Invited
Inducing cooperative catalysis on solid surfaces for the promotion of C-C coupling

Aldol reactions are important for C-C bond formation in chemical synthesis and have received significant attention in the upgrading of biomass-derived feedstocks. Industrially such reactions are catalyzed by simple alkaline bases such as NaOH and KOH. The choice of these catalyst although cheap comes with substantial negative environmental repercussions, high energy consumption, and waste treatment. In nature such reactions are catalyzed via a cooperative mechanism by enzymes at significantly milder reaction condition and with high selectivity, which avoids these limitations. However, the use of enzymes for such processes is industrially not cost competitive. Hence, the challenge is to incorporate key catalytic features inherent to enzymatic systems into heterogeneous catalysts, which can cooperatively promote these reactions. In the current talk I will highlight the main limitations of inducing cooperative catalytic interaction on heterogeneous surfaces. I will then describe our approaches for material design and synthetic methodology for tuning the active site properties and the effect of the immediate chemical environment surrounding the active site. The first system is based on grafted Sn and Ti sites on a chitosan backbone. In this system the structural degrees of freedom of the polymeric backbone is shown to have a dramatic effect on the ability to promote cooperative interactions in the Henry reaction. In the second system, based on a metal organic framework based on a di-copper Robson ligand, the structural flexibility is constrained. Using this material configuration, changes in the active site properties and its immediate chemical environment are shown to controllably affect the ability to promote cooperative catalysis. It will be shown that tuning the level of structural flexibility is critical for maintaining efficient cooperative interactions. Finally, I will discuss our approach for tuning reaction selectivity by controlling the 3D structure of a rigid backbone system such as functionalized layered double hydroxides.