Organozinc Research Articles

Nanoribbon-structured organo zinc phosphite polymorphs with white-light photoluminescence.

The first neutral organo zinc phosphites composed of 2.8 nm-wide ribbons were obtained in pure phases and exhibit near-white-light photoluminescence (PL). By using the "mesitylene strategy", interesting polymorphism in the system of NTHU-14 was discovered. The S-shaped ribbons are arranged into R and L arrays, resulting in RLR and RRR stacking for two polymorphs. π-π interactions exist within each array and hydrogen bonding between adjacent arrays. Besides a common ligand-based emission band at 410 nm, the PL curves of polymorphs 14-α and 14-β are distinctly different: 14-α gave a defect-based emission at 565 nm, whereas 14-β primarily shows a π-excimer-based emission at 535 nm. Electron paramagnetic resonance (EPR) data disclosed that radical species exist in the reaction and that the two phases were growing from different environments. Based on these results, the origin of the 565 nm band can be ascribed to lattice defects, and one possible cause of 14-β not showing noticeable yellow emission is identified.

Tridentate pyrrolylzinc compounds: Synthesis, structures, reactivities and catalytic cyclotrimerization reaction of isocyanate

The reactions of ZnEt2 with NNN-tridentate pincer type pyrrolyl ligands, 2,5-bis((dimethylamino)methylene)-1H-pyrrole (HL1), 2,5-bis((pyrrolidin-1-yl)methylene)-1H-pyrrole (HL2) and 2,5-bis((piperidino)methylene)-1H-pyrrole (HL3), afford zinc ethyl compounds [C4H2N(2,5-CH2NMe2)2]ZnC2H5 (1), [C4H2N(2,5-CH2N(CH2)4)2]ZnC2H5 (2), and [C4H2N(2,5-CH2N(CH2)5)2]ZnC2H5 (3) in high yield. Subjecting 1, 2, 3 with one equivalent of tert-butylphenol in THF generated {[C4H2N(2,5-CH2NMe2)2]Zn(O–C6H4-4-tBu)}2 (4), {[C4H2N(2,5-CH2N(CH2)4)2]Zn(O–C6H4-4-tBu)}2 (5), {[C4H2N(2,5-CH2N(CH2)5)2]Zn(O–C6H4-4-tBu)}2 (6), respectively. Each has been characterized by satisfactory C, H and N microanalysis, NMR spectroscopy at ambient temperature, and single crystal X-ray structural analysis. The compounds Et6Zn6O2[C4H2N(2,5-CH2N(CH2)4)2]2 (7) and Et6Zn6O2[C4H2N(2,5-CH2N(CH2)5)2]2 (8) obtained accidentally from zinc ethyl compounds with traces of water. Each of compound 1–6 has been used as initiator for cyclotrimerization of isocyanate, and the organozinc compound 3 shows moderate reactivity toward the cyclotrimerization of isocyanate in Et2O solvent under mild conditions.

Structural determination and gas-phase synthesis of monomeric, unsolvated IZnCH3 (X̃(1)A(1)): a model organozinc halide.

The first experimental structure of a monomeric organozinc halide, IZnCH3, has been measured using millimeter-wave direct absorption spectroscopy in the frequency range 256-293 GHz. IZnCH3 is a model compound for organozinc halides, widely used in cross-coupling reactions. The species was produced in the gas phase by reaction of zinc vapor with iodomethane in the presence of a dc discharge. IZnCH3 was identified on the basis of its pure rotational spectrum as well as those of the isotopically substituted species I(66)ZnCH3, I(64)Zn(13)CH3, and I(64)ZnCD3. IZnCH3 is unmistakably a symmetric top molecule (X̃(1)A1) belonging to the C3v point group, in agreement with DFT calculations, with the following experimentally determined structural parameters: rIZn = 2.4076(2) Å, rZnC = 1.9201(2) Å, rCH = 1.105(9) Å, and ∠H-C-H = 108.7(5)°. The basic methyl group geometry is not significantly altered in this molecule. Experimental observations suggest that IZnCH3 is synthesized in the gas phase by direct insertion of activated atomic zinc into the carbon-iodine bond of iodomethane.

Cover Picture: Continuous Synthesis of Organozinc Halides Coupled to Negishi Reactions (Adv. Synth. Catal. 18/2014)

Cover Picture: Continuous Synthesis of Organozinc Halides Coupled to Negishi Reactions (Adv. Synth. Catal. 18/2014)

The tantalum-catalyzed carbozincation of 1-alkenes with zinc dialkyls

The TaCl5-mediated reaction between monosubstituted alkenes and Et2Zn affords 3-(R-substituted)-n-butylzincs in high yield (up to 92%) and regioselectivity. Organozinc reagents bearing a longer alkyl chain (R = Prn, Bun, Amn, Hexn) react with 1-alkenes in the presence of TaCl5 as the catalyst to give two types of organozinc compound having iso-alkyl structure. The probable mechanism of the carbozincation reaction implies the formation of β-substituted and β,β'-disubstituted tantalacyclopentanes as the key intermediates. The thermodynamic probability of the mechanistic elementary stages for the ethylzincation of terminal alkenes has been estimated using DFT PBE/SBK method.

