Organometallic Synthesis Research Articles

Organometallic Chemistry Tools for Building Biologically Relevant Nanoscale Systems.

The recent emergence of organometallic chemistry for modification of biomolecular nanostructures has begun to rewrite the long-standing assumption among practitioners that small-molecule organometallics are fundamentally incompatible with biological systems. This Perspective sets out to clarify some of the existing misconceptions by focusing on the growing organometallic toolbox for biomolecular modification. Specifically, we highlight key organometallic transformations in constructing complex biologically relevant systems on the nanomolecular scale, and the organometallic synthesis of hybrid nanomaterials composed of classical nanomaterial components combined with biologically relevant species. As research progresses, many of the challenges associated with applying organometallic chemistry in this context are rapidly being reassessed. Looking to the future, the growing utility of organometallic transformations will likely make them more ubiquitous in the construction and modification of biomolecular nanostructures.

Elemental tellurium in organoelement synthesis of tellurium-containing organometallics and telluracycles

An overview presents the known methods of using elemental tellurium in the synthesis of various acyclic and cyclic, saturated and unsaturated compounds containing Te–E bonds (E = main group atom or transition metal atom). These methods include the insertion of tellurium into the C–E (E = halogen, Al, Ga, Sn, Zr) and P–E (E = Li, P, Si, Ge and Sn) and Sn–Sn single bonds and the addition to the E=E (E = Si, Ge and Sn) double bond, and PC triple bond, as well as the breakdown of the C=C double bond and the exchange of metal (Hg, Ag) and non-metal (B, I) for Te. Reactions with carbenes, their heavier (Si, Ge, Sn) analogs and free radicals are also discussed, as are the oxidation of organophosphorous (III) compounds, silanes and germanes with Te and the direct cyclisation of alkanes, arenes and heteroarenes containing two halogenomethyl fragments with elemental Te. Three-component heterocyclizations involving elemental tellurium and leading to telluracycles are also discussed. The reactions mentioned above are compared to those involving lighter chalcogens.

Aqueous organometallic synthesis: Ammonia borane (NH3.BH3) as a convenient metal-free reagent for the reduction of ferrocenyl and ferrocenium carbonyl derivatives in water

Herein, we present a green methodology for the reduction of ferrocene-derived aldehydes and ketones to their respective alcohols, employing ammonia borane as the reducing agent and neat water as the solvent. We also report the deoxygenation of the same precursors to the corresponding alkyl ferrocenes when reactions are performed under solvent-free conditions. Both methods, applicable to various carbonyl derivatives of ferrocene, give product yields in the range of 40–95 % and, in most cases, a product purification that does not require column chromatography. The investigation for the deoxygenation of alkyl derivatives was extended to the cobalt sandwich compound –[(COCH3)C5H4]Co(η4-C4Ph4) and ketone derivatives of ruthenocene as well. Ammonia borane has also been found to be useful as a convenient reducing reagent for the selective reduction of ferrocenium compounds to their respective ferrocene derivatives at room temperature in water medium. Control experiments have been carried out to explore the mechanistic details of these reactions.

Mechanism of Ni-Catalyzed Photochemical Halogen Atom-Mediated C(sp3)-H Arylation.

Within the context of Ni photoredox catalysis, halogen atom photoelimination from Ni has emerged as a fruitful strategy for enabling hydrogen atom transfer (HAT)-mediated C(sp3)-H functionalization. Despite the numerous synthetic transformations invoking this paradigm, a unified mechanistic hypothesis that is consistent with experimental findings on the catalytic systems and accounts for halogen radical formation and facile C(sp2)-C(sp3) bond formation remains elusive. We employ kinetic analysis, organometallic synthesis, and computational investigations to decipher the mechanism of a prototypical Ni-catalyzed photochemical C(sp3)-H arylation reaction. Our findings revise the previous mechanistic proposals, first by examining the relevance of SET and EnT processes from Ni intermediates relevant to the HAT-based arylation reaction. Our investigation highlights the ability for blue light to promote efficient Ni-C(sp2) bond homolysis from cationic NiIII and C(sp2)-C(sp3) reductive elimination from bipyridine NiII complexes. However interesting, the rates and selectivities of these processes do not account for the productive catalytic pathway. Instead, our studies support a mechanism that involves halogen atom evolution from in situ generated NiII dihalide intermediates, radical capture by a NiII(aryl)(halide) resting state, and key C-C bond formation from NiIII. Oxidative addition to NiI, as opposed to Ni0, and rapid NiIII/NiI comproportionation play key roles in this process. The findings presented herein offer fundamental insight into the reactivity of Ni in the broader context of catalysis.

