Aminoarenethiolate Aluminum Complexes: Synthesis, Characterization, and Use in l‑Lactide Polymerization
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Reaction of AlMe3 with S(SiMe3)(C6H3-2-CH2NRR′-5-tBu) (RR′ = C5H10 (1a), C4H8 (1b), Me2 (1c)), at ambient temperature, affords the amino adducts [AlMe3{S(SiMe3)(C6H3-2-CH2NRR′-5-tBu)}-κN] (RR′ = C5H10 (2a), C4H8 (2b), Me2 (2c)), which undergo TMS elimination upon heating to give the monomeric aminoarenethiolate aluminum complexes [AlMe2{S(C6H3-2-CH2NRR′-5-tBu)-κ2S,N}] (RR′ = C5H10 (3a), C4H8 (3b), Me2 (3c)). Following the same procedure, treatment of AlCl2Me and AlCl3 with 1 yields analogous aminoarenethiolate aluminum complexes with different degrees of methylation, the chloro methyl and dichloro complexes [AlClMe{S(C6H3-2-CH2NRR′-5-tBu)-κ2S,N}] (RR′ = C5H10 (4a), C4H8 (4b), Me2 (4c)) and [AlCl2{S(C6H3-2-CH2NRR′-5-tBu)}-κ2S,N] (RR′ = C5H10 (5a), C4H8 (5b) Me2 (5c)), respectively. These complexes have been characterized by multinuclear NMR spectroscopy and elemental analysis. Moreover, the molecular structures of 3a,b have been determined by X-ray diffraction methods. Aluminum complexes 3 have been investigated for the ring-opening polymerization (ROP) of l-lactide, achieving high conversions in relatively short periods of time. The PLAs obtained feature an aminoarenethiolate end functionality, as inferred from MALDI-TOF mass analysis.
