Characterization of DMSO Coordination to Palladium(II) in Solution and Insights into the Aerobic Oxidation Catalyst, Pd(DMSO)₂(TFA)₂

Abstract

Recent studies have shown that Pd(DMSO)2(TFA)2 (TFA = trifluoroacetate) is an effective catalyst for a number of different aerobic oxidation reactions. Here, we provide insights into the coordination properties of DMSO to palladium(II) in both the solid state and in solution. A crystal structure of Pd(DMSO)2(TFA)2 confirms that the solid-state structure of this species has one O-bound and one S-bound DMSO ligand, and a crystallographically characterized mono-DMSO complex, trans-Pd(DMSO)(OH2)(TFA)2, exhibits an S-bound DMSO ligand. 1H and 19F NMR spectroscopic studies show that, in EtOAc and THF-d8, Pd(DMSO)2(TFA)2 consists of an equilibrium mixture of Pd(S-DMSO)(O-DMSO)(TFA)2 and Pd(S-DMSO)2(TFA)2. The O-bound DMSO is determined to be more labile than the S-bound DMSO ligand, and both DMSO ligands are more labile in THF relative to EtOAc as the solvent. DMSO coordination to PdII is substantially less favorable when the TFA ligands are replaced with acetate. An analogous carboxylate ligand effect is observed in the coordination of PdII to the bidentate sulfoxide ligand, 1,2-bis(phenylsulfinyl)ethane. DMSO coordination to Pd(TFA)2 is shown to be incomplete in AcOH-d4 and toluene-d8, resulting in PdII/DMSO adducts with < 2:1 DMSO:PdII stoichiometry. Collectively, these results provide useful insights into the coordination properties of DMSO to PdII under catalytically relevant conditions.

Non-directed allylic C–H acetoxylation in the presence of Lewis basic heterocycles

“…The predominance of unbound Pd(OAc) 2 in the presence of PhS(O)C 2 H 4 S(O)Ph has also been observed experimentally. 56,57 In contrast, the Pd(OAc) 2 /4,5-diazafluorenone complex is exergonic by 4.2 kcal/mol with respect to unbound Pd(OAc) 2 , indicating that the latter is not the resting state in this catalytic system (see the Supplementary Information for details). We also considered the involvement of a Lewis base-coordinated Pd-π-allyl species in these studies of theoretical binding affinities (see the Supplementary Information for further details).…”

A new Pd(II) complex of a sulfur ylide; Synthesis, X-ray characterization, theoretical study and catalytic activity toward the Suzuki–Miyaura reaction

“…Crystallization of DMSO solutions of complexes 3a and 3b led to formation of a yellow single crystal of complex 4 and, as mentioned above, such a ligand replacement reaction was expected. Also, the presence of non-bulky sulfur ylide ligands and the soft metal Pd(II) ion in complexes 3a and 3b led to the preferential S-bonding coordination mode of the DMSO ligand [54]. Although attempts to achieve suitable single crystals of complexes 3a and 3b were unsuccessful, we obtained a single crystal of the new DMSO coordinated complex 4.…”

Phosphine-free atmospheric carbonylation of aryl iodides with aniline derivatives in the presence of a reusable silica-supported palladium catalyst

“…In contrast, in DMSO a noticeable carbonylation took place in the absence of the heterogeneous catalyst and, at a lower rate, even in the presence of mercury (Table 4, entries 3,4). As DMSO is a good ligand for M a n u s c r i p t palladium [24], it can be assumed that in this case soluble palladium complexes are among the active catalytic species. This can explain the higher amount of leached palladium in reactions carried out in DMSO (Table 3, entries 10-12).…”