NHC-Based Iridium Catalysts for Hydrogenation and Dehydrogenation of N-Heteroarenes in Water under Mild Conditions

We present a set of iridium complexes containing triazolylidene ligands that are highly active for the reduction of quinoline under 5 atm of H-2 pressure and using water as a solvent. This reduction is effective also with a wide variety of quinolines having functionalities at the 2-, 3-, 6-, and 8-positions. One complex is active as well in catalyzing the reverse, viz., the dehydrogenation of tetrahydroquinoline, in high yields and in the same medium without the need of an external hydrogen scavenger. The use of a single catalyst for both hydrogenation and dehydrogenation processes is highly attractive for reversible hydrogen storage in liquid organic hydrogen carriers.