Zirconium Catalysts Research Articles

Direct amide formation from unactivated carboxylic acids and amines

The direct coupling of unactivated carboxylic acids with amines can be performed in toluene 110 °C in the absence of catalyst. The use of simple zirconium catalysts at 5 mol% loading gave amide formation in as little as 4 h.

Concerted C–N/C–H Bond Formation in Highly Enantioselective Yttrium(III)-Catalyzed Hydroamination

A highly active oxazolinylborato yttrium hydroamination catalyst provides 2-methyl-pyrrolidines with excellent optical purities. The proposed mechanism, in which a yttrium(amidoalkene)amine complex reacts by concerted C–N and C–H bond formation, is supported by the rate law for conversion, substrate saturation under initial rates conditions, kinetic isotope effects, and isotopic perturbation of enantioselectivity. These features are conserved between oxazolinylborato Mg-, Y-, and Zr-mediated aminoalkene cyclizations, suggesting related transition states for all three systems. However, inversion of the products’ absolute configuration between yttrium and zirconium catalysts coordinated by the same 4S-oxazolinylborate ligands highlight dissimilar mechanisms of stereoinduction.

Structure and Dynamics in Solution of Bis(phenoxy-amine)Zirconium Catalysts for Olefin Polymerization

The activity of two bis(phenoxy-amine)ZrR2 precatalysts (bis(phenoxy-amine) = N,N′-(3-tBu-5-OMe-2-C6H2OCH2)2-N,N′-Me2-(NCH2CH2N); R = Me (1), Bn (2, benzyl)) toward propene polymerization has been evaluated using different activators and cocatalysts: MAO, MAO/TBP, B(C6F5)3/TIBA, and [CPh3][B(C6F5)4]/TIBA (MAO = methylalumoxane, TBP = 2,6-di-tert-butylphenol, TIBA = triisobutylaluminum). It was found that the nature of the activator affects the activity only to a small extent. NMR studies in solution and DFT calculations on the 3a–c and 4a–c (a, MeB(C6F5)3–; b, BnB(C6F5)3–; c, B(C6F5)4–) ion pairs deriving from the activation processes of 1 and 2, respectively, showed that three isomers can form. All of them have the anion in the second coordination sphere, whereas the binding modality of the ligand leads to the mer-mer most stable isomer, fac-mer isomer of intermediate stability, and fac-fac least stable isomer. Notably, the energy of the fac-fac isomer, which is supposed to be the active species in the p...

A Highly Enantioselective Zirconium Catalyst for Intramolecular Alkene Hydroamination: Significant Isotope Effects on Rate and Stereoselectivity

Ein chiraler Zr-Komplex katalysiert die cyclisierende Hydroaminierung von Aminopentenen zu 2-Methylpyrrolidinen. Das Geschwindigkeitsgesetz spricht für eine reversible Substrat-Katalysator-Wechselwirkung vor dem geschwindigkeitsbestimmenden Schritt. Auf der Grundlage kinetischer Isotopeneffekte und des signifikanten Effekts der Isotopensubstitution auf die Enantioselektivität wird ein neuer Mechanismus für die Zr-katalysierte Hydroaminierung vorgeschlagen.

A Highly Enantioselective Zirconium Catalyst for Intramolecular Alkene Hydroamination: Significant Isotope Effects on Rate and Stereoselectivity

A Highly Enantioselective Zirconium Catalyst for Intramolecular Alkene Hydroamination: Significant Isotope Effects on Rate and Stereoselectivity

ChemInform Abstract: Stereoselective Synthesis of β‐Amino Ketones Possessing β‐[(2H‐Pyran‐2‐one)‐3‐yl]‐β‐chlorovinyl Moiety via Three‐Component Direct Mannich Reaction, Catalyzed with ZrOCl2·8H2O.

AbstractThe new β‐chloroacrolein with a pyranone moiety (III) is subjected to a three‐component Mannich‐type reaction with anilines (IV), cyclic ketones (V), and acyclic ketones in the presence of a zirconium catalyst.

ChemInform Abstract: Zirconium(IV)‐ and Hafnium(IV)‐Catalyzed Highly Enantioselective Epoxidation of Homoallylic and Bishomoallylic Alcohols.

AbstractThe hafnium catalytic system bearing a chiral bishydroxamic acid ligand in general exhibits better results in terms of reactivity and enantioselectivity than the analogous zirconium catalyst.

