PCP-pincer and related iridium complexes are the most effect catalysts known for alkane dehydrogenation reactions.1,2 These reactions typically make use of an olefinic sacrificial hydrogen acceptor which is hydrogenated by a pincer iridium dihydride to generate the key 14e Ir(I) intermediate, which then oxidatively adds an alkane C-H bond and undergoes β-hydride elimination to afford the olefin product3. The need for a sacrificial acceptor can limit the utility of these systems for reasons both economic and chemical (e.g. reagents for secondary reactions can react with the sacrificial olefin). Hence, we envisioned a new strategy to generate the 14e Ir(I) intermediate from the dihydride complexes through the use of proton and electron acceptors. Ultimately, our target is an electrochemical system in which the hydrogen removed from the alkane is electrochemically oxidized as in a fuel cell. We envision the use of chemical oxidants acting as agents for electron-transfer to the anode, or to model an electrochemical system. We have had encouraging result with several oxidant/base systems. For example, using AgBF4 and KOtBu as electron and proton acceptors respectively, we have successfully dehydrogenated cyclooctane and achieved close to 14 turnovers or 93% yield based on added oxidant and base.

New catalytic route to dehydrogenate alkanes by PCP-pincer iridium complexes using proton and electron acceptors

2019 Fall National Meeting

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