Cationic Zirconocene Complexes Research Articles

Structure of Zirconocene Complexes Relevant for Olefin Catalysis: Infrared Fingerprint of the Zr(C5H5)2(OH)(CH3CN)+ Cation in the Gas Phase

Cationic zirconocene complexes are active species in Ziegler-Natta catalysis for olefin polymerization. Their structure and metal-ligand bond strength strongly influence their activity. In the present work, the infrared multiphoton dissociation (IRMPD) spectrum of mass selected Zr(C(5)H(5))(2)(OH)(CH(3)CN)(+) cations was obtained in the 300-1500 cm(-1) fingerprint range by coupling a Fourier-transform ion cyclotron resonance (FT-ICR) mass spectrometer equipped with an electrospray ionization (ESI) source and the infrared free electron laser (IR-FEL) at the Centre Laser Infrarouge d'Orsay (CLIO). The experimental efforts are complemented by quantum chemical calculations at the MP2 and B3LYP levels using the 6-311G* basis set. Vibrational assignments of transitions observed in the IRMPD spectra to modes of the Zr-O-H, C(5)H(5), and CH(3)CN moieties are based on comparison to calculated linear absorption spectra. Both the experimental data and the calculations provide unprecedented information about structure, metal-ligand bonding, charge distribution, and binding energy of the complex.

Formation and Structural and Dynamic Features of Atropisomeric η2-Iminoacyl Zirconium Complexes

The Cp2ZrCl(μ-1,4-diphenylbutenyne)PX2 complexes 7a [−P(C6H5)2] and 10 [−P(C6F5)2] insert tert-butylisonitrile into the Zr−C(sp2) σ bond to yield the N-inside η2-iminoacyl zirconocene complexes 13a and 13b. X-ray crystal structure analysis of complexes 13a and 13b revealed the presence of a chiral atropisomeric structure with a torsion angle of 74.8(2)° (13a) and 72.9(6)° (13b), respectively, around the central iminoacyl/alkenyl C(sp2)−C(sp2) σ bond. In solution an analogous chiral structure is observed. The barrier of interconversion of the enantiomeric atropisomers of 13a and 13b was determined at ΔG⧧ (327K) = 14.9 ± 0.3 kcal mol-1 (13a) and ΔG⧧ (325K) = 14.8 ± 0.3 kcal mol-1 (13b) by temperature-dependent dynamic NMR spectroscopy. Reaction of 7a and 10 with methyllithium followed by treatment with B(C6F5)3 gave the corresponding cationic zirconocene complexes 12a and 12b. These complexes took up 2 mol equiv of tert-butylisonitrile to yield the cationic N-inside η2-iminoacyl zirconocene systems 14a and ...

Explanation of the Different Reaction Behaviors of Bridged and Unbridged Cationic Single Component Zirconocene Catalysts in MMA Polymerizations: a Density Functional Study

Density functional (DFT) calculations were carried out on the B3LYP level of theory on bridged and unbridged cationic zirconocene complexes to clarify why unbridged [Zr(Cp)2(Me)(thf)][BPh4] is not active in the polymerization of methyl methacrylate (MMA), whereas [Zr{(Cp)2CMe2}(Me)(thf)][BPh4] polymerizes MMA readily, as we showed experimentally. It is shown, that the initial step of the polymerizationthe transfer of the metallocene bound methyl group to the first MMA moleculeis endothermic for [Zr(Cp)2(Me)(MMA)]+ but exothermic for [Zr{(Cp)2CMe2}(Me)(MMA)]+. Furthermoreand more importantthe activation energy is higher for the reaction of the unbridged compound compared to the activation energy of the bridged compound. From these results and an estimation of the rate constants it follows that in the temperature range investigated experimentally (−30 to +30 °C) either the endothermic product is not formed at all and/or the reversed reaction to the reactant is much faster than the reaction with the next MMA...

