Palladium acetate chemistry

The chemistry of vinyl acetate synthesis from the gas-phase oxidative coupling of acetic acid with ethylene has been shown to be facilitated by many co-catalysts. Since the inception of the ethylene-based homogeneous liquid-phase process by Moiseev et al. (1960), the active c ytic species in both the liquid and gas-phase process has always been seen to be some form of palladium acetate [Nakamura et al, 1971 Augustine and Blitz, 1993]. Many co-catalysts which help to enhance the productivity or selectivity of the catalyst have appeared in the literature over the years. The most notable promoters being gold (Au) [Sennewald et al., 1971 Bissot, 1977], cadmium acetate (Cd(OAc)j) [Hoechst, 1967], and potassium acetate (KOAc) [Sennewald et al., 1971 Bissot, 1977]. 

In most cases, the oxidative addition process consumes stoichiometric amount of Pd(OAc>2. One of the earliest examples of the use of palladium in pyrrole chemistry was the Pd(0Ac)2 induced oxidative coupling of A-methylpyrrole with styrene to afford a mixture of olefins 18 and 19 in low yield based on palladium acetate [28]. 

Although complexes with these ligands are common in palladium(II) chemistry, their occurrence is more scarce in platinum(II) compounds. Nevertheless these complexes can be prepared, examples being platinum(II) complexes of the optically active quadridentate Schiff base of salicylaldehyde and (R)-l, 2-diamines.1212 An alternative synthesis involves formation of the Schiff base by reaction of a complexed amino ligand on platinum(II) with amide acetates (equation 372).1213... 

In contrast, the closely related palladium acetate-promoted intramolecular alkylation of alkenes by tri-methylsilyl enol ethers (Scheme 4)6,7 has been used to synthesize a large number of bridged carbocyclic systems (Table 1). In principle, this process should be capable of being made catalytic in palladium(II), since silyl enol ethers are stable to a range of oxidants used to carry the Pd° -> Pd11 redox chemistry required for catalysis. In practice, catalytically efficient conditions have not yet been developed, and the reaction is usually carried out using a full equivalent of palladium(II) acetate. This chemistry has been used in the synthesis of quadrone (equation 2).8 With the more electrophilic palladium(II) trifluoroace-tate, methyl enol ethers underwent this cyclization process (equation 3).9... 

Heck reaction of 5-iodo-2,4-dimethoxypyrimidine and the furanose 3-deoxyglycal 147 with catalytic quantities of palladium acetate gives a mixture of the 2,3- and 3,4-enes 148 and 149 (Scheme 15). With triphenylarsine also present the latter product is favored, whereas with triphenylphosphine the 2-ene is produced without its isomer.164 Further examples of this type of chemistry have been reviewed by Daves.118... 

The more electrophilic reagent Pd(OAc)2 is another usefril reagent in organopalladium chemistry. It is monomeric in benzene at 80 °C, but is trimeric at room temperature in benzene. For even greater reactivity, Pd(02CCF3)2 can be used. Both the acetate and trifluoroacetate are soluble in organic solvents. Reaction of palladium acetate with acetylacetone produces Pd(acac)2. This acetylacetonate and especially the hexafluoroacetylacetonate, Pd(hfac)2, are useful as volatile sources of palladium in metalorganic chemical vapor deposition. 

Next, the process chemistry for a large-scale synthesis of (+)-6a (MGS0008) is presented (see Scheme 3.2) [41], The reaction of racemic (+)-16 with TMSC1 and LHMDS, followed by dehydrosilylation with palladium acetate afforded enone ( )-2 (90% yield), which was stereoselectively epoxidized using tert-butyl hydroperoxide (TBHP) in the... 

Subsequent examples, reported by Czernecki, et al.,2 elaborate upon this chemistry. As shown in Scheme 4.1.2, various acetate protected glycals were reacted with benzene and 1,3-dimethoxybenzene. In all cases, palladium acetate was used as the catalyst. However, varying equivalents were used. Consequently, the variances observed in the composition of the product mixture reflected the specific conditions used to induce reaction and the highest observed yields were approximately 50%. 

In similar Heck-type reactions, commercially available palladium acetate is used as a catalyst, providing a new route for synthesizing indoles, benzofurans, 1,2-dihydroisoquinolines and other interesting derivatives, quite gratifyingly with regioselectivities often matching those reported in our chemistry. ... 

In this experiment, we will conduct some modern organic chemistry using a palladium catalyst. It is a rare opportunity for students in undergraduate laboratories to experience this powerful chemistry. We will react the lodosubstituted aromatic compounds, shown below, with 1-pentyne, 1-hexyne, or 1-heptyne in the presence of the catalysts, palladium acetate and cuprous iodide, to yield 4-substituted-l-pentynyl, 4-substituted-l-hexynyl, or 4-substituted-l-heptynylaromatic compounds. This reaction is called the Sonogashira coupling reaction. The reaction will be carried out in refluxing 95% ethanol as the solvent. In addition, piperazine will be employed both as a base and as a hydride donor. 

Another metallization chemistry [9-11] involves the formation of a covalent bond between palladium and platinum ions and the amine groups of DNA bases. A solution of palladium acetate is mixed with a solution of DNA and the palladium ions become associated with DNA by forming covalent bonds with the amine groups of the DNA bases. Subsequent reduction of the palladium ions allows them to form autocatalytic sites for the deposition of a palladium metal coating on the surface of the DNA. Reduction of the palladium bonded to the DNA results in very small metal deposits of palladium. However, there may not be enough metal to form a continuous conducting wire after a single treatment with the palladium... 

---