Hydroxypyridine/Pyridone Interconversions within Ruthenium Complexes and Their Application in the Catalytic Hydrogenation of CO 2 .

Reaction of a new ligand (6-diisopropylphosphino-2-pyridone) with 0.5 equiv of [RuCl(-cymene)] resulted in the formation of a mixture of [RuCl(-cymene)(κ-)] () and [RuCl(-cymene)(κ--)]Cl ([]) (where = 6-diisopropylphosphino-2-hydroxypyridine). The ratio between the two products can be controlled by the nature of the solvent. The similar reaction between and [RuCl(-cymene)] in the presence of AgOTf and Na[BArF] (where BArF = [{3,5-(CF)CH}B]) resulted in the formation of the complexes [RuCl(-cymene)(κ--)]OTf, ([]) and [RuCl(-cymene)(κ--)]BArF ([]), respectively. Reactions between complex [], [], or [] and a base (either DBU or NaOMe) resulted in the deprotonation of the hydroxyl functional group to form a novel neutral orange-colored dearomatized complex, . The identity of complex was confirmed as [RuCl(-cymene)(κ--)], where is the anionic species (6-diisopropylphosphino-2-oxo-pyridinide), which contains the deprotonated moiety. The new ligand and its corresponding air stable half-sandwich derivative ruthenium complexes , [], [], and were all isolated in good yields and fully characterized by spectroscopic and analytical methods. The interconversions between the neutral and anionic forms of the ligands , , and offer the potential for novel secondary sphere interactions and proton shuttling reactivity. The consequences for this have been explored in the activation of H and the subsequent catalytic hydrogenations of CO into formate salts in the presence of a base.