Sterically Hindered Phosphonium Salts: Structure, Properties and Palladium Nanoparticle Stabilization

Abstract

A new family of sterically hindered alkyl(tri-tert-butyl) phosphonium salts (n-CnH2n+1 with n = 2, 4, 6, 8, 10, 12, 14, 16, 18, 20) was synthesized and evaluated as stabilizers for the formation of palladium nanoparticles (PdNPs), and the prepared PdNPs, stabilized by a series of phosphonium salts, were applied as catalysts of the Suzuki cross-coupling reaction. All investigated phosphonium salts were found to be excellent stabilizers of metal nanoparticles of small catalytically active size with a narrow size distribution. In addition, palladium nanoparticles exhibited exceptional stability: the presence of phosphonium salts prevented agglomeration and precipitation during the catalytic reaction.

Tri-tert-butyl(n-alkyl)phosphonium Ionic Liquids: Structure, Properties and Application as Hybrid Catalyst Nanomaterials

“…Enlargement of the alkyl chain likely leads to increase in a number of crystallographically independent ion pairs (Z') and disorder augmentation. The crystal packing of sterically hindered PILs with significantly different length of alkyl substituent was reported earlier [54]. metric unit of 2b contains one [t-Bu3PPr] + cation and one disordered [BF4] − anion (Z' = 1 (Figure 5).…”

“…The next slight increase in the melting point of long-chained PILs is caused by hydrophobic intermolecular interactions. The corresponding dependence of Tm on the elongation of alkyl substituents in the series of homologous compounds was reported earlier [54,63]. The first two members of the PIL series have high melting points above 200 • C and melt with decomposition that is caused by the pronounced ionic nature of the compounds.…”

“…This effect is similar to the catalysis by Pd complexes with sterically demanded phosphines, although the mechanism of the processes is definitely different [52,53]. Previously, we have synthesized and investigated sterically hindered PILs with even numbers of carbon atoms in side chain [54]. Here, we systematically extended the series of sterically hindered PILs with compounds containing odd numbers of methylene fragments in alkyl substituents and characterized them.…”

“…The next slight increase in the melting point of long-chained PILs is caused by hydrophobic intermolecular interactions. The corresponding dependence of Tm on the elongation of alkyl substituents in the series of homologous compounds was reported ear lier [54,63].…”

“…For the current study, PdNPs were obtained by the reduction of palladium acetate in ethanol in the presence of the corresponding PIL (Supplementary Materials, Table S10). According to previous investigation, ethanol is the solvent of choice for efficient synthesis of hybrid NP systems [54]. The PdNP synthesis procedure does not require any reducing agent, elevated temperature or inert atmosphere.…”