Solvation and stabilization of palladium nanoparticles in phosphonium-based ionic liquids: a combined infrared spectroscopic and density functional theory study

Abstract

Analysis of infrared spectra of palladium nanoparticles (NPs) immersed in the tri-tert-butyl-R-phosphonium-based ionic liquids (ILs) demonstrates that both cations and anions of the ILs interact with the NPs. According to quantum-chemical simulations of these interactions, the binding energy of anions to the Pd6 cluster, taken as a minimal-size model of the NPs, increases from ∼6 to ∼27 kcal mol(-1) in the order [PF6](-)≈ [BF4](-) < [Tf2N](-) < [OTf](-) < [Br](-)≪ [TFA](-). In contrast, the binding energy for all types of the [Bu(t)3PR](+) cations slightly varies at about ∼22 kcal mol(-1) only moderately depending on the choice of the R moiety (n-pentyl, 2-hydroxyethyl, 2-methoxyethyl, 2-ethoxy-2-oxoethyl). As a result, the energies of interaction between a Pd6 cluster and various ion pairs, formed by the abovementioned counter-ions, follow the order found for the anions and vary from ∼24 to ∼47 kcal mol(-1). These values are smaller than the energy of addition of a Pd atom to a Pdn cluster (∼58 kcal mol(-1)), which suggests kinetic stabilization of the NPs in phosphonium-based ILs rather than thermodynamic stabilization. The results are qualitatively similar to the trends found earlier for interactions between palladium clusters and components of imidazolium-based ILs, in spite of much larger contributions of the London dispersion forces to the binding of the [Bu(t)3PR](+) cations to the cluster (up to 80%) relative to the case of 1-R-3-methylimidazolium cations (up to 40%).

Solvation of Palladium Clusters in an Ionic Liquid: A QM/MM Molecular Dynamics Study

“…These values are ca. 10 kcal·mol –1 larger than those found in previous gas-phase calculations because of the influence of the IL environment.…”

“…On the basis of computational studies published elsewhere, ,,, the palladium atom and palladium clusters Pd n with n = 6 and 19 were chosen as simple and computationally tractable models of Pd species in the IL. The most stable octahedral Pd 6 and Pd 19 structures were used.…”

Phosphonium salts and P-ylides

“…Zvereva and co-workers reported a study based on infrared spectroscopy and density functional theory to investigate the solvation and stabilization of palladium NPs in phosphonium-based ionic liquids. 237 Stucky and co-workers described a general approach for the synthesis of micro-/nano-structured metal chalcogenide semiconductors from elemental precursors. 238 The excellent solubility of sulfur, selenium, and tellurium in [P 4444 ]Cl promoted fast reactions between chalcogens and various metal powders upon microwave heating, giving crystalline products.…”

Computationally deciphering palladium‐catalyzed reaction mechanisms

“…Besides the computational investigation of Pd dimers also multinuclear Pd complexes such as smaller Pd clusters and even bigger Pd nanoparticles (NPs) have been explored. In this context, a combined computational and experimental study on the interaction of Pd 6 clusters as well as Pd NPs with phosphonium‐based ionic liquids (ILs) was reported by Zvereva and co‐workers . The binding energies of interactions between various phosphonium cations and their counterions with Pd 6 clusters and Pd NPs were calculated at the COSMO (EtOH) PBE0‐D3(BJ)/def2‐TZVP//COSMO (EtOH) TPSS/def2‐TZVP level of theory and were compared to experimental values obtained from IR spectroscopic measurements.…”