Synthesis of nitrogen-containing compounds using chromium Fischer carbene complexes

Synthetic utility of the Fischer-type carbene complexes of chromium for the preparation of nitrogen-containing compounds is demonstrated. Alkoxy carbene complexes reacted with imines to give (optically active) 3-pyrrolines and beta-methoxy allylic amine derivatives in good yields. The amino carbene complexes reacted with alpha,beta-unsaturated aldehydes to give substituted pyrroles in good yields.     

Synthesis of aminocyclopentitols from chromium carbene complex derived aminocyclobutanones

Functionalized cyclopentenones were synthesized by the diazomethane ring expansion of cyclobutanones, produced by the photochemical reaction of vinyl oxazolidinones with chromium carbene complexes.     

Synthesis of chromium N-heterocyclic carbene complexes using chromium Fischer carbenes as a source of chromium carbonyls

Chromium Fischer carbene complexes, [Cr{OMe(R)}(CO)₅] have been utilized as a source of chromium carbonyls in the synthesis of chromium NHC complexes. Using the synthetic method, chromium complexes of various NHC ligands were isolated in reasonable yields. Moreover, the method can be employed for the synthesis of molybdenum and tungsten NHC compounds.     

Diaryl ethers using Fischer chromium carbene mediated benzannulation

[formula: see text] The biological relevance and irresistible synthetic challenge of compounds containing the diaryl ether linkage encourages the development of new methodologies targeted toward this structural subunit. The syntheses of diaryl ethers 2 using a benzannulation strategy that formally involves a [3 + 2 + 1] cycloaddition between aryloxy-substituted Fischer carbenes 1 and alkynes are described. This methodology provides a neutral near ambient temperature formation of diaryl ethers.     

In situ generation of gold nanoparticles on a protein surface: Fischer carbene complex as reducing agent

Suitably designed, hydrophilic Fischer carbene complexes reduce HAuCl4 to produce stable gold nanoparticles localized on proteins in aqueous buffer solution.     

Chemistry of the podocarpaceae: LXX. Synthesis and cyclopentaannulation of a diterpenoid chromium carbene complex

A pentacarbonylcarbene chromium complex of the diterpenoid methyl O-methylpodocarpate has been prepared and its reactions with some alkynes have been studied with the aim fo synthesising ring-C aromatic steroids. The use of diphenylacetylene resulted in cyclisation to give steroidal derivatives in moderate yield.     

Coupling of propargylsilanes with Fischer carbene chromium complexes: a new synthesis of conjugated dienes

The reaction of propargylsilanes with Fischer carbene complexes has been examined. If the silane-containing carbon is secondary the predominant pathway involves formation of conjugated dienes through a 1,2-silicon shift process of the initially formed vinylcarbene complex intermediate. If a primary propargylsilane is employed, the silicon does not shift and normal alkyne-Fischer carbene coupling processes are observed. The process is moderately stereoselective, resulting in the E enol ether and Z alkenylsilane.     

Synthesis of indenes from alkynes and phenyl amino chromium carbene complexes

Reactions of phenyl morpholino or pyrrolidino chromium carbene complexes with alkynes in DMF at 120–125°C resulted in exclusive formation of the indene derivatives.     

Synthesis and stabilization of monodisperse Fe nanoparticles

Monodisperse Fe nanoparticles are synthesized via a simple one-pot thermal decomposition of Fe(CO)5 in the presence of oleylamine. Controlled oxidation of the iron surface leads to crystalline Fe3O4 shell and results in dramatic increase of chemical and dispersion stability of the nanoparticles. Surface ligand exchange is readily applied to transfer the core/shell nanoparticles from hydrophobic to hydrophilic, and a stable aqueous nanoparticle dispersion in PBS is formed. The functionalized nanoparticles are suitable for biomolecule attachment and biomedical applications.     

Iron in the service of chromium: the ortho-benzannulation of trans,trans-dienyl Fischer carbene complexes

Chromium Fischer carbene complexes with trans,trans-dienyl substituents on the carbene carbon will react with diiron nonacarbonyl to give 2-alkoxycyclohexa-2,4-dienone iron tricarbonyl complexes and/or 2-alkoxyphenols in excellent yields. In the presence of silica gel or base, the cyclohexadienone complex will suffer loss of the iron and aromatization to give 2-alkoxyphenols. The formation of 2-alkoxyphenols from dienyl chromium carbene complexes is a known process (ortho-benzannulation) that only occurs with certain cis,trans-dienyl complexes. Control experiments show that trans,trans-dienyl chromium carbene complexes do not undergo conversion to 2-alkoxyphenols in the absence of an iron source. The process most likely occurs either via coordination of the dienyl unit in the chromium carbene complex to an iron tricarbonyl group and then loss of the chromium or via direct trans-metalation of the carbene ligand to give an iron carbene complex and then internal coordination to the dienyl unit such that cis to trans isomerization of the alpha,beta-double bond occurs.     

Novel synthesis of lactam from alkyne having amide in a tether using fischer chromium carbene complex

A novel lactam synthesis from alkyne having amide in a tether was developed. The reaction proceeds via a vinylketene complex generated from alkyne and Fischer chromium carbene complex, and the lactam ring was formed from carbon monoxide, alkyne carbon and nitrogen of tosylamide. The four-,five-, six-, and seven-membered lactams having a substituent at the -position were obtained in good yields.     

Synthesis, structure and benzannulation of chalcogen-tethered Fischer carbene complexes

Addition of PhSH-NEt₃ or PhSeNa to PhCCC(OC₂H₅)M(CO)₅ [M = Cr or W] afforded stable, β-chalcogenide tethered conjugated carbene complexes 3-6 as a mixture of E,Z-isomers. The Z-configuration was ascribed to those isomers that readily yield cyclometallated complexes. Aminolysis with methylamine yielded corresponding amino carbene complexes as mixtures of E,Z-isomers. Alkylation by methyl iodide afforded separable E,Z-isomers of dimethylamino complexes. One-step aminolysis of ethoxy carbene complexes with dimethylamine furnished only the Z-isomer of the dimethylamino complex. The Z-isomer of dimethylamino carbene complexes yielded cyclometallated products on warming. Representative crystal structures of these complexes confirm isomer assignments. Only E-isomers of the S or Se-tethered ethoxy complexes undergo benzannulation reaction with alkynes, with loss of chalcogenide atom.     

Biscarbene complexes from the reactions of O-ethyl lactim and 1-alkynyl Fischer carbene complexes of chromium and tungsten

Reactions of O-ethyl lactim ∼(CH₂)₃-NC(OEt)∼ with 1-alkynyl Fischer carbene complexes (OC)₅MC(OEt)CCPh (M = Cr, W) afforded biscarbene complexes with an azabicyclo[3.2.0]heptene core. Under a nitrogen atmosphere, the resultant chromium biscarbene complex gave a SiO₂-promoted rearrangement complex in 86% yield. Thermal annelation of the rearrangement product followed by hydrolysis over SiO₂ formed a cyclopentenone derivative. A cyclopentadiene derivative was obtained as a rare example of intermediate Fischer carbene species, suggesting a possible reaction pathway for the thermal annelation of the rearrangement complex. Stepwise oxidation of the chromium biscarbene complexes with an azabicyclo[3.2.0]heptene core with pyridine-N-oxide (PNO) under mild controlled conditions generated partially and completely demetalated carbonyl products, respectively. The key carbene complexes and demetalated compounds were structurally characterized by X-ray crystallographic studies.     

Synthesis and electrochemical properties of novel tetrametallic macrocyclic Fischer carbene complexes

[reaction: see text] Metallomacrocyclic compounds can be easily prepared by 1,4-addition of diamines to alpha,beta-unsaturated Fischer bis-carbene templates. This method allows the preparation of a new family of homo- and heterotetrametallic compounds having macrocyclic cyclophanic structures.     

Synthesis of pyrroles through coupling of enyne-hydrazones with Fischer carbene complexes

[reaction: see text] The coupling of enyne-imines with Fischer carbene complexes leads to the formation of alkenylpyrrole derivatives. Maximum yields of pyrrole adducts were obtained using N,N-dimethylhydrazones. A mechanism involving alkyne insertion followed by nucleophilic attack of the imine nitrogen at the intermediate alkenylcarbene complex was proposed.     

Synthesis and characterization of monodisperse silica-polyaniline core-shell nanoparticles

Monodisperse silica-polyaniline core-shell nanoparticles with an average diameter of 26 nm were synthesized by in-situ polymerisation of aniline monomers adsorbed on the silica surface through electrostatic interactions.     

Synthesis and self-assembly of nearly monodisperse nanoparticles of a naturally occurring polymer

Nearly monodisperse nanoparticles have been synthesized based on a naturally occurring polymer of hydropropylcellulose (HPC) using precipitation polymerization method. It is found that when the polydispersity index value of the HPC nanoparticles is less than 1.10, the HPC particles can self-assemble into an ordered structure, displaying bright colors. UV-visible spectroscopy reveals that the color shifts to a lower wavelength as the interparticle distance decreases following the Bragg diffraction equation. The HPC nanoparticle assembly in water has been further stabilized by covalently bonding neighboring particles to form a three-dimensional network. This network contains a large amount of water similar to a conventional bulk gel but displays colors as a result of its ordered structure.     

The first examples of a meta-benzannulation from the reaction of Fischer carbene complexes with alkynes

The intramolecular benzannulations of carbene complexes with alkynes are examined where the alkyne is tethered to the alpha-carbon of the vinyl carbene complex. These reactions are sensitive to the length of the tether and to the nature of the solvent. With a tether length of 16 methylenes, the reaction occurs in the same fashion as the intermolecular reactions to give a p-cyclophane. With intermediate tether lengths (n = 10, 13), the reaction gives an additional p-cyclophane in which the two oxygen substituents are meta on the arene ring. This type of product is unprecedented from the reaction of carbene complexes and alkynes and is quite surprising because the formation of this product requires that the carbon-carbon bond between the alpha- and beta-carbons of the vinyl carbene complex is broken. A mechanism is proposed to account for this process which involves the crossed intramolecular [2 + 2] cycloaddition of the alkene and a ketene in a conjugated dienyl ketene to give a benzvalenone paddalane intermediate.