Cyclopentadienyliron Dicarbonyl Research Articles

A C-H functionalization approach to diverse nitrogenous scaffolds through conjugate addition of catalytic allyliron nucleophiles.

Cyclopentadienyliron(ii) dicarbonyl complexes capable of coordinating to and enhancing the acidity of a range of unsaturated substrates have emerged as a new class of base-metal derived catalysts for C-H functionalization. In this manuscript, the iron-catalyzed C-H functionalization of allylic C(sp3)-H bonds using nitrogen containing α,β-unsaturated carbonyl compounds as coupling partners is reported. Employing a cationic cyclopentadienyliron dicarbonyl complex, this redox neutral process converts simple alkenes into allylic anion equivalents for 1,4-addition into maleimides, acyclic α,β-unsaturated imides, and vinylogous amides. The judicious pairing of pyridine and alkylamine bases with Lewis acid additives allowed each of these classes of substrates to be successfully employed, allowing for the formation of a diverse collection of cyclic and acyclic nitrogen-containing compounds featuring C-C unsaturation. The resulting Michael adducts can be further transformed into a variety of useful scaffolds such as allylated pyrroles, pyrrolidines, and carbocyclic acids.

Concave Structural Carbon Co-Doped with Iron Atom Pairs and Nitrogen as Ultra-High Performance Catalyst Toward Oxygen Reduction.

It is crucial to rationally design and synthesize atomic-scale transition metal-doped carbon catalysts with high electrocatalytic activity to achieve a high-efficient oxygen reduction reaction (ORR). Herein, an electrocatalyst comprised of Fe-Fe dual atom pairs and N-doped concave carbon are reported (N-CC@Fe DA) that achieves ultrahigh electrocatalytic ORR activity. The catalyst is prepared by a gaseous doping approach, with zeolitic imidazolate framework-8 (ZIF-8) as the carbon framework precursor and cyclopentadienyliron dicarbonyl dimer as the Fe-Fe atom pair precursor. The catalyst exhibits high cathodic ORR catalytic performance in an alkaline Zn/air battery and proton exchange membrane fuel cell (PEMFC), yielding peak power densities of 241 mW cm-2 and 724mWcm-2, respectively, compared to 127 mW cm-2 and 1.20Wcm-2 with conventional Pt/C catalysts as cathodes. The presence of Fe atom pairs coordinate with N atoms is revealed by X-ray photoelectron spectroscopy(XPS) and X-ray absorption spectroscopy (XAS) analysis, and Density Functional Theory (DFT) calculation results show that the Fe-Fe pair structure is beneficial for adsorbing oxygen molecules, activating the O─O bond, and desorbing OH* intermediates formed during oxygen reduction, resulting in a more efficient oxygen reaction. The findings may provide a new pathway for preparing ultra-high-performance doped carbon catalysts with Fe-Fe atom pair structures.

Iron-Catalyzed Coupling of Alkenes and Enones: Sakurai-Michael-type Conjugate Addition of Catalytic Allyliron Nucleophiles.

The iron-catalyzed coupling of alkenes and enones through allylic C(sp3)-H functionalization is reported. This redox-neutral process employs a cyclopentadienyliron(II) dicarbonyl catalyst and simple alkene substrates to generate catalytic allyliron intermediates for 1,4-addition to chalcones and other conjugated enones. The use of 2,4,6-collidine as the base and a combination of triisopropylsilyl triflate and LiNTf2 as Lewis acids was found to facilitate this transformation under mild, functional group-tolerant conditions. Both electronically unactivated alkenes as well as allylbenzene derivatives could be employed as pronucleophilic coupling partners, as could a range of enones bearing electronically varied substituents.

Synthesis of 1,1-Disubstituted Allenylic Silyl Ethers Through Iron-Catalyzed Regioselective C(sp2)─H Functionalization of Allenes.

We report a synthesis of allenylic silyl ethers through iron-catalyzed functionalization of the C(sp2)─H bonds of monosubstituted alkylallenes. In the presence of a cyclopentadienyliron dicarbonyl based catalyst and triisopropylsilyl triflate as a silylation agent, a variety of aryl aldehydes were suitable coupling partners in this transformation, furnishing a collection of 1,1-disubstituted allenylic triisopropylsilyl ethers as products in moderate to excellent yields as a single regioisomer. Lithium bistriflimide was identified as a critical additive in this transformation. The optimized protocol was scalable, and the products were amenable to further transformation to give a number of unsaturated, polyfunctional derivatives.

Designed Iron Catalysts for Allylic C-H Functionalization of Propylene and Simple Olefins.

Propylene gas is produced worldwide by steam cracking on million-metric-ton scale per year. It serves as a valuable starting material for π-bond functionalization but is rarely applied in transition metal-catalyzed allylic C-H functionalization for fine chemical synthesis. Herein, we report that a newly-developed cationic cyclopentadienyliron dicarbonyl complex allows for the conversion of propylene to its allylic C-C bond coupling products under catalytic conditions. This approach was also found applicable to the allylic functionalization of simple α-olefins with distinctive branched selectivity. Experimental and computational mechanistic studies supported the allylic deprotonation of the metal-coordinated alkene as the turnover-limiting step and led to insights into the multifaceted roles of the newly designed ligand in promoting allylic C-H functionalization with enhanced reactivity and stereoselectivity.

Designed Iron Catalysts for Allylic C−H Functionalization of Propylene and Simple Olefins

AbstractPropylene gas is produced worldwide by steam cracking on million‐metric‐ton scale per year. It serves as a valuable starting material for π‐bond functionalization but is rarely applied in transition metal‐catalyzed allylic C−H functionalization for fine chemical synthesis. Herein, we report that a newly‐developed cationic cyclopentadienyliron dicarbonyl complex allows for the conversion of propylene to its allylic C−C bond coupling products under catalytic conditions. This approach was also found applicable to the allylic functionalization of simple α‐olefins with distinctive branched selectivity. Experimental and computational mechanistic studies supported the allylic deprotonation of the metal‐coordinated alkene as the turnover‐limiting step and led to insights into the multifaceted roles of the newly designed ligand in promoting allylic C−H functionalization with enhanced reactivity and stereoselectivity.

Isolation and Reactivity of Tetrylene-Tetrylone-Iron Complexes Supported by Bis(N-Heterocyclic Imine) Ligands.

The germanium iron carbonyl complex 3 was prepared by the reaction of dimeric chloro(imino)germylene [IPrNGeCl]2 (IPrN=bis(2,6-diisopropylphenyl)imidazolin-2-iminato) with one equivalent of Collman's reagent (Na2 Fe(CO)4 ) at room temperature. Similarly, the reaction of chloro(imino)stannylene [IPrNSnCl]2 with Na2 Fe(CO)4 (1 equiv) resulted in the Fe(CO)4 -bridged bis(stannylene) complex 4. We observed reversible formation of bis(tetrylene) and tetrylene-tetrylone character in complexes 3 vs. 5 and 4 vs. 6, which was supported by DFT calculations. Moreover, the Li/Sn/Fe trimetallic complex 12 has been isolated from the reaction of [IPrNSnCl]2 with cyclopentadienyl iron dicarbonyl anion. The computational analysis further rationalizes the reduction pathway from these chlorotetrylenes to the corresponding complexes.

Isolation and Reactivity of Tetrylene‐Tetrylone‐Iron Complexes Supported by Bis(N‐Heterocyclic Imine) Ligands

The germanium iron carbonyl complex 3 was prepared by the reaction of dimeric chloro(imino)germylene [IPrNGeCl]2 (IPrN=bis(2,6-diisopropylphenyl)imidazolin-2-iminato) with one equivalent of Collman's reagent (Na2Fe(CO)4) at room temperature. Similarly, the reaction of chloro(imino)stannylene [IPrNSnCl]2 with Na2Fe(CO)4 (1 equiv) resulted in the Fe(CO)4-bridged bis(stannylene) complex 4. We observed reversible formation of bis(tetrylene) and tetrylene-tetrylone character in complexes 3 vs. 5 and 4 vs. 6, which was supported by DFT calculations. Moreover, the Li/Sn/Fe trimetallic complex 12 has been isolated from the reaction of [IPrNSnCl]2 with cyclopentadienyl iron dicarbonyl anion. The computational analysis further rationalizes the reduction pathway from these chlorotetrylenes to the corresponding complexes.

Synthesis, anticancer and antimalarial activities of organosulfur and organoselenium derivatives of cyclopentadienyliron dicarbonyl as photoCORMs

The reactions of [CpFe(CO)2]2 with 2 mol equivalents of R2E2 (R = C6H11, C4H3S, CH2C6H5; E = S, Se) have yielded dinuclear products of [CpFe(CO)(μ-L)]2 (L = C6H11S (1), C4H3S2 (2) and CH2C6H5Se (3)), respectively. An additional trinuclear compound, C24H22O2Se2Fe3 (4) was isolated only from the reaction with dibenzyl diselenide. All the products have been fully characterized by FT-IR,1H and13C NMR, CHN elemental analysis, and structurally elucidated by single crystal X-ray diffraction. The stability of 1–3 both under dark and UV conditions were investigated by monitoring the changes in their respective UV–Vis spectra in phosphate buffered saline (PBS) solution. Their potential application as photoCORMs were also evaluated by standard myoglobin assay. 2 showed the shortest half-life and highest equivalent of CO-released. The anticancer studies of 1–3 were evaluated in-vitro on breast cancer cell lines (MCF-7, MDA-MB-231 and MDA-MB-468) and the cytotoxicity of 2 had increased approximately 4 times against MDA-MB-468 cell line upon UV irradiation, which was 11.5 ± 2.7 μM. All complexes exhibited cytotoxic effect on specific sub-types of breast cancer cells. Antimalarial activities of 1–3 had also been studied and reported in this work. Unfortunately, these complexes did not display any significant effect on the Plasmodium falciparum 3D7 strains.

Photoinduced Free Radical Promoted Cationic RAFT Polymerization toward “Living” 3D Printing

Three-dimensional (3D) printing utilizing controlled polymerization systems is emerging as a powerful approach to fabricate "living" objects, which can be further modified with various functionalities. Here, we report photoinduced free radical-promoted cationic reversible addition-fragmentation chain transfer (RAFT) polymerization under broad wavelengths from ultraviolet (UV) to near-infrared (NIR) light. A commercially available iron catalyst, cyclopentadienyl iron dicarbonyl dimer (Fe2(Cp)2(CO)4), was used as the photocatalyst, and several diphenyliodonium salts were examined as oxidants. Various poly(vinyl ether)s with controlled molecular weights and a narrow dispersity (1.06-1.32) were prepared through this method. Relatively high chain-end fidelity can be observed and has been demonstrated by successful chain-extension experiments. In addition, benefiting from the penetrating ability of NIR light, 3D objects with different thicknesses were achieved by employing stereolithography-based 3D printing techniques. Furthermore, the postfunctionalization of these 3D printed objects with fluorescent monomers provides a facile method to build 3D objects with complex functionality and potential applications in anticounterfeiting materials.

Iron-Catalyzed Contrasteric Functionalization of Allenic C(sp2)-H Bonds: Synthesis of α-Aminoalkyl 1,1-Disubstituted Allenes.

An iron-catalyzed C-H functionalization of simple monosubstituted allenes is reported. An efficient protocol for this process was made possible by the use of a newly developed electron-rich and sterically hindered cationic cyclopentadienyliron dicarbonyl complex as the catalyst and N-sulfonyl hemiaminal ether reagents as precursors to iminium ion electrophiles. Under optimized conditions, the use of a mild, functional-group-tolerant base enabled the conversion of a range of monoalkyl allenes to their allenylic sulfonamido 1,1-disubstituted derivatives, a previously unreported and contrasteric regiochemical outcome for the C-H functionalization of electronically unbiased and directing-group-free allenes.

Regiocontrolled Coupling of Alkynes and Dipolar Reagents: Iron-Mediated [3 + 2] Cycloadditions Revisited

Cyclopentadienyliron dicarbonyl based allenyliron complexes were prepared, and their formal [3 + 2] cycloaddition with a number of dipolar reagents was investigated as a means of preparing heterocy...

Near-Infrared, Light-Induced Cationic and Radical RAFT Polymerization Catalyzed by Iron Complex.

A near-infrared (NIR) light induced controlled cationic polymerization is presented here. The halide abstraction reaction between the cyclopentadienyl iron dicarbonyl dimer (Fe2(Cp)2(CO)4) and an organic halide is utilized to generate initial radicals or cations under mild conditions, which can be further combined with both radical and cationic reversible addition-fragmentation chain transfer (RAFT) polymerization. Well-defined poly(vinyl ether)s and polyacrylates are prepared successfully under NIR light by this method. The excellent penetration ability of NIR light through thick barriers has been verified by polymerization in the presence of an A4 paper. In addition, iron-based radical polymerization has been used for three-dimensional (3D) printing to fabricate materials with different thicknesses.

Proton reduction using cyclopentadienyl Fe(II) (benzene-1,2-dithiolato) carbonyl complexes as electrocatalysts

The UV photolysis of cyclopentadienyl iron dicarbonyl dimer [CpFe(CO)2]2 and benzene-1,2-dithiol or 3,6-dichloro-1,2-benzenedithiol afforded dinuclear iron complexes [Cp2Fe2(CO)(bdt)(μ-CO)] (1) and [Cp2Fe2(CO)(Cl2-bdt)(μ-CO)] (2) respectively (bdt = benzene-1,2-dithiolato, Cl2-bdt = dichloro-1,2-benzenedithiolato). Further oxidation of the two complexes resulted in the release of CO and generated [CpFe(bdt)]2 (3) and [CpFe(Cl2-bdt)]2 (4). All four complexes were found to catalyse proton reduction at a similar overpotential and rate when trifluoroacetic acid (TFA) was used as a proton source. Both experimental and computational studies lent support to a mononuclear iron intermediate species carrying the CpFe(bdt) or CpFe(Cl2-bdt) moiety acting as the catalyst in the proton reduction process.

Redox-Neutral Propargylic C–H Functionalization by Using Iron Catalysis

AbstractIn spite of their rich stoichiometric chemistry, cyclopentadienyliron(II) dicarbonyl complexes are rarely used as catalysts in organic synthesis. Inspired by precedents in the chemistry of cationic olefin complexes and neutral allylmetal species, our group has developed a coupling of alkynes or alkenes with aldehydes and other carbonyl electrophiles to give homopropargylic and homoallylic alcohols, respectively, by using a substituted cyclopentadienyliron(II) dicarbonyl complex as the catalyst. In this article, we first contextualize this development within the conceptual background of C–H functionalization chemistry and relative to key stoichiometric precedents. We then give an account of our group’s discovery and development of the catalytic α-functionalization of alkenes and alkynes with electrophilic reagents.IntroductionPreliminary Stoichiometric WorkHydroxyalkylation Development and ScopeConclusions and Future Directions

Transition metal catalyzed Fe–C coupling reactions in synthesis of dicarbonyl(2-thienylethynyl)(η5-cyclopentadienyl)iron complex: Spectroscopic, structure and electrochemical study

The new σ-alkynyl iron(II) complex Cp(CO)2Fe-C≡C-(2-C4H3S) was synthesized with application of several known approaches based on the transition metal (Pd/Cu–, Au–, Cu– and Pd–) catalyzed Fe–C coupling reactions of 2-ethynylthiophene or 2-[(trimethylsilyl)ethynyl]thiophene with cyclopentadienyliron dicarbonyl iodide. The yield of the complex in these reactions was found to strongly depend on the catalyst used. The conditions, catalysts, and reagents that provide the highest yields of the desired 2-thienylethynyl iron complex were determined. The complex was characterized by IR, 1H and 13C NMR spectroscopy. The molecular structure of Cp(CO)2Fe–C≡C-(2-C4H3S) established by X-ray diffraction analysis exhibits a three-leg piano stool geometry. The redox properties of the new complex were studied.

Pd/Cu-Catalyzed Coupling of Cyclopentadienyliron Dicarbonyl Iodide and Methyl Propiolate in Synthesis of Cp(CO)₂Fe-C≡C-COOMe

The conditions of successful iron-carbon coupling in the reaction between cyclopentadienyliron dicarbonyl iodide and methyl propiolate upon the Pd/Cu catalysis were determined. A new high-yield synthetic approach to the methoxycarbonylethynyl iron complex Cp(CO)₂Fe-C≡C-COOMe were developed

Low-Cost Catalyst Ink for Simple Patterning and Growth of High-Quality Single- and Double-Walled Carbon Nanotubes

Research into carbon nanotubes (CNTs) has been a hot topic for almost 3 decades, and it is now that we are beginning to observe the impact of advanced applictions ofthis nanomaterial in areas such as electronics. Currently, in order to mass produce CNT devices, either large-scale synthesis, followed by numerous energy-intensive processing steps or photolithography processes, including several sputter-deposition steps, are required to pattern this material to fabricate functional devices. In the work reported here, through the utilization of a universal catalyst precursor (cyclopentadienyl iron dicarbonyl dimer)and the optimization of solution parameters, patterned high-quality vertically aligned arrays of single- and few-walled CNTs have been synthesized via various inexpensive, commercially scalable methods such as inkjet printing, stamp printing, spray painting, and even handwriting. The two-step process of precursor printing, followed immediately by CNT growth, results in CNTs with a RamanID/IG ratio of 0.073, demonstrating very high-quality nanotubes. This process eliminates time-consuming and costly CNT post processing techniques or the deposition of numerous substrate barrier and catalyst layers to achieve device manufacturing. As a result, this method has the potential to provide a route for the large-scale synthesis of high-quality single- and few-walled CNTs that can be applied in industrial settings.

α-C-H Functionalization of π-Bonds Using Iron Complexes: Catalytic Hydroxyalkylation of Alkynes and Alkenes.

The discovery of catalytic systems based on earth-abundant transition metals for the functionalization of C-H bonds enables streamlined and sustainable solutions to problems in synthetic organic chemistry. In this Communication, we disclose an iron-based catalytic system for the functionalization of propargylic and allylic C-H bonds. Inexpensive and readily available cyclopentadienyliron(II) dicarbonyl complexes were employedas catalysts for a novel deprotonative activation mode for C-H functionalization, an approach that allows for the direct union of unsaturated building blocks with aryl aldehydes and other carbonyl electrophiles to deliver a range of unsaturated alcohol coupling products under operationally simple and functional group tolerant reaction conditions.

A Nontrigonal Tricoordinate Phosphorus Ligand Exhibiting Reversible "Nonspectator" L/X-Switching.

We report here a "nonspectator" behavior for an unsupported L-function σ3 -P ligand (i.e. P{N[o-NMe-C6 H4 ]2 }, 1a) in complex with the cyclopentadienyliron dicarbonyl cation (Fp+ ). Treatment of 1a⋅Fp+ with [(Me2 N)3 S][Me3 SiF2 ] results in fluoride addition to the P-center, giving the isolable crystalline fluorometallophosphorane 1aF ⋅Fp that allows a crystallographic assessment of the variance in the Fe-P bond as a function of P-coordination number. The nonspectator reactivity of 1a⋅Fp+ is rationalized on the basis of electronic structure arguments and by comparison to trigonal analogue (Me2 N)3 P⋅Fp+ (i.e. 1b⋅Fp+ ), which is inert to fluoride addition. These observations establish a nonspectator L/X-switching in (σ3 -P)-M complexes by reversible access to higher-coordinate phosphorus ligand fragments.