Gold Functionalized Platinum M12L24-Nanospheres and Their Application in Cyclization Reactions

Nanospheres can be formed by combining 24 bispyridinyl building blocks with a palladium or platinum precursor. These spheres can be functionalized on the inside with a gold(I) chloride complex leading to a high local concentration of gold(I) complexes. The high local concentration makes the neutral gold species an active catalyst. Furthermore, the platinum-gold spheres can be post modified with a silver(I) salt to form cationic gold(I) catalysts. The platinum assemblies are demonstrated to be stable in the presence of various substrates and as a result several cyclization reactions have been carried out using these new spheres as catalysts.
Higher conversions in a [4+2] cycloaddition are observed for the sphere catalyst compared to the mono-nuclear analogues. Also the cyclization of 1,6-enynes can be facilitated by the confined gold catalyst and high activity is observed in the activation of allenes. For the lactonization of alkynoic acids, different selectivity is observed compared to a standard gold(I) complex, demonstrating that the high local concentration due to a confined space can induce other selectivity in catalysis.

Keywords: supramolecular catalysis; gold catalysis; local concentration; nanospheres; cyclization reactions