Pd₂(dba)₃ as a Precursor of Soluble Metal Complexes and Nanoparticles: Determination of Palladium Active Species for Catalysis and Synthesis

Abstract

Tris(dibenzylideneacetone)dipalladium (Pd 2 (dba) 3 ) is ubiquitously used as a source of soluble Pd species for catalysis and as a precursor in the synthesis of more complex Pd structures. In spite of the massive usage of this convenient Pd complex, its nature in solution has not been revealed in detail and the applications rely on the assumed state and purity of the compound. In the present study we have developed a convenient NMR procedure to reveal the nature of Pd 2 (dba) 3 and to determine the purity of the complex. Surprisingly, it was found that commercially available samples of Pd 2 (dba) 3 may readily contain up to 40% of Pd nanoparticles in a wide range of sizes (10−200 nm). The study has shown that the routinely accepted practice of utilization of Pd 2 (dba) 3 without analysis of the purity (both commercially available and prepared by common procedures) can introduce significant errors in the estimation of catalyst efficiency and lead to incorrect values of TON, TOF, and reported mol % values in the catalytic procedures. The presence of Pd nanoparticles in the catalyst precursor provides an opportunity for heterogeneous catalytic systems of different nature to be directly accessible from Pd 2 (dba) 3 . In the present study we report a modified procedure for the synthesis of Pd 2 (dba) 3 •CHCl 3 with 99% purity.

Plausible role of nanoparticle contamination in the synthesis and properties of organic electronic materials

“…An example of the analysis of nanoparticle content and the synthesis/purification of a palladium catalyst has been reported for Pd 2 dba 3 [18].…”

“…Detailed analysis has revealed noticeable batch-to-batch variations in the quality of commercially available metal compounds. For example, the well-known Pd(0) precursor tris(dibenzylideneacetone)dipalladium(0) (Pd 2 dba 3 ) may contain up to 40% of Pd nanoparticles as contamination [18]. Freshly synthesized Pd 2 dba 3 demonstrated a high purity of 99%, while commercial samples were found to vary in purity in the range of 64-92% [18].…”

“…For example, the well-known Pd(0) precursor tris(dibenzylideneacetone)dipalladium(0) (Pd 2 dba 3 ) may contain up to 40% of Pd nanoparticles as contamination [18]. Freshly synthesized Pd 2 dba 3 demonstrated a high purity of 99%, while commercial samples were found to vary in purity in the range of 64-92% [18]. The presence of nanoparticles was clearly confirmed by a number of experimental techniques, including direct visualization with electron microscopy ( Figure 6).…”

“…The presence of nanoparticles was clearly confirmed by a number of experimental techniques, including direct visualization with electron microscopy ( Figure 6). Of course, such varying composition of the catalysts makes it difficult to carry out stable and reproducible synthetic procedures [18]. Nanoparticle contamination and the effect of residual metal have been discussed for a variety of catalytic transformations and metal salts used [19][20][21][22][23].…”

Multiple Absolute Stereocontrol in Pd-Catalyzed [3+2] Cycloaddition of Oxazolidinones and Trisubstituted Alkenes Using Chiral Ammonium–Phosphine Hybrid Ligands

“…[Pd 2 (dba) 3 ]¢CHCl 3 was purchased from Sigma-Aldrich Co. and purified by following a literature procedure. 43 3 ¢CHCl 3 ] (Pd, 2.5 mol %) and 2d¢I (5 mol %) in 1.0 mL of toluene. b) Isolated yield.…”