Hydrolysis of Scandium Alkyl Derivatives Supported by a Pentadentate Diborate Ligand: Interconversion of Hydroxo and Oxo Complexes

Uncontrolled reaction of water with scandium alkyls (compounds 1-R) supported by a dianionic, pentadentate ligand leads to rapid formation of an oxo-bridged dimer (2). Solid state samples can be exposed to ambient atmosphere to generate samples enriched in the bridging dihydroxo dimer 3, which slowly converts to the m-oxo species with elimination of water. DFT computations show that 3 is actually more thermodynamically stable than 2, but the reactivity of 3 with the water eliminated leads to its decomposition to 2 and several hydrolysis products. Some of these products were characterized by X-ray crystallography, specifically a hexameric scandium dihydroxo cluster (4) in which the pentadentate ligand has partially demetallated. Attempts to synthesize hydroxo complex 3 by protonation of 2 also lead to hydrolysis products.