Conformational Features of Group-4ansa-Metallocenes with Long −(CH2)n− Chains Connecting Their Cyclopentadienyl Ligands

Jödicke, Tim; Menges, Frederik; Kehr, Gerald; Erker, Gerhard; Höweler, Udo; Fröhlich, Roland

doi:10.1002/1099-0682(200108)2001:8<2097::aid-ejic2097>3.0.co;2-l

Cited by 27 publications

(8 citation statements)

References 32 publications

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“…In the crystal complex 6 features a bent metallocene structure that is characterized by a near to C 2 -symmetric metallocene conformation . The Cp(centroid)−Zr−Cp(centroid) angle amounts to 125.7°.…”

Section: Resultsmentioning

confidence: 99%

Functional Group Chemistry at the Group 4 Bent Metallocene Frameworks: Formation and “Metal-Free” Catalytic Hydrogenation of Bis(imino-Cp)zirconium Complexes

et al. 2009

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Treatment of 6-dimethylaminofulvene 1 with lithio-2,6-diisopropylanilide 2 gave the lithiated 6-(2,6-diisopropylanilido)fulvene 3. Its treatment with Me3SiCl afforded the N-silylated derivative (C5H4)CH-N(Ar)SiMe3 (4), which was characterized by X-ray diffraction. Protonation of 3 was effected by treatment with acetylacetone to yield a mixture of syn- and anti-5 [(C5H4)CH-N(Ar)H] contaminated with some 2,6-diisopropylaniline. The minor isomer, syn-5, was also characterized by an X-ray crystal structure analysis. Treatment of this mixture with Zr(NMe2)4 led to in situ deprotonation and formation of complex [(C5H4)-CHNAr]2Zr(NMe2)2 (6) in a mixture with the exchange product [(C5H4)-CHNAr]2Zr(NMe2)(NH-Ar) (7) as a minor component (both characterized by X-ray diffraction). The corresponding reaction with the reagent Zr(benzyl)4 or Cl2Zr(NMe2)2(THF)2 resulted in the clean formation of the products [(C5H4)-CHNAr]2Zr(benzyl)2 (8) (also characterized by X-ray diffraction) and [(C5H4)-CHNAr]2ZrCl2 (9), respectively. Complex 9 was subjected to a “metal-free” catalytic hydrogenation reaction by treatment with a substoichiometric amount of B(C6F5)3 under mild conditions (2 bar H2, rt) to yield the product [(C5H4)-CH2-NH-Ar]2ZrCl2 (10), which was also characterized by an X-ray crystal structure analysis. Treatment of 9 with 1 or 2 molar equiv of B(C6F5)3 gave “frustrated” Lewis pairs that split dihydrogen heterolytically at near to ambient conditions to give the salts {[(C5H4)-CH2NH2 +Ar][(C5H4)-CH2NHAr]}ZrCl2/[HB(C6F5)3 −] (11) and [(C5H4)CH2NH2 +Ar]2ZrCl2/2 [HB(C6F5)3 −] (12), respectively. The system 12 itself was shown to be an active catalyst for the hydrogenation of bulky imines and of a bulky silyl enol ether.

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Section: Resultsmentioning

confidence: 99%

Functional Group Chemistry at the Group 4 Bent Metallocene Frameworks: Formation and “Metal-Free” Catalytic Hydrogenation of Bis(imino-Cp)zirconium Complexes

et al. 2009

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“…The presence of the smaller −NMe 2 groups leads to a better ansa -metallocene formation than the more bulky −NEt 2 systems. This congruent substituent dependency of the photostationary equilibrium in both the alkenyl- and the enamino-substituted (RCp) 2 ZrCl 2 systems is not so easy to rationalize; it may perhaps indicate that a metallocene local minimum conformer needs to be populated in a preequilibrium situation that brings the two −C(R)CH 2 double bonds in a favorable orientation relative to each other to allow the intramolecular [2+2]photocycloaddition reaction to take place. This would in fact place the here observed reaction type within the family of the topochemical reactions and might justify describing the 5 to 7 interconversion as an example of a reaction proceeding under “dynamic topochemical control”, just as we had proposed previously for the related 1 to 2 interconversions. − …”

