Scientists Achieve Difficult Chemical Step with Lower Energy Input

Source: PNNL December 2018

Ba Tran, a PNNL postdoctoral scientist, made the crucial discovery that the molecular rhodium starting complex is not the actual catalyst. Under reaction conditions, the soluble rhodium complex is transformed into rhodium nanoparticles that carry out the catalysis. Knowing this key information will allow scientists to further hone the process and ensure only the desired reactions occur.

Why it matters: Catalysis can reduce energy costs and minimize waste, while increasing synthetic efficiency. Pursuing catalysts creatively can reshape how chemicals are transformed in reactions important to the chemical industry.

Summary: Hydrogenation of arenes (cyclic 6-membered aromatic rings) is traditionally carried out at high temperatures. The experiments recently reported yielded catalytic hydrogenation of arenes at room temperature and low pressure of dihydrogen (H2) starting from a cyclic alkyl amino carbene ligand bound to rhodium. A key accomplishment was that only the desired aromatic ring is hydrogenated, even in the presence of other groups, such as esters and amides, that could potentially also be hydrogenated. The reaction is also site-selective in that one arene is preferentially hydrogenated over other arenes in the same molecule.

The results demonstrate the importance of synergy among the scientists participating in the Institute for Integrated Catalysis (IIC). Chemists who study soluble molecular (homogeneous) catalysts generally use different techniques and approaches than heterogeneous catalysis experts. The research reported in this article relied on the combined expertise of scientists in molecular catalysis,heterogeneous catalysis, and spectroscopy. Further, the experiments relied on the specialized X-ray absorption spectroscopy technique available at the Advanced Photon Source national user facility at Argonne National Laboratory.

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