A Stable Manganese Pincer Catalyst for the Selective Dehydrogenation of Methanol

Abstract

For the first time, structurally defined manganese pincer complexes catalyze the dehydrogenation of aqueous methanol to hydrogen and carbon dioxide, which is a transformation of interest with regard to the implementation of a hydrogen and methanol economy. Excellent long‐term stability was demonstrated for the Mn‐PNPiPr catalyst, as a turnover of more than 20 000 was reached. In addition to methanol, other important hydrogen carriers were also successfully dehydrogenated.

Manganese‐Mediated Formic Acid Dehydrogenation

“…Complex 5 generated pressure slowly, yet reached equilibrium pressure over a 16 hour period. A comparison to the previously reported 6 is also reported (Table , entry 16; Figure A).…”

“…The only manganese system currently reported for FA dehydrogenation is ( i Pr PNP)Mn(CO) 2 , ( i Pr PNP=bis(2‐diisopropylphosphine)amine), which suffered from poor turnover and poor selectivity of dehydrogenation vs. dehydration of FA in acidic conditions . Under highly basic conditions, Beller reported dehydrogenation of methanol with water using the same complex …”

Cobalt‐Catalyzed Aqueous Dehydrogenation of Formic Acid

“…However, no gas evolution was observed underlining the importance of the pincer ligand in this system. Finally, we compared the activity of these new complexes with other well‐known pincer complexes, which are active in methanol and/or FA dehydrogenation . Surprisingly, the manganese complex 7 was completely inactive under these aqueous conditions, and even the ruthenium benchmark complex 8 gave only marginal hydrogen production.…”

Practical (asymmetric) transfer hydrogenation of ketones catalyzed by manganese with (chiral) diamines ligands

“…[5] The potential of manganese catalysts in such redox reactions was exemplified with various type of tridendate ligands, mainly phosphorus and nitrogen atoms. [6][7][8][9][10][11][12][13][14][15][16][17][18][19] Interestingly, in the case of hydrogen transfer reaction, using isopropanol as hydrogen donor, Beller has shown that tridentate nitrogen ligand, namely di(picolyl)amine, could promote the reduction of ketones, at 70°C, in 24 h, with a ratio substrate:catalyst of 100:1. [20] Asymmetric reduction of ketones with manganese is far less developed and the two first example were reported by Clarke [21] and Kirchner [22], using related chiral ferrocenyl based tridentate PNN or PNP' ligands.…”