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Hydrogenation of CO 2 to Formic Acid with a Highly Active Ruthenium Acriphos Complex in DMSO and DMSO/Water
Author(s) -
Rohmann Kai,
Kothe Jens,
Haenel Matthias W.,
Englert Ulli,
Hölscher Markus,
Leitner Walter
Publication year - 2016
Publication title -
angewandte chemie international edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.831
H-Index - 550
eISSN - 1521-3773
pISSN - 1433-7851
DOI - 10.1002/anie.201603878
Subject(s) - formic acid , chemistry , catalysis , ruthenium , reagent , amine gas treating , solvent , turnover number , inorganic chemistry , organic chemistry
The novel [Ru(Acriphos)(PPh 3 )(Cl)(PhCO 2 )] [ 1 ; Acriphos=4,5‐bis(diphenylphosphino)acridine] is an excellent precatalyst for the hydrogenation of CO 2 to give formic acid in dimethyl sulfoxide (DMSO) and DMSO/H 2 O without the need for amine bases as co‐reagents. Turnover numbers (TONs) of up to 4200 and turn o ver frequencies (TOFs) of up to 260 h −1 were achieved, thus rendering 1 one of the most active catalysts for CO 2 hydrogenations under additive‐free conditions reported to date. The thermodynamic stabilization of the reaction product by the reaction medium, through hydrogen bonds between formic acid and clusters of solvent or water, were rationalized by DFT calculations. The relatively low final concentration of formic acid obtained experimentally under catalytic conditions (0.33 mol L −1 ) was shown to be limited by product‐dependent catalyst inhibition rather than thermodynamic limits, and could be overcome by addition of small amounts of acetate buffer, thus leading to a maximum concentration of free formic acid of 1.27 mol L −1 , which corresponds to optimized values of TON=16×10 3 and TOF avg ≈10 3 h −1 .