Palladium pivalate

Daniela Sustac Roman University de Montreal, Montrial, Quibec, Canada 

Alternative Name trimethylacetic acid, palladium salt palladium 2,2-dimethylpropanoate palladium 2,2-dimethylpropionate 2,2-dimethylpropanoic acid palladium salt. 

Solubility sol in ethyl acetate, methanol, chloroform, tetrahydrofuran, 1,4-dioxane. Insol in water. 

Handling, Storage, and Precautions Toxicity data for this compound is unknown. The title compound is air and moisture sensitive and should he stored in a dry/inert atmosphere. Proper safety precautions include working in a laboratory fume hood while wearing safety eyewear, appropriate gloves, and a laboratory coat. Compound causes skin and eye irritation. In case of exposure, wash with copious amounts of water and contact a physician immediately. 

Introduction. Palladium pivalate has received much recent attention as an effective catalyst in several C-H coupling processes. The title compound has also been demonstrated to be a precursor to Pd-complexes that undergo hydride reductions as well as NO2 disproportionation. Furthermore, the reagent has been used in the preparation of bimetallic paddlewheel complexes. 

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They were able to extend the scope of the direct arylation to simple, completely unactivated arenes, such as benzenes by development of a palladium-pivalic acid co-catalyst system (Scheme 28) [48]. 

A study of the palladium-catalysed reaction of benzene with iodoarenes has included a synthesis of a phosphine-ligated aryl palladium pivalate complex. However, this species fails to form the biaryl product and it is suggested that a ligandless arylpalladium(II) carboxylate complex is involved in the carbon-hydrogen cleavage step. In the palladium-catalysed reaction of cyanobenzene with iodoarenes in trifluoroacetic acid, biphenyl derivatives are formed by substitution of hydrogen ortho to the cyano group. The first step in the process is likely to involve co-ordination of... 

Coupling Reactions. Palladium pivalate is an effective catalyst for mild and efficient direct arylation reactions. One account described the intramolecular arylation phenolic ethers (eq 1). Initial optimization with Pd(OAc)2 in conjunction with electron-deficient phosphines led to the desired biphenyl in low yield. Upon the addition of carboxylic acid additives, the yield improved markedly with the optimal additive being pivalic acid. Indeed it was determined that the additive was not needed when Pd(OPiv)2 was errqtloyed as a catalyse although improved yields were observed when the title compound was used in conjunction with the acid additive. The role of the pivalate is believed to be that of a proton shuttle in a concerted metallation-deprotonation (CMD) sequence. A further advantage of using Pd(OPiv)2 was the rate enhancement of the arylation with most reactions complete in less than 6 h (vs. 12 or more hours with Pd(OAc)2). The catalyst was applied to a range of electron-rich and -deficient arenes with good to excellent yields. 

Palladium pivalate has been applied in the synthesis of Pd-based mixed-metal lanthanide alloys that may be of interest as catalysts in material science. The resulting Pd metal is bound to the lanthanide by four pivalate bridging ligands. Several of these complexes were prepared and structural properties investigated through crystallography. 

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