Abstract:CeCl 3 (thf) reagiert bei niedrigen Temperaturen mit MeLi, t-BuLi und n-BuLi zu isolierbaren Organocer-Komplexen.E ine lçsemittelabhängige,z .T .s tark ausgeprägte Dissoziation von n-BuLi konnte durch 7 Li-NMR-Spektroskopie aufgeklärt werden. Dieses Verhalten deutet darauf hin, dass "Ce(n-Bu) 3 (thf) x "o der Solvens-separierte Ionenpaare wie "[Li(thf) 4 ][Ce(n-Bu) 4 (thf) y ]" die dominanten Spezies des Imamoto-Reagenzes sind. Die Stabilitätder Komplexe Li 3 Ln-(n-Bu) 6 (thf) 4 steigt mit der Abnahme der Ln I… Show more
“… Top: Original and current syntheses of MeLi. [6, 10.11] Middle: Examples for use of “salt‐contaminated” MeLi in organometallic synthesis: popular reagents for organic transformations [14–17] . Bottom: donor effect on MeLi structure [23, 24, 29] …”
Section: Figurementioning
confidence: 99%
“…Organolithium compounds including methyllithium feature also cornerstones in organometallic chemistry as transmetalation reagents (Figure 1). [14–17] Here, as for organic transformations, the availability and use of pure organolithium reagents is considered beneficial if not essential [18] . Hard to separate LiX contaminations do not only affect reagent/catalyst design and elucidation but also have a marked effect on the crystallographic and nuclear magnetic resonance properties of the synthesized complexes, and hence any interpretations made.…”
Commercially available stock solutions of organolithium reagents are well-implemented tools in organic and organometallic chemistry. However, such solutions are inherently contaminated with lithium halide salts, which can complicate certain synthesis protocols and purification processes. Here, we report the isolation of chloride-free methyllithium employing K[N(SiMe 3 ) 2 ] as a halide-trapping reagent. The influence of distinct LiCl contaminations on the 7 Li-NMR chemical shift is examined and their quantification demonstrated. The structural parameters of new chloride-free monomeric methyllithium complex [(Me 3 TACN)LiCH 3 ], ligated by an azacrown ether, are assessed by comparison with a halide-contaminated variant and monomeric lithium chloride [(Me 3 TACN)LiCl], further emphasizing the effect of halide impurities.
“… Top: Original and current syntheses of MeLi. [6, 10.11] Middle: Examples for use of “salt‐contaminated” MeLi in organometallic synthesis: popular reagents for organic transformations [14–17] . Bottom: donor effect on MeLi structure [23, 24, 29] …”
Section: Figurementioning
confidence: 99%
“…Organolithium compounds including methyllithium feature also cornerstones in organometallic chemistry as transmetalation reagents (Figure 1). [14–17] Here, as for organic transformations, the availability and use of pure organolithium reagents is considered beneficial if not essential [18] . Hard to separate LiX contaminations do not only affect reagent/catalyst design and elucidation but also have a marked effect on the crystallographic and nuclear magnetic resonance properties of the synthesized complexes, and hence any interpretations made.…”
Commercially available stock solutions of organolithium reagents are well-implemented tools in organic and organometallic chemistry. However, such solutions are inherently contaminated with lithium halide salts, which can complicate certain synthesis protocols and purification processes. Here, we report the isolation of chloride-free methyllithium employing K[N(SiMe 3 ) 2 ] as a halide-trapping reagent. The influence of distinct LiCl contaminations on the 7 Li-NMR chemical shift is examined and their quantification demonstrated. The structural parameters of new chloride-free monomeric methyllithium complex [(Me 3 TACN)LiCH 3 ], ligated by an azacrown ether, are assessed by comparison with a halide-contaminated variant and monomeric lithium chloride [(Me 3 TACN)LiCl], further emphasizing the effect of halide impurities.
“…Organolithiumverbindungen und insbesondere Methyllithium spielen ebenfalls eine Schlüsselrolle als Transmetallierungsreagenzien in der Organometallchemie (Abbildung 1). [14–17] In diesen Fällen ist, wie schon bei den organischen Transformationen, die Verfügbarkeit und Verwendung von reinen Organolithiumreagienzen von großem Vorteil, wenn nicht sogar unabdingbar [18] . Schwer abtrennbare LiX‐Verunreinigungen beeinflussen nicht nur Reagenz‐ sowie Katalysatorentwicklung und ‐aufklärung, sondern haben auch einen merklichen Effekt auf die kristallographischen und NMR‐spektroskopischen Eigenschaften der synthetisierten Komplexe und somit auch auf die getroffenen Schlussfolgerungen.…”
Section: Figureunclassified
“… Oben: Ursprüngliche und aktuelle Syntheserouten von MeLi [6, 10, 11] . Mitte: Beispiele der Anwendung von “Salz‐verunreinigtem” MeLi in der organometallischen Synthese: Gängige Reagenzien für organische Transformationen [14–17] Unten: Effekt von Donoren auf MeLi‐Strukturen [23, 24, 29] …”
Kommerziell erhältliche Stammlösungen von Organolithiumverbindungen sind vielfach eingesetzte Reagenzien in der Organischen und Metallorganischen Chemie. Solche Lösungen sind jedoch von "Natur aus" mit Lithiumhalogenidsalzen verunreinigt, die viele Syntheseprotokolle und Aufreinigungsprozesse erheblich einschränken. In dieser Arbeit beschreiben wir die Isolierung von chloridfreiem Methyllithium mithilfe von K[N(SiMe 3 ) 2 ] als Halogenidfällungsreagenz. Der Einfluss von definierten LiCl-Verunreinigungen auf die 7 Li-NMR chemische Verschiebung wurde systematisch untersucht und quantifiziert. Die strukturellen Parameter des neuen chloridfreien Methyllithiumkomplexes [(Me 3 TACN)LiCH 3 ] wurden mit der halogenidverunreinigten Variante und monomerem Lithiumchlorid [(Me 3 TACN)LiCl] verglichen.
Rare‐earth‐metal (Ln) alkyl and aryl compounds feature highly reactive, thermally labile [Ln–C] s‐bonds which result in rapid and violent decomposition in the presence of air and moisture. Nevertheless, such [Ln–C] moieties display important intermediate species in numerous organic transformations. Reagents containing [Ln–C] bonds are deliberately generated in situ like Imamoto‐type reagents Ln(III)Cl3/RLi (routinely at low temperatures) or “heavy” lanthanide‐Grignard compounds RLnX. Samarium(III)‐alkyl species are supposed intermediates of SmI2‐promoted Barbier‐type carbon– carbon coupling reactions. Alkyl/aryl ligand exchange at Ln(III) centers has been identified as the crucial step of lanthanide–halogenexchange reactions. In the meantime, several such mixed alkyl/halogenido complexes, devoid of an ancillary ligand, could be isolated and scrutinized with regard to structure and reactivity. More recently, Ln(III)‐alkylidene complexes could be accessed, structurally authenticated and successfully employed in Tebbe‐like olefination reactions of ketones.
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