Synthesis of alkenyl ylide and alkyne-coordinated rhenium complexes

Additions of nucleophiles like phosphines to coordinated alkynes are important processes in organometallic synthesis. In this work, exocyclic alkenyl ylide phenolate (1–2) and benzoate (5) Re(V) complexes are obtained from the reactions of internal 2-alkynylphenols, and 2-ethynylbenzoic acid with ReOCl2(OEt)(PPh3)2, respectively. The Re(V) complexes 1–2 can be reduced to η2-alkyne Re(III) complexes 3–4 with P-C bond cleavage.

Synthesis and aromaticity of metallacyclopropene complexes.

Metallacycloprop-1-ene and metallacycloprop-2-ene complexes are the smallest unsaturated metallacycles, and have attracted continuing attention for their importance in organometallic synthesis and catalysis. This feature article summarizes the syntheses of monocyclic and fused metallacycloprop-2-enes, and monocyclic, spiro, and fused metallacycloprop-1-enes, all with crystallographically characterized structures. The aromatic properties of mononuclear metallacyclopropene complexes are also described.

Evaluating the synthesis of Mg[Al(hfip)4]2 electrolyte for Mg rechargeable batteries: purity, electrochemical performance and costs

Different organometallic and inorganic synthesis methods for MgAlhfip salt are explored, evaluating purity, electrochemical performance, cost of Mg electrolyte, as well as the impact of salt purification and electrolyte additives.

Organometallic synthesis of a high-density Pt single atom catalyst on nickel for the alkaline hydrogen evolution reaction

Single atom platinum catalysts, characterized by isolated Pt atoms dispersed on suitable supports, exhibit high hydrogen evolution catalytic mass activity.

Bismuth-Centered Radical Species: Access and Applications in ­Organic Synthesis

AbstractRecent advances in the isolation of tamed bismuth radicals and the selective in situ generation of highly reactive bismuth radicals have set the stage for the application of these compounds in organic and organometallic synthesis and catalysis. Here, we provide a summary of the methodological approaches in the field. Important strategies for accessing bismuth radical species are presented and key examples of their applications in organic synthesis are outlined, highlighting how this class of compounds has emerged as new set of valuable tools for synthetic practitioners.1 Introduction2 Generation of Bismuth Radical Species by Homolysis2.1 Temperature-Induced Homolysis2.2 Light-Induced Homolysis2.3 Light-/Temperature-Induced Bi–C Homolysis of Polar Oxidative Addition Complexes3 Applications of Bismuth-Centered Radical Species in Organic Synthesis3.1 Bismuth-Catalyzed Cycloisomerization of Iodo Olefins3.2 Controlled Radical Polymerization Reactions3.3 Bismuth-Promoted Pn–Pn and C–S Coupling3.4 Bismuth-Catalyzed Dehydrocoupling of Silanes with TEMPO3.5 Bismuth-Catalyzed C–N Coupling with Redox-Active Electrophiles3.6 Bismuth-Catalyzed Giese-Type Coupling Reactions3.7 Oxidative Addition of Aryl Electrophiles to Photoactive Bismuthinidenes4 Conclusions

Recyclable bispyridine functionalized polyacrylonitrile fibers as ligand of Cu(II) for A3 coupling reaction

