Abstract Ruthenium (II) complexes [(η 6-cymene) RuCl (apypm)] BPh 4 with bidentate 2- amino-4-(2-pyridinyl) pyrimidine (apypm) ligands catalyze the transfer hydrogenation of acetophenone. Their activities are strongly dependent on the substituent pattern of the pyrimidine ring. Complexes bearing a primary amino group in the 2-position of the pyrimidine ring do not perform the catalysis in terms of a “bifunctional mechanism”, ...