A Novel Approach for the Stabilization and Structural Characterization of Group 13 Organometallic Hydroxides:  The Way to Well Defined Crystalline Methylalumoxanes

The controlled hydrolysis products of R 3 M (M = Al, Ga; R = Mes, Ph, Me) have been found to be stabilized by deprotonation reactions using alkyllithium reagents. (Mes 3 Ga·OHLi)·3THF ( 1 ) and (Mes 3 Al·OHLi)·3THF ( 3 ) were synthesized by the reaction of LiOH with Mes 3 Ga and Mes 3 Al, respectively. The hydroxides, (R 2 MOH) n, resulting from the reaction of water and R 3 M were deprotonated with RLi (R = t Bu, Me) to give (Mes 2 GaOLi) 2 ·4THF ( 2 ), (Mes 2 AlOLi) 2 ·4THF ( 4 ), (Ph 2 AlOLi) 3 ·6THF ( 5 ), and (Me 2 AlOLi) 4 ·7THF·LiCl ( 6 ). The molecular structures of compounds 1, 2, 4, 5, and 6 have been determined by X-ray structure analysis. Whereas 2 undergoes metathesis reactions, compounds 1, 3, 4, 5, and 6 are stable at room temperature. Compound 6 is the first structurally characterized intermediate on the pathway to cocatalytically active methylalumoxane used in metallocene catalyzed olefin polymerization reactions. Moreover, it represents the first structurally characterized alumoxane stabilized by a separated cation.