Developing an effective and economical technology to achieve the recovery of catalysts in the process of organometallic synthesis has attracted significant attention. Herein, a novel functional fiber catalyst with bispyridine structure was successfully constructed by modifying the commercial polyacrylonitrile fiber. Modified bidentate ligand fiber-based can be used to efficiently complexe Cu(II). The functional fibers were fully characterized by FTIR, ICP, XPS, XRD, SEM, and TGA. To verify the catalytic activity of PANbis(Py)-Cu(II)F, A3 coupling reaction was applied in this work. The results showed that only 0.1 mol% catalyst dosage was needed and the maximum isolated yield was up to 99%. Recycle experiments showed that PANbis(Py)-Cu(II)F has fine recycling performance, and there is no decrease in catalytic efficiency during the first six cycles. Consequently, as a recyclable functional fiber catalyst based on commercial polyacrylonitrile fiber, it provided a new insight for green synthesis and industrial production.

Trimethylsilyl Chloride Aids in Solubilization of Oxidative Addition Intermediates from Zinc Metal.

Trimethylsilyl chloride (TMSCl) is commonly used to "activate" metal(0) powders toward oxidative addition of organohalides, but knowledge of its mechanism remains limited by the inability to characterize chemical intermediates under reaction conditions. Here, fluorescence lifetime imaging microscopy (FLIM) overcomes these prior limitations and shows that TMSCl aids in solubilization of the organozinc intermediate from zinc(0) metal after oxidative addition, a previously unknown mechanistic role. This mechanistic role is in contrast to previously known roles for TMSCl before the oxidative addition step. To achieve this understanding, FLIM, a tool traditionally used in biology, is developed to characterize intermediates during a chemical reaction-thus revealing mechanistic steps that are unobservable without fluorescence lifetime data. These findings impact organometallic reagent synthesis and catalysis by providing a previously uncharacterized mechanistic role for a widely used activating agent, an understanding of which is suitable for revising activation models and for developing strategies to activate currently unreactive metals.

Trimethylsilyl Chloride Aids in Solubilization of Oxidative Addition Intermediates from Zinc Metal

AbstractTrimethylsilyl chloride (TMSCl) is commonly used to “activate” metal(0) powders toward oxidative addition of organohalides, but knowledge of its mechanism remains limited by the inability to characterize chemical intermediates under reaction conditions. Here, fluorescence lifetime imaging microscopy (FLIM) overcomes these prior limitations and shows that TMSCl aids in solubilization of the organozinc intermediate from zinc(0) metal after oxidative addition, a previously unknown mechanistic role. This mechanistic role is in contrast to previously known roles for TMSCl before the oxidative addition step. To achieve this understanding, FLIM, a tool traditionally used in biology, is developed to characterize intermediates during a chemical reaction—thus revealing mechanistic steps that are unobservable without fluorescence lifetime data. These findings impact organometallic reagent synthesis and catalysis by providing a previously uncharacterized mechanistic role for a widely used activating agent, an understanding of which is suitable for revising activation models and for developing strategies to activate currently unreactive metals.

Gold(I)-N-Heterocyclic Carbene Synthons in Organometallic Synthesis.

The prominent role of gold-N-heterocyclic carbene (NHC) complexes in numerous research areas such as homogeneous (photo)catalysis, medicinal chemistry and materials science has prompted organometallic chemists to design gold-based synthons that permit access to target complexes through simple synthetic steps under mild conditions. In this review, the main gold-NHC synthons employed in organometallic synthesis are discussed. Mechanistic aspects involved in their synthesis and reactivity as well as applications of gold-NHC synthons as efficient pre-catalysts, antitumor agents and/or photo-emissive materials are presented.

Characterizing Excited States of a Copper-Based Molecular Qubit Candidate with Correlated Electronic Structure Methods.