Section: Discussionmentioning

confidence: 99%

Synthesis of an Amino-Functionalized ansa-Zirconocene by Intramolecular Photochemical Enamine [2+2]Cycloaddition

et al. 2009

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Deprotonation of 6-dimethylamino-6-methylpentafulvene (3a) with methyl lithium yielded the (1-dimethylaminoethenyl)Cp lithium reagent 4a. Its treatment with zirconium tetrachloride under carefully controlled reaction conditions gave the corresponding bis(enamino-Cp)ZrCl2 complex 5a. The product 5a is very sensitive to acid-catalyzed Mannich condensation. Photolysis of 5a (HPK 125, Pyrex filter) resulted in a rapid intramolecular [2+2]cycloaddition reaction to yield the cis-bis(dimethylamino)cyclobutylene-bridged ansa-zirconocene complex 7a in a photostationary equilibrium (5a:7a ≈ 30:70). After acid-catalyzed Mannich conversion of the minor component (5a to 6a) the new photoproduct 7a was isolated pure by fractional crystallization. The complexes 5a and 7a were both characterized by X-ray diffraction.

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“…It occurred to us that bent-metallocene frameworks could offer a unique new possibility to set the scene for a different type of topochemical reaction control, namely by bringing the reacting CC double bonds into a suitable orientation by means of their characteristic conformational features. The bent metallocenes usually undergo rapid rotation around their Cp−metal vectors . Because of the typical bent Cp−M−Cp situation this may bring conjugated alkenyl substituents in a manifold of relative orientations to each other.…”

Section: Introductionmentioning

confidence: 99%

Dynamic Topochemical Reaction Control−A Principle and Its Application in ansa-Metallocene Synthesis

et al. 2010

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The Cp-alkenyl and Cp-dienyl ligand systems 5 and 8 were prepared by fulvene routes. Subsequent transmetalation gave the respective (Cp-propenyl) 2 -, (Cp-butenyl) 2 -, (Cp-pentadienyl) 2 -, and (Cphexadienyl) 2 ZrCl 2 and -HfCl 2 complexes 6, 9, and 10. In the crystal these complexes favor metallocene conformations that feature the alkenyl and dienyl substituents far separated from each other at the open front side of the bent metallocene wedge. Photolysis in the solid state consequently did not result in an intramolecular C-C coupling reaction but led to E/Z isomerization of the alkenyl units. In solution rapid conformational metallocene equilibration takes place. Photolysis of the (Cp-alkenyl) 2 ZrCl 2 complexes 6 in solution very efficiently resulted in the formation of the cyclobutylene-bridged ansa-zirconocene isomers 11 by rapid intramolecular [2 þ 2] cycloaddition reaction by means of a dynamic topochemical reaction control. Photolysis of the (Cp-dienyl) 2 ZrCl 2 and -HfCl 2 complexes (9, 10) in solution proceeded analogously to efficiently yield the cyclooctadienylene bridged ansa-metallocenes (12, 13) by formal dynamic topochemical [4 þ 4] cycloaddition reaction control.

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Conformational Features of Group-4ansa-Metallocenes with Long −(CH2)n− Chains Connecting Their Cyclopentadienyl Ligands

Cited by 27 publications

References 32 publications

Functional Group Chemistry at the Group 4 Bent Metallocene Frameworks: Formation and “Metal-Free” Catalytic Hydrogenation of Bis(imino-Cp)zirconium Complexes

Functional Group Chemistry at the Group 4 Bent Metallocene Frameworks: Formation and “Metal-Free” Catalytic Hydrogenation of Bis(imino-Cp)zirconium Complexes

Synthesis of an Amino-Functionalized ansa-Zirconocene by Intramolecular Photochemical Enamine [2+2]Cycloaddition

Dynamic Topochemical Reaction Control−A Principle and Its Application in ansa-Metallocene Synthesis

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