Methyl Formate as a Liquid Organic Hydrogen Carrier: Mn(I)-Pincer Complex-Catalyzed Dehydrogenation and Transfer...

The search for practical liquid organic hydrogen carriers has intensified in recent years. In this context, methyl formate has emerged as a promising candidate due to its relatively high hydrogen content, large-scale availability, low cost, and favorable thermodynamics. Herein, we describe a well-defined homogeneous Mn(I)-pincer catalyst that enables hydrogen release from aqueous MF under mild conditions via metal-ligand cooperation. The catalyst performs exceptionally well, reaching turnover numbers above 165,000 and average turnover frequencies exceeding 3,450 h-1, and this performance holds up at a meaningful scale: 500 mmol reactions run over 48 h with consistent gas output across three collection cycles. To understand the origin of this activity, we combined kinetic measurements, multinuclear NMR spectroscopy, and DFT calculations to map out a coherent catalytic cycle with identifiable Mn(I) intermediates and a moderate 98.9 ± 0.2 kJ mol-1 activation barrier. The H2 produced in situ was also used for transfer hydrogenation, thereby reducing aromatic carbonyls, nitriles, and conjugated substrates to the corresponding alcohols and amines in a single pot, generally with good chemoselectivities and moderate to good yields. Overall, the Mn-pincer/MF system provides a means to integrate hydrogen storage with synthetic chemistry within a single setup.