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

## TL;DR

The paper describes a new method for synthesizing carboxyalumoxanes using controlled hydrolysis and structural analysis.

## Contribution

A novel two-step synthesis and structural characterization of carboxyalumoxanes with specific alumoxane units.

## Key findings

- A two-step synthesis of carboxyalumoxane containing the (t-Bu2Al)2OAlMe2 alumoxane unit was successfully developed.
- A one-step reaction forms a carboxy methylalumoxane with a neutral Me6Al4O2 scaffold.
- Molecular and crystal structures were confirmed using single-crystal X-ray diffraction.

## Abstract

Alumoxanes are compounds of composition (R2AlOAlR2)n and (RAlO)n 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 (t-Bu2Al)2OAlMe2 alumoxane unit. The method involves
the synthesis of carboxylatoaluminum hydroxides by the reaction of t-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 t-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.

Alumoxanes are compounds of composition
(R2AlOAlR2)n and
(RAlO)n that are traditionally obtained
by controlled hydrolysis
of aluminum trialkyls, although non-hydrolytic approaches to alumoxanes
are also use.