Sc(iii) complexes with neutral N3- and SNS-donor ligands – a spectroscopic study of the activation of ethene polymerisation catalysts

Bartlett, Stuart A., Cibin, Giannantonio, Dent, Andrew J., Evans, John, Hanton, Martin J., Reid, Gillian, Tooze, Robert P. and Tromp, Moniek (2013) Sc(iii) complexes with neutral N3- and SNS-donor ligands – a spectroscopic study of the activation of ethene polymerisation catalysts. Dalton Transactions, 42 (6), 2213-2223. (doi:10.1039/c2dt31804k). (PMID:23192302)

Abstract

Scandium trichloride complexes with tridentate N-3- and S2N-donor ligands (L-3) have been synthesised and characterised by IR, H-1, C-13{H-1} and Sc-45 NMR spectroscopy, microanalysis, and solid state and solution XAFS spectroscopy. Catalytic testing of a subset of these complexes with ethene has been undertaken in chlorobenzene with MMAO-3A and PMAO-IP at 60 degrees C and 40 bar ethene, giving low activity ethene polymerisation. The reactions of these complexes with MeLi and AlMe3 were studied by H-1, C-13{H-1}, Al-27 and Sc-45 NMR spectroscopy and in situ via Sc K-edge XAFS spectroscopy. Three or four mol. equivalents of MeLi react with [ScCl3(Me-3-tacn)] in THF solution to form [ScMe3(Me-3-tacn)] cleanly, while complexes of type [ScCl3(R-SNS)] {R-SNS = HN(CH2CH2SC10H21)(2)} form two different species proposed to be [ScMe3(R-SN(Li)S)] and [ScMe2(R-SN-S)]. In contrast, in situ Sc-45 NMR and Sc K-edge XAFS spectroscopic studies of the reaction of [ScCl3(Me-3-tacn)] with 10 mol. equivalents of AlMe3 strongly suggest that alkylation at the Sc(III) centre does not occur, instead retaining the Cl3N3 coordination environment and most likely forming Sc-Cl-AlMe3 bridging interactions. Similar studies on [ScCl3(decyl-SNS)] with 10 mol. equivalents of AlMe3 are also consistent with this, indicating that alkylation at the Sc centre does not occur except in the presence of co-catalyst [Ph3C][Al{OC(CF3)(3)}(4)] and the alpha-alkene, hex-1-ene.

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Contributors

Author: John Evans

Author: Gillian Reid

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