Development of Metal Nanoparticle Catalysis toward Drug Discovery

Transition-metal nanoparticles (NPs) catalysts supported on solid material represent one of the most important subjects in organic synthesis due to their reliable carbon-carbon or carbon-heteroatom bond-forming cross-coupling reactions. Therefore methodologically and conceptually novel immobilization methods for nonprecious transition-metal NPs are currently required for the development of organic, inorganic, green, materials, and medicinal chemistry. We discovered a self-assembled Au-supported Pd NPs catalyst (SAPd(0)) and applied it as a catalyst to Suzuki-Miyaura coupling, Buchwald-Hartwig reaction, Carbon(sp² and sp³)-Hydrogen bond functionalization, double carbonylation, removal of the allyl protecting groups of allyl esters, and redox switching. SAPd(0) comprises approximately 10 layers of self-assembled Pd(0) NPs, whose size is less than 5 nm on the surface of a sulfur-modified Au. The Pd NPs are wrapped in a sulfated p-xylene polymer matrix. We thought that the self-assembled Au-supported Pd NPs could be made by in situ metal NP and nanospace simultaneous organization (PSSO). This methodology involves 4 kinds of simultaneous procedures: i) reduction of a higher valence metal salt, ii) growth of metal NPs with appropriate size, iii) growth of a matrix with appropriate pores, and iv) wrapping of the metal NPs by matrix nanopores. This methodology is different from previously reported metal NPs-immobilizing methods, which use solid supports with preformed pores or coordination sites. We also applied the in situ PSSO method to prepare various immobilized transition-metal NPs, including base metals. For example, the in situ PSSO method can be applicable to easily prepare Ni, Ru, and Fe NPs with good recyclability and low metal leaching for use in organic synthesis.

High-density monolayers of metal complexes: preparation and catalysis

Catalysts are one of the key materials for realizing a sustainable society. However, we may encounter problematic cases where conventional catalyst systems cannot provide effective solutions. We thus believe that the establishment of novel methods of catalyst preparation is currently necessary. Utilization of high-density monolayers of molecular metal complexes is our strategy, and we expect that this methodology will enable facile and systematic screening of unique and efficient catalysts. This Personal Account describes our challenges to establish such an immature method in catalyst preparation as well as the related background and perspective. Preparation and catalysis by high-density monolayers of Rh complexes with N-heterocyclic carbene, structurally compact phosphine and diisocyanide ligands on gold surfaces are presented. The catalytic application of a high-density Pd-bisoxazoline complex prepared on a single-crystal silicon surface is also shown. Uniquely high catalyst turnover numbers and high chemoselectivities were observed with these catalyst systems.