Bis(enamino-Cp) Group 4 metal complex chemistry: developing a Mannich-type carbon–carbon coupling reaction at the bent metallocene famework

Knüppel, Stephanie; Wang, Cun; Kehr, Gerald; Fröhlich, Roland; Erker, Gerhard

doi:10.1016/j.jorganchem.2004.08.021

Cited by 50 publications

(32 citation statements)

References 83 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…However, carbon-carbon coupling reactions at the intact group 4 bent metallocene frameworks were close to nonexistent before our work (13)(14)(15). Meanwhile, a few leading examples have emerged from the literature, using, e.g., olefin-metathesis (16)(17)(18)(19) or even a variant of the Mannich reaction (20)(21)(22) for carrying out carbon-carbon coupling reactions at the reactive group 4 bent metallocene frameworks.…”

mentioning

confidence: 80%

Ansa-metallocene polymerization catalysts derived from [2+2]cycloaddition reactions of bis(1-methylethenyl-cyclopentadienyl)zirconium systems

Paradies

Kehr

Fröhlich

et al. 2006

Proc. Natl. Acad. Sci. U.S.A.

Self Cite

View full text Add to dashboard Cite

Bis(1-methylethenyl-cyclopentadienyl)zirconium dichloride (7a) was prepared by a fulvene route. Photolysis at 0°C with Pyrexfiltered UV light resulted in a rapid and complete intramolecular [2؉2]cycloaddition reaction to yield the corresponding cyclobutylene-bridged ansa-zirconocene dichloride isomer (8a). This is one of the rare examples of an organic functional group chemistry that leads to carbon-carbon coupling at the framework of an intact sensitive group 4 bent metallocene complex. More sterically hindered open metallocenes that bear bulky isopropyl or tert-butyl substituents at their Cp rings in addition to the active 1-methylethenyl functional group undergo the photochemical ansa-metallocene ring closure reaction equally facile. The metallocene systems used and obtained in this study have served as transition metal components for the generation of active metallocene propene polymerization catalysts.photochemistry ͉ topochemical reaction M etallocene catalysis has become of great significance in olefin polymerization, especially for polyethylene, stereospecific polypropylene formation, and the production of some copolymers. The ansa-metallocenes of the group 4 metals and related systems play an essential role in this important development (1-3). Various methods have been devised and applied to construct such bent metallocene frameworks that feature a short carbon-or heteroatom-containing bridge between their substituted cyclopentadienyl, indenyl, or fluorenyl ligands. Because of the sensitive character of the organometallic group 4 metal complexes, ligand construction and variation is usually carried out at the free ligand stage before the final transmetallation step to the transition metal in the practical preparative sequences. This is a serious synthetic limitation. It would be highly desirable to have an organic functional group chemistry developed for framework variation at the actual metallocene stage. Previously, some addition reactions to metallocene frameworks had been reported, such as catalytic hydrogenation (4), hydrosilylation (5), hydroboration (6-9), or borylation (refs. 10, 11 and references therein, and 12). However, carbon-carbon coupling reactions at the intact group 4 bent metallocene frameworks were close to nonexistent before our work (13-15). Meanwhile, a few leading examples have emerged from the literature, using, e.g., olefin-metathesis (16-19) or even a variant of the Mannich reaction (20-22) for carrying out carbon-carbon coupling reactions at the reactive group 4 bent metallocene frameworks.Intramolecular photochemical [2ϩ2]cycloaddition reactions may become of a prime importance in this development. We had previously observed that bis(alkenyl-Cp)ZrCl 2 complexes such as, e.g., meso-1 underwent ansa-metallocene formation to yield meso-2 by intramolecular [2ϩ2]cycloaddition when irradiated with UV light. However, this specific reaction was not synthetically useful for a clean ansa-metallocene catalyst development because of its reversibility under the photochemical conditions t...

show abstract

mentioning

confidence: 80%

Ansa-metallocene polymerization catalysts derived from [2+2]cycloaddition reactions of bis(1-methylethenyl-cyclopentadienyl)zirconium systems

Paradies

Kehr

Fröhlich

et al. 2006

Proc. Natl. Acad. Sci. U.S.A.

Self Cite

View full text Add to dashboard Cite

show abstract

“…However, no resonances were apparent that corresponded to the carbon atoms of the aromatic rings; a phenomenon which has been observed before for the related Ph(Me)N=B(C 6 F 5 ) 2 by Knüppel and co-workers. [56] 19 F NMR spectroscopy, however, was consistent with the incorporation of pentafluorophenyl units, with three resonances at δ = -133.1 (singlet), -157.7 (triplet, J FF = 19.7 Hz) and -162.8 (broad singlet) ppm. High-resolution electrospray ionisation mass spectrometry (ESI-MS) confirmed the successful synthesis of the desired compound, Crystals of 1 suitable for single-crystal X-ray diffraction were grown from toluene/hexanes at -40°C ( Figure 1).…”

