Using Second Coordination Sphere Interactions of Rhenium(I) Complexes to Promote

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DESCRIPTION (provided by applicant): Given the limited resources on this planet, it is imperative that chemical industries adopt more sustainable practices to ensure future economic growth as well as to protect the welfare of people and the environment. Our current reliance on petroleum as fuel and organic raw materials is inadequate due to uncertainty in its supply and the enormous amount of pollution associated with its processing. Finding an alternative carbon source requires: 1) identifying a reliable and naturally abundant chemical feedstock, and 2) discovering clean technologies to convert it into value-added products. With regard to these goals, a promising area of research is in the industrial use of synthesis gas (syngas), CO and H2, which can be readily obtained from coal and biomass. Although several large-scale manufacturing plants utilize syngas to produce hydrocarbons and oxygenates, current synthetic methods that rely on Fischer-Tropsch chemistry is non-selective. The additional steps needed to separate syngas products greatly reduce its overall synthetic efficiency. Homogeneous catalysts that mediate C-H and C-C bond forming reactions from syngas may allow selective coupling of CO by circumventing the thermodynamic and kinetic restrictions that have traditionally hindered such reactivity. Bercaw and coworkers have demonstrated that some of the key reaction steps in a possible catalytic cycle involving CO can be achieved using phosphine-supported metal carbonyl complexes and hydride donors obtained from heterolytic cleavage of H2. Although these studies led to successful reductive coupling of two CO molecules, the resulting product was too stable to be regenerated for a viable catalytic reaction. This proposal describes the design of a novel rhenium carbonyl platform for reductive coupling of CO using syngas as the exclusive source of carbon, hydrogen, and electrons. A multi-functional ligand provides an opportunity to explore the influence of second coordination sphere interactions, such as hydrogen bonding, Lewis acid activation, and electrostatic attraction, on the reactivity of metal carbonyl species toward hydride donors. The primary goal of this work is to determine what factors promote C-H and C-C bond forming processes, knowledge of which will be used to design catalytic systems for selective transformation of syngas into higher-carbon containing materials. PUBLIC HEALTH RELEVANCE: If immediate actions are not taken to remedy the harmful effects of industrialization on our ecosystems, further damage to our habitat will also threaten human health. One positive step toward a more sustainable future is to develop greener technologies to utilize earth abundant resources for fuel and material goods. This work aims to discover new synthetic methods to convert synthesis gas, which can be readily obtained from coal and biomass, into more valuable commodities with a low environmental footprint.