Zirconocene Bis Research Articles

Recent Synthetic and Catalytic Applications of Group 4 Metallocene Bis(trimethylsilyl)acetylene Complexes

With the 30 years old first example of a stable group 4 metallocene bis(trimethylsilyl)acetylene (btmsa) complex Cp2Ti(η2‐btmsa) a series of similar complexes like Cp′2M(η2‐btmsa) (M = Ti, Zr; Cp′ = Cp, Cp* as η5‐pentamethylcyclopentadienyl and Cp′2 = rac‐(ebthi) as rac‐1,2‐ethylene‐1,1′‐bis(η5‐tetrahydroindenyl) ) represent excellent sources for the generation of the very reactive coordinatively and electronically unsaturated complex fragments [Cp'2M], which were used in many synthetic and catalytic reactions. Examples for this were oresented in several papers and summarized in some reviews. In this update new reactions of group 4 metallocene bis(trimethylsilyl)acetylene complexes towards symmetrically and unsymmetrically α‐dihetero‐substituted alkynes, reactions with other alkynes, di‐ and polyynes to metallacyclopentadienes as well as the conversions of the formed products are summarized. Additionally, novel synthetic applications of the formed metallacyclopentadienes on the basis of the zirconocene bis(trimethylsilyl)acetylene complex Cp2Zr(py)(η2‐btmsa) are highlighted. Reactions with imines, neutral N‐donor ligands, E‐H compounds (E = N, O, P), molecular hydrogen, water, phosphino‐ and aminoboranes, E‐Cl compounds (E = C, P), disilylated germylenes and aryloxy ketones were described. Different self‐assembly reactions to multinuclear complexes by using group 4 metallocene bis(trimethylsilyl)acetylene complexes in C‐C coupling reactions with or without C‐H bond activation to tri‐ or tetranuclear complexes are considered, too. These examples are discussed following the general L‐M‐S principle for stoichiometric and catalytic reactions, whereby different ligands L (L = Cp′ = Cp, Cp*, rac‐ebthi), metals M (M = Ti, Zr, Hf) and substrate substituents S influence the reactivity and the obtained products.

ChemInform Abstract: Air‐Stable Zirconocene Bis(perfluorobutanesulfonate) as a Highly Efficient Catalyst for Synthesis of N‐Heterocyclic Compounds.

AbstractIt is demonstrated, that the title catalyst ZRC exhibits high catalytic activity for the synthesis of benzimidazoles, benzodiazepines, dihydropyrimidines, and dihydropyridines under neat conditions.

Air-stable zirconocene bis(perfluorobutanesulfonate) as a highly efficient catalyst for synthesis of N-heterocyclic compounds

Zirconocene bis(perfluorobutanesulfonate) is air- and water-stable and proved to be ionic on basis of conductivity measurements. It exhibits high catalytic efficiency for the synthesis of N-heterocyclic compounds under solvent-free condition, such as benzimidazoles, benzodiazepines, dihydropyrimidinones and dihydropyridines under mild condition. Furthermore, it can be reused without loss of activity in a test of five cycles. This catalytic system affords a simple and efficient approach for the synthesis of N-heterocyclic compounds.

Synthesis and structure of an air-stable binuclear complex of bis(ethylcyclopentadienyl)zirconium perfluorooctanesulfonate and its catalytic application in one-pot three-component aza-Friedel–Crafts reactions

An air-stable Lewis acidic binuclear complex of bis(ethylcyclopentadienyl)zirconium perfluorooctanesulfonate (1a) was successfully synthesized by the reaction of (CH3CH2Cp)2ZrCl2 with C8F17SO3Ag. The complex 1a was characterized by different techniques and found to have the nature of air-stability, water tolerance, thermal-stability, and strong Lewis-acidity. In addition, its solubility was higher than that of our previously reported uninuclear zirconocene bis(perfluorooctanesulfonate). This complex showed high catalytic efficiency, good recyclability, and reusability in the one-pot three-component aza-Friedel–Crafts reactions of indoles with aldehydes and N,N-dimethylaniline. The yields of the corresponding 3-diarylmethyl indoles are higher than those from the traditional Lewis acidic catalysts.

