Metallacyclische Fünfring‐Allenoide: Synthese und Struktur stabiler stark verzerrter cyclischer Allen‐Derivate

Ugolotti, Juri; Dierker, Gereon; Kehr, Gerald; Fröhlich, Roland; Erker, Gerhard

doi:10.1002/ange.200705615

Cited by 45 publications

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“…[1] In den letzten Jahren galt unser Interesse der Synthese, der Bildung und den Reaktionen drei-, vier-und fünf-gliedriger Titana-, Zircona-und Hafnacyclen, [1,2] die wir durch den Einsatz des reaktiven Metallocenfragmentes {Cp 2 M} (Cp = Cyclopentadienyl; M = Ti, Zr, Hf), das "versteckt" im h 2 -gebundenen Bis(trimethylsilyl)acetylenkomplex vorliegt, erhalten konnten. Die Anwendung und Einsatzbreite solcher Metallocenkomplexe in stöchiometrischen oder katalytischen Reaktionen, die z.…”

Section: In Memoriam Herbert Schumannunclassified

“…B. zur Bildung von ungewöhnlichen, reinen Kohlenstoff-Metallacyclen führen, sind bereits vielfach beschrieben worden. [1,2] Besonders wenn kumulierte Doppel-oder Dreifachbindungen in kleinen, reinen Kohlenstoff-Metallacyclen auftreten, müssen sterische Spannungen berücksichtigt werden. [3] Zum Beispiel berechneten Johnson et al Ringspannungsenergien von 55 und 90 kcal mol À1 für 1,2-Cyclopentadien bzw.…”

Section: In Memoriam Herbert Schumannunclassified

“…[1,2,4] Aufgrund von Rehybridisierungseffekten verringert die externe Komplexierung (d. h. eine Koordination der Mehrfachbindung an ein zusätzliches Metallzentrum außerhalb des Rings) der C = C = C=C-, C=C=C-oder CC-Einheiten signifikant die Ringspannung. Aber auch eine interne Komplexierung (d. h. eine Koordination der Mehrfachbindung an das Metallatom des Metallacyclus) führt zur Stabilisierung von sterisch ungewöhnlich gespannten fünfgliedrigen Metallacyclen der frühen Übergangsmetalle Ti, Zr und Hf, darunter Metallacyclocumulene (1-Metallacyclopenta-2,3,4-triene; A), Metallacyclopentine (1-Metallacyclopent-3-ine; B) und Metallacycloallene (1-Metallacyclopenta-2,3-diene; C; Schema 1).…”

Section: In Memoriam Herbert Schumannunclassified

“…Weiterhin verringert eine isolobale Substitution der Kohlenstoffatome durch Heteroatome wegen einer längeren Heteroatom-Kohlenstoff-Bindung die Ringspannung. [1,2] Kleinere Ringe führen zu einer größeren Ringspannung, einem Problem, dem man sich stellen muss, wenn man von fünf-zu viergliedrigen reinen Kohlenstoff-Metallacyclen wie Metallacycloallenen (1-Metallacyclobuta-2,3-diene; D) oder diversen Metallaheterocycloallenen übergeht (Schema 2). Bislang gelang es uns nicht, solche Metallacycloallene zu isolieren.…”

Section: In Memoriam Herbert Schumannunclassified

“…Unserem Interesse an sterisch gespannten Metallacyclen der 4. Gruppe folgend, [1][2][3] [8] ]. Der N1-N2-C1-Ti2-Ring ist leicht verzerrt und enthält zwei kurze C-N-Bindun- (4) ); AEr cov (C-N) = 1.47 und AEr cov (C= N) = 1.27 ; r cov = Kovalenzradius], [9] die auf einen partiellen C = N-Doppelbindungscharakter schließen lassen, und zwei leicht geweitete Ti-N-Einfachbindungen [d(Ti2-N1) = 2.154(3), d(Ti2-N2) = 2.144(3) ; vgl.…”

Section: In Memoriam Herbert Schumannunclassified

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[Cp₂Ti^III(NCy)₂C‐Ti^IIICp₂]: ein transienter Titanocen‐Carbenkomplex?

et al. 2010

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Carben oder doch kein Carben? Durch den Einsatz von [Cp2Ti(η2‐Me3SiC2SiMe3)] (Cp=Cyclopentadienyl) als Reduktionsmittel wie auch als Abfangreagens gelang es, in der Reaktion mit RNCNR einen ungewöhnlichen, paramagnetischen Titanocen(III)‐Carben‐ähnlichen Komplex zu isolieren. Dieser Dimetallkomplex verfügt über die Topologie eines viergliedrigen NHC‐Komplexes (NHC=N‐heterocyclisches Carben) mit TiIII als Teil des Heterocyclus (siehe Struktur).