A Peek at Polymerization

Chemistry The properties of plastics depend intimately on the dynamics of the polymerization reactions used to produce them. Because the reactions are often quite rapid, though, they can prove hard to track. Christianson et al. have adapted a nuclear magnetic resonance (NMR) spectrometer in order to monitor polymerization reactions on a millisecond time scale. Using a stopped-flow approach more common in optical spectroscopy, they set up the probe to acquire data just after pneumatically driven mixing of a catalyst solution stream with a stream of reactive monomer. With this system in hand, they examined the room-temperature polymerization of 1-hexene by a borane-activated zirconium catalyst. They were able to observe initiation and chain propagation steps directly, and also monitor buildup of a transiently deactivated form of the catalyst, resulting from borane binding to a zirconium hydride ligand after chain elimination from the metal center. The results bolster previous mechanistic hypotheses surrounding this catalyst's behavior and highlight the utility of stopped-flow NMR. J. Am. Chem. Soc. 132 , 10.1021/ja105107y (2010).

ChemInform Abstract: Catalytic, Enantioselective Synthesis of α-Aminonitriles with a Novel Zirconium Catalyst.

Strecker reactions of aldimines with Bu3 SnCN in the presence of the novel chiral zirconium binuclear catalyst 1 provide α-aminonitriles in good yields and with high enantioselectivities. The reaction can be applied to a wide range of substrates. Since both enantiomers of the chiral sources are readily avaibable, both enantiomers of the α-aminonitriles are easily prepared according to this method. L=N-methylimidazole.

ChemInform Abstract: Chiral Catalyst Optimization Using Both Solid-Phase and Liquid-Phase Methods in Asymmetric Aza Diels-Alder Reactions.

[formula: see text] In the presence of 1-5 mol % of a chiral zirconium catalyst, aza Diels-Alder reactions of aldimines with Danishefsky's dienes proceeded smoothly to afford the corresponding piperidine derivatives in high yields with high enantioselectivities. For the catalyst optimization, solid-phase and liquid-phase methods were successfully used. In the solid-phase approach, polymer-supported (R)-1,1'-binaphthols (BINOLs) have been synthesized and rapid optimization using the solid-phase reactions has been achieved. On the other hand, novel chiral zirconium cyanides were developed as excellent catalysts using the liquid-phase approach.

Synthesis of isophorone diisocyanate (IPDI) based waterborne polyurethanes: Comparison between zirconium and tin catalysts in the polymerization process

In this work, a comparative study of the catalytic activity of tin and zirconium compounds in the polymerization of isophorone diisocyanate (IPDI) based waterborne polyurethanes is presented. Zirconium acetyl acetonate is much less toxic than the commonly used dibutyltin diacetate but it is deactivated in the presence of acid groups. Nevertheless, acid groups are commonly used in the synthesis of waterborne polyurethanes and therefore these groups have to be neutralized in advance for carrying out the synthesis using the zirconium catalyst. Moreover, FTIR and 13C NMR results have shown that in the presence of triethyl amine and tin catalyst, the secondary isocyanate group is more reactive than the primary group, while using the zirconium catalyst, the two isocyanate groups show the same reactivity.

Asymmetric meso-aziridine ring-opening reactions using a chiral zirconium catalyst

A chiral zirconium catalyst prepared from Zr(O(t)Bu)4 and a chiral tridentate BINOL was found to be effective for asymmetric meso-aziridine ring-opening reactions with aniline derivatives. The N-benzhydryl group on the product obtained was easily cleaved to give the corresponding amine in high yield under reductive conditions.

An Exploration of the Effects of Reversibility in Chain Transfer to Metal in Olefin Polymerization

A kinetic model was derived to investigate the effects of reversibility in chain transfer to metal in olefin polymerization. The model predicts both number- and weight-average molecular weights, Mn and Mw, as a function of several reactor input variables including the constants for chain transfer and reversible transfer. A number of interesting and nonobvious insights into molecular weight distributions are gained from these simulations. The most revealing result is the variation of the molecular weight distribution (Mw/Mn) with conversion. In the absence of reversible transfer, the Mw/Mn is always greater than or equal to 2. Regardless of the magnitude of the reversible transfer constant, Mw/Mn approaches 2 as Mn approaches its maximum value. More dramatic deviations from Mw/Mn = 2 are observed for higher chain transfer constants. Polymerization data from two bis(phenoxyimine)zirconium catalyst systems are presented to demonstrate these effects. These results indicate that singular polymerizations should not be used to explore for reversible transfer characteristics, but rather a series of polymerizations should be conducted over a range of polymer conversions.

Synthesis and Behavior of ?-Iminocarboxyamide Nickel and Zirconium Catalysts Towards Olefin Polymerization

Synthesis and investigations of Nickel-based olefin oligomerization and polymerization catalysts, ?-Iminocarboxyamide µ3-Penzyl Ni(II) Complex(2) is reported. The attempt to improve the yield of the synthesis of the above mentioned catalysts by the direct reaction of the potassium salt of the ligand, Ni(COD)2(bis(1,5-cyclooctadiene)-nickel, and Benzyl halide in THF and starting temperature of -35°C. Led instead to disclose that the less hindered N-aryal moieties on the diimine complexes the more difficult to synthesize the ethylene polymerization catalyst, Instead, yielding the di ? -Iminocarboxyamide Ni-complex(5) which is inactive towards ethylene polymerization. This promoted us to synthesize the complex di ?-Iminocarboxyamide Zr-complex(6) which is activated by MAO for ethylene polymerization.

