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

Abstract

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.

Room Temperature Hydrogenation of CO2 Utilizing a Cooperative Phosphorus Pyridone‐Based Iridium Complex

“…Furthermore, Breit and Meuwly demonstrated the potential for these ligands to form pseudo chelates or form ligand bridging motifs via hydrogen bonding between two 2‐pyridone units (Figure 1, bottom) [12,13] . Related ligand systems where metal‐ligand cooperation has been observed within a hydroxypyridine based unit have been reported [14,15] . In our previous work, [11] we outlined the successful application of a ruthenium p ‐cymene complex containing the isopropyl analogue of these ligands in the hydrogenation of CO 2 in the presence of DBU (Figure 2).…”