polymerization of sterically hindered a-olefins with singlesite group 4 metal catalyst precursors
Authors
abstract
a variety of group 4 metal catalytic systems (c2-symmetric {ebthi}-, {sbi}-type zirconocene complexes (c2-1–4); c1-symmetric (c1-5–8) and cs-symmetric (cs-9) {cp/flu}-type zirconocene complexes; cp*2zrcl2 (cp* 2-10)), half-metallocene complexes (cpticl3, hm-11), constrained-geometry (cgc-12) titanium catalysts) and post-metallocene catalysts (dow’s ortho-metallated amido-pyridino hafnium complex (pm-13)) have been screened in the polymerization of the sterically demanding 3-methylbut-1-ene (3mb1) and vinylcyclohexane (vch). all systems proved to be sluggishly active under regular conditions (toluene, 20°c; mao as cocatalyst) towards 3mb1, with productivities in the range 0–15 kg.mol–1.h–1. higher productivities (up to 75 kg.mol–1.h–1) were obtained in the polymerization of vch with c1-symmetric metallocene catalysts under the same conditions, while cs-symmetric systems were found to be completely inactive. for both 3mb1 and vch, under all conditions tested, the most productive catalyst appeared to be dow’s post-metallocene system pm-13/mao. optimization of the polymerization conditions led to a significant enhancement of the productivities of this catalyst system towards both 3mb1 and vch up to 390 and 760 kg.mol–1.h–1, respectively (tpolym = 70°c). 13c nmr spectroscopy studies revealed that all isolated p(3mb1) and p(vch) polymers were isotactic, regardless the nature/symmetry of the (pre)catalyst used. the nature of the chain-end groups in p(3mb1) is consistent with two different chaintermination mechanisms, namely b-h elimination/transfer-to-monomer for c2-1/mao and chain-transfer to me3al for pm-13/mao systems, respectively. for polymerization of vch with pm-13/mao at 70°c, b-h elimination / transfer-to-monomer appeared to be the main chain termination reaction.
similar resources
Polymerization of sterically hindered a-olefins with single-site group 4 metal catalyst precursors
A variety of group 4 metal catalytic systems (C2-symmetric {EBTHI}-, {SBI}-type zirconocene complexes (C2-1–4); C1-symmetric (C1-5–8) and Cs-symmetric (Cs-9) {Cp/Flu}-type zirconocene complexes; Cp*2ZrCl2 (Cp* 2-10)), half-metallocene complexes (CpTiCl3, HM-11), constrained-geometry (CGC-12) titanium catalysts) and post-metallocene catalysts (Dow’s ortho-metallated amido-pyridino hafnium comple...
full textIncreased efficiency in cross-metathesis reactions of sterically hindered olefins.
Efficiency in olefin cross-metathesis reactions is affected upon reducing the steric bulk of N-heterocyclic carbene ligands of ruthenium-based catalysts. For the formation of disubstituted olefins containing one or more allylic substituents, the catalyst bearing N-tolyl groups is more efficient than the corresponding N-mesityl catalyst. In contrast, the formation of trisubstituted olefins is mo...
full textEfficient Hydrogenation of Sterically Hindered Olefins with Borane-Methyl Sulfide Complex
Sterically hindered olefins are efficiently reduced to the corresponding alkanes by the boranemethyl sulfide (BMS) complex at room temperature (or below) in dichloromethane containing a mild one-electron oxidant (such as an aromatic cation radical) or by the passage of an anodic current. In an alternative procedure, the hydrogenation of the same (electron-rich) olefins with the BMS complex (in ...
full textGroup (IV) Metallocene Complexes with Bulky ω-aryloxyalkyl-Substituted Indenyl Ligands as Catalyst Precursors for Homogeneous Ethylene Polymerization
A series of seven new complexes of zirconium and hafnium with bulky ω-aryloxyalkyl substituted indenyl ligands were synthesized and characterized by NMR spectroscopy and elemental analysis. These complexes were activated with methylaluminoxane and tested for homogeneous ethylene polymerization. The zirconium catalysts showed higher activities than their hafnium an...
full textA highly active Suzuki catalyst for the synthesis of sterically hindered biaryls: novel ligand coordination.
A catalyst system for the preparation of biaryls containing four ortho substituents via Suzuki coupling is described. The combination of a catalytic quantity of Pd2(dba)3 with either an electron-rich biarylphosphine or DPEPhos is effective using a wide range of substrates. The X-ray crystal structure of (dba)Pd(2-(9-phenanthryl)phenyl-dicyclohexylphosphine), in which the Pd is coordinated to th...
full textSome highly sterically hindered organosilicon compounds
The chemistry of organometallic compounds with bulky ligands such as (Me3Si)3C(Tsi) or (Me2PhSI)3C(Tpsi) attached to a variety of metal centres is reviewed. The compounds Tsi2M (M = Zn, Cd, Hg) and the rare two co-ordinate TsiMn show exceptional thermal and hydrolytic stability. The corresponding alkylmetal halides form ring or cage structures. In a range of new boron compounds the structures o...
full textMy Resources
Save resource for easier access later
Journal title:
polyolefins journalجلد ۴، شماره ۱، صفحات ۱۲۳-۱۳۶
Hosted on Doprax cloud platform doprax.com
copyright © 2015-2023