title: Catalytic behaviour in the ring-opening polymerisation of organoaluminiums supported by bulky heteroscorpionate ligands.
abstract: A series of alkyl organoaluminium complexes based on bulky heteroscorpionate ligands were designed as catalysts for the ring-opening polymerisation of cyclic esters. Thus, the treatment of AlX3 (X = Me, Et) with bulky acetamide or thioacetamide heteroscorpionate ligands nbptamH (1) [nbptamH = N-naphthyl-2,2-bis(3,5-dimethylpyrazol-1-yl)thioacetamide], fbpamH (2) [fbpamH = N-fluorenyl-2,2-bis(3,5-dimethylpyrazol-1-yl)acetamide], ptbptamH (3) [ptbptamH = N-phenyl-2,2-bis(3,5-di-tert-butylpyrazol-1-yl)thioacetamide], ntbptamH (4) [ntbptamH = N-naphthyl-2,2-bis(3,5-di-tert-butylpyrazol-1-yl)thioacetamide], ptbpamH (5) [ptbpamH = N-phenyl-2,2-bis(3,5-di-tert-butylpyrazol-1-yl)acetamide] and (S)-mtbpamH (6) [(S)-mtbpamH = (S)-(−)-N-α-methylbenzyl-2,2-bis(3,5-di-tert-butylpyrazol-1-yl)acetamide] for 1 hour at 0 °C afforded the dialkyl aluminium complexes [AlX2{κ(2)-nbptam}] (X = Me 7, Et 8), [AlX2{κ(2)-fbpam}] (X = Me 9, Et 10), [AlX2{κ(2)-ptbptam}] (X = Me 11, Et 12), [AlX2{κ(2)-ntbptam}] (X = Me 13, Et 14), [AlX2{κ2(-)ptbpam}] (X = Me 15, Et 16) and [AlX2{κ(2)-(S)-mtbpam}] (X = Me 17, Et 18). The structures of the complexes were determined by spectroscopic methods and the X-ray crystal structure of 14 was also established. The alkyl-containing aluminium complexes 7–18 can act as efficient single-component initiators for the ring-opening polymerisation of ε-caprolactone and rac-lactide. The polymerisations are living, as evidenced by the narrow polydispersities of the isolated polymers and the linear nature of the number average molecular weight versus conversion plot. Finally, a comparative study of ring-opening polymerisation for new bulky heteroscorpionate aluminium initiators and the less congested aluminium analogues is reported.
authors.affiliation: Departamento de Química Inorgánica, Orgánica y Bioquímica-Centro de Innovación en Química Avanzada (ORFEO-CINQA), Facultad de Ciencias y Tecnologías Químicas, Universidad de Castilla-La Mancha, 13071-Ciudad Real, Spain. Antonio.Otero@uclm.es Agustin.Lara@uclm.es.
authors.forename: Jose A
authors.initials: JA
authors.lastname: Castro-Osma
authors.forename: Carlos
authors.initials: C
authors.lastname: Alonso-Moreno
authors.forename: Agustín
authors.initials: A
authors.lastname: Lara-Sánchez
authors.forename: Antonio
authors.initials: A
authors.lastname: Otero
authors.forename: Juan
authors.initials: J
authors.lastname: Fernández-Baeza
authors.forename: Luis F
authors.initials: LF
authors.lastname: Sánchez-Barba
authors.forename: Ana M
authors.initials: AM
authors.lastname: Rodríguez