Reactions of [(Me 3Si) 3CAlMe 2] with substituted benzoic acids. Isolation of a rare organoalumoxane carboxylate

Abstract

The reactivity of bulky tris(trimethylsilyl)methyl group substituted aluminum trialkyl [(Me 3Si) 3CAlMe 2·THF] ( 1) with a series of substituted benzoic acid derivatives has been investigated. An equimolar reaction of 4-methyl benzoic acid or 4- tert-butyl benzoic acid with 1 in toluene at 50 °C leads to the formation of cyclic dimeric aluminum carboxylates [(Me 3Si) 3CAl(Me)(μ-O 2CC 6H 4R)] 2 (R = Me 2; t Bu 3). Reaction of 3,5-di- iso-propylsalicylic acid (H 2dipsa) with 1 leads to the exclusive isolation of a trimeric organoaluminum carboxylate [(Me 3Si) 3CAl(μ-dipsa)] 3 ( 4), in which each aluminum is bound to two carboxylates, a phenoxide, and an alkyl group and produce a 12-membered macrocycle. Deliberate, but controlled, introduction of water in the form of 3,5-di- tert-butyl salicylic acid monohydrate (H 2dtbsa·H 2O) in the reaction with 1 in toluene leads to the isolation of carboxylate [(Me 3Si) 3CAl(μ-O)(μ-Hdtbsa)} 2] ( 5) with a bicyclic structure. Compound 5 represents a rare example of an organoalumoxane carboxylate that simultaneously possesses alkyl, oxo, and carboxylate moieties on aluminum.