The structure and dynamics of cationic zirconocene complexes with phenyl coordination †

Density functional computations (BP86/ECP1 and B3LYP/II level) have revealed that the phenyl group in [Zr(η-C5H5)(η-C5H4CR2C6H5)Me]+ (R = H) is coordinated to the Zr atom via one of the phenyl carbon atoms, rather than via an agostic Zr–H contact, as suggested previously. A stationary point with such an agostic interaction is the transition structure for phenyl rotation with a barrier higher than 50 kJ mol−1 (B3LYP/II level), consistent with results from dynamic NMR spectroscopy for a closely related compound (R = Me). The structural assignments are supported by the good accord between the computed (GIAO-B3LYP/II level) and experimental NMR chemical shifts. A second dynamic process with a very similar activation barrier is indicated to involve dissociation of the coordinated phenyl moiety from the Zr atom and inversion at the latter. The same structural motif (i.e. η1-bonded aryl group) is also found for the [Zr(η-C5H4CH2C6H5)2]2+ dication.

Cationic zirconocene complexes with benzyl and Si(SiMe3)3 substituted cyclopentadienyl ligands

Alkyl zirconocenes [Zr(η-C5H4R)2X2] (where R = CH2Ph, X = Cl 1a or Me 1b; R = CHPh2, X = Cl 2a or Me 2b; R = Si(SiMe3)3, X = Cl 4a or Me 4b) and for comparison [Zr(η-C5H5)(η-C5H4CH2Ph)Cl2] 3a were prepared and characterised. The reactions of these compounds with the methide abstracting reagents B(C6F5)3, B(o-C6F5C6F4)3 and [Ph3C]+[B(C6F5)4]– were investigated by low temperature NMR spectroscopy. Compound 1b reacts with [Ph3C]+[B(C6F5)4]– to form the homodinuclear complex [{Zr(η-C5H4CH2Ph)2Me}2(µ-Me)]+[B(C6F5)4]–. The related compound [{Zr(C5H4CH2Ph)2Me}2(µ-Me)]+[MeB(C6F5)3]– 5a was formed from the reaction of 1b with 0.5 equivalent of B(C6F5)3. Reaction between 1b and 1 equivalent B(C6F5)3 gave [Me(η-C5H4CH2Ph)2Zr(µ-Me)B(C6F5)3] 6a and the ion pair [Zr(η-C5H4CH2Ph)2Me][MeB(C6F5)3] 6b which are in equilibrium with each other. A similar observation was made when 2b was used instead of 1b. The sterically more demanding 4b does not show this behaviour. The role of the ligands in ethylene polymerisation was investigated.

Evidence for cationic Group 4 zirconocene complexes with intramolecular phenyl co-ordination

The mono- and bis-ring substituted zirconocenes with pendant phenyl groups [Zr(η-C5H5)(η-C5H4CMe2Ph)Me2] 2, [Zr(η-C5H5)(η-C5H4CMe2C6H4Me-p)Me2] 3, [Zr(η-C5H4CMe2Ph)2Me2] 4, and [Zr(η-C5H4CMe2C6H4Me-p)2Me2] 5 have been prepared. The crystal structures of 3 and 4 have been determined. Compounds 2–5 react with methyl abstracting reagents such as B(C6F5)3 or [Ph3C]+[B(C6F5)4]– to form cationic zirconocene complexes 6–9 as solvent separated ion pairs as shown by low temperature NMR spectroscopy. For the cationic complexes [Zr(η-C5H5)(η-C5H4CMe2Ph)Me]+[RB(C6F5)3]– (R = Me 6a or C6F56b) and [Zr(η-C5H5)(η-C5H4CMe2C6H4Me-p)Me]+[RB(C6F5)3]– (R = Me 7a or C6F57b) evidence for the co-ordination of a phenyl group to the zirconium centre via agostic C–H–M interaction was obtained by NMR spectroscopy. These cationic complexes can be considered as models for solvent adducts in Kaminsky catalysts. The cationic complexes [Zr(η-C5H4CMe2Ph)2Me]+[RB(C6F5)3]– (R = Me 8a or C6F58b) (derived from 4) and [Zr(η-C5H4CMe2C6H4Me-p)2Me]+[RB(C6F5)3]– (R = Me 9a or C6F59b) (derived from 5), respectively, exhibit more complex behaviour. These observations contrast with those from the previously published benzyl congener [Zr(η-C5H4CH2Ph)2Me2] 1 which, with methyl abstracting agent, generates both a solvent separated cation/anion pair and a tight ion pair.

