Reversible Chain Transfer between Organoyttrium Cations and Aluminum: Synthesis of Aluminum‐Terminated Polyethylene with Extremely Narrow Molecular‐Weight Distribution

Kretschmer, Winfried P.; Meetsma, Auke; Hessen, Bart; Schmalz, Thomas; Qayyum, Sadaf; Kempe, Rhett

doi:10.1002/chem.200600660

Cited by 150 publications

(107 citation statements)

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“…Criteria for very fast, reversible, chain transfer are very narrow molecular-weight distributions < 1.1 up to the precipitation point, [13] linear time-dependent chain growth during which b-H transfer/elimination is suppressed giving rise to Poisson distributed polymers. [21] Only a few systems have been described that meet these requirements so far: the Sm/Mg system based on 1, the Y + /Al system based on 3, the Zr + or Hf + /Al-Zn system based on 9 and 10 and the Fe + /Al-Zn based on 7 or 22.…”

Section: Discussionmentioning

confidence: 99%

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How to Polymerize Ethylene in a Highly Controlled Fashion?

Kempe

2007

Chemistry A European J

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Very fast, reversible, polyethylene (PE) chain transfer or complex-catalysed "Aufbaureaktion" describes a "living" chain-growing process on a main-group metal or zinc atom; this process is catalysed by an organo-transition-metal or lanthanide complex. PE chains are transferred very fast between the two metal sites and chain growth takes place through ethylene insertion into the transition-metal- or lanthanide-carbon bond-coordinative chain-transfer polymerisation (CCTP). The transferred chains "rest" at the main-group or zinc centre, at which chain-termination processes like beta-H transfer/elimination are of low significance. Such protocols can be used to synthesise very narrowly distributed PE materials (M(w)/M(n)<1.1 up to a molecular weight of about 4000 g mol(-1)) with differently functionalised end groups. Higher molecular-weight polymers can be obtained with a slightly increased M(w)/M(n), since diffusion control and precipitation of the polymers influences the chain-transfer process. Recently, a few transition-metal- or lanthanide-based catalyst systems that catalyse such a highly reversible chain-growing process have been described. They are summarised and compared within this contribution.

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Section: Discussionmentioning

confidence: 99%

“…Consequently, reversible chain transfer to aluminium was observed for organoyttrium cations. [13] Such cations are accessible in high yield [14] with one equivalent of sterically demanding aminopyridines, for instance, (2,6-diisopropylphenyl)- [6-(2,4,6-triisopropylphenyl)…”

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How to Polymerize Ethylene in a Highly Controlled Fashion?

Kempe

2007

Chemistry A European J

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“…[13][14][15] 4 ] with 1 in toluene leads to the mono substituted complexes 4a and 4b, respectively, due to clean elimination of one toluene molecule (Scheme 1).…”

Section: Synthesis and Structures Of The Zr And Hf Tribenzyl Complexesmentioning

confidence: 99%

Synthesis and Structure of Zirconium and Hafnium Polymerisation Catalysts Stabilised by Very Bulky Aminopyridinato Ligands

et al. 2008

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Mono(aminopyridinato) complexes of the type [ApM(CH2C6H5)3] [M = Zr, Hf and Ap = aminopyridinate] were prepared by treating the three different sterically demanding aminopyridines with one equiv. of tetrabenzylzirconium or ‐hafnium. One of the three benzyl groups is η2‐coordinated in the solid state. However all of the three benzyl substituents are equivalent in solution as evidenced by the 1H NMR spectrum. Treatment of these neutral complexes with B(C6F5)3 afforded the corresponding zwitterionic dibenzyl complexes. The η6‐coordination of the phenyl ring of the B‐bound benzyl group to the metal centre was supported by 1H NMR spectroscopy and confirmed by single‐crystal X‐ray diffraction analysis. These zwitterionic complexes show very low activity for ethylene polymerisation at low temperature since the coordination site is blocked by the η6‐coordinated phenyl ring. At elevated temperature, moderate activity with the formation of high molecular weight polyethylene (PE) was observed. An attempted abstraction of the second benzyl group failed when the zwitterionic complexes were treated with an additional equivalent of B(C6F5)3. Using one equiv. of [R2(Me)NH][B(C6F5)4] (R = C16H33–C18H37) instead of B(C6F5)3, moderate activities of ethylene polymerisation were observed. Treatment of the aminopyridinato metal tribenzyls with [R2(Me)NH][B(C6F5)4] (R = C16H33–C18H37) gave active ethylene polymerisation catalysts which produced low molecular weight PE in the case of the zirconium analogues and higher molecular weight PE in the case of the hafnium example. Propylene homopolymerisation under the same conditions failed. Ethylene–propylene copolymers with separated propene units and alternating sequences were observed in the presence of both monomers.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