Section: Introductionmentioning

confidence: 91%

Experimental and Theoretical Studies of the Potential Interconversion of the Amine–Borane iPr₂NH·BH(C₆F₅)₂ and the Aminoborane iPr₂N=B(C₆F₅)₂ Involving Hydrogen Loss and Uptake

et al. 2011

View full text Add to dashboard Cite

The amine-borane adduct iPr 2 NH·BH(C 6 F 5 ) 2 (1) and the aminoborane iPr 2 N=B(C 6 F 5 ) 2 (2) have been prepared and crystallographically characterised. Interconversion between the two compounds has been attempted using thermal and transition-metal-catalysed dehydrogenation and hydrogenation protocols and the overall reaction thermodynamics were probed by computational methods. Thermal dehydrogenation of 1 was found to yield 2, together with uncharacterised by-products. Treatment of 1 with the carbene 1,3-di-tert-butyl-4,5-dihydroimidazol-2-ylidene (3) under ambient conditions did not lead to the elimination of hydrogen, but instead

show abstract

“…The use of aryl lithium in the synthesis of other metallocenes is well known [26][27][28][29][30], and it has recently been used for the synthesis of achiral titanocene dichlorides [13,14]. This time, the carbolithiation method led to the synthesis of a new group of titanocenes that contain stereo centres (5a-c).…”

Section: Resultsmentioning

confidence: 99%

“…It is believed that, once passed the cell membrane, a mono-or dication is formed by hydrolysis of one or two of the chlorine groups. At this point, the coordination of the extra NMe 2 donor groups to the titanium centre [30] could stabilise these cationic intermediates and finally increase the number of titanocene-DNA interactions leading to cell death at a lower concentration. The possible intramolecular stabilisation of the monocation of titanocene 5a is shown in Fig.…”

Section: Resultsmentioning

confidence: 99%

Dimethylamino-functionalised and N-heteroaryl-substituted titanocene anticancer drugs: synthesis and cytotoxicity studies

et al. 2007

View full text Add to dashboard Cite

From the carbolithiation of 6-N,N-dimethylamino fulvene (3a) and different lithiated N-heterocyclic compounds (N,N-dimethylaminomethylpyrrole, 1-methylimidazole and 2,4-[bis(N',N'-dimethylaminomethyl)]-N-methyl pyrrole), the corresponding lithium cyclopentadienide intermediate (4a-c) was formed. These three lithiated intermediates underwent a transmetallation reaction with TiCl4 resulting in dimethylamino-functionalised titanocenes 5a-c. When these titanocenes were tested against LLC-PK cells, the IC50 values obtained were of 13, and 63 microM for titanocenes 5b and 5c, respectively. The most cytotoxic titanocene in this paper (5a) with an IC50 value of 6.8 microM is found to be almost as cytotoxic as cis-platin, which showed an IC50 value of 3.3 microM, when tested on the epithelial pig kidney LLC-PK cell line, and titanocene 5c is approximately 400 times better than titanocene dichloride itself.

show abstract

Bis(enamino-Cp) Group 4 metal complex chemistry: developing a Mannich-type carbon–carbon coupling reaction at the bent metallocene famework

Cited by 50 publications

References 83 publications

Ansa-metallocene polymerization catalysts derived from [2+2]cycloaddition reactions of bis(1-methylethenyl-cyclopentadienyl)zirconium systems

Ansa-metallocene polymerization catalysts derived from [2+2]cycloaddition reactions of bis(1-methylethenyl-cyclopentadienyl)zirconium systems

Experimental and Theoretical Studies of the Potential Interconversion of the Amine–Borane iPr₂NH·BH(C₆F₅)₂ and the Aminoborane iPr₂N=B(C₆F₅)₂ Involving Hydrogen Loss and Uptake

Dimethylamino-functionalised and N-heteroaryl-substituted titanocene anticancer drugs: synthesis and cytotoxicity studies

Contact Info

Product

Resources

About

Bis(enamino-Cp) Group 4 metal complex chemistry: developing a Mannich-type carbon–carbon coupling reaction at the bent metallocene famework

Cited by 50 publications

References 83 publications

Ansa-metallocene polymerization catalysts derived from [2+2]cycloaddition reactions of bis(1-methylethenyl-cyclopentadienyl)zirconium systems

Ansa-metallocene polymerization catalysts derived from [2+2]cycloaddition reactions of bis(1-methylethenyl-cyclopentadienyl)zirconium systems

Experimental and Theoretical Studies of the Potential Interconversion of the Amine–Borane iPr2NH·BH(C6F5)2 and the Aminoborane iPr2N=B(C6F5)2 Involving Hydrogen Loss and Uptake

Dimethylamino-functionalised and N-heteroaryl-substituted titanocene anticancer drugs: synthesis and cytotoxicity studies

Contact Info

Product

Resources

About

Experimental and Theoretical Studies of the Potential Interconversion of the Amine–Borane iPr₂NH·BH(C₆F₅)₂ and the Aminoborane iPr₂N=B(C₆F₅)₂ Involving Hydrogen Loss and Uptake