Abstract
A new family of cobalt complexes (CoCl2-H, CoCl2-Me, CoCl2-iPr, CoBr2-H, CoBr2-Me, CoBr2-iPr, CoI2-H, CoI2-Me, and CoI2-iPr) supported by a PN3 ligand (6-(N,N′-di-t-butylphosphino)-2-pyrazol-yl-aminopyridine) have been prepared and fully characterized by FT-IR, elemental analysis, and X-ray analysis. The X-ray analysis reveals a trigonal bipyramidal conformation in the solid state for all representative complexes, CoCl2-H, CoBr2-H, CoBr2-iPr and CoI2-Me. The cobalt center is chelated by the PN3 ligand through the pyridinyl nitrogen, the pyrazol nitrogen and the phosphorus donor, with a long Co-P bond distance indicating a labile character. On activation with AlEt2Cl, Al2Et3Cl3, MAO, [Ph3C]+[B(C6F5)4]-/AliBu3 or AliBu3, cis-1,4 selective butadiene polymerization was achieved with up to 98.6% selectivity. The polymerization results show that the cis-1,4 selectivity is influenced by the steric hindrance, increasing with the bulkiness of the substituent groups (CoX2-iPr > CoX2-Me > CoX2-H) at the 3,5-positions of the pyrazole moiety, together with a slight decrease in activity. The activity changes in the order CoCl2L ≈ CoBr2L > CoI2L (for the same ligand L) when MAO is used as the activator, while the high level of cis-1,4 selectivity is maintained. It is possible to switch the selectivity from cis-1,4 to syndiotactic-1,2 by adding PPh3 © The Royal Society of Chemistry.
Original language | English (US) |
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Pages (from-to) | 19399-19407 |
Number of pages | 9 |
Journal | Dalton Trans. |
Volume | 45 |
Issue number | 48 |
DOIs | |
State | Published - 2016 |
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CCDC 1431671: Experimental Crystal Structure Determination : dichloro-(P,P-di-t-butyl-N-(6-(3,5-dimethyl-1H-pyrazol-1-yl)pyridin-2-yl)phosphinous amide)-cobalt
Gong, D. (Creator), Zhang, X. (Creator), Huang, K.-W. (Creator) & Zhang, X. (Creator), Cambridge Crystallographic Data Centre, Nov 24 2016
DOI: 10.5517/ccdc.csd.cc1k1ry9, http://hdl.handle.net/10754/624527
Dataset
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CCDC 1431673: Experimental Crystal Structure Determination : dibromo-(P,P-di-t-butyl-N-(6-(3,5-diisopropyl-1H-pyrazol-1-yl)pyridin-2-yl)phosphinous amide)-cobalt
Gong, D. (Creator), Zhang, X. (Creator), Huang, K.-W. (Creator) & Zhang, X. (Creator), Cambridge Crystallographic Data Centre, Nov 24 2016
DOI: 10.5517/ccdc.csd.cc1k1s0d, http://hdl.handle.net/10754/624529
Dataset
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CCDC 1431672: Experimental Crystal Structure Determination : (P,P-di-t-butyl-N-(6-(3,5-dimethyl-1H-pyrazol-1-yl)pyridin-2-yl)phosphinous amide)-diiodo-cobalt
Gong, D. (Creator), Zhang, X. (Creator), Huang, K.-W. (Creator) & Zhang, X. (Creator), Cambridge Crystallographic Data Centre, Nov 24 2016
DOI: 10.5517/ccdc.csd.cc1k1rzb, http://hdl.handle.net/10754/624528
Dataset