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Published March 12, 2012 | Supplemental Material
Journal Article Open

Zirconium and Titanium Propylene Polymerization Precatalysts Supported by a Fluxional C_2-Symmetric Bis(anilide)pyridine Ligand


Titanium 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.

Additional Information

© 2012 American Chemical Society. Received: December 20, 2011. Publication Date (Web): February 16, 2012. We thank Lawrence Henling 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).

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