Synthesis, Structure, and Reactivity of (C5H4SiMe3)2Y{(μ-FC6F4)(μ-Me)B(C6F5)2}:  Tight Ion Pairing in a Cationic Lanthanide Complex

Song, Xingyou; Bochmann, Manfred

doi:10.1021/om971044s

Cited by 59 publications

(26 citation statements)

References 24 publications

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“…B. im Komplex [{Cp′ 2 Y} δ + {(μ‐CH 3 )B(C 6 F 5 ) 3 } δ − ] (Cp′=C 5 H 4 SiMe 3 ), ausgebildet werden (Abbildung 14). 176 Auch das [Sb 2 F 11 ] − ‐Ion kann durch ein geeignetes elektrophiles Kation, z. B.…”

Section: Grenzen Schwach Koordinierender Anionenunclassified

Nichtkoordinierende Anionen – Traum oder Wirklichkeit? Eine Übersicht zu möglichen Kandidaten

2004

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Gibt es so etwas wie ein wirklich nichtkoordinierendes Anion? Wäre es nicht großartig, jede verrückte, schöne oder einfach nur nützliche kationische Spezies herstellen zu können, sei es, weil sie einen gerade interessiert oder weil man sie vielleicht schon einmal im Massenspektrum entdeckt hat? Um dieses Ziel in kondensierter Phase zu erreichen, müssen die Zielkationen mit einem geeigneten Gegenion versehen werden – dies ist der Moment, bei dem häufig Schwierigkeiten auftreten und viele gute Ideen wegen einer Koordination oder Zersetzung des Anions im Abguss enden. Zur Lösung des Problems bietet sich womöglich eines der neuen schwach koordinierenden Anionen (WCAs) an, die Gegenstand dieses Aufsatzes sind. Vorgestellt werden neue Entwicklungen, Anwendungen, Ausgangsmaterialien und allgemeine Strategien zur Einführung von WCAs in ein System. Einige der ungewöhnlichen Eigenschaften von WCA‐Salzen wie hohe Löslichkeit in unpolaren Medien, Pseudo‐Gasphasenbedingungen in der kondensierten Phase oder die Stabilisierung von schwach gebundenen und niedrig geladenen Komplexen werden anhand thermodynamischer Betrachtungen plausibel gemacht. Die Grenzen bei der Verwendung von WCAs – durch Koordination und Zersetzung – werden aufgezeigt, und eine quantenchemische Analyse der WCA‐Typen wird vorgestellt. Dies ermöglicht es, die Entscheidung für ein spezielles WCA auf der Basis von harten quantitativen Daten aus einer Vielzahl von Anionen zu gründen.

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Section: Grenzen Schwach Koordinierender Anionenunclassified

Nichtkoordinierende Anionen – Traum oder Wirklichkeit? Eine Übersicht zu möglichen Kandidaten

2004

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“…Comparatively short bonds La···C1 (2.78(1) ) and La···C2' (2.79(1) ) suggest a tight interaction of the electron-deficient lanthanum cation with the counterion. [24,25] (All hydrogen atoms at the sp 3hybridized C1 and C2 carbon atoms were located and refined isotropically.) The electron deficiency is further substantiated by significantly shortened LaÀC(C 5 Me 5 ) bonds (av.…”

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confidence: 99%

Cationic Rare‐Earth‐Metal Half‐Sandwich Complexes for the Living trans‐1,4‐Isoprene Polymerization

