Unexpected stabilization of the heterocyclic form of oxidized dithizone: Synthesis and molecular structures of chromium and tungsten 5-mercapto-2,3-diphenyltetrazolium pentacarbonyls

New chromium and tungsten pentacarbonyl complexes with 5-mercapto-2,3-diphenyltetrazole coordinated through the sulfur atom (Cr-S, 2.4655(7) Å; W-S, 2.5755(13) Å) were synthesized and structurally characterized.     

Diastereoselective synthesