Non-trivial behavior of palladium(ii) acetate

Abstract

Reaction of activated palladium metal with a HNO₃/acetic acid mixture produces both orange Pd₃(OAc)₆, 1, and purple Pd₃(OAc)₅(NO₂), 2. Compound 2 has a trinuclear structure derived from that of the well-known triangular complex 1 in which one acetate group has been replaced by a nitrite group which is bonded to one palladium atom by the nitrogen atom and to another Pd atom using one of the oxygen atoms. Highly pure 1 can be made by continuous removal of the nitric oxides from the reaction mixture using a flow of N₂. ¹H NMR spectra of solutions of 1 in CDCl₃ and C₆D₆ show several signals of various intensities when a small amount of water is present in the deuterated solvents but only one signal when the solvents are thoroughly dried. These results are consistent with the occurrence of one or more hydrolysis processes when the solvents contain water and suggest that hypotheses about various [Pd(OAc)₂]_n aggregates that have previously been brought forward in the literature to explain the complexity of the spectrum of 1 are unnecessary, especially for nonpolar solvents. Compound 2 does not hydrolyze, and in wet or dried solvents shows a ¹H NMR spectrum that consists of five equal-intensity signals due to the five nonequivalent acetate groups.