Formation of self-assembled multi-layer stable palladium nanoparticles for ligand-free coupling reactions

Abstract

The structure of a recently developed Pd catalyst, named sulfur-modified gold-supported palladium (SAPd), has been determined to be composed of multi-layered Pd nanoparticles. SAPd is easily prepared by selfassembly on a sulfur-modified gold surface, and near-edge X-ray absorption fine structure (NEXAFS) analysis at the Pd K-edge determined that the Pd in SAPd is zero-valence analogous to metallic Pd.However, transmission electron microscopy (TEM) analyses and extended X-ray absorption fine structure (EXAFS) analysis clarified that SAPd has approximately 10 layers and consists of nanoparticles with a diameter less than 5 nm. High-density Pd nanoparticles were embedded without condensation. NEXAFS analysis at the S and C K-edge revealed that the organic matter containing sulfate and xylene as a major ingredient is distributed between Pd nanoparticles, and it seems to prevent condensation. These findings suggest that a highly efficient cross-coupling reaction, which was reported in earlier works, has been achieved by the high-density Pd nanoparticles.

Self‐Assembled Multilayer‐Stabilized Nickel Nanoparticle Catalyst for Ligand‐Free Cross‐Coupling Reactions: in situ Metal Nanoparticle and Nanospace Simultaneous Organization

“…A comparison of the XANES spectrum of SANi with those of standard materials suggests that the sulfur in SANi is strongly oxidized and is present as SO 4 2À . [5] The chemical shift of the sulfur in SANi is similar to that previously reported for SAPd. These results strongly indicate that SANi consists of a matrix containing SO 4 2À and is similar to SAPd, which consists of Pd NPs implanted in a matrix formed by complexation of SO 4 2À and pxylene.…”

“…[4] The preparative method for SAPd, in situ metal NP and nanospace simultaneous organization (PSSO), is illustrated in Figure 2; it involves four simultaneous procedures: i) reduction of a high-valence metal source, ii) growth of transition metal NPs of appropriate size, iii) growth of a matrix with appropriate pores, and iv) encapsulation of the metal NPs by matrix nanopores. [5] This method is totally different from conventional NP-immobilizing methods using solid supports with preformed pores or coordination sites. Based on these results, we decided that the in situ PSSO method could be used to immobilize various transition metal NPs, including those of base metals.…”

Development of a Sulfur-Modified Glass-Supported Pd Nanoparticle Catalyst for Suzuki–Miyaura Coupling

“…Organic materials containing sulfate and xylene as the major ingredients are distributed between the Pd nanoparticles, allowing for the formation of stable high-density PdNPs without condensation. [17][18][19][20][21][22][23][24][25][26][27] The results of the XANES analysis suggest that the oxidized sulfur preserves the structure of the PdNPs in SGlPd as well as SAPd.…”

“…As reported in our previous research, [17][18][19][20][21][22][23][24][25][26][27] SAPd absorbs very few organic compounds and can therefore be used in combinatorial synthesis because of its small surface area. It was envisaged that SGlPd would perform in a similar manner to SAPd.…”

“…[17][18][19][20][21][22][23][24][25][26][27] In 2015, we successfully analyzed the structure of our SAPd catalyst by X-ray absorption fine structure (XAFS) and transmission electron microscopy (TEM) analyses and found that the Au particles in this material simply acted as a solid support for the SAPd membrane. 27) SAPd is now commercially available as a safe, facile, recyclable and low-leaching PdNP catalyst. However, one of the big disadvantages of using SAPd as a catalyst is that it contains Au as a key ingredient, making it particularly expensive.…”