Air-stable zirconocene bis(perfluorobutanesulfonate) as a highly efficient catalyst for synthesis of α-aminophosphonates via Kabachnik–Fields reaction under solvent-free condition

Zirconocene bis(perfluorobutanesulfonate) [Cp2Zr(OSO2C4F9)2·2H2O] was successfully synthesized by treatment of Cp2ZrCl2 with C4F9SO3Ag, and was found to have the nature of air-stability, water tolerance, high thermal stability and strong Lewis acidity. This complex showed high catalytic efficiency for the synthesis of α-aminophosphonates via Kabachnik–Fields reaction of aldehydes/ketones, amines and diethyl phosphite under mild and solvent-free conditions. Furthermore, it can be reused without loss of activity in a test of five cycles. Compared with our previously reported complex of Cp2Zr(OSO2C8F17)2·3H2O·THF, this complex showed better catalytic activity.

Synthesis and structure of an air-stable μ2-hydroxy-bridged binuclear complex of bis(methylcyclopentadienyl)dizirconium(IV) perfluorooctanesulfonate and its application in Lewis acid-catalyzed reactions

Air-stable binuclear complex of bis(methylcyclopentadienyl)zirconium perfluorooctanesulfonate (1a) was successfully synthesized by the reaction of (CH3Cp)2ZrCl2 with C8F17SO3Ag. The compound 1a was characterized by different techniques and found to have the nature of air-stability, water tolerance, thermally-stability and strong Lewis-acidity. In addition, its solubility was higher than that of our previously reported uninuclear zirconocene bis(perfluorooctanesulfonate). It showed high catalytic efficiency in the Friedel–Crafts acylation of alkyl aryl ethers and the Mannich reaction and could be reused.

ChemInform Abstract: Zirconocene Bis(perfluorooctanesulfonate) S‐Catalyzed Highly Efficient Synthesis of 1,3,5‐Triaryl Benzene via Cyclotrimerization of Ketones.

AbstractThe catalyst can be recycled at least 10 times.

As–As Bond Formation via Reductive Elimination from a Zirconocene Bis(dimesitylarsenide) Compound

A new zirconocene bis(arsenide) derivative, Cp2Zr(AsMes2)2 (1; Cp = cyclopentadienyl, Mes = 2,4,6-trimethylphenyl), has been prepared by the metathetical reaction of 2 equiv of LiAsMes2 with Cp2ZrCl2 and structurally characterized. Efforts to prepare Cp2ZrCl(AsMes2) (2) by reaction of 1 equiv of LiAsMes2 with Cp2ZrCl2 yielded a mixture of products that could not be separated, including 1 and 2, as identified by 1H NMR spectroscopy. Compound 1 thermally decomposes with formation of As2Mes4, suggestive of reductive elimination to form an As–As bond. Further evidence for reductive elimination comes from effective interception of a putative zirconium(II) intermediate with diphenylacetylene to give Cp2Zr(C4Ph4).

Zirconocene Bis(perfluorooctanesulfonate)s-Catalyzed the Reaction of Indoles and Carbonyl Compounds

In the presence of 1.0 mol% zirconocene bis(perfluorooctanesulfonate)s, indoles reacted with aldehyde/ketone at room temperature in tetrahydrofuran for 10~25 min to give diindolylmethane derivatives in 86%~96% yields. The catalyst zirconocene bis(perfluorooctanesulfonate)s can be reused 6 times, and the conversion rate is still as high as 90%. This reaction does not require strict anhydrous conditions. This procedure provides a new and efficient way for preparing diindolylmethane derivatives.

Zirconocene Bis(perfluorooctanesulfonate)s-Catalyzed Highly Efficient Synthesis of 1,3,5-Triaryl Benzene via Cyclotrimerization of Ketones

Air-stable zirconocene bis(perfluoroctanesulfonate)s [Cp2Zr]OSO2C8F17)2] (1) with high Lewis acidity and high thermal stability was prepared by the reaction between Cp2ZrCl2 and AgOSO2C8F17. The as-prepared complex 1 exhibits good activity and selectivity in the cyclotrimerization of various ketones to the desired 1,3,5-triaylbenzenes. Furthermore, in the cyclic experiments, the complex 1 shows little loss of activity after 10 cycles. The results afford a general and efficient method for the cyclotrimerization of ketones using Cp2Zr(OSO2C8F17)2 as catalyst.

