Synthesis, structural characterization and catalytic evaluation of the ring-opening polymerization of discrete five-coordinate alkyl aluminium complexes
2013; Royal Society of Chemistry; Volume: 42; Issue: 25 Linguagem: Inglês
10.1039/c3dt32657h
ISSN1477-9234
AutoresJosé A. Castro‐Osma, Carlos Alonso‐Moreno, Isabel Márquez‐Segovia, Antonío Otero, Agustín Lara‐Sánchez, Juan Fernández‐Baeza, Ana M. Rodrı́guez, Luis F. Sánchez‐Barba, Joaquín C. Garcı́a-Martı́nez,
Tópico(s)Organometallic Complex Synthesis and Catalysis
ResumoFive-coordinate alkyl aluminium complexes [AlR(κ2-pbpam)2] (R = Me 1, Et 2), [AlR(κ2-sbpam)2] (R = Me 3, Et 4) and [AlR{κ2-(S)-mbpam}2] (R = Me 5, Et 6), –pbpam [pbpam = N-phenyl-2,2-bis(3,5-dimethylpyrazol-1-yl)acetamidate], sbpam [sbpam = N-sec-butyl-2,2-bis(3,5-dimethylpyrazol-1-yl)acetamidate] and (S)-mbpam [(S)-mbpam = (S)-(−)-N-α-methylbenzyl-2,2-bis(3,5-dimethylpyrazol-1-yl)acetamidate] were obtained by an alkane elimination route involving the reaction of the previously reported acetamide heteroscorpionate precursors with 0.5 equiv. of the corresponding AlR3. In the solid state, complexes 1–6 adopt a distorted trigonal bipyramidal structure with the heteroscorpionate ligands arranged in a κ2-NO coordination mode. The molecular structures of 1–6 in solution were studied by VT NMR spectroscopy and a fluxional exchange between coordinated and noncoordinated pyrazole rings was observed. This process led to interconversion between the different isomers. Compounds 4 and 6 were used as precursors for the synthesis of the aryloxide aluminium compounds [Al(OR)(κ2-sbpam)2] (7) and [Al(OR){κ2-(S)-mbpam}2] (8) (R = 2,6-Me2C6H3O) by reaction with the corresponding 2,6-dimethylphenol. The structures of the complexes were determined by spectroscopic methods, and the X-ray crystal structures of 2, 6 and 7 were also established. Five-coordinate compounds 1–8 were evaluated as initiators in the ring-opening polymerization of rac-lactide. Compound 5 was also evaluated in the presence of a co-initiator. Finally, a study of the block and random copolymerization of ε-caprolactone and L-lactide was carried out.
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