Dalton Transactions PAPER Cite this: Dalton Trans., 2013, 42, 2213 Received 7th August 2012, Accepted 14th November 2012 DOI: 10.1039/c2dt31804k www.rsc.org/dalton Sc(III) complexes with neutral N 3 - and SNS-donor ligands – a spectroscopic study of the activation of ethene polymerisation catalysts†‡ Stuart A. Bartlett, a Giannantonio Cibin, b Andrew J. Dent, b John Evans,* a Martin J. Hanton, c Gillian Reid,* a Robert P. Tooze c and Moniek Tromp* d Scandium trichloride complexes with tridentate N 3 - and S 2 N-donor ligands (L 3 ) have been synthesised and characterised by IR, 1 H, 13 C{ 1 H} and 45 Sc NMR spectroscopy, microanalysis, and solid state and solu- tion XAFS spectroscopy. Catalytic testing of a subset of these complexes with ethene has been under- taken in chlorobenzene with MMAO-3A and PMAO-IP at 60 °C and 40 bar ethene, giving low activity ethene polymerisation. The reactions of these complexes with MeLi and AlMe 3 were studied by 1 H, 13 C{ 1 H}, 27 Al and 45 Sc NMR spectroscopy and in situ via Sc K-edge XAFS spectroscopy. Three or four mol. equivalents of MeLi react with [ScCl 3 (Me 3 -tacn)] in THF solution to form [ScMe 3 (Me 3 -tacn)] cleanly, while complexes of type [ScCl 3 (R-SNS)] {R-SNS = HN(CH 2 CH 2 SC 10 H 21 ) 2 } form two different species proposed to be [ScMe 3 (R-SN(Li)S)] and [ScMe 2 (R-SN − S)]. In contrast, in situ 45 Sc NMR and Sc K-edge XAFS spectro- scopic studies of the reaction of [ScCl 3 (Me 3 -tacn)] with 10 mol. equivalents of AlMe 3 strongly suggest that alkylation at the Sc(III) centre does not occur, instead retaining the Cl 3 N 3 coordination environment and most likely forming Sc−Cl−AlMe 3 bridging interactions. Similar studies on [ScCl 3 (decyl-SNS)] with 10 mol. equivalents of AlMe 3 are also consistent with this, indicating that alkylation at the Sc centre does not occur except in the presence of co-catalyst [Ph 3 C][Al{OC(CF 3 ) 3 } 4 ] and the α-alkene, hex-1-ene. Introduction In the early 1980s, scandium complexes were reported to be the basis of a Ziegler-Natta type polymerisation of terminal alkynes, 1 with polymerisation of alkenes reports some 20 years ago. 2 Due in part to the success in Ziegler-Natta ethylene poly- merisation, 3 the cyclopentadienyl (cp) ligand has dominated much of the organometallic chemistry, in terms of the Group 3 metals. 4 From the 90s onwards, Group 3 non-cp based com- plexes emerged in the context of olefin polymerisation 5–8 Bercaw et al., 8 synthesised [MCl 3 (Me 3 -tacn)] and [MMe 3 - (Me 3 -tacn)] (M = Sc, Y; Me 3 -tacn = 1,4,7-trimethyl-1,4,7- triazacyclononane) complexes and demonstrated that upon activation with [HN(Me) 2 Ph][B(C 6 F 5 ) 4 ], [ScMe 3 (Me 3 -tacn)] promoted the slow formation of polyethene (PE). Following this, a notable system included the study of half sandwich, cp-functionalised yttrium complexes, with 89 Y NMR analysis. 9 In the absence of a co-catalyst, coordinated THF proved to be more tenacious, reducing the polymerisation activity compared to scandium analogues. In a scandium complex free of cp, Hayes 10 used a β-diketimidato ligand to give some activity toward ethene polymerisation in the presence of [Ph 3 C]- [B(C 6 F 5 ) 4 ] or PMAO-IP. The yttrium(III) complex, [Y{CH 2 Si- (CH 3 ) 3 ) 2 (Me 3 -tacn)], has been shown to give high molecular weight PE upon activation with [HN(CH 3 ) 2 Ph][B(C 6 F 5 ) 4 . 11 Developing the Group 3 metal tacn chemistry further, Mountford and co-workers 12 used modified neutral fac-triden- tate N 3 -donor ligands to constrain metal centres, in one case forcing a similar geometry to that of the established titanium polymerisation catalyst, 6 only to give largely inactive mixtures. When using the simplified Me 3 -tacn and tris( pyrazolyl)- methane ligand, giving the corresponding [Sc{CH 2 Si(CH 3 ) 3 } 3 - (N 3 -tridentate)], activities competitive with post-cp based scandium polyethene catalysts were observed, upon activation with B(C 6 F 5 ) 3 Lewis acid co-catalyst. 12 Since incorporation of –CH 2 Si(CH 3 ) 3 groups at the Sc(III) sites, focus has shifted to † Dedicated to Professor David Cole-Hamilton on the occasion of his retirement and for his outstanding contribution to transition metal catalysis. ‡ Electronic supplementary information (ESI) available: Fig. S1 to S3 provide EXAFS and Fourier transforms of Sc K-edge spectra. See DOI: 10.1039/c2dt31804k a School of Chemistry, University of Southampton, Southampton SO17 1BJ, UK. E-mail: je@soton.ac.uk, gr@soton.ac.uk b Diamond Light Source Ltd, Didcot, OX11 0DE, UK. E-mail: andy.dent@diamond.ac.uk c Sasol Technology UK, Purdie Building, North Haugh, St Andrew, Fife KA16 9SR, UK d Strukturanalytik in der Katalyse, Chemie, Catalysis Research Center, Technische Universität München, Lichtenbergstrasse 4, 85748 Garching, Germany. E-mail: moniek.tromp@tum.de This journal is © The Royal Society of Chemistry 2013 Dalton Trans., 2013, 42, 2213–2223 | 2213 Published on 15 November 2012. Downloaded by University of Southampton on 11/7/2022 9:43:11 AM. View Article Online View Journal | View Issue