Symmetrical Hydrogen Bonds in Iridium(III) Alkoxides with Relevance to Outer Sphere Hydrogen Transfer

A chelating ligand formed by deprotonation of 2-(2′-pyridyl)-2-propanol stabilizes a distorted trigonal bipyramidal geometry in a 16e^– d⁶ 5-coordinate iridium complex with the alkoxide acting as a π donor. Ambiphilic species such as AcOH bearing both nucleophilic and electrophilic functionality form adducts with the unsaturated iridium complex which contain strong intramolecular O···H···O hydrogen bonds that involve the basic alkoxide oxygen. Density functional theory (DFT) calculations on the isolated cations reproduce with high accuracy the geometrical features obtained via X-ray diffraction and corroborate the presence of very short hydrogen bonds with O···O distances of about 2.4 Å. Calculations further confirm the known trend that the hydrogen position in these bonds is sensitive to the O···O distance, with the shortest distances giving rise to symmetrical O···H···O interactions. Dihydrogen is shown to add across the Ir–O π bond in a presumed proton transfer reaction, demonstrating bifunctional behavior by the iridium alkoxide.