Progress Towards the Synthesis of a Novel 4-Carbon Linked ansa-Zirconcocene: [(CH2C(CH3)C(CH3)CH 2)(3-t-BuC5H3)2]ZrCl 2

Ansa-zirconocenes have been shown to function as homogenous Ziegler-Natta catalysts for ethylene and propylene polymerization. We are pursuing the synthesis of a novel ansa-zirconocene [(CH 2C(CH3)C(CH3)CH2)(3-t-BuC 5H3)2]ZrCl2 with a tetra-substituted alkene via ring closing metathesis (RCM). Our ultimate goal is to use the ansa product as a polymerization catalyst for ethylene, propylene and copolymers of these two monomers. We have reproducibly synthesized the precursor, bis[tert-butyl-(2-methyl-2-propenyl)cyclopentadienyl]zirconium dichloride with purification and characterization of the isomers ongoing. A second-generation Grubbs catalyst, with ortho-methyl substituted aryl rings of an N-hetereocyclic carbene, was tested to make the desired ansa product. Elevated reaction temperatures and arrayed 1H NMR experiments were employed to assess the effectiveness of this RCM catalyst; there was no evidence of the desired ansa product under these conditions and the RCM catalyst was found to decompose over time. Future studies willrequire a more thermally robust catalyst in order to re-attempt synthesis of the target ansa metallocene.