Catalytic behaviour in the ring-opening polymerisation of organoaluminiums supported by bulky heteroscorpionate ligands

Jose A Castro-Osma, Carlos Alonso-Moreno, Agustín Lara-Sánchez, Antonio Otero, Juan Fernández-Baeza, Luis F Sánchez-Barba, Ana M Rodríguez

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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 () [nbptamH = N-naphthyl-2,2-bis(3,5-dimethylpyrazol-1-yl)thioacetamide], fbpamH () [fbpamH = N-fluorenyl-2,2-bis(3,5-dimethylpyrazol-1-yl)acetamide], ptbptamH () [ptbptamH = N-phenyl-2,2-bis(3,5-di-tert-butylpyrazol-1-yl)thioacetamide], ntbptamH () [ntbptamH = N-naphthyl-2,2-bis(3,5-di-tert-butylpyrazol-1-yl)thioacetamide], ptbpamH () [ptbpamH = N-phenyl-2,2-bis(3,5-di-tert-butylpyrazol-1-yl)acetamide] and (S)-mtbpamH () [(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 , Et ), [AlX2{κ(2)-fbpam}] (X = Me , Et ), [AlX2{κ(2)-ptbptam}] (X = Me , Et ), [AlX2{κ(2)-ntbptam}] (X = Me , Et ), [AlX2{κ(2)-ptbpam}] (X = Me , Et ) and [AlX2{κ(2)-(S)-mtbpam}] (X = Me , Et ). The structures of the complexes were determined by spectroscopic methods and the X-ray crystal structure of was also established. The alkyl-containing aluminium complexes 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.

Original languageEnglish
Pages (from-to)12388-12400
Number of pages13
JournalDalton Transactions
Issue number27
Publication statusPublished - 2 Jul 2015

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