Chiral ligands derived from monoterpenes: application in the synthesis of optically pure secondary alcohols via asymmetric catalysis.

The preparation of optically pure secondary alcohols in the presence of catalysts based on chiral ligands derived from monoterpenes, such as pinenes, limonenes and carenes, is reviewed. A wide variety of these ligands has been synthesized and used in several catalytic reactions, including hydrogen transfer, C-C bond formation via addition of organozinc compounds to aldehydes, hydrosilylation, and oxazaborolidine reduction, leading to high activities and enantioselectivities.

Carbon dioxide as a polymer feedstock.

This review describes the progress made over the last 45 years since the seminal paper by Inoue's group in Tokyo on the utilisation of CO2 as a component of a polymerising system. This approach, rapidly taken up by others, focused initially on the copolymerisation of CO2 with an epoxide to yield a polycarbonate of high molecular weight. The initial catalysts for this process were based on organozinc compounds; these were extended to zinc phenoxides and then a series of metal-centred compounds, particularly metal porphyrins where the central metal was aluminium, cobalt, chromium, copper, manganese and various lanthanides. Later work developed in the direction of producing stereoregular polymers. The most recent advance has concerned the copolymerisation of CO2 with butadiene via a lactone intermediate; the butadiene and CO2 are initially combined with a Pd-centred catalyst to give the lactone which is then subjected to radical polymerisation. The significance of this work is that it offers a way of utilising what is normally a waste and environmentally hazardous product of many processes to synthesise a useful product.

Cobalt‐Catalyzed Cross‐Coupling of Organozinc Halides with Bromoalkynes

AbstractThe cobalt‐catalyzed cross‐coupling of organozinc bromides is described. In the case of arylzinc reagents, the same cobalt catalyst, CoBr2(phen), can be used for both the synthesis of the organozinc species and the cross‐coupling reaction. In the case of alkylzinc halides, which allow access to dialkylalkynes, the method used for the preparation of the organozinc species has a significant impact on the yields.magnified image

ChemInform Abstract: Zinc Hydroxides and Oxides Supported by Organic Ligands: Synthesis and Structural Diversity

AbstractReview: 94 refs.

ChemInform Abstract: Efficient Access to 3‐Substituted‐γ‐hydroxylactams: The Uncatalyzed Addition of Diorganozinc Reagents to Cyclic Imides with Heterocyclic Substitution.

Abstract A range of 3-substituted-γ-hydroxylactams have been prepared via the uncatalyzed addition of organozinc nucleophiles to cyclic imides. This reactivity is primarily limited to imides containing heterocyclic N-substitution, but proceeds efficiently with a variety of diorganozinc reagents, including those prepared and utilized without purification, as well as organozinc halides. It is hypothesized that the presence of a Lewis basic directing group is required for optimum reactivity.

Diastereoselective nucleophilic ring-opening reactions of 2,6-diazasemibullvalenes for the synthesis of diverse functionalized δ(1) -bipyrroline derivatives.

Nucleophilic ring-opening reactions of 2,6-diazasemibullvalenes (NSBVs) were investigated. Different types of nucleophile (alcohols, phenols, thiols, carboxylic acids, water, enols, amines, indoles, metal-halide salts, sodium azide, organozinc compounds, lithium alkynethiolate, and sulfoxonium ylides) were used to afford diverse functionalized Δ(1) -bipyrroline derivatives in good yields with high regio- and diastereoselectivity. Most of the reactions featured milder conditions and higher reactivity relative to those for common aziridine derivatives, probably because of the rigid ring system and substitution patterns of NSBVs.

Continuous Synthesis of Organozinc Halides Coupled to Negishi Reactions

AbstractThe Negishi cross‐coupling is a powerful CC bond forming reaction. The method is less commonly used relative to other cross‐coupling methods in part due to lack of availability of organozinc species. While organozinc species can be prepared, problems with reproducibility and handling of these sensitive species can complicate these reactions. Herein, we describe the continuous formation, using an activated packed‐bed of metallic zinc, and subsequent use of organozinc halides. We demonstrate that a single column of zinc can provide excellent yields of organozinc halides and that they can be used downstream in subsequent Negishi cross‐couplings. The preparation of the zinc column and the scope of the reaction are discussed.magnified image

ChemInform Abstract: Functionalized Organozinc Reagents in Medicinal Chemistry: Discovery of Novel Drug Candidates

AbstractReview: [43 refs.

Efficient access to 3-substituted-γ-hydroxylactams: the uncatalyzed addition of diorganozinc reagents to cyclic imides with heterocyclic substitution

A range of 3-substituted-γ-hydroxylactams have been prepared via the uncatalyzed addition of organozinc nucleophiles to cyclic imides. This reactivity is primarily limited to imides containing heterocyclic N-substitution, but proceeds efficiently with a variety of diorganozinc reagents, including those prepared and utilized without purification, as well as organozinc halides. It is hypothesized that the presence of a Lewis basic directing group is required for optimum reactivity.

