Ruthenium Complexes with N-Bound 2-Pyridonato Ligand as O-Donors: A New Synthetic Approach and the Effect on Reactivity.

In this study, Ru complexes [(η6-p-cymene)RuX(2-{(2,6-iPr2-C6H3)N=CH}-C5H3N-6-(O))] (3: X=Cl; 4: X=I) were prepared with N-bound 2-pyridonato ligand by thermal base-free MeX elimination from ionic N,N-chelated Ru complexes [(η6-p-cymene)RuX(κ2-L1)](X) (1: X=Cl; 2: X=I; L1={2-[(2,6-iPr2-C6H3)N=CH]-6-(OMe)C5H3N}). The Ru complex 3 was used as O-donor for Lewis (LA) or Brönsted acids. The reactions of 3 with SnCl2, Ph3SnCl, ZnCl2 or HCl provided [(η6-p-cymene)Ru(SnCl3)(2-{(2,6-iPr2-C6H3)N=CH}-C5H3N-6-(O→SnCl2)] (6), [(η6-p-cymene)RuCl(2-{(2,6-iPr2-C6H3)N=CH}-C5H3N-6-(O→SnPh3Cl)] (7), and [(η6-p-cymene)RuCl(2-{(2,6-iPr2-C6H3)N=CH}-C5H3N-6-(O→)]2(µ-ZnCl2) (8) and [(η6-p-cymene)RuCl(2-{(2,6-iPr2-C6H3)N=CH}-C5H3N-6-(OH)}](Cl) (9). The easy conversion of the 2-pyridonato ligand in 3 to its 2-hydroxypyridine in 9 evoked testing of 3 and 4 as potential catalysts in base-free transfer-hydrogenation of ketones.