Molecular spins have a variety of potential advantages as qubits for quantum computation, such as tunability and well-understood design pathways through organometallic synthesis. Organometallic and heavy-metal-based molecular spin qubits can also exhibit rich electronic structures due to ligand field interactions and electron correlation. These features make consistent and reliable modeling of these species a considerable challenge for contemporary electronic structure techniques. Here, we elucidate the electronic structure of a Cu(II) complex analogous to a recently proposed room-temperature molecular spin qubit. Using active space methods to describe the electron correlation, we show the nuanced interaction between the metal d orbitals and ligand σ and π orbitals makes these systems challenging to model, both in terms of the delocalized spin density and the excited state ordering. We show that predicting the correct spin delocalization requires special consideration of the Cu d orbitals and that the excited state spectrum for the Cu(III) complex also requires the explicit inclusion of the π orbitals in the active space. These interactions are rather common in molecular spin qubit motifs and may play an important role in spin-decoherence processes. Our results may lend insight into future studies of the orbital interactions and electron delocalization of similar complexes.

Nanoprobes based on fluorescent semiconductor nanocrystals and single-domain antibodies for highly sensitive detection of epidermal growth factor receptor in tumor cells

Background. The development of highly oriented conjugates of quantum dots (QDs) and single-domain antibodies (sdAbs) as innovative fluorescence imaging nanoprobes that specifically recognize tumor biomarkers, in particular, epidermal growth factor receptor (EGFR), is a promising approach to improving immunohistochemical tumor typing.Aim. The study was aimed at developing fluorescent nanoprobes based on QDs and sdAbs that specifically recognize EGFR, as well as evaluating their functional characteristics (size and optical properties) and functional activity.Materials and methods. QDs were obtained using high-temperature organometallic synthesis and transferred into the aqueous phase by means of stepwise replacement of ligands on the QD surface. The QDs and sdAbs were conjugated in an oriented manner using a bifunctional cross-linking agent. Detailed characteristics of the resulting conjugates were analyzed by the dynamic light scattering and immunoassay methods. Functional activity was assessed on the model human epidermoid carcinoma cells line A431.Results. The QD–sdAb conjugates have been standardized in terms of control parameters determining their functional activity, in particular, hydrodynamic diameter and efficiency of binding with target tumor cells. They are characterized by high dispersity, homogeneity, and specific functional activity towards their molecular target.Conclusion. The results demonstrate the potential use of the designed QD–sdAb conjugates for EGRF detection in immunohistochemical typing of tumor.

The preparation of 2,2′-bithiophene-based conjugated microporous polymers by direct arylation polymerization and their application in fluorescence sensing 2,4-dinitrophenol

In this paper, we report the synthetic strategy of direct arylation polymerization (DAP) for four 2,2′-bithiophene-based conjugated microporous polymers (the 2,2′-BTh-based CMPs) by coupling 2,2′-bithiophene with the building blocks containing bromine. Compared to conventional coupling polymerization, this synthetic scheme is simple, facile and atomically efficient owing to neither preactivating the C–H bonds in 2,2′-bithiophene using organometallic reagents nor synthesis of complex thiophene-based building blocks. The resulting 2,2′-BTh-based CMPs exhibit excellent thermal stability, high specific surface areas, and good microporosity. Their specific surface areas are higher than that of other previously reported CMPs prepared with DAP. The four 2,2′-BTh-based CMPs can be utilized for multicolor fluorescence sensing of 2,4-dinitrophenol (DNP) with the high sensitivity and selectivity. The sensitivities appear to increase with the degree of structural distortion.

Organometallic one-pot synthesis of ZnO quantum dots coated by sulfoxides as L-type ligands

The introduction of low-molecular-weight L-type-protectors (i.e., sulfoxides) in non-surfactant-assisted one-pot organometallic procedure leads to brightly luminescent and solution-processable ZnO QDs.

