A continuing goal in catalysis is the transformation of processes from homogeneous to heterogeneous. To this end, nanoparticles represent a new frontier in heterogeneous catalysis, where this conversion is supplemented by the ability to obtain new or divergent reactivity and selectivity. We report a novel method for applying heterogeneous catalysts to known homogeneous catalytic reactions through the design and synthesis of electrophilic platinum nanoparticles. These nanoparticles are selectively oxidized by the hypervalent iodine species PhICl 2 , and catalyze a range of π-bond activation reactions previously only homogeneously catalyzed. Multiple experimental methods are utilized to unambiguously verify the heterogeneity of the catalytic process. The discovery of treatments for nanoparticles that induce the desired homogeneous catalytic activity should lead to the further development of reactions previously inaccessible in heterogeneous catalysis. Furthermore, our size and capping agent study revealed that Pt PAMAM dendrimer-capped nanoparticles demonstrate superior activity and recyclability compared to larger, polymer-capped analogues.The field of homogeneous catalysis can be characterized as a source of easily tuned, selective catalysts with high activity.Heterogeneous catalysts also offer many advantages, some of which are not displayed by their homogeneous counterparts, including recyclability, ease of separation from the reaction mixture and use in continuous flow processes. It is highly desirable to develop new systems that blend the many advantages of heterogeneous catalysis with the versatility of homogeneous catalysts. [1][2][3] Most efforts approach from the homogeneous side and are comprised of immobilized homogeneous catalyst species that promote reactions already accessible by homogeneous solution-state conditions. 1, 4 We sought to utilize an alternative method wherein heterogeneous catalysts are extended to reactions previously only catalyzed by homogeneous species. Metal nanoparticles (NPs) that serve as heterogeneous catalysts in which the metal particle size and oxidation state can be characterized are well-suited for our study. In addition, it is known that the reactivity and selectivity of monodisperse metal NPs can be altered by changes in their size and shape. [5][6][7][8][9][10][11][12][13][14][15] Although Pd and Au NPs have been demonstrated to catalyze a range of cross-coupling and oxidation/reduction reactions in solution, [16][17][18][19][20][21][22][23][24][25] studies have not yet yielded the control necessary to develop new NP catalysts applicable to a wider variety of reactions.A further challenge involves the specific nature of the catalyst. In particular, the distinction between homogeneous and heterogeneous catalysis is often difficult to determine. This is due to the possibility that metal leaches from a heterogeneous catalyst into solution and acts as the catalytically active species. Thus, it was important for us to consider in our studies the fact that for many of the...

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The design and development of metal-cluster-based heterogeneous catalysts with high activity, selectivity, and stability under solution-phase reaction conditions will enable their applications as recyclable catalysts in large-scale fine chemicals production. To achieve these required catalytic properties, a heterogeneous catalyst must contain specific catalytically active species in high concentration, and the active species must be stabilized on a solid catalyst support under solution-phase reaction conditions. These requirements pose a great challenge for catalysis research to design metal-cluster-based catalysts for solution-phase catalytic processes. Here, we focus on a silica-supported, polymer-encapsulated Pt catalyst for an electrophilic hydroalkoxylation reaction in toluene, which exhibits superior selectivity and stability against leaching under mild reaction conditions. We unveil the key factors leading to the observed superior catalytic performance by combining X-ray absorption spectroscopy (XAS) and reaction kinetic studies. On the basis of the mechanistic understandings obtained in this work, we also provide useful guidelines for designing metal-cluster-based catalyst for a broader range of reactions in the solution phase.

A highly active heterogeneous Pd-nanoparticle catalyst for the intramolecular addition of phenols to alkynes was developed and employed in a continuous flow reaction system. Running the reaction in flow mode revealed reaction kinetics, such as the activation energy and catalyst deactivation, and provides many potential practical advantages.