Stepwise Synthesis of Carboxyalumoxanes through Well-Defined Organoaluminum and Organogallium Carboxylatohydroxides Obtained by Controlled Hydrolysis

Alumoxanes are compounds of composition (R₂AlOAlR₂)<i>_n</i> and (RAlO)<i>_n</i> that are traditionally obtained by controlled hydrolysis of aluminum trialkyls, although nonhydrolytic approaches to alumoxanes are also used. To reduce the reactivity of alumoxanes in contact with air, in the 1990s, researchers attempted to replace alkyl groups with other substituents, leading to the synthesis of carboxyalumoxanes with bulky alkyl groups. In this paper, we report on the study of carboxy methylalumoxane synthesis and structural characterization. We present a two-step synthesis of carboxyalumoxane containing the (<i>t</i>-Bu₂Al)₂OAlMe₂ alumoxane unit. The method involves the synthesis of carboxylatoaluminum hydroxides by the reaction of <i>t</i>-Bu₃Al with carboxylic acid and water with a molar ratio of reagents of 2:1:1 in the first step, followed by the reaction with Me₃Al. On the other hand, the one-step reaction of Me₃Al with carboxylic acid and water in a molar ratio of 3:1:1 leads to the formation of a carboxy methylalumoxane incorporating a neutral Me₆Al₄O₂ scaffold trapped by two carboxylate units. The reaction of carboxylatogallium hydroxides with Me₃Al occurred with the exchange of <i>t</i>-Bu₂Ga groups for Me₂Al, leading to the formation of carboxyalumoxanes with a Me₆Al₄O₂ scaffold. The molecular and crystal structures of the compounds were determined via single-crystal X-ray diffraction (SCXRD) crystallography.