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Section: In Memoriam Herbert Schumannunclassified

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[Cp₂Ti^III(NCy)₂C‐Ti^IIICp₂]: ein transienter Titanocen‐Carbenkomplex?

et al. 2010

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Reaction of Bis(alkynyl)silanes with Tris(pentafluorophenyl)borane: Synthesis of Bulky Silole Derivatives by Means of 1,1‐Carboboration under Mild Reaction Conditions

et al. 2009

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)diphenylsilane (1d) with tris(pentafluorophenyl)-borane gave the corresponding boryl-substituted silole derivative (7d) featuring six bulky substituents attached at the central heterocyclic framework. Both the starting materials (1c, 1d) and the products (7c, 7d) were characterized by X-ray crystal structure analyses.Keywords: boranes; 1,1-carboboration; Lewis acids; siloles IntroductionThe synthetic chemistry of siloles has found increased interest lately. [1,2] This is mostly due to their use in modern materials chemistry. Suitably substituted silole derivatives have found extensive use due to their photoluminescent properties. [1b,c,3-7] Some derivatives were used as sensor materials. [8] Early synthetic entries to siloles [9] include salt metathesis routes, e.g., by reacting substituted 1,4-dilithiobutadiene reagents with R 2 SiCl 2 substrates. [10,11] A related route was used more recently to prepare lithio-A C H T U N G T R E N N U N G siloles. [12] Other work reported in the last 15 years makes use of the ready formation of the group 4 metallacyclopentadienes [13] and related complexes [14] followed by direct or indirect transmetallation from titanium or zirconium to silicon. [15] Tamao et al. developed an ingenious method of silole formation from bisA C H T U N G T R E N N U N G (alkynyl)silanes (1a) by treatment with Li/naphthalene. [16] The formation of the silole products (3) probably takes place by means of an intramolecular ring closure of a bis-radical anion intermediate (2) (see Scheme 1). This route has extensively been applied for the preparation of novel silole-based electronic materials. [6,7a,b,d-f,h] In this context, boron-and silicon-containing systems have become of interest, and easy accesses to specifically functionalized boryl-substituted siloles or similar compounds are becoming increasingly important.[17] Wrackmeyer et al. have developed and described a fascinating one-pot procedure for the preparation of boryl-substituted silole derivatives (7b) by treatment of a bisA C H T U N G T R E N N U N G (alkynyl)silane (1b) with, for example, triethylborane. [1a,2a,18,19] The unique reaction sequence involves alkynyl abstraction/1,1-carboboration followed by a 1,1-alkenylboration step to directly lead to the boryl-functionalized silole derivative (see Scheme 1).[20] Unfortunately, the reaction with simple alkylboranes often requires elevated temperatures (ca. 100 8C).When more reactive boranes were used (e.g., triallylborane, 1-boraadamantane) the reaction conditions FULL PAPERSof the 1,1-organoboration reactions were milder but sometimes the formation of side products took place. [21] We have now found that this general reaction sequence can very favourably be used for the synthesis of substituted siloles containing a combination of C 6 F 5 and BA C H T U N G T R E N N U N G (C 6 F 5 ) 2 groups that are probably of great advantage in the respective areas of silole-derived materials science. We describe two representative examples in this article. Results and DiscussionFollowing proced...

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Transformation of a 1‐Zirconacyclopent‐3‐yne, a Five‐Membered Cycloalkyne, into a 1‐Zirconacyclopent‐3‐ene and Formal “1‐Zirconacyclopenta‐2,3‐dienes”

