Ruthenium Complexes Bearing N–H Acidic Pyrazole Ligands

Chelate ligands containing at least one pyrazole group were treated with RuCl 2 (PPh 3 ) 3 , RuHCl(CO)(PPh 3 ) 3 and RuH 2 (CO)(PPh 3 ) 3 to form ruthenium complexes bearing protic N–H groups in close proximity to the catalytically active ruthenium centre. In the case of the hydridoruthenium complex RuHCl(CO)(PPh 3 ) 3 the resulting complexes also contain abasic hydrido ligand. The combination of acidic and basic hydrogen species in one molecule and the arising two‐site reactivity was thoroughly investigated spectroscopically and by DFT calculations. Catalytic tests on the hydrogenation and transfer hydrogenation of acetophenone showed a general activity of these systems.