Zr/Zr and Zr/Fe dinuclear complexes with flexible bridging ligands. Preparation by olefin metathesis reaction of the mononuclear precursors and properties as polymerization catalysts

摘要

Mononuclear Zr complexes CpZrCl2{eta(5)-C5H4(CH2)(n)CH=CH2} (n = 1, 2, 3) undergo intermolecular metathesis of the vinyl group catalyzed by a Ru complex to produce dinuclear complexes with bridging ligands, (CpZrCl2)(2){mu-eta(5),eta(5),-C5H4(CH2),CH=CH(CH2)(n)C5H4}. Hydrogenation of the products catalyzed by Pd/C affords complexes with a flexible polymethylene chain that bridges two Cp2ZrCl2 groups. A dinuclear complex with a bridging bisfluorenyl ligand, (CpZrCl2)(2)(mu-eta(5),eta(5)-C13H8CH2CH=CHCH2C13H8), is also obtained from the metathesis of a mononuclear Zr complex with the allylfluorenyl ligand. X-ray crystallography of (CpZrCl2)(2)(mu-eta(5),eta(5)-C13H8CH2CH=CHCH2C13H8) revealed the molecular structure with a transC=C double bond and the two Zr centers situated at different sides of the bridging bisfluorenyl ligand. Cross metathesis reaction of CpZrCl2{eta(5)-C5H4(CH2)(2)CH=CH2} and ferrocenylmethyl acrylate produces the Zr/Fe dinuclear complex CpZrCl2{eta(5)-C5H4(CH2)(2)-CH=CHCOOCH2C5H4}FeCp. The dinuclear complexes catalyze polymerization of ethylene and propylene in the presence of MAO (methylaluminoxane). The activity of the Zr/Zr dinuclear complexes for ethylene polymerization is higher than that of the mononuclear precursors. The length and flexibility of the bridging group of the biscyclopentadienyl ligand also influence the catalytic activity.