Hydrozirconation Reaction Research Articles

Hydrozirconation of C=X Functionalities with Schwartz's Reagent

Hydrozirconation of various C=X functionalities with Schwartz's reagent is a powerful method for preparing functionalized organic molecules, for instance aldehydes, amines, and amides. The reactions of [Cp2Zr(H)Cl] with amides, lactams, nitriles or isocyanates proceed under mild conditions. These transformations are remarkably chemoselective as Schwartz's reagent is compatible with various functional groups, including electrophilic functionalities such as ester, nitrile, nitro, and halogens. This compatibility enables many hydrozirconation reactions to be combined with other synthetic methods, and enables performing the reactions in a one‐pot fashion as multicomponent processes.

Hydrozirconated styrene copolymer as a macroinitiator to in situ synthesize polyethylene/polystyrene-g-polyethylene alloy via coordination polymerization

A new method to in situ synthesize polyethylene/polystyrene-g-polyethylene (PE/PS-g-PE) alloy based on hydrozirconation reaction with Cp2ZrHCl and coordination polymerization was reported. Hydrozirconation of vinyl-containing polystyrene (copolymer of styrene and 4-(vinylphenyl)-1-butene (PSVS)) was found to be an efficient way for immobilization of zirconocene pre-initiator onto polymer backbone by carbon-zirconium (C-Zr) sigma (σ) bond. By activation with MAO, the resultant hydrozirconated PSVS could act as a macroinitiator with multiple-initiating sites (Zrδ+-Cδ-) for ethylene insertion and propagation in “graft from” fashion. The hydrozirconation and the following ethylene polymerization were monitored by NMR and GPC, revealing the successful synthesis of PS-g-PE and the following formation of free PE chains due to chain transfer characteristic of metallocene catalyst. Thus we could prepare PE/PS-g-PE alloy through in situ ethylene polymerization by this method. The presence of PS-g-PE in the resultant alloy endowed some special functionalization, for example, acting as compatibilizer in PE/PS blends.

Synthesis and linear rheological property of comb-like styrene-based polymers with a high degree of branch chain

A series of model comb-like polymers (PSVS-g-PS) with high branching degree were synthesized by nucleophilic substitution reaction between iodinated copolymer of styrene (St) with 4-(vinylphenyl)-1-butene (VSt) (PSVSI, backbone) and living polystyrene lithium (PSLi, side chain). This method is a facile way for modular synthesis of graft copolymers based on living anionic polymerization and hydrozirconation reaction. The branching density of PSVS-g-PS (the number of branch chain per 100 repeat backbone units) ranged from 2.4 to 20.7%. The backbone length of PSVS-g-PS was larger than the entanglement molecular weight (Me) of PS, while the molecular weight of branch chain was designed to be below or above the Me of PS. The results from the linear rheological properties of the PSVS-g-PS showed hierarchical relaxation process. One appeared in the intermediate angular frequency region, corresponding to the relaxation of the side chain. The other is in the terminal region, which is related to the movement of the whole comb polymer. From scaling law of zero shear viscosity (η0) of PSVS-g-PS with versus molecular weight, it could be seen that the dynamical behavior of PSVS-g-PS was different from those of both poly(macromonomers) and entangled linear polymer chains, indicating that there is certain entanglement for PSVS-g-PS with long branch chain.

Hydrozirconation of four-, five-, six- and seven-membered N-alkoxycarbonyl lactams to lactamols

A general, practical, and efficient reduction of four-, five-, six- and, seven-membered N-alkoxycarbonyl lactams to the aldehyde oxidation state is reported. The reduction methodology involves the hydrozirconation reaction by Cp2Zr(H)Cl under mild conditions and proceeds with very short reaction times and in excellent to good yields. The hydrozirconation of N-alkoxycarbonyl lactams with the Schwartz reagent demonstrated to be the mildest and most general method for the formation of lactamols with a high functional group tolerance.

Access to Enantiomerically Enriched cis-2,3-Disubstituted Azetidines via Diastereoselective Hydrozirconation

An asymmetric variant of the hydrozirconation reaction has been established starting from Boc-protected chiral allylic amines. The resulting diastereoselectively formed N-functionalized organozirconiums can be considered as promising chirons. In this case, they have been transformed into enantiomerically enriched cis-2,3-disubstituted azetidines through a iodination/cyclization sequence.

