Hydrolysis of Trimesitylgallium and Trimesitylaluminum: Structures Along a Reaction Pathway

Hydrolyses of trimesitylgallium and -aluminum were monitored by
1H NMR spectroscopy in the temperature
range −60 °C to room temperature using deuterated THF as solvent.
The first intermediate of the reaction using
water and trimesitylgallium is the monomeric water adduct,
(Mes3Ga·OH2)·2THF,
1. Elimination of mesitylene
leads to the dimeric hydroxide
(Mes2GaOH)2·THF, 2.
Excess of water gives
Mes6Ga6O4(OH)4·4THF,
3. As a
result of this reaction course the corresponding hydrolysis of
trimesitylaluminum leads to
(Mes3Al·OH2)·nTHF,
4
and (Mes2AlOH)2·2THF, 5.
The molecular structures of compounds 1, 2,
and 5 have been determined by low
temperature X-ray structure analysis. The Lewis acidities of the
mesityl containing hydroxides are discussed and
compared with those of known aryl- and alkyl aluminum and gallium
hydroxides.