Awakening a dormant catalyst: salicylaldimine systems for ethene/tert-butylstyrene copolymerization

A group of readily available zirconium catalysts incapable of ethene-co-styrene polymerization are remarkably active and selective for the production of the new polymer ethene-co-tert-butylstyrene via a single site mechanism.

Synthesis of a new zirconium catalyst for ethylene polymerization

A novel complex dichlorobis(2-ethyl-3-hydroxy-4-pyrone)zirconium(IV) (ZrCl 2 (ethylpyrone) 2 ) was synthesized. Complexation of the pyrone ligand to the zirconium was confirmed by UV, 1 H and 13 C-NMR, and electrochemical studies. NMR showed the presence of four isomers and density functional theory calculations indicated that the main isomer had a cis configuration. The catalyst was shown to be active in ethylene polymerization in the presence of the cocatalyst methylaluminoxane. The highest catalyst activity for the zirconium complex was achieved at Al/Zr = 2500, 70 °C and when a small concentration of catalyst was used (1 μmol).

Comparison of olefin polymerization behavior of sterically crowded tris(pyrazolyl)borate group 4 metal complexes

The ethylene polymerization and ethylene/α-olefin copolymerization behavior of the sterically crowded tris(pyrazolyl)borate group 4 metal complexes Tp Ms*TiCl 3 ( 1, Tp Ms* = HB(3-mesitylpyrazolyl) 2(5-mesitylpyrazolyl) −), {K[Tp Ms*TiCl 3]} 2 ( 2), Tp Ms*TiCl 2(O-2,4,6- tBu 3-Ph) ( 3), Tp Ms*ZrCl 3 ( 4), Tp MsZrCl 3 ( 5, Tp Ms = HB(3-mesitylpyrazolyl) 3 −), and Tp Ms*HfCl 3 ( 6) were studied with dried-MAO activation in toluene solution. These catalysts all produce very high molecular weight ( M v > 10 6) linear polyethylene. Zirconium catalyst 5 excels in productivity in ethylene homopolymerization and ethylene/1-hexene copolymerization, molecular weight, and hexene incorporation ability. Catalyst 5 produces moderately alternating ethylene/1-hexene copolymer (41 mol% hexene) with ultra-high molecular weight ( M w = 1.3 × 10 6), narrow molecular weight distribution ( M w/ M n = 2.2) and narrow composition distribution with high efficiency.

Are MgCl2-Immobilized Single-Center Catalysts for Polyethylene Really Single-Center? Confirmation and Refutation Using Melt Rheometry

Investigation of the melt rheological properties of polyethylenes prepared with chromium, titanium, vanadium, and zirconium catalysts immobilized on MgCl2 supports has confirmed narrow (Schulz−Flory) molecular weight distribution, indicative of single-center catalysis, for Cr-, V-, and Zr-based systems, but not for Ti. In the case of polymers prepared with MgCl2-immobilized Ti complexes and having narrow MWD (Mw/Mn 2−3) according to GPC, deviation from a Schulz−Flory distribution was evident from a decrease in storage modulus with decreasing angular frequencies, whereas polyethylenes prepared with analogous vanadium complexes exhibited a constant (plateau) modulus over a wide frequency range. The presence of the constant plateau modulus in high molecular weight polyethylenes is characteristic for narrow MWD, so that melt rheology provides a valuable tool to prove, or disprove, the presence of a Schulz−Flory distribution in cases where GPC does not provide a definitive answer.

Selective Dehydrocoupling of Phosphines by Triamidoamine Zirconium Catalysts

New zirconium triamidoamine complexes (N3N)ZrR (N3N = N(CH2CH2NSiMe3)33-; R = Me, 1; PHPh, 2; PHCy, 4) are effective catalysts for the dehydrocoupling of primary and secondary phosphines and select for the diphosphine product. Mechanistic analysis revealed that metal-catalyzed P−P bond formation occurs via σ-bond metathesis steps.

Storable, powdered chiral zirconium complex for asymmetric aldol and hetero Diels–Alder reactions

A storable, powdered chiral zirconium catalyst for asymmetric aldol and hetero Diels-Alder reactions has been developed. The catalyst has the same activity as that prepared in situ even after being stored for 3 months. Moreover, this chiral Zr catalyst worked efficiently not only for asymmetric aldol reactions but also for asymmetric hetero Diels-Alder reactions affording the corresponding addition products with high enantioselectivities.