Catalytic Dehydrogenation of Formic Acid with Ruthenium-PNP-Pincer Complexes: Comparing N-Methylated and NH-Ligands

Complexes Ru(H)(Cl)(CO)(HN{CH2CH2P(iPr)(2)}(2)) 7 and Ru(H)(Cl)(CO)(CH3N{CH2CH2P(iPr)(2)}(2)) 8 were compared for the selective dehydrogenation (DH) of formic acid (FA) at different pH values. Remarkably, highest activities were observed in acidic environment (pH 4.5). Under all investigated conditions, the N-methylated complex 8 showed improved performance compared to 7. These observations can be mechanistically explained with protonation of 4H/3Me being the key step in formic acid DH for both complexes.