Enantioselective CC and CH Bond Formation Mediated or Catalyzed by Chiral ebthi Complexes of Titanium and Zirconium

AbstractThe development of catalytic processes that effect enantioselective bond formation under mild conditions is an important and challenging task in modern chemical synthesis. In this connection, chiral C2‐symmetric ansa‐metallocenes (bridged metallocenes) have found notable applications as catalysts. This article discusses the chemistry of this class of chiral metallocene complexes with regard to their utility in catalytic and enantioselective CC and CH bond formation reactions. In addition, where applicable, a brief comparison with other related catalytic enantioselective processes is offered. Many of the reactions effected with high levels of enantioselectivity by catalytic amounts of these complexes are of great significance to the preparation of new materials and in the synthesis of therapeutic agents. For example, zirconocene complexes readily catalyze the enantioselective addition of alkylmagnesium halides to alkenes, and cationic zirconocene complexes may promote the highly stereoregulated copolymerization of terminal alkenes. Furthermore, the related chiral titanocenes are involved in an impressive range of useful asymmetric catalytic reactions, including the enantioselective hydrogenation of olefins and reduction of imines or ketones. This review attempts to bring together the practical aspects of the use of [(ebthi)M] complexes of Group 4 transition metals (catalyst synthesis and resolution), outline the manner in which the C2‐symmetric chiral ligands are believed to initiate stereoselective bond formation, and highlight the aspects of this chemistry that are less well understood and require further research.

Preparation of Narrow Polydispersity Polycaprolactone Catalyzed by Cationic Zirconocene Complexes

Abstract Various cationic zirconocene complexes effectively catalyzed polymerization of ε-caprolactone in a living fashion at ambient temperature to afford polycaprolactone possessing narrow molecular weight distribution (Mw/Mn = 1.06–1.3). The efficiency of the catalyst in the polymerization was enhanced by modifying the structure of cyclopentadienyl ligands.

Stabilizing interactions and coordination in cationic zirconocene complexes: Cp2ZrL+. A MO theoretical study. [Erratum to document cited in CA119(19):203534a

Stabilizing interactions and coordination in cationic zirconocene complexes: Cp2ZrL+. A MO theoretical study. [Erratum to document cited in CA119(19):203534a

Stabilizing interactions and coordination in cationic zirconocene complexes: Cp2ZrL+. A MO theoretical study

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTStabilizing interactions and coordination in cationic zirconocene complexes: Cp2ZrL+. A MO theoretical studyRolf Gleiter, Isabella Hyla-Kryspin, Shuqiang Niu, and Gerhard ErkerCite this: Organometallics 1993, 12, 10, 3828–3836Publication Date (Print):October 1, 1993Publication History Published online1 May 2002Published inissue 1 October 1993https://doi.org/10.1021/om00034a014RIGHTS & PERMISSIONSArticle Views76Altmetric-Citations28LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-Alerts Get e-Alerts

Catalysis of the Mukaiyama aldol reaction using cationic zirconocene complexes

Catalysis of the Mukaiyama aldol reaction using cationic zirconocene complexes

BPh as a Ligand in Cationic Zirconium Complexes: Novel Bonding Mode and Fluxionality

Cationic zirconocene complexes containing BPh coordinated via the meta and para-carbons of one phenyl ring are isolable when the cyclopentadienyl ligands are of intermediate steric bulk. A novel fluxional process, involving phenyl “ring flipping”, has been observed in complexes like 1 with chiral ligands; such complexes catalyze isotactic polypropylene formation.