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

Mononuclear Zr complexes CpZrCl 2 {η 5 -C 5 H 4 (CH 2 ) n CH=CH 2 } (n = 1, 2, 3) undergo intermolecular metathesis of the vinyl group catalyzed by a Ru complex to produce dinuclear complexes with bridging ligands, (CpZrCl 2 ) 2 {μ-η 5 ,η 5 -C 6 H 4 (CH 2 ) n CH=CH(CH 2 ) n C 5 H 4 }. Hydrogenation of the products catalyzed by Pd/C affords complexes with a flexible polymethylene chain that bridges two Cp 2 ZrCl 2 groups. A dinuclear complex with a bridging bisfluorenyl ligand, (CpZrCl 2 ) 2 (μ-η 5 ,η 5 -C 1 3 H 8 CH 2 CH=CHCH 2 C 1 3 H 8 ), is also obtained from the metathesis of a mononuclear Zr complex with the allylfluorenyl ligand. X-ray crystallography of (CpZrCl 2 ) 2 (μ-η 5 ,η 5 -C 1 3 H 8 CH 2 CH=CHCH 2 C 1 3 H 8 ) revealed the molecular structure with a trans-C=C double bond and the two Zr centers situated at different sides of the bridging bisfluorenyl ligand. Cross metathesis reaction of CpZrCl 2 {η 5 -C5H4(CH2)2CH=CH2} and ferrocenylmethyl acrylate produces the Zr/Fe dinuclear complex CpZrCl 2 {μ-η 5 ,η 5 -C5H4(CH2)2-CH=CHCOOCH 2 C 5 H 4 }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.