Can Palladium Acetate Lose Its “Saltiness”? Catalytic Activities of the Impurities in Palladium Acetate

Abstract

Commercially available palladium acetate often contains two major impurities, whose presence can impact the overall catalytic efficacy. This systematic study provides a comparison of the differences in catalytic activity of pure palladium acetate, Pd3(OAc)6, with the two impurities: Pd3(OAc)5(NO2) and polymeric [Pd(OAc)2]n in a variety of cross-coupling reactions. The solid state (13)C NMR spectra of all three compounds in conjunction with DFT calculations confirm their reported geometries.

Understanding Palladium Acetate from a User Perspective

“…The trimeric structure of 1 in benzene or glacial acetic acid at room temperature, determined by osmometry, was first reported by Wilkinson and co‐workers . We also recently verified the trimeric structure in the solid state through 13 C NMR solid‐state spectroscopy in conjunction with DFT calculations (Figure ) . This is important as some suppliers incorrectly claim that palladium acetate is monomeric in nature.…”

“…Cotton found that by using anhydrous solvent a single peak for 1 can be obtained by 1 H NMR spectroscopy . While we have found that sodium‐dried C 6 D 6 stored in a N 2 ‐filled glovebox works best to obtain a single peak for a pure sample of 1 ( δ =1.63 ppm in C 6 D 6 ), the use of CDCl 3 (stored over K 2 CO 3 ) is more practical in determining the amount of 2 present because of the higher resolution gained between 1 and 2 (Figure ) in the proton spectrum. Thus, using dried CDCl 3 and an internal standard (1,4‐dimethoxybenzene), we developed a simple method to quantitatively measure the concentration of 2 present in a commercial sample (Figure )…”

“…Inspired by Wilkinson's comment on the carboxylate exchange (transesterification) on Pd, we recently reported a method which, thus far, has produced very pure palladium acetate (>99.8 %) without trace formation of 2 or 3 by conversion of palladium(II) pivalate to 1 through ligand exchange [Eq. (2)] . This method avoids the use of water which may lead to reduced yield by forming the hydrolysis product 4 .…”

“…In addition to solution‐phase 1 H NMR spectroscopy, we recently reported solid‐state 13 C NMR data for 1 – 3 (Figure ) . As there are limited methods available to analyze insoluble 3 , this provided an additional technique to characterize the complex, in comparison to 1 and 2 .…”

“…Each spectrum is shown with fitted peaks (blue) and the sum of fitted peaks (red). Schematic spectra (green) show the positions of the calculated chemical shifts …”