalyst [147], in order to obtain aqueous latexes of crosslinked poly(p-phenylene ethynylene) with good optoelectronic properties. The Glaser couphng reaction was also used to synthesize fluorescent conjugated particles of poly(arylene diethynylenes) in direct miniemulsions [148]. For this, 4,4 -dinonyl-2,2 -bipyridine was found to be a suitable ligand for solubilizing the copper (I) chloride catalyst in the toluene droplets. In this case, a solution of the monomers in toluene was first mixed with the solution of the catalyst, and the resultant mixture then miniemulsified in an aqueous solution of cationic surfactant. 

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