Synthesis and Simple Immobilization of Palladium(II) Acyclic Diaminocarbene Complexes on Polystyrene Support as Efficient Catalysts for Sonogashira and Suzuki–Miyaura Cross-Coupling

Abstract

Immobilization of palladium­(II) acyclic diaminocarbene (Pd­(II)-ADC) complexes on a resin support surface has been easily performed by metal-mediated addition of amino groups of benzhydrylamine-polystyrene to the coordinated isocyanide ligand of cis-PdCl2(CNR)2 (R = t-Bu, Cy). The investigation of the benzhydrylamine reaction with palladium-coordinated isocyanides in solution has revealed that, depending on the reaction conditions, two carbene-type complexes can be obtained as a result of the addition to the CN triple bond, as well as a third complex which is formed via substitution of the isocyanide ligand by benzhydrylamine. Nucleophilic addition of an amino group to the isocyanide ligand has led to a cis-acyclic diaminocarbene complex or a cationic diaminocarbene complex with trans configuration and an intramolecular hydrogen-bonded chloride anion (the nature of this noncovalent interaction was analyzed by DFT calculations, including AIM analysis). The unsupported and resin-supported palladium catalysts have demonstrated high catalytic activity in both Sonogashira and Suzuki–Miyaura cross-coupling. The supported catalyst can be recovered and repeatedly reused without a significant loss in efficiency. The degree of the palladium binding with polystyrene, the oxidation state, and the palladium leaching level were investigated by XPS and XRF analyses.

Diiodomethane as a halogen bond donor toward metal-bound halides

“…This approach has already been successfully used by our group in studies of different non-covalent interactions (e.g., hydrogen, halogen and chalcogen bonding, metallophilic interactions, stacking) and properties of coordination bonds in various transition metal complexes. 17,22,[55][56][57][58][59][60][61] The contour line diagrams of the Laplacian distribution ∇ 2 ρ(r), bond paths, and selected zeroflux surfaces for intermolecular H⋯Cl HBs and I⋯Cl XBs are shown in Fig. 11.…”

Efficient and green catalytic system incorporating new benzimidazolium salts for the Sonogashira cross‐coupling reaction

“…In this context, PEG has been used as a solvent, phase-transfer catalyst and to enhance the recyclability of catalysts. [43][44][45] Optimization data are shown in Table 1. It was found that the Sonogashira coupling reaction catalysed by 1, 1 mol% of Pd(OAc) 2 , 4 mol% of CuNPc as co-catalyst and base catalyst system gave the highest yield when using PEG as a solvent and Cs 2 CO 3 as a base at 100°C with microwave heating in 10 min (Table 1, entry 19).…”

Solid-Supported Palladium Catalysts in Sonogashira Reactions: Recent Developments

“…It is interesting to note that a related supported catalyst with a shorter spacer has also been prepared showing a lower performance, indicating the importance of achieving accessibility to active catalytic sites. Moreover, the aminocarbene palladium complex with polystyrene support 7 has been used as catalyst in the typical copper-cocatalyzed Sonogashira coupling of aryl iodides and bromides with monosubstituted alkynes (Figure 2) [20]. Recycling experiments were conducted, and it was possible to reuse the catalyst up to eight times, although considerable palladium leaching minimized by the addition of triphenylphosphine was observed.…”

“…Recycling experiments were conducted on a Heck reaction in five runs, observing a sharp decrease in the activity after the fourth. Cellulose (20) (Figure 7) has also been functionalized with ethylenediamine, the resulting material (EDAC) being used to support PdNPs, suitable to heterogeneously catalyze the Sonogashira reaction [45]. Thus, this PdNPs@EDAC can cross-couple aryl iodides and bromides with phenylacetylene in water at 100 °C, the presence of copper(I) iodide as cocatalyst being necessary.…”