(513o) Mechanisms and Control of Industrial Multistage Chemical Reactions from Renewable Resource

The consumption of petrochemicals is not only leading towards the depletion of fossil fuels but also has serious impact on the environment. Oleochemicals from sustainable resources have been established as valuable alternatives. Quantum chemical studies play a key role in the field of mechanistic organometallic chemistry, as they go hand-in-hand with experimental studies and provide complementary information. Here, we study the complex transition metal-catalyzed reaction mechanism of the reductive hydroaminomethylation (HAM) reaction and the control of reaction parameters i.e. temperature, pressure, solvent and catalytic effects for elementary reactions to describe the kinetics and thermodynamics of each microstep. The reductive hydroaminomethylation is a tandem process of hydroformylation plus subsequent amination and reduction steps (See Figure).

The Rh-BiPhePhos catalyst has been selected for both hydroformylation and hydrogenation steps. A careful benchmarking of the accuracy of computational methods provided the most suitable quantum chemical approach. The complete reaction mechanism has been elucidated including all intermediates and transition states. The effects of solvent on all elementary reactions were considered using implicit and cluster/continuum solvation models. It could be shown that the solvent selection is vital to achieve high selectivity and fast turnover since solvent properties such as polarity and proticity influence the kinetics and thermodynamics of the reaction. The choice of solvent and co-catalyst not only influence the kinetics of the reaction but also alter the preferred reaction pathway and drives the thermodynamic equilibrium towards the product side. Olefin insertion was identified to be the rate determining step for HAM, a protic solvent acts as co-catalyst in the amination and a low CO pressure is favorable for the reduction step.

Figure 1. Simplified reaction cycle for multistage hydroaminomethylation reaction.