Functionalized Organozinc Reagents in Medicinal Chemistry: Discovery of Novel Drug Candidates

Discovery, optimization, and early development of drug candidates are very challenging and require a versatile synthetic chemistry toolbox. Organozinc chemistry is a powerful methodology for carbon–carbon bond formation which tolerates several functional groups that are critical for maintaining good physicochemical properties of drug molecules. Here we demonstrate that organozinc chemistry offers facile solutions to otherwise challenging medicinal chemistry problems commonly encountered during lead optimization. In this review, we summarize several examples in which utilization of organozinc-mediated couplings enabled us to rapidly explore a medicinal chemistry hypothesis using readily available intermediates. This chemistry allowed us to make rapid decisions with limited chemistry resources. 1 Introduction 2.1 Alpha4 Integrin Antagonists 2.2 CRTH2 Antagonists 2.3 Glucokinase (GK) Activators 2.4 Leukotriene B4 (LTB4) Receptor Antagonists 2.5 Janus Activated Kinase 3 (JAK3) Inhibitors 2.6 Synthesis of Novel Scaffolds 3 Conclusions 4 Experimental Methods

Pd-catalyzed Fukuyama cross-coupling of secondary organozinc reagents for the direct synthesis of unsymmetrical ketones

The coupling of acyl electrophiles with organometallic reagents represents a convergent route toward complex and versatile ketone products. Despite the mild conditions and high functional group tolerance, the cross-coupling of carboxylic acid derivatives, such as thioesters, and secondary organometallic reagents is an underdeveloped transformation. Herein, we disclose a convenient and efficient protocol for the Pd-catalyzed Fukuyama cross-coupling of secondary organozinc reagents with thioester electrophiles. Under these mild conditions, a range of thioesters possessing sensitive functional groups can be coupled with either activated or unactivated secondary organozinc halides in good yields. This method was expanded to include an acid chloride substrate, generating an aryl alkyl ketone in high yield. In addition, a modest dynamic kinetic resolution of the organozinc reagent can be achieved using chiral phosphoramidite ligands to furnish enantioenriched ketone products.

Organozinc Catalyst on a Phenalenyl Scaffold for Intramolecular Hydroamination of Aminoalkenes

The syntheses and characterization of two organozinc compounds were accomplished by reacting phenalenyl (PLY)-based ligands with ZnMe2. Reactions of [HN(Cy),O-PLY] and [HN(Cy),N(Cy)-PLY] ligands with ZnMe2 led to the formation of the dimeric orange-colored organozinc compound [N(Cy),O-PLY-ZnMe]2 (1) and red-colored monomeric organozinc compound [N(Cy),N(Cy)-PLY-ZnMe] (2) under evolution of methane. Both 1 and 2 were characterized by NMR spectroscopy, elemental analysis, and single-crystal X-ray diffraction study. The organozinc compound 2 was tested as a catalyst for intramolecular hydroamination of both unactivated primary and secondary aminoalkenes in the presence of an externally added activator, which generated the zinc-based cation in situ. The catalytic result obtained from the present catalyst 2 was compared with the catalysts having similar structure from previous studies. The DFT calculation indicates that the stability of the in situ generated cation plays a significant role in the catalytic activity in the hydroamination reaction.

Influence of type of zinc salts on photoinitiated living cationic polymerization of vinyl ethers

Activities of a series of zinc salts in Lewis-acid-mediated cationic photopolymerization of vinyl ethers have been studied. Readily soluble zinc salts including zinc stearate, zinc acetate and zinc oxide; zinc iodide; and metallic zinc were employed as a Lewis acid in propagation stage of the cationic polymerization initiated by photolysis of a substituted vinyl halide, 1-bromo-1,2,2-tris(p-methoxyphenyl)ethene (AAAVB). As a model monomer isobutyl vinyl ether (IBVE) was polymerized by the described system in the presence of the zinc salts or metallic zinc for investigation of efficiencies of the Lewis acids. Novel system containing organo-zinc compounds yielded polymers in more controlled manner. For further evaluation of potential living character of the system, polymerization of IBVE catalyzed by zinc stearate was monitored, and as a result, the polymerization showed quasi-living nature. Activity of the catalyst system in photo-induced crosslinking of difunctional vinyl ether was evaluated as well.

ChemInform Abstract: Catalytic Enantioselective Alkylation of Aldehydes by Using Organozinc Halide Reagents.

Functionalized alkylzinc halides can be employed in the enantioselective addition to aldehydes by using a titanium(IV) catalyst derived from a H(8)-binaphthol derivative in the presence of [Ti(OiPr)(4)] and MgBr(2). A range of functionalities, including olefin, chlorine atoms, protected alcohols, amides, and cyano groups, are tolerated in the present reaction, providing the corresponding functionalized alcohols in high yields and enantioselectivities (see scheme).

ChemInform Abstract: Trimethylsilyl Chloride Promoted Synthesis of α‐Branched Amines by Nucleophilic Addition of Organozinc Halides to Nitrones.

AbstractThe present new method proceeds in the presence of trimethylsilyl chloride which acts as an essential reaction promoter and a protection reagent for the sensitive N‐hydroxylamine group.