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“…三烷基钇与胺基吡啶进行烷烃消除反应, 生成的单烷基配合物随即发生 sp 2 C-H 键活化反应生成苯基钇环状配合物, 该产物与 PhSiH 3 反应生成二聚体氢化物 [208] . 噻吩或苯并呋喃取代的胺基吡啶在烷烃消除反应中, 杂芳基 3-位同样发生分子内 sp 2 C-H 键活化反应 [209] .…”

Section: β-二亚胺稀土金属有机配合物 β-二亚胺是最为重要的双齿配体unclassified

Sixty Years of the Chemistry of Rare-earth Organometallic Complexes

Changtao¹,

Wang²,

Chen³

2014

Acta Chim. Sinica

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Rare-earth elements include scandium, yttrium and fifteen lanthanides. Since Wilkinson and Birmingham reported the fist example of rare-earth organometallic complex, the chemistry of rare-earth organometallic complexes has had a great advance during the past sixty years. A variety of Cp containing rare-earth metal complexes, including mono-Cp, bis-Cp, and tri-Cp complexes, have been synthesized. Variation of the size of substituent on Cp ring, introducing the nitrogen or oxygen containing pendant arm to Cp ring or using ansa bis-Cp ligands make the synthesis and stabilization of these three types of rare-earth metal Cp complexes available. The Cp related ligands, such as indenyl and fluorenyl, also have been applied for the rare-earth organometallic complexes. From 1990's, there was a tendency to explore the rare-earth organometallic complexes with ancillary ligands beyond Cp and its derivatives in order to search for more efficient rare-earth metal catalysts. Non-Cp ligands, such as biphenolates, β-diketiminates, amidinates, guanidinates, etc. have been introduced into the chemistry of rare-earth organometallic complexes, and a larger number of non-Cp rare-earth organometallic complexes have been synthesized and characterized. The application of non-cyclopentadienyl ligands not only resulted in the rare-earth organometallic complexes with new structural features, but also the catalysts with high activity and high selectivity for the polymer synthesis and organic synthesis. The rare-earth organometallic complexes catalyze homo-and co-polymerization of olefins as well as specific polymerization of dienes and polar monomers. The discovery of the catalytic system composed of the neutral rare-earth metal dialkyls/borate enables to synthesize some interesting polymers which are difficult to be prepared by using other catalytic system. The rare-earth organometallic complexes are also able to catalyze some important organic reactions, such as hydroamination, hydrophosphinylation, and hydroalkoxylation, etc. Different from the late-translation metal catalyzed organic reactions, most of the rare-earth metal catalyzed ones do not involve oxidative addition and reductive elimination steps. The review describes some important developments of the chemistry of rare-earth organometallic complexes in the past sixty years.

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Reversible Chain Transfer between Organoyttrium Cations and Aluminum: Synthesis of Aluminum‐Terminated Polyethylene with Extremely Narrow Molecular‐Weight Distribution

Cited by 150 publications

References 53 publications

How to Polymerize Ethylene in a Highly Controlled Fashion?

How to Polymerize Ethylene in a Highly Controlled Fashion?

Synthesis and Structure of Zirconium and Hafnium Polymerisation Catalysts Stabilised by Very Bulky Aminopyridinato Ligands

Sixty Years of the Chemistry of Rare-earth Organometallic Complexes

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