Zirconocene bis(perfluorooctanesulfonate)s-catalyzed acylation of alcohols, phenols, thiols, and amines under solvent-free conditions

Air-stable zirconocene bis(perfluorooctanesulfonate)s [Cp2Zr(OPf)2, OPf = OSO2C8F17] showing high Lewis acidity and high thermal stability was prepared by reacting Cp2ZrCl2 with AgOPf, and examined as a catalyst for acylation reactions. It was found that in the acetylation of various alcohols, phenols, thiols, and amines by equimolar of acetic anhydride, Cp2Zr(OPf)2 exhibits high activity and selectivity to desired products under mild and solvent-free conditions. In the acylation of 2-phenylethanol across various acylating reagents, it also shows good catalytic efficiency. In a test of ten cycles, Cp2Zr(OPf)2 shows little loss of activity. The results afford a general and efficient method for the acylation of alcohols, phenols, thiols, and amines using zirconium bis(perfluorooctanesulfonate) as catalyst.

Neutral Metallocene Ester Enolate and Non-Metallocene Alkoxy Complexes of Zirconium for Catalytic Ring-Opening Polymerization of Cyclic Esters

Four neutral zirconocene bis(ester enolate) and non-zirconocene bis(alkoxy) complexes have been employed for ring-opening polymerizations and chain transfer polymerizations of l-lactide (l-LA) and ϵ-caprolactone (ϵ-CL). All C2v-, C2-, and Cs-ligated neutral zirconocene bis(ester enolate) complexes effectively polymerize ϵ-CL at 80 °C with high (>90%) initiator efficiencies. The Cs-ligated complex Ph2C(Cp)(Flu)Zr[OC(OiPr)═CMe2]2 (1) also promotes highly efficient polymerization of l-LA and is at least 100 times more reactive than the C2v- and C2-ligated analogues. The l-LA polymerization by 1 exhibits living characteristics, producing PLA with quantitative isotacticity (no sign of monomer epimerization) and controlled molecular weight. This polymerization follows first-order kinetics with respect to both [l-LA] and [1], consistent with a monometallic, coordination–anionic propagation mechanism. The structurally characterized non-zirconocene bis(alkoxy) complex [(2,6-iPr2C6H4)N(CH2)3N(2,6-iPr2C6H4)]Zr(OiPr)...

Five-membered metallacycles of titanium and zirconium ? attractive compounds for organometallic chemistry and catalysis

In these days a renaissance of metallacycles as an increasingly important class of organometallic compounds for synthetic and catalytic applications is evident, making such very attractive for a plethora of investigations. Titanocene and zirconocene bis(trimethylsilyl)acetylene complexes, regarded as three-membered metallacycles (1-metallacyclopropenes), present a rich chemistry towards unsaturated molecules. By elimination of the alkyne these complexes form by reaction with unsaturated compounds five-membered titana- and zirconacycles, all of which are relevant to stoichiometric and catalytic C-C coupling and cleavage reactions of unsaturated molecules.

Diastereospecific Ion-Pairing Polymerization of Functionalized Alkenes by Metallocene/Lewis Acid Hybrid Catalysts

This work studies the mechanism and application of the novel diastereospecific ion-pairing polymerization (DIPP) effected by a catalyst system comprising chiral zirconocene bis(ester enolate) rac-(EBI)Zr[OC(OiPr)CMe2]2 [1, EBI = C2H4(Ind)2] and 2 equiv of Lewis acid Al(C6F5)3. The 1/2Al(C6F5)3 system effectively promotes DIPP of functionalized alkenes such as methyl methacrylate (MMA), producing polymers having various stereoregularities, including isotactic, syndiotactic, and isotactic-b-syndiotactic multiblock microstructures, depending on the [monomer]/[catalyst] ratio employed. Our detailed investigations into the polymerization characteristics and kinetics, elementary reactions, characterization and behavior of the isolated key intermediates, as well as temperature and Lewis acid effects have yielded a mechanism for the DIPP of MMA by the 1/2Al(C6F5)3 system. This mechanism consists of four manifoldsisospecific, syndiospecific, anion-monomer exchange, and chain-transfer domainsand satisfactorily explains the formation of various polymer stereomicrostructures under given conditions. The most significant part of this overall mechanism is for the production of the isotactic-b-syndiotactic stereomultiblock structure, which is made possible by two pathways that can interconvert diastereospecific propagating manifolds: exchange between the coordinated anion and monomer as well as chain transfer. This unique polymerization technique has also been applied to the copolymerization of MMA with methacrylates having longer alkyl chains, leading to functionalized polymeric materials with tunable properties that are controlled by their stereomicrostructures and nature of the comonomer.

