title: Synthesis, structural characterization and catalytic evaluation of the ring-opening polymerization of discrete five-coordinate alkyl aluminium complexes.
abstract: Five-coordinate alkyl aluminium complexes [AlR(κ(2)-pbpam)2] (R = Me 1, Et 2), [AlR(κ(2)-sbpam)2] (R = Me 3, Et 4) and [AlR{κ(2)-(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 κ(2)-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)(κ(2)-sbpam)2] (7) and [Al(OR){κ(2)-(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.
authors: Departamento de Química Inorgánica, Orgánica y Bioquímica, Facultad de Ciencias y Tecnologías Químicas, Universidad de Castilla-La Mancha, 13071-Ciudad Real, Spain.
authors: Jose A
authors: JA
authors: Castro-Osma
authors: Carlos
authors: C
authors: Alonso-Moreno
authors: Isabel
authors: I
authors: Márquez-Segovia
authors: Antonio
authors: A
authors: Otero
authors: Agustín
authors: A
authors: Lara-Sánchez
authors: Juan
authors: J
authors: Fernández-Baeza
authors: Ana M
authors: AM
authors: Rodríguez
authors: Luis F
authors: LF
authors: Sánchez-Barba
authors: Joaquín C
authors: JC
authors: García-Martínez
mesh_terms: D000535:Aluminum / Q000737:chemistry*; D002208:Caproates / Q000737:chemistry; D002384:Catalysis; D004146:Dioxanes / Q000737:chemistry; D007783:Lactones / Q000737:chemistry; D008958:Models, Molecular; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D058105:Polymerization
chemical_list: D002208:Caproates; D004146:Dioxanes; D007783:Lactones; D009942:Organometallic Compounds; C121056:caprolactone; C091880:dilactide; D000535:Aluminum