et al. 2008

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Cycloalkynes smaller than seven-membered rings are generally unstable and difficult to isolate, whereas the synthesis and reactivity of cyclopentynes, five-membered cycloalkynes, have been studied extensively.[1] Most reactions of the labile species involved formal 1,2-addition to the triple bond. There have been some reports of cyclopent-1-en-3-ynes, [2] but 1,4-addition to these compounds has not been shown. Cyclopentynes conjugated with alkylidene moieties have not been reported to date. We were interested in investigating the reactivity of cyclopentynes with alkylidene groups.We described previously the synthesis and reactivity of 1-metallacyclopent-3-yne compounds, five-membered cycloalkynes, and showed that these compounds were surprisingly stable in pure form at room temperature [Eq. (1)]. [3a,b] Titanium and hafnium analogues have also been prepared.[3c, 4a] Several reactions of these unique molecules have been reported; [3][4][5] however, their transformation into cycloalkenes or cycloallenes has not been shown. We reasoned that 1-metallacyclopent-3-ynes of conjugated systems would show more varied reactivities. We report herein the synthesis of a 2,5-bisalkylidene-1-metallacyclopent-3-yne compound and its transformation into 1-metallacyclopent-3-ene and formal "1-metallacyclopenta-2,3-diene" compounds.The treatment of a low-valent zirconocene-bisphosphine complex, [Cp 2 Zr(PMe 3 ) 2 ], [6] with 1,1,6,6-tetrakis(4-ethylphenyl)-1,2,3,4,5-hexapentaene (2) [7] at room temperature for 4 days gave the 2,5-bisalkylidene-1-zirconacyclopent-3-yne compound 3 in 70 % yield [Eq. (2)]. The reaction gave 3 predominantly, and the possible isomer 2-allenylidene-1-zirconacyclopent-3-yne (4) was not obtained, probably because of the steric hindrance of the aryl groups. Although several transition-metal complexes of hexapentaenes have been reported, none of them have 1-metallacyclopent-3-yne structures.[8] The molecular structure of 3 is shown in Figure 1.[9] The triple bond in 3 (C3ÀC4) is significantly longer than that in the nonsubstituted 1-zirconacyclopent-3-yne complex 1 (R = H; 1.237(5) ), [3e] whereas the adjacent single bonds (C2 À C3 and C4 À C5) are slightly shorter in 3 than in 1 (1.406-1.408 in 1). These differences may reflect differences between the bond lengths of hexapentaene 2 and those of butatrienes: Compound 2 has a longer central bond (1.311(2) ), [7,10] whereas butatrienes have a shorter central bond (1.22-1.28 ). The alkylidene moieties are bent away from the metal center; the four carbon atoms C2-C5 and the Zr center are coplanar, and C1 and C6 are located 0.24 and 0.27 from this plane, respectively.When a red solution of 3 in tetrahydrofuran was treated with lithium powder or potassium graphite at room temperature, the color of the solution changed to deep blue. Protonation of this solution with catechol (1 equiv) gave the 1-zirconacyclopent-3-ene compound 6 as the major product [46 % yield (as determined by 1 H NMR spectroscopy), M = K; Eq. (3)]. This result indicates the formation of a dian...

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Metallacyclische Fünfring‐Allenoide: Synthese und Struktur stabiler stark verzerrter cyclischer Allen‐Derivate

Cited by 45 publications

References 45 publications

[Cp₂Ti^III(NCy)₂C‐Ti^IIICp₂]: ein transienter Titanocen‐Carbenkomplex?

[Cp₂Ti^III(NCy)₂C‐Ti^IIICp₂]: ein transienter Titanocen‐Carbenkomplex?

Reaction of Bis(alkynyl)silanes with Tris(pentafluorophenyl)borane: Synthesis of Bulky Silole Derivatives by Means of 1,1‐Carboboration under Mild Reaction Conditions

Transformation of a 1‐Zirconacyclopent‐3‐yne, a Five‐Membered Cycloalkyne, into a 1‐Zirconacyclopent‐3‐ene and Formal “1‐Zirconacyclopenta‐2,3‐dienes”

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Metallacyclische Fünfring‐Allenoide: Synthese und Struktur stabiler stark verzerrter cyclischer Allen‐Derivate

Cited by 45 publications

References 45 publications

[Cp2TiIII(NCy)2C‐TiIIICp2]: ein transienter Titanocen‐Carbenkomplex?

[Cp2TiIII(NCy)2C‐TiIIICp2]: ein transienter Titanocen‐Carbenkomplex?

Reaction of Bis(alkynyl)silanes with Tris(pentafluorophenyl)borane: Synthesis of Bulky Silole Derivatives by Means of 1,1‐Carboboration under Mild Reaction Conditions

Transformation of a 1‐Zirconacyclopent‐3‐yne, a Five‐Membered Cycloalkyne, into a 1‐Zirconacyclopent‐3‐ene and Formal “1‐Zirconacyclopenta‐2,3‐dienes”

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[Cp₂Ti^III(NCy)₂C‐Ti^IIICp₂]: ein transienter Titanocen‐Carbenkomplex?

[Cp₂Ti^III(NCy)₂C‐Ti^IIICp₂]: ein transienter Titanocen‐Carbenkomplex?