Reactions of [(Me3Si)3CAlMe2] with substituted benzoic acids. Isolation of a rare organoalumoxane carboxylate

The reactivity of bulky tris(trimethylsilyl)methyl group substituted aluminum trialkyl [(Me3Si)3CAlMe2·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 [(Me3Si)3CAl(Me)(μ-O2CC6H4R)]2 (R = Me 2; tBu 3). Reaction of 3,5-di-iso-propylsalicylic acid (H2dipsa) with 1 leads to the exclusive isolation of a trimeric organoaluminum carboxylate [(Me3Si)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 (H2dtbsa·H2O) in the reaction with 1 in toluene leads to the isolation of carboxylate [(Me3Si)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.

Mono-, bi- and polycyclic organoaluminum caboxylates are easily accessible through the reaction of the sterically hindered trialkylaluminum [(Me3Si)3CAlMe2·THF] with benzoic acid derivatives such as 4-methyl benzoic acid, 3,5-di-iso-propylsalicylic acid and 3,5-di-tert-butyl salicylic acid monohydrate. The controlled introduction of water permits isolation of an organoalumoxane carboxylate.Figure optionsDownload as PowerPoint slideHighlights
► A rare organoalumoxane carboxylate has been structurally characterized.
► A new structural form of organoaluminum carboxylate has been unraveled.
► Hydrated salicylic acid was employed source for isolating a rare organoalumoxane carboxylate.