(101e) Unravelling the Nature of the Active Sites in Bimetallic MOFs and Their Role in C-C Activation for Room Temperature Propylene Hydrogenation

Olefins, a big component of natural gas, can be found in abundance and require selective conversion. The selective cleavage of C-C bonds remains an important goal for the preferential formation of necessary commodity materials essential to meet global demands. The activation of olefins homolytically or heterolytically depends on the feasibility of bond dissociation by assisted pi interactions through the utilization of transition metals. A CuBTC (copper-based benzene tricarboxylic acid-based metal organic framework (MOF)) is prepared with the addition of an active Rh component, resulting in a bimetallic configuration of Rh-Cu. Unlike catalysts that contain purely Rh-Rh bonds, we showed for the first time that Rh-Cu is catalytic active for propylene hydrogenation at low temperatures. CuRhBTC represents one of the first bimetallic metal organic framework (MOF) materials which demonstrates remarkable catalytic chemistry for olefin hydrogenation. The hypothesis explaining its catalytic activity relies on the assumption that Cu pairs up with Rh at the paddlewheel structure of this MOF. By combining a multimodal characterization approach, we link the structure and reactivity of this bimetallic system and help establish its mechanism. Our preliminary ex situ experiments established good spectral contrast between possible oxidation states of Rhodium. Here we present information on Rh ion speciation under in situ conditions, using a multimodal approach. The information obtained by understanding the nature of the Rh in its active state and atomic coordination geometry and reactant/catalyst interactions during reaction conditions will advance our understanding of the mechanistic relationship between metal ions and reactivity for olefin hydrogenation. This will guide further synthetic design and optimization of room temperature hydrogenation catalysts.