Palladium reactions

The conversion of ethylene to acetaldehyde using a soluble palladium complex, developed in the late 1950s, was one of the early applications of homogeneous catalysis and the first organo-palladium reaction practised on an industrial scale [40], Typically this reaction requires stoichiometric amounts of CuCl under aerobic conditions. The use of copper represents not only an environmental issue, but often limits the scope of ligands that can be used in conjunction with Pd. 

In conclusion, the already rich chemistry of pyrroles is greatly expanded by the palladium reactions presented in this chapter. The abundance of both 2- and 3-pyrrolyl halides and triflates has led to many examples of high-yielding Negishi, Suzuki, Stille, Sonogashira, and Heck reactions. Noteworthy are the excellent approaches to alkynyl pyrroles and porphyrins using Sonogashira, Stille, and Suzuki reactions. 

I note that some data in the paper emphasize, for the examples given, that nickel and palladium reactions are considerably faster than the platinum (I I) reactions. This, I believe, is true for all the examples cited in the paper. It might be interesting to discuss this point. I would like now to open the topic for discussion from the audience. 

Reaction (1) was carried out in n-hexane solvent. The excess butyl lithium was either removed by washing with n-hexane or decomposed by thermal treatment. Anchoring of palladium (reaction (2)) was carried out in acetone solution followed by washing with acetone and methanol. The formed Surface Complex (SC) was stabilized by thermal treatment in nitrogen at 100-3DDQC for 3 hours. Further details on catalyst preparation will be given in the Results and Discussion. ... 

Reversible phosphine binding to palladium Reaction rates 6... 

Palladium catalyzes the carbonylation of allylic, vinylic, benzylic, and aromatic halides in alcohols to form esters under conditions similar to those required by the nickel carbonyl catalyst (11). The palladium-catalyzed reaction offers the advantage of not requiring the use of highly toxic and volatile nickel carbonyl, and perhaps higher catalyst activity, although accurate comparisons have not been made. Like the nickel reaction, the palladium reaction... 

Aldehyde C-H bonds can also undergo cyclometalation with palladium salts. Reaction of 8-quinolinecarbaldehyde with PdCLt gives a chloride-bridged dimer with a palladium-acyl bond (equation 75). No intermediates could be isolated in case of the palladium reaction, but when [(PEt3)PtCl2]2 is reacted with 8-quinolinecarbaldehyde, a platinum complex is isolated with an intact aldehyde C-H bond. The nitrogen atom of the quinoline is coordinated to the platinum, and the aldehyde C-H bond occupies an axial site in the complex. Heating this material results in insertion into the aldehyde C-H bond and formation of a chelated platinmn acyl. 

Trost has discovered that Pd(OAc)2 and other Pd" compounds catalyze the cyclization of terminal 1,6-enynes to give ene-type adducts. Treatment of (117) with 5 mol % Pd(OAc)2 at 60-66 C gives metal-locyclopentene (118), which reacts further to give a 6 94 mixture of (119) and (120) in 80% yield. Flash vacuum pyrolysis of (117) at 625 C gives a 1(X) 0 mixture of (119) and (120) in 83% yield. The palladium reaction not only occurs under much milder conditions but gives different isomer ratios. In many other cases the palladium-catalyzed cyclization gives products which are not available from a thermal ene reaction. 

Formation of 1,1-diacetates—e,g., ethylidene diacetate from ethylene or hexylidene diacetate from hexene—by simple acetate displacement of palladium (Reaction 16) is a much more satisfactory reaction scheme than any previously proposed. On the other hand, accounting for 1,2-diol type products is diflBcult by this scheme, necessitating a reverse hydrogen transfer to form a two-carbon insertion product intermediate. This type... 

Addition of a variety of nucleophiles to rf-alkene and alkyne ligands has been investigated, particularly when these ligands are complexed with iron and palladium. Reactions shown in equation 8.39 demonstrate well the typical stereochemistry resulting from the trans mode of attack by external nucleophiles on t 2—7t systems.56 Careful analysis of the reaction of amines with ( )- and (Z)-2-butenyl iron complexes (the CpFe(CO)2 group is abbreviated Fp, which is pronounced fip ) showed the stereochemistry to be cleanly anti.51... 

Chlorotrifluoroethylene monomer serves as a building block for the CTFE telomer oils as well as the solid higher polymer and various copolymers. CFC-113 also may be used in the production of trifluoroethylene monomer by vapor-phase reduction using hydrogen and a precious metal catalyst, usually palladium [reaction (9)]. Copolymers of trifluoroethylene and vinylidene fluoride show interesting piezoelectric properties. 

As alluded to above, this version of the Jt-allyl palladium reaction uses an allylic acetate or chloride. The use of the acetate is more common because acetate is a much weaker nucleophile than chloride. When it involves a substrate where diastereomeric products can result, the stereochemistry of the nucleophilic displacement is an important issue. Palladium assisted alkylation proceeds with net retention of configuration of the acetate or chloride, as seen in the conversion of 375 to 376.223e,f... 

Since the Jt-allyl species is bound to palladium, there is a template effect in the Jt-allyl palladium reactions that can be exploited to form large rings (sec. 6.6.B).228 Ester 388 was converted to 389 in 70% yield by this procedure, but the yields have been poor in some cases.228... 

The disconnections for catalytic allyl palladium reactions are essentially the same as for the uncatalyzed version. A few representative examples are... 

Although no nucleophile was added in the palladium reaction, a small amount of free radical decomposition would give enough triethylphosphine to initiate the displacement. The trace of methane may be a measure of the extent of simple radical decomposition. 

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