Remarkably stable iron porphyrins bearing nonheteroatom-stabilized carbene or (alkoxycarbonyl)carbenes: isolation, X-ray crystal structures, and carbon atom transfer reactions with hydrocarbons

Highly diastereoselective and enantioselective olefin cyclopropanation using engineered myoglobin-based catalysts

Using rational design, an engineered myoglobin-based catalyst capable of catalyzing the cyclopropanation of aryl-substituted olefins with catalytic proficiency (up to 46,800 turnovers) and excellent diastereo- and enantioselectivity (98-99.9%) was developed. This transformation could be carried out in the presence of up to 20 g L(-1) olefin substrate with no loss in diastereo- and/or enantioselectivity. Mutagenesis and mechanistic studies support a cyclopropanation mechanism mediated by an electrophilic, heme-bound carbene species and a model is provided to rationalize the stereopreference of the protein catalyst. This work shows that myoglobin constitutes a promising and robust scaffold for the development of biocatalysts with carbene-transfer reactivity.

Synthesis and Characterization of Iron Complexes based on Bis-Phosphinite PONOP and Bis-Phosphite PONOP Pincer Ligands

A series of bis-phosphinite and bis-phosphite PONOP iron complexes were prepared and characterized by NMR and IR spectroscopy. Bis-phosphinite PONOP iron dichloride complexes (^RPONOP)FeCl₂ (^RPONOP = 2,6-(R₂PO)₂(C₅H₃N) and R = ⁱPr, ^tBu) were prepared through complexation of the free ligands with FeCl₂ and their solid-state structures were determined. Bis-phosphite PONOP iron complexes (^OEtPONOP)Fe(PMe₃)₂ and (^CatPONOP)Fe(PMe₃)₂ (Cat = catechol) were synthesized through complexation of the free ligands to Fe(PMe₃)₄. Carbonyl complexes of both bis-phosphinite and bis-phosphite PONOP were prepared and characterized by IR. The monocarbonyl (^iPrPONOP)Fe(CO)Cl₂ was accessed through exposure of (^iPrPONOP)FeCl₂ to an atmosphere of CO and the CO stretching frequency was observed at 1969 cm^-1. Dicarbonyl complexes (^iPrPONOP)Fe(CO)₂ and (^OEtPONOP)Fe(CO)₂ were accessed through reduction of the corresponding chloride complexes with sodium amalgam under a CO atmosphere. Carbonyl stretching frequencies for (^iPrPONOP)Fe(CO)₂ and (^OEtPONOPFe)(CO)₂ were observed at 1824 and 1876 cm^-1, and at 1871 and 1927 cm^-1 respectively. The bis-phosphite PONOP complexes exhibit a less electron rich metal center than the bis-phosphinite PONOP complexes, as would be expected based on the stronger π-acceptor character of these ligands. The electronic properties of the bis-phosphinite PONOP and bis-phosphite PONOP iron complexes are intermediate between previously reported PNP and PDI iron complexes, with the PONOP ligands exhibiting stronger electron donating ability than PDI ligands, but promoting a less electron rich metal center than found in analogous PNP iron complexes.

Iron-catalyzed transformations of diazo compounds

Although iron-promoted diazo transformations were only discovered during the 1990s, iron can undergo facile changes in its oxidation state and possesses distinct Lewis acid character, and these properties have afforded iron a privileged position as a catalyst in the transformations of diazo compounds. In this review, we have provided an overview of the iron-catalyzed diazo transformation reactions reported in the literature by the end of 2013 with the aim of stimulating further interest in this area of research.

Enantioselective iron-catalyzed intramolecular cyclopropanation reactions

An iron-catalyzed asymmetric intramolecular cyclopropanation was realized in high yields and excellent enantioselectivity (up to 97% ee) by using the iron complexes of chiral spiro-bisoxazoline ligands as catalysts. The superiority of iron catalysts exhibited in this reaction demonstrated the potential abilities of this sustainable metal in asymmetric carbenoid transformation reactions.

Iron porphyrin carbenes as catalytic intermediates: structures, Mössbauer and NMR spectroscopic properties, and bonding

Iron porphyrin carbenes (IPCs) are thought to be intermediates involved in the metabolism of various xenobiotics by cytochrome P450, as well as in chemical reactions catalyzed by metalloporphyrins and engineered P450s. While early work proposed IPCs to contain Fe(II), more recent work invokes a double-bond description of the iron-carbon bond, similar to that found in Fe(IV) porphyrin oxenes. Reported herein is the first quantum chemical investigation of IPC Mössbauer and NMR spectroscopic properties, as well as their electronic structures, together with comparisons to ferrous heme proteins and an Fe(IV) oxene model. The results provide the first accurate predictions of the experimental spectroscopic observables as well as the first theoretical explanation of their electrophilic nature, as deduced from experiment. The preferred resonance structure is Fe(II)←{:C(X)Y}(0) and not Fe(IV)={C(X)Y}(2-), a result that will facilitate research on IPC reactivities in various chemical and biochemical systems.

