No abstract

Group 4 ansa-cyclopentadienylamido (CpA) complexes [Me2Si(Cp‘)(NR)]MCl2 (R = alkyl, M = Ti, Zr) efficiently copolymerize ethylene with a variety of α-olefins. Ethylene/norbornene copolymerization reactivity ratios were determined at 40 °C for CpA catalysts [Me2Si(Cp‘)(N t Bu)]TiCl2 (Cp‘ = Me4Cp, 2,4-Me2Cp, 3- t BuCp, Ind), and the resulting values are low (r 1 = 2.0−5.1, r 2 → 0), suggesting a tendency toward alternating comonomer insertion at high norbornene/ethylene feed ratios. As reaction temperature is increased and norbornene concentration is decreased, productivity increases and norbornene incorporation decreases. No more than 46 mol % norbornene is incorporated into the copolymer using these CpA catalysts even at low feed ratios (E/N ≥ 0.02), and norbornene homopolymerizations with [Me2Si(Me4Cp)(N t Bu)]TiCl2 proceed to very low conversion (<1%). 13C NMR spectroscopy of CpA-derived poly(ethylene-co-norbornene)s shows the copolymers contain virtually no consecutive norbornene sequences, and the microstructure of the resulting ethylene norbornene copolymers is dependent on catalyst geometry.

Mono-Cp−amido complexes [η5:η1-Cp‘SiMe2(NR)]MCl2 (M = Ti, Zr) have been synthesized by metathesis and amine elimination routes in low to moderate yields (5−50%). Two optically active examples based on (S)-(−)-(α)-methylbenzylamine are presented, and the molecular structure of (+)-(R)-[η5: η1-(Ind)SiMe2-(S)-NCHMePh]TiCl2 (4) has been determined by X-ray crystallography. These complexes are active in the presence of methylaluminoxane for propylene polymerization and yield high molecular weight atactic polymers with slight syndiotactic enrichment. Productivities, molecular weights, and tacticities are dependent on Cp‘ and NR. Incorporation of a chiral amine into the ligand framework has little effect on stereospecificity. Polypropylenes derived from the titanium catalysts show significant amounts of 2,1-monomer insertion (2−5%).

organic chemistry, review organic chemistry, review Z 0200 04 -274 Group 4 ansa-Cyclopentadienyl-Amido Catalysts for Olefin Polymerization -[104 refs.] -(MCKNIGHT, ANDREW L.; WAYMOUTH, ROBERT M.; Chem. Rev. (Washington, D. C.) 98 (1998) 7, 2587-2598; Dep. Chem., Stanford Univ., Stanford, CA 94305, USA; EN)

Triethylbismuth reacts slowly with HOAr (Ar = C6F5, Ph) in refluxing toluene to yield the compounds [BiEt,OAr], which are shown by single crystal X-ray diffraction to exist as chiral chain polymers in which bridging alkoxides join Et2Bi groups containing a stereoactive lone pair of electrons.