2008

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Dedicated to Professor William J. Evans on the occasion of his 60th birthday Nature provides mankind with highly stereoregular polyterpenes, i.e., polymers of isoprene, featuring distinct properties.[1] Natural rubber (NR, caoutchouc or cis-1,4-polyisoprene, cPIP; > 99 % cis content, M n % 2 10 6 g mol À1 ) is the most important polymer produced by plants and is the raw material for numerous rubber applications. Taking into account new developments in synthetic polymer chemistry, a mechanism for living carbocationic polymerization has recently been proposed for NR biosynthesis.[2] Gutta-percha obtained from Palaquium gutta and several other evergreen trees of East Asia is an isomer of NR displaying an all-trans (> 99 %) configuration and much lower molecular weight (M n = 1.4-1.7 10 5 g mol À1 ).[1] Unlike NR it is a thermoplastic crystalline polymer with a melting point (T m ) of 628C. Although for most applications gutta-percha has been superseded by advanced functional polymers, controlled crosslinking of synthetic trans-1,4-polyisoprene or its blending (with, for example, natural rubber, styrene-butadiene rubber, and butadiene rubber) and block copolymerization (e.g., with a-olefins) might afford new high-performance materials.[3]The synthesis of highly stereoregular cPIP with Zieglertype catalysts is well established. [4,5] In particular, catalyst mixtures with rare-earth-metal components such as neodymium represent a prominent class of high-performance catalysts for the industrial stereospecific polymerization (> 98 % cis-1,4) of 1,3-dienes, even though the molecular weights and molecular weight distributions remain difficult to control.[6] Molecular systems based on lanthanide metallocene and postmetallocene congeners afford polymers with very narrow molecular weight distributions and very high stereoregularity. [7][8][9][10] A combination of [(C 5 Me 5 ) 2 Ln(AlMe 4 )]/Al-(iBu) 3 /[Ph 3 C][B(C 6 F 5 ) 4 ] (Ln = Sm, Gd) gave cis-1,4-polybutadiene with excellent stereocontrol (up to 99.9 % cis) and narrow molecular weight distributions (M w /M n = 1.20-1.23), while the polymerization of isoprene was not observed to be living. [7] cPIP with comparable characteristics (95-99 % cis-1,4; M w /M n = 1.3-1.7) was obtained with neodymium allyl complexes in the presence of aluminum alkyls as activators [8,9] as (PNP Ph = ({2-(Ph 2 P)C 6 H 4 } 2 N], Ln = Sc, Y, Lu) were reported to yield high cis-1,4 selectivity in the living polymerization of isoprene and butadiene in the absence of any aluminum additive (> 99 % cis-1,4; M w /M n = 1.05).[11] The fabrication of synthetic gutta-percha and gutta-balata has been achieved by utilization of mixed organo-Ln/Mg initiators such as [(CMe 2 C 5 H 4 ) 2 Sm(C 3 H 5 )MgCl 2 (OEt 2 ) 2 LiCl(OEt 2 )] (> 95 % trans-1,4; M w /M n = 1.32) [12] and half-sandwich-based [(C 5 Me 4 nPr)Nd(BH 4 ) 2 (thf) 2 ]/Mg(nBu) 2 (Mg/Nd = 0.9; 98.5 % trans-1,4, M w /M n = 1.15).

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“…However, the potentiality of yttrium complexes for isobutene polymerization has been shown by Bochmann and co-workers who have used a yttrium metallocene complex as cationic initiator. [2] In this paper, we show that lanthanide chlorides can be activated in order to provide efficient catalysts for isobutene polymerization.…”

Section: Introductionmentioning

confidence: 93%

Highly Active Yttrium and Lanthanide Catalysts for Polymerization of Isobutene

Touchard

Spitz

Boisson

et al. 2004

Macromol. Rapid Commun.

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Summary: Highly active catalysts for isobutene polymerization were obtained by mixing silica with yttrium or lanthanide chloride salts. Solid catalysts were investigated using transmission electron microscopy and Raman spectroscopy. Both Lewis and Brönsted acid sites were detected on the surface. Polymers of low and medium molecular weight were prepared and their unsaturated chain ends were fully investigated by one‐ and two‐dimensional NMR analyses.13C NMR spectrum of a low‐molecular‐weight polyisobutene (high‐field resonance region).image13C NMR spectrum of a low‐molecular‐weight polyisobutene (high‐field resonance region).

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Synthesis, Structure, and Reactivity of (C₅H₄SiMe₃)₂Y{(μ-FC₆F₄)(μ-Me)B(C₆F₅)₂}: Tight Ion Pairing in a Cationic Lanthanide Complex

Cited by 59 publications

References 24 publications

Nichtkoordinierende Anionen – Traum oder Wirklichkeit? Eine Übersicht zu möglichen Kandidaten

Nichtkoordinierende Anionen – Traum oder Wirklichkeit? Eine Übersicht zu möglichen Kandidaten

Cationic Rare‐Earth‐Metal Half‐Sandwich Complexes for the Living trans‐1,4‐Isoprene Polymerization

Highly Active Yttrium and Lanthanide Catalysts for Polymerization of Isobutene

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