Cascade reactions initiated by radical addition of tetrahydrofuran to β-bromonitrostyrenes

Silver(i) catalyzed addition of THF radical to β-bromonitrostyrenes under mild basic condition in the presence of air has been developed.

Synthesis, electronic structure and reactivity of bis(imino)pyridine iron carbene complexes: evidence for a carbene radical

The reactivity of the disubstituted diazoalkane, N₂CPh₂ with a family of bis(imino)pyridine iron dinitrogen complexes was examined.

Iron porphyrin-catalyzed three-component reaction of ethyl diazoacetate with aliphatic amines and β,γ-unsaturated α-keto esters

An iron porphyrin-catalyzed three-component reaction of ethyl diazoacetate with aliphatic amines and β,γ-unsaturated α-keto esters is reported. The use of iron porphyrin catalyst allows aliphatic amines to be used as the substrate without encountering catalyst poisoning issue and a series of β-hydroxy-α-amino esters are produced in high yields with excellent regioselectivities.

Synthesis, Characterisation and Magnetic Behaviour of Ionic Metalloporphyrins: Metal–Tetrakis(N-Octyl-4-Pyridinium)–Porphyrins with Tetrabromoferrate(III) Anions

A series of magnetic, ionic-substituted tetrapyridyl metalloporphyrins, [tetrakis(N-octyl-4-pyridinium)–metal–porphy-rin][tetrabromoferrate(III)]4 (metal=iron, cobalt, manganese, copper or zinc), have been synthesised. All compounds show weak ferromagnetic behaviour at room temperature and respond to an external neodymium magnet.

Metalloporphyrin catalysts for organic synthesis

Novel chiral systems for the catalytic asymmetric oxidation and cyclopropanation of olefins based on metalloporphyrins containing iron, ruthenium and manganese, have been recently introduced. High catalyst turnover numbers and sometimes high enantiomeric excess were observed. New catalytic reactions with metalloporphyrins have recently been reported; these are the olefination of aldehydes and cyclotrimerization of terminal alkynes. Dendrimers and polymers containing metalloporphyrins, have also been found to be efficient catalysts for oxidation and carbene transfer.

5,10,15,20-tetrakis(pentafluorophenyl)porphyrin: a versatile platform to novel porphyrinic materials

5,10,15,20-tetrakis(pentafluorophenyl)porphyrin reacts with a range of nucleophiles (amines, alcohols, thiols, nitrogen heterocycles, and others) resulting in the nucleophilic aromatic substitution of the para-F atoms of the pentafluorophenyl groups. This reaction, which was fortuitously discovered by Kadish and collaborators in 1990, is now being extensively used to synthesize porphyrins bearing electron-donating substituents in the para-position of their meso-aryl groups. This mini-review highlights the methods of synthesis of 5,10,15,20-tetrakis(pentafluorophenyl)porphyrin, the use of its metal complexes in catalysis and its reaction with nucleophiles to yield new monomeric porphyrins, porphyrins supported in polymers or new polymeric porphyrin matrices useful for heterogeneous catalysis.

A water-soluble ruthenium glycosylated porphyrin catalyst for carbenoid transfer reactions in aqueous media with applications in bioconjugation reactions

Water-soluble [Ru(II)(4-Glc-TPP)(CO)] (1, 4-Glc-TPP = meso-tetrakis(4-(beta-D-glucosyl)phenyl)porphyrinato dianion) is an active catalyst for the following carbenoid transfer reactions in aqueous media with good selectivities and up to 100% conversions: intermolecular cyclopropanation of styrenes (up to 76% yield), intramolecular cyclopropanation of an allylic diazoacetate (68% yield), intramolecular ammonium/sulfonium ylide formation/[2,3]-sigmatroptic rearrangement reactions (up to 91% yield), and intermolecular carbenoid insertion into N-H bonds of primary arylamines (up to 83% yield). This ruthenium glycosylated porphyrin complex can selectively catalyze alkylation of the N-terminus of peptides (8 examples) and mediate N-terminal modification of proteins (four examples) using a fluorescent-tethered diazo compound (15). A fluorescent group was conjugated to ubiquitin via 1-catalyzed alkene cyclopropanation with 15 in aqueous solution in two steps: (1) incorporation of an alkenic group by the reaction of N-hydroxysuccinimide ester 19 with ubiquitin and (2) cyclopropanation of the alkene-tethered Lys(6) ubiquitin (23) with the fluorescent-labeled diazoacetate 15 in the presence of a catalytic amount of 1. The corresponding cyclopropanation product (24) was obtained with approximately 55% conversion based on MALDI-TOF mass spectrometry. The products 23, 24, and the N-terminal modified peptides and proteins were characterized by LC-MS/MS and/or SDS-PAGE analyses.

Corrole-based applications

Despite of the many similarities between corroles and porphyrins, the chemistry of the former remained undeveloped for decades because of severe synthetic obstacles. The recent discoveries of facile methodologies for the synthesis of triarylcorroles and the corresponding metal complexes allowed for their utilization in various fields. This survey reveals many examples where corroles were used as the key components in catalysis, sensing of gaseous molecules and medicine-oriented research. The focus in all these cases was on the special features of corroles: stabilization of high valent transition metal ions, unique photophysical properties, large NH acidity, facile synthetic manipulation and distinct catalytic properties. The latter aspect includes several examples of reactions that are not catalyzed by any non-corrole metal complex, such as the iron-based aziridination by Chloramine-T, the clean disproportionation of peroxynitrite, and the very facile N-H activation of amines.

Sidearm effects in the enantioselective cyclopropanation of alkenes with aryldiazoacetates catalyzed by trisoxazoline/Cu(i)

A highly enantioselective cyclopropanation of alkenes with phenyldiazoacetates catalyzed by CuPF6(CH3CN)4/trisoxazoline has been developed.

Alkene cyclopropanation catalyzed by Halterman iron porphyrin: participation of organic bases as axial ligands

With the iron(III) complex of the Halterman iron porphyrin [P*Fe(Cl)] and ethyl diazoacetate (EDA) as catalyst and carbene source, respectively, styrene-type substrates were converted to cyclopropyl esters with high trans/cis ratio (not less than 12) and high enantioselectivity for the trans-isomers (74-86% ee). The isomeric distribution of the cyclopropyl esters so obtained is akin to that obtained from the previously reported Ru(II) counterpart [P*Ru(CO)]. A linear Hammett correlation log(k(X)/k(H)) = sigma(+)rho was observed with rho = -0.57 suggesting the involvement of an electrophilic cyclopropanating species derived from the iron(II) center as the reactive intermediate in the catalytic cycle. This is further supported by a dramatic decrease in the enantioselectivity and trans/cis ratio observed in an experiment of styrene cyclopropanation when the reaction mixture was deliberately exposed to air. Axial ligand effects on the selectivities was also investigated. Substantial improvement in trans/cis ratios could be achieved by addition of organic bases such as pyridine (py) and 1-methylimidazole (MeIm) to the catalytic reaction. The existence of axially ligated iron carbene moieties, [P*Fe(CHCO(2)Et)(py)] and [P*Fe(CHCO(2)Et)(MeIm)], was established by electrospray mass spectrometry. Study of secondary kinetic isotope effect indicated that a more product-like transition state was generated by addition of MeIm.

Discrete Bridging and Terminal Copper Carbenes in Copper-Catalyzed Cyclopropanation

The Cu(I) beta-diketiminate [Me2NN]Cu(eta2-ethylene) (2) catalyzes the cyclopropanation of styrene with N2CPh2 to give 1,1,2-triphenylcyclopropane in 67% yield. Addition of N2CPh2 to 2 equiv of 2 allows for the isolation of the dicopper carbene [[Me2NN]Cu]2(mu-CPh2) (3) in which the diphenylcarbene moiety is symmetrically bound between two [Me2NN]Cu fragments (Cu-C = 1.922(4) and 1.930(4) A) with a Cu-Cu separation of 2.4635(7) A. In toluene-d8 solution, 3 reversibly dissociates a [Me2NN]Cu fragment to give [Me2NN]Cu(toluene) and the terminal carbene [Me2NN]Cu=CPh2. Dicopper carbene 3 reacts with 3 equiv of styrene to give 1,1,2-triphenylcyclopropane and 2 equiv of [Me2NN]Cu(eta2-styrene) within minutes. DFT studies with simplified ligands indicate a stronger Cu-C pi-back-bonding interaction from two Cu(I) centers to the carbene acceptor orbital in a dicopper carbene than that present in a monocopper carbene. Nonetheless, the terminal carbene [Me3NN]Cu=CPh2 (8) that possesses a p-methyl group on each beta-diketiminato N-aryl ring may be isolated and exhibits a shortened Cu-C distance of 1.834(3) A. The stoichiometric cyclopropanation of styrene by 8 in 1,4-dioxane is first-order in both copper carbene 8 and styrene with activation parameters DeltaH = 10.4(3) kcal/mol and DeltaS = -32.3(9) cal/mol.K. In 1,4-dioxane, 8 decomposes to Ph2C=CPh2 via first-order kinetics with activation parameters DeltaH = 21(1) kcal/mol and DeltaS = -8(3) cal/mol.K. Arene solutions of thermally sensitive terminal carbene 8 decompose to [Me3NN]Cu(arene), which reacts with 8 still present in solution to give the more thermally stable [[Me3NN]Cu]2(mu-CPh2).