Ruthenium NNN complexes with a 2‐hydroxypyridylmethylene fragment for transfer hydrogenation of ketones

Four NNN tridentate ligands L 1 –L 4 containing 2‐methoxypyridylmethene or 2‐hydroxypyridylmethene fragment were synthesized and introduced to ruthenium centers. When (HOC 5 H 3 NCH 2 C 5 H 3 NC 5 H 7 N 2 ) (L 2 ) and (HOC 5 H 3 NCH 2 C 5 H 3 NC 6 H 6 N 3 ) (L 4 ) reacted with RuCl 2 (PPh 3 ) 3 , two ruthenium chloride products Ru(L 2 )(PPh 3 )Cl 2 ( 1 ) and Ru(L 4 )(PPh 3 )Cl 2 ( 2 ) were isolated, respectively. Reactions of (MeOC 5 H 3 NCH 2 C 5 H 3 NC 5 H 7 N 2 ) (L 1 ) and (MeOC 5 H 3 NCH 2 C 5 H 3 NC 6 H 6 N 3 ) (L 3 ) with RuCl 2 (PPh 3 ) 3 in the presence of NH 4 PF 6 generated two dicationic complexes [Ru(L 1 ) 2 ][PF 6 ] 2 ( 3 ) and [Ru(L 3 ) 2 ][PF 6 ] 2 ( 4 ), respectively. Complex 1 reacted with CO to afford product [Ru(L 2 )(PPh 3 )(CO)Cl][Cl]. The catalytic activity for transfer hydrogenation of ketones was investigated. Complex 1 showed the highest activity, with a turnover frequency value of 1.44 × 10 3  h −1 for acetophenone, while complexes 3 and 4 were not active.