Improved methanol electro-oxidation reaction on PdRh-PVP/C electrodes

Here we report on the organometallic synthesis of polyvinylpyrrolidone (PVP)-stabilized palladium-rhodium nanostructures that display high electrochemical properties when used as carbon-supported electrodes (PdxRh1-x-PVP/C) for methanol oxidation reaction (MOR). These nanostructures were synthesized by hydrogenation of the tris(dibenzylideneacetone)dipalladium(0) (Pd2(dba)3) and tris(allyl) rhodium (Rh(η3-C3H5)3) complexes, in tetrahydrofuran (THF) under mild reaction conditions (room temperature and 3 bar H2) and in the presence of PVP as stabilizer. The influence of methanol concentration (0.5, 1.0 and 2.0 M) as well as different scan rates (5–100 mV s−1) was evaluated to determine changes in the stability and catalytic activity. The organometallic approach and the use of PVP for the preparation of PdRh electrode materials promoted the formation of highly dispersed nanostructures, that led to a remarkably enhanced methanol electro-oxidation in alkaline medium. This high catalytic behavior can reasonably arise from a synergistic effect between Pd and Rh metals as, under the applied conditions, Rh is expected to enhance the Pd ability to oxidize methanol to CO2 (oxophilic character) as well as the catalyst stability. From all the evaluated electrode materials, Pd8Rh2-PVP/C electrode showed the highest mass activity at high methanol concentration (2.0 M) and low scan rate (10 mV s−1). This catalyst showed a performance up to 26 times higher than that of Pd-PVP/C and interestingly an electroactivity superior to that of previously reported PdRh catalysts.

Organometallic Synthesis of 2,3,6,7-Tetrasubstituted 1,8-Bis(dimethylamino)naphthalenes for Investigation of the Double Buttressing Effect in Proton Sponges.

The lithiation of 2,7-disubstituted derivatives of 1,8-bis(dimethylamino)naphthalene (DMAN, proton sponge) bearing potentially ortho-directing OMe, NMe2, and SMe groups was studied. It has been shown that OMe groups facilitate selective dual β-lithiation of the naphthalene moiety while the 2(7)-NMe2 groups allow only monolithiation presumably due to the decreased acidity of the ring C-H bonds and conformational immobilization after coordination to the lithium atom. In contrast, the SMe groups provided no ring lithiation and underwent deprotonation of their methyl fragment. The first representatives of previously unknown 2,3,6,7-tetrasubstituted DMANs have been synthesized in good yield after treatment of 2,7-dimethoxy-3,6-dilithio DMAN with the appropriate electrophiles (MeI, Me2S2, Me3SiCl, DMF, etc.). Because the exceedingly high basicity of 2,7-dimethoxy DMAN is commonly attributed to the so-called "buttressing effect" (BE), the availability of 2,3,6,7-tetrasubstituted species provided the first opportunity to study the double BE version. Using X-ray diffraction and basicity measurements, we showed that due to the high conformational mobility of the methoxy groups, the most striking manifestations of double BE are the strong planarization of peri-NMe2 groups and a significant decrease in basicity, while the length and the other properties of the intramolecular NHN hydrogen bond in the corresponding protonated species undergo minor changes.

Selecting the Reaction Path in On-Surface Synthesis through the Electron Chemical Potential in Graphene.

The organometallic on-surface synthesis of the eight-membered sp2 carbon-based ring cyclooctatetraene (C8H8, Cot) with the neighboring rare-earth elements ytterbium and thulium yields fundamentally different products for the two lanthanides, when conducted on graphene (Gr) close to the charge neutrality point. Sandwich-molecular YbCot wires of more than 500 Å length being composed of an alternating sequence of Yb atoms and upright-standing Cot molecules result from the on-surface synthesis with Yb. In contrast, repulsively interacting TmCot dots consisting of a single Cot molecule and a single Tm atom result from the on-surface synthesis with Tm. While the YbCot wires are bound through van der Waals interactions to the substrate, the dots are chemisorbed to Gr via the Tm atoms being more electropositive compared to Yb atoms. When the electron chemical potential in Gr is substantially raised (n-doping) through backside doping from an intercalation layer, the reaction product in the synthesis with Tm can be tuned to TmCot sandwich-molecular wires rather than TmCot dots. By use of density functional theory, it is found that the reduced electronegativity of Gr upon n-doping weakens the binding as well as the charge transfer between the reaction intermediate TmCot dot and Gr. Thus, the assembly of the TmCot dots to long TmCot sandwich-molecular wires becomes energetically favorable. It is thereby demonstrated that the electron chemical potential in Gr can be used as a control parameter in an organometallic on-surface synthesis to tune the outcome of a reaction.