Group‐IV Metal Complexes as Hydroamination Catalysts

AbstractFor Abstract see ChemInform Abstract in Full Text.

Group‐IV Metal Complexes as Hydroamination Catalysts

AbstractDuring the last 50 years, group‐IV metal complexes have been used extensively as catalysts in organic chemistry. However, a new and rapidly growing field for group‐IV metal catalysis evolved in the 1990s when the groups of Bergman, Livinghouse and Doye found that zirconium and titanium complexes catalyze the inter‐ and intramolecular hydroamination of alkynes and allenes. Starting from early results obtained with zirconocene bis(amides), this review deals mostly with hydroamination reactions based on titanium catalysts. In this context, studies directed towards catalyst development are presented as well as applications of corresponding processes for the synthesis of biologically interesting compounds. However, the Microreview covers group‐IV metal complex catalyzed hydroamination reactions of alkynes and allenes that appeared in the literature before July 31, 2002. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

Synthesis and coordination behavior of a zirconocene bis(borylphosphane)

The reaction of LiP(H)B(N i Pr 2)[N(SiMe 3) 2]·DME with Cp 2ZrCl 2 in a 2:1 ratio yields the metallodiphosphane Cp 2Zr{P(H)B(N i Pr 2)[N(SiMe 3) 2]} 2 ( 3a). Combination of 3a with Mo(CO) 4 (norbornadiene) provides the adduct Cp 2Zr{P(H)B(N i Pr 2)[N(SiMe 3) 2]} 2·Mo(CO) 4 ( 4a) in which the metallo-diphosphane 3a acts as a chelating ligand. The compounds have been characterized by spectroscopic methods and the molecular structures of 3a and 4a have been determined by single-crystal X-ray diffraction methods. The chemical and structural features are compared and contrasted with related metallo-diphosphanes that contain organic substituents on the diphosphane P atoms.

ChemInform Abstract: Mukaiyama Aldol Reactions Catalyzed by Zirconocene Bis(triflate) Complexes: Stereochemistry and Mechanisms for C—C Bond Formation.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Mukaiyama Aldol Reactions Catalyzed by Zirconocene Bis(triflate) Complexes: Stereochemistry and Mechanisms for C−C Bond Formation

The aldol condensations of α- and β-(benzyloxy) aldehydes with enol silanes, catalyzed by Cp2Zr(OTf)2·THF or Cp2Zr(OTf)2, in a variety of solvents were studied. The simple diastereoselectivity of these reactions is modest and comparable to that observed using simple aldehydes of similar steric requirements. Studies have revealed that TMSOTf is directly produced on reaction with the zirconocene catalyst with the enol silane in nitroalkane solvent or is formed during catalysis in dichloromethane solution. Although TMSOTf is known to catalyze cross-aldol reactions under these conditions, the rate of this process is not always competitive with that observed using the zirconocene catalysts. In particular, sterically unhindered or aromatic aldehydes react via a mechanism that appears to be mainly Zr-catalyzed, based on both the difference in rate between Zr- and Si-mediated reactions as well as differences in enol silane/silyl triflate reactivity in crossover-type experiments. With sterically hindered aldehydes...

Diels−Alder Reactions of Oxazolidinone Dienophiles Catalyzed by Zirconocene Bis(triflate) Catalysts: Mechanism for Asymmetric Induction

The Diels−Alder cycloaddition reaction between enoyl−oxazolidinones 3 and dienes is efficiently catalyzed by zirconocene bis(triflate) catalysts (4 and 8) in CH2Cl2 or nitroalkane solvents. The use...