Catalytic (Ni, Pd, Pt, Rh and Au) and Non-Catalytic Reactions for Atom- Economic Carbon-Sulfur, Carbon-Selenium and Carbon-Tellurium Bonds Formation

Non-catalytic and catalytic addition reactions were compared in this review, with a special attention paid to the factors controlling selectivity and yields. The scope and limitations of Ni, Pd, Pt, Rh and Au catalysts for the formation of C-S, C-Se and C-Te bonds were discussed with an impact of development of Green chemical methods. Keywords: Catalysis, stereoselectivity, vinyl sulfides, vinyl selenides, C-S bond formation, C-Se bond formation, catalyst poisons, alkynes, vinyl chalcogenides, toxic selenium species, bis-chalcogen-substituted alkenes, Green Synthetic methods, mono-chalcogen-substituted, nucleophilic, hydrothiolation, aromatic dichalcogenides, Diphenyl Dise-lenide, isomerisation, thioselenation, di-tert-butyl, dibenzoyl peroxide, photoirradiation, Propargyl Alcohol, methyl disulfide, hexafluoro-2, phenylacetylene, Benzenethiol, Radical, Diaryl Dichalcogenides, Phenylthioalkynes, Benzeneselenol, Hydrozirconation Reac-tion

Replacing Chloride by Alkoxide: Cp2Zr(H)OR, Searching for Alternatives to Schwartz's Reagent

Attempts to synthesize zirconocene hydrido alkoxide species, Cp2Zr(H)OR, via several synthetic pathways consistently failed to yield the targeted complexes, which seem prone to undergo disproportionation into Cp2ZrH2 and a bisalkoxide complex. Reaction of Cp2ZrH2 with HOR, Me3SiOR, or Ph2CO yielded the corresponding bisalkoxide complexes Cp2Zr(OR)2, of which Cp2Zr{OC(H)Ph2}2 was characterized by an X-ray diffraction study. Insertion of vinyl ethers into Cp2ZrH2 yielded Cp2Zr(OR)2 and Cp2Zr(Et)OR. Attempted hydrogenation of Cp2Zr(Me)OR or reaction of Cp2Zr(BH4)OR with NEt3 did not yield the targeted complexes. Cp2Zr(H)OC6H5 and Cp2Zr(H)OC6F5 could be obtained, however, as transient species by β-H elimination from Cp2Zr(tBu)OR, ligand exchange between Cp2ZrH2 and Cp2Zr(OC6F5)2, or protonation in the presence of olefin to yield the corresponding hydrozirconation products. In hydrozirconation reactions of styrene both species are highly regioselective. The alkoxide substituent failed to inhibit β-H eliminatio...

Dinuclear metallocene complexes as catalyst precursors for homogeneous ethylene polymerization

Abstract Four dinuclear alkylidene-bridged zirconocene complexes were synthesized applying hydrozirconation reaction of α,ω-dienes with the “Schwartz’ reagent” and tested for the polymerization of ethylene. The polyethylenes obtained with alkylidene-bridged dinuclear complexes showed higher molecular weights M w and polydispersities revealing that more catalytically active species exist in the polymerization system.

Stereoselective Synthesis of (E)‐α‐Silylvinyl Tellurides via the Hydrozirconation Reaction of Alkynylsilanes.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Studies on Hydrozirconation of 1‐Alkynyl Sulfoxides or Sulfones and the Application for the Synthesis of Stereodefined Vinyl Sulfoxides or Sulfones.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Stereoselective Preparation of (Z)‐γ‐Silyl‐γ,δ‐Unsaturated Ketones and Their Application in the Synthesis of 1,4‐Diketones.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Studies on hydrozirconation of 1-alkynyl sulfoxides or sulfones and the application for the synthesis of stereodefined vinyl sulfoxides or sulfones.

The hydrozirconation reaction of 1-alkynyl sulfoxides or sulfones with Cp2Zr(H)Cl in THF at room temperature predominantly gave Z-beta-zirconated vinyl sulfoxides or sulfones with excellent regioselectivity. Compared with 1-alkynyl sulfoxides, the hydrozirconation reaction of 1-alkynyl sulfones exhibits great synthetic potential, leading to the efficient preparation of Z-beta-halovinyl sulfones, Z-beta-sulfonyl alpha,beta-unsaturated ketones, and Z-beta-alkynyl vinyl sulfones. Although the reaction mechanisms are still not clear, the neighboring group participation of the sulfinyl or sulfonyl group may be playing an important role in this unique hydrozirconation reaction.

Stereoselective Preparation of (Z)-γ-Silyl-γ,δ-Unsaturated Ketones and their Application in the Synthesis of 1,4-Diketones

Hydrozirconation reaction of alkynylsilanes I followed by Michael addition to α,β-unsaturated ketones in the presence of CuBr.Me 2 S complex produced (Z)-γ-silyl-γ,δ-unsaturated ketones 3 stereoselectively. 1,4-Diketones were prepared via epoxidation and hydrolysis of 3.

Cyanophosphine Derivatives: Nitrile or Cyanide Functionality?

Treatment of dicyanophosphines R-P(CN) 2 with 1 equiv of Schwartz's reagent, [Cp 2Zr(H)Cl] n, led: (i) via a substitution reaction to the formation of the stable hydrocyanophosphines R-P(H)CN (R = Me, tBu, Mes*) or (ii) through a hydrozirconation reaction to the synthesis of the aldiminocyanophosphine R-P(CH double bond NZrCp 2Cl)CN (R = N iPr 2). Further addition of 1 equiv of [Cp 2Zr(H)Cl] n to R-P(H)CN (R = Me, tBu, Mes*) gave the primary phosphine R-PH 2 (R = Me) or the aldimino secondary phosphine R-P(H)(CH double bond NZrCp 2Cl) (R = tBu, Mes*) after the hydrozirconation reaction. Interestingly, the dialdiminophosphorus compound R-P(CH double bond NZrCp 2Cl) 2 (R = N iPr 2) was obtained after addition of [Cp 2Zr(H)Cl] n to R-P(CH double bond NZrCp 2Cl)CN (R = N iPr 2). The difference in reactivity observed for the dicyanophosphines R-P(CN) 2 with the metal hydride [Cp 2Zr(H)Cl] n have been studied with the help of experimental analysis (UV-photoelectron spectroscopy, NMR, IR, X-ray) and computational methods.

Hydrogen Transfer Hydrozirconation of Alkenes withiBuZrCp2Cl Catalyzed by Lewis-Acidic Metal Compounds Containing Al, Zn, Si, Ag, and Pd

The hydrozirconation reaction of monosubstituted alkenes with iBuZrCp2Cl can be significantly accelerated by catalytic amounts of various Lewis acidic metal compounds, most notably AlCl3, Me3SiI, and Pd complexes, such as Li2PdCl4 and Cl2Pd(PPh3)2.

Kinetic vs. thermodynamic control in hydrozirconation reactions

Abstract

Hydrozirconation of alkenyloxirane derivatives: Preparation of cycloalkylmethanols

Cyclopentyl and cyclopropylmethanol derivatives were efficiently prepared through a chemoselective hydrozirconation reaction of (1-butenyl)oxirane and vinyloxirane with Cp 2ZrHCl. However, the attemped reaction of (1-pentenyl)oxirane or (1-propenyl)oxirane failed to yield cyclohexyl or cyclobutylmethanols. The ring formation was stereospecific and proceeded with the inversion of the configuration at the reacting oxirane carbon. The origin of stereospecificity and the stereoselectivity in the formation of cyclopropylmethanols was presumed by the approach of the Schwartz reagent from the less hindered site of the stable gauche-conformer of the vinyloxirane compound in the transition state. (Cyclopropylmethyl)amine derivatives were also prepared by the treatment of vinylaziridine derivatives with Cp 2ZrHCl.

An efficient method in stannylcupration of a methyl substituted enyne or alkyne by kinetic control using methanol

Stannylcupration of enyne 5 was performed with the homostannylcuprate (Bu 3Sn) 2CuCNLi 2 to deliver in a stereoselective way the distal dienylstannane 7 in 77% yield. This reaction was reproducible only when methanol was added to the cuprate solution. In comparison, hydroboration or hydrozirconation reactions failed in this case to produce the corresponding boron or zirconium derivative.

Migration of groups from zirconium to boron: Aspects of synthesis and utility

The hydrozirconation of alkenes or alkynes yields the dicyclopentadienyl alkyl- or alkenylzirconium chloride, respectively, in high yields and with high regioselectivity. The reaction of these organozirconium compounds with a boron halide results in the exchange of the halogen and organic group, forming the organoborane. We report here a systematic investigation of the transmetallation of organic groups from zirconium to a variety of boron compounds. The migration is facile to a variety of boron halides, yielding structurally different types of alkyl or alkenylboranes in good to high yields. Exploiting the unique reactivity and selectivity of the hydrozirconation reaction for the preparation of organoboranes expands the range of potential of both metals for synthesis.

ChemInform Abstract: Reverse Hydrozirconation Reaction: A Regio‐ and Diastereospecific Route to New Diphosphanes.

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