Ruthenium(II) and Iridium(III) Complexes Bearing Phosphinepyridonate and Phosphinequinolinolate Chelates

Abstract

International audienceStraightforward preparation of five-membered P,N and P,O prochelates was easily achieved from 6-methyl-2-pyridinol and 2-quinolinol. From these ligands, access to the corresponding well-defined ruthenium(II) and iridium(III) complexes was investigated. Owing to the hemilability as well as the reversible proton-responsive character of these chelates, the resulting well-defined ruthenium complexes exhibit interesting activities in hydrogenatio

Ruthenium Phosphine–Pyridone Catalyzed Cross-Coupling of Alcohols To form α-Alkylated Ketones

“…Our group recently disclosed a series of new proton responsive bi- and tridentate phosphine pyridon-e/-ate ligands. The corresponding transition metal complexes have shown impressive reactivity for alcohol dehydrogenation and selective formation of acetals or esters . Observing the efficiency of Ru-1 in dehydrogenative coupling of primary alcohols, we envisaged the formation of a corresponding α-alkylated ketone when a secondary alcohol is introduced in the system via dehydrogenative cross-coupling of the two alcohols (Scheme ).…”

Cooperative or Oxidative Hydrogen Addition to 2‐Hydroxypyridonate Iridium Complexes: Dependence on Oxidation State

“…[1a], The majority of reports employs simple unsubstituted 2‐hydroxypyridine, 6,6′‐dihydroxy‐2,2′‐bipyridine or 2,9‐dihydroxyphenanthroline, coordinated by iridium. A recent example with a slightly more complex ligand architecture, 2‐hydroxy‐6‐methyl(diphenylphosphino)pyridine, was reported by Achard et al To the best of our knowledge, all reported work relating to cooperative iridium–pyridone catalysis involves iridium(III) metal centres. Rauchfuss has reported the reaction of Cp*Ir(κ 2 ‐2‐pyridonate)Cl with dihydrogen and hydrogen donors .…”

Hydroxypyridine/Pyridone Interconversions within Ruthenium Complexes and Their Application in the Catalytic Hydrogenation of CO2

“…In contrast, Achard and co-workers found a κ 2 -P,N coordination mode for the complex resulting from the same metal precursor with the analogous (6-Ph 2 PCH 2 )(2-hydroxy)pyridine ligand. 8 In this case, the ligand was found to be in the hydroxypyridine form, and the bidentate coordination resulted in the removal of one of the chloride ligands from the coordination sphere to form the cationic complex. It should be noted that the utilization of polar solvent methanol may have influenced this selectivity.…”

“…The crystal structure of [ 2 ] OTf (Figure , left) shows that the cation adopts a three-legged piano stool complex containing the neutral 6-D i PPin ligand (in the 2-hydroxypyridine form) coordinated via the phosphorus (L) and nitrogen (L) atoms with a κ 2 - P,N coordination mode. The ruthenium center in the cations contains Ru–P, Ru–N, and Ru–Cl bond distances that are comparable to those of the related structures, [RuCl( p -cymene)(κ 2 - P,N -{(6-Ph 2 PCH 2 )(2-hydroxy)pyridine})]Cl and [RuCl(benzene)(κ 2 - P,N -{(6-Ph 2 PCH 2 CH 2 )(2-hydroxy)pyridine})]PF 6 , which both contain a 2-hydroxypyridinephosphine ligand with a κ 2 - P,N coordination mode. , These two latter complexes differ from [ 2 ] OTf in the size of the rings formed upon chelation, which are five- and six-membered chelates, respectively. As expected, however, the N1–Ru1–P1 angles around the ruthenium centers in [ 2 ] OTf are reduced significantly to 67.60(4)° and 67.16(4)° (two angles since there are two independent complexes in the asymmetric unit) due to the strained four-membered ring formed upon chelation.…”

“…7 In 2015, Achard and co-workers reported hydrogenation of acetophenone using [RuCl(p-cymene)(κ 2 -P,N-{(6-Ph 2 PCH 2 )(2-hydroxypyridine)})]Cl. 8 This ligand is related to 6-DPPon but has a methylene linker between the phosphorus and pyridine unit (Scheme 1, middle). The κ 2 -P,N chelate provides a five-membered ring to stabilize the metal center.…”