Immobilized Palladium Nanoparticles on Zirconium Carboxy-Aminophosphonates Nanosheets as an Efficient Recoverable Heterogeneous Catalyst for Suzuki–Miyaura and Heck Coupling

Abstract

Zirconium phosphate glycine diphosphonate nanosheets (ZPGly) have been used as support for the preparation of solid palladium nanoparticles, namely Pd@ZPGly. Thanks to the presence of carboxy-aminophosponate groups on the layer surface, ZPGly-based materials were able to stabilize a high amount of palladium (up to 22 wt %) also minimizing the amount of metal leached in the final products of representative important cross-coupling processes selected for proving the catalysts' efficiency. The catalytic systems have been fully characterized and used in low amounts (0.1 mol %) in the Suzuki-Miyaura and Heck cross-couplings. Moreover, the protocols were optimized for the use of recoverable azeotropic mixtures (aq. EtOH 96% or aq. CH 3 CN 84%, respectively) and in the flow procedure allowing one to isolate the final pure products, without any purification step, with very low residual palladium content and with a very low waste production.

Morpholine-Modified Pd/γ-Al2O3@ASMA Pellet Catalyst with Excellent Catalytic Selectivity in the Hydrogenation of p-Chloronitrobenzene to p-Chloroaniline

“…Compared with the γ-Al2O3 pellets encapsulated with ASMA, intensities of the diffraction peaks of the samples after loading with palladium decrease obviously, which might be caused by the changes in the charge distribution and electrostatic field because of the existence of palladium nanoparticles and interaction with the surface of support [26]. The characteristic peaks at 40.2° and 46.8° can be attributed to the (111) and (200) planes of Pd, respectively [27]. However, the supports treated with ASMA encapsulation and morpholine modification did not show significant changes of crystality.…”

New Directions in Metal Phosphonate and Phosphinate Chemistry

“…Importantly, the minimal leaching of Pd and no significant nanoparticle sintering were observed, suggesting the effectiveness of the support in binding the catalytically active species. The same catalyst was later successfully employed also for the hydrogenation in batch conditions of alkynes and nitroarenes [109] and for the Heck reaction [110], proving its wide applicability. dispersion led to the coordination of the metal to the non-coordinating carboxylic and phosphonic acid groups and enabled the deposition of palladium nanoparticles with size <2 nm onto the nanosheets with variable loadings, with the highest being reported at 19 wt.…”

“…Importantly, the minimal leaching of Pd and no significant nanoparticle sintering were observed, suggesting the effectiveness of the support in binding the catalytically active species. The same catalyst was later successfully employed also for the hydrogenation in batch conditions of alkynes and nitroarenes [109] and for the Heck reaction [110], proving its wide applicability. More recently, a new strategy was adopted to obtain a zirconium phosphate-phosphonate decorated with very small gold nanoparticles on its surface [111].…”

Readily Available Immobilized Pd Catalysts for Suzuki‐Miyaura Coupling under Continuous‐flow Conditions

“…They obtained a wide substrate scope and high conversion under mild reaction conditions within only a short residence time (20 s) . As mentioned above, several immobilized Pd catalysts have been investigated for application to flow reactions . However, the type of catalyst that is most suitable for continuous‐flow cross‐coupling reactions remains unclear because it is difficult to directly compare catalytic performance owing to differences in substrates and reaction conditions .…”

“…[21] As mentioned above, several immobilized Pd catalysts have been investigated for application to flow reactions. [22][23][24][25][26][27][28] However, the type of catalyst that is most suitable for continuous-flow crosscoupling reactions remains unclear because it is difficult to directly compare catalytic performance owing to differences in substrates and reaction conditions. [8] Therefore, we propose herein a consistent method for evaluating the catalytic performance of immobilized catalysts.…”