Nature of Reactive Mn–Oxygen Complexes in the Catalytic Oxidative Coupling of Aryllithiums: A Combined Mass Spectrometric and Theoretical Approach

The catalytic aerobic coupling of organometallic lithium and Grignard reagents using MnCl2 is a useful method to synthesize homo- or heterocoupled products, including biaryls, dialkynes, or arylalkynes. For the case of aryllithiums, we herein provide insights into the mechanistic scenario using a combined study involving [18O] labeling experiments, mass spectrometry, and DFT calculations. A highly reactive manganate complex [MnPh3]− could be detected in ESI-MS and reacted in the gas phase with molecular oxygen to provide biphenyl and a Mn–oxygen complex, whereas in the absence of oxygen, only very limited amounts of biphenyl were produced. An alternative C–O bond-forming reaction was also unveiled from this Ion–Molecule Reaction. Based on these results, a theoretical study was conducted to shine some light on the gas phase and solution processes. Taking into account the specificities of the condensed phase, DFT calculations have revealed a number of potential mechanistic scenarios for this oxidative C–C coupling reaction.