Zirconium and Titanium Propylene Polymerization Precatalysts Supported by a Fluxional C 2 -Symmetric Bis(anilide)pyridine Ligand
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AbstractTitanium and zirconium complexes supported by a bis(anilide)pyridine ligand (NNN = pyridine-2,6-bis(N-mesitylanilide)) have been synthesized and crystallographically characterized. C 2-symmetric bis(dimethylamide) complexes were generated from aminolysis of M(NMe 2) 4 with the neutral, diprotonated NNN ligand or by salt metathesis of the dipotassium salt of NNN with M(NMe 2) 2Cl 2. In contrast to the case for previously reported pyridine bis(phenoxide) complexes, the ligand geometry of these complexes appears to be dictated by chelate ring strain rather than metal-ligand π bonding. The crystal structures of the five-coordinate dihalide complexes (NNN)MCl 2 (M = Ti, Zr) display a C 1-symmetric geometry with a stabilizing ipso interaction between the metal and the anilido ligand. Coordination of THF to (NNN)ZrCl 2 generates a six-coordinate C 2-symmetric complex. Facile antipode interconversion of the C 2 complexes, possibly via flat C 2v intermediates, has been investigated by variable-temperature 1H NMR spectroscopy for (NNN)MX 2(THF) n (M = Ti, Zr; X = NMe 2, Cl) and (NNN)Zr(CH 2Ph) 2. These complexes were tested as propylene polymerization precatalysts, with most complexes giving low to moderate activities (10 2-10 4 g/(mol h)) for the formation of stereoirregular polypropylene. © 2012 American Chemical Society.
CitationTonks IA, Tofan D, Weintrob EC, Agapie T, Bercaw JE (2012) Zirconium and Titanium Propylene Polymerization Precatalysts Supported by a Fluxional C 2 -Symmetric Bis(anilide)pyridine Ligand . Organometallics 31: 1965–1974. Available: http://dx.doi.org/10.1021/om201262h.
SponsorsWe thank Lawrence Hen ling and Dr. Michael Day for assistance with the X-ray studies. The Bruker KAPPA APEXII X-ray diffractometer was purchased via an NSF CRIF:MU award to the California Institute of Technology, CHE-0639094. DFT calculations were carried out using the Molecular Graphics and Computation Facility, College of Chemistry, University of California, Berkeley, CA, with equipment support from NSF Grant No. CHE-0233882. We acknowledge Dr. Jo Ann Canich (Exxon) for the GPC data and for experimental insight. This work has been supported by the USDOE Office of Basic Energy Sciences (Grant No. DE-FG03-85ER13431) and by the KAUST Center-In-Development at King Fahd University of Petroleum and Minerals (Dhahran, Saudi Arabia).
PublisherAmerican Chemical Society (ACS)