Symmetrical Hydrogen Bonds in Iridium(III) Alkoxides with Relevance to Outer Sphere Hydrogen Transfer
摘要:
A chelating ligand formed by deprotonation of 2-(2'-pyridyl)-2-propanol stabilizes a distorted trigonal bipyramidal geometry in a 16e(-) d(6) 5-coordinate iridium complex with the alkoxide acting as a pi donor. Ambiphilic species such as AcOH bearing both nucleophilic and electrophilic functionality form adducts with the unsaturated iridium complex which contain strong intramolecular O center dot center dot center dot H center dot center dot center dot 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 center dot center dot center dot O distances of about 2.4 angstrom. Calculations further confirm the known trend that the hydrogen position in these bonds is sensitive to the O center dot center dot center dot O distance, with the shortest distances giving rise to symmetrical O center dot center dot H center dot center dot center dot O interactions. Dihydrogen is shown to add across the Ir-O pi bond in a presumed proton transfer reaction, demonstrating bifunctional behavior by the iridium alkoxide.