A cyclometalated iridium complex is shown to catalyse the transfer hydrogenation of various nitrogen heterocycles, including but not limited to quinolines, isoquinolines, indoles and pyridinium salts, in an aqueous solution of HCO2H/HCO2Na under mild conditions. The catalyst shows excellent functional-group compatibility and high turnover number (up to 7500), with catalyst loadings as low as 0.01 mol % being feasible. Mechanistic investigation of the quinoline reduction suggests that the transfer hydrogenation proceeds via both 1,2- and 1,4-addition pathways, with the catalytic turnover being limited by the step of hydride transfer.

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cycles. -Optimized reaction conditions including 2-propanol-d 8 as the deuterium source are developed for the deuterodehalogenation of various bromo-and chloro--substituted heterocycles. -(DONALD*, C. S.; MOSS, T. A.; NOONAN, G. M.; ROBERTS, B.; DURHAM, E. C.; Tetrahedron Lett. 55 (2014) 22, 3305-3307, http://dx.

Transfer hydrogenation Transfer hydrogenation is a simple safe way for reduction reactions and using water as a solvent has the additional benefit of being “green”. In their Full paper on J. Xiao et al. report that a cyclometalated iridium complex catalyzes the transfer hydrogenation of various nitrogen heterocycles in an aqueous solution of formate under mild conditions. The catalyst shows excellent functional‐group compatibility and high turnover number, with loadings as low as 0.01 mol % being feasible. A mechanistic study of quinoline reduction suggests that the reaction proceeds via both 1,2‐ and 1,4‐addition pathways, with the catalytic turnover limited by hydride transfer.

First time, a cyclometalated iridium complex is used to catalyze the transfer hydrogenation of (iso)quinolines, indoles, and pyridinium salts in an aqueous solution of HCOOH/HCOONa under mild conditions. The catalyst shows excellent functional-group compatibility and a high turnover number. The catalyst loading can be diminished as low as 0.01 mol% being feasible [shown for (IIb)]. Hydrogenation of pyrazine (VII) results in the formation of the N-formyl derivative (IX). Interestingly, 1H-cyclopenta[b]pyridine (X) is reduced at the carbocycle ring to give pyridine (XI). -(TALWAR, D.; LI, H. Y.; DURHAM, E.; XIAO*, J.; Chem. -Eur. J. 21 (2015) 14, 5370-5379, http://dx.doi.org/10.1002/chem.201500016 ; Dep. Chem., Univ. Liverpool, Liverpool L69 7ZD, UK; Eng.) -S. Adam