WILLIAM CAROLE, THOMAS COLACOT
Johnson Matthey Fine Chemicals,
Paulsboro, USA

Abstract

Palladium acetate is commonly used to catalyse organic transformations such as C–H activation, cross-coupling and pre-catalyst manufacture. It is widely used for manufacturing pharmaceuticals and agrochemicals, but its synthesis typically results in two common impurities that could contaminate commercial samples. This study provided a systematic investigation of high purity palladium acetate (1) with its two impurities, palladium acetate nitrite (2) and polymeric palladium acetate (3). It was discovered that (3) can be equally active as (1) or (2) under certain conditions in various organic transformations, but may be inferior at reduced temperatures and in the absence of a phosphine ligand. In pre-catalyst manufacture, pure (1) gave optimal yield and purity, and this may be the best choice for reliable results.

Palladium acetate (Pd₃(OAc)₆) (1) is the most widely-used palladium-based precursor employed in a variety of transformations such as cross coupling (1) and C-H activations. Consequently it is being consumed on multi-tonne quantities for many commercial processes. Typically prepared via modifications to Wilkinson’s (2) original method, commercial samples of palladium acetate may contain varying amounts of two common byproducts: trispalladium pentacetate mononitrite (Pd₃(OAc)₅(NO₂)) (2), and polymeric palladium acetate (Pd(OAc)₂)_n, (3) (Figure 1).

In 2005, Cotton et al. reported a seminal paper on the non-trivial behaviour of palladium acetate, in which byproduct 2 was isolated and characterised for the first time (3). Subsequent studies by Stolyarov et al. demonstrated that commercially available material may contain up to 20 mol % of byproduct 2 (4), which results from an incomplete reaction. Prior to our investigation, polymeric palladium acetate 3 was believed to be catalyt ...