New N,N,N‐Donors Resulting in Highly Active Ruthenium Catalysts for Transfer Hydrogenation at Room Temperature

Abstract

AbstractA series of ruthenium complexes of the general formula [RuCl2(L)(NNN)] were synthesized starting from tridentate N,N,N‐ligands containing pyridine and allylated pyrazole donor groups and [RuCl2(PPh3)3]. The N,N,N‐donors introduced herein are accessible in a few steps from versatile precursors. The primary products, [RuCl2(NNN)(PPh3)], can be converted into the corresponding carbonyl complexes, [RuCl2(CO)(NNN)], by bubbling CO into a solution in toluene at elevated temperatures. All ruthenium complexes were investigated as catalysts for the transfer hydrogenation of aryl ketones. The phosphane complexes show high activities with turnover frequency values of up to 1200 h–1 in the presence of just one equivalent of KOH, whereas the carbonyl complexes are only poorly active.