Aminoarenethiolate Aluminum Complexes: Synthesis, Characterization, and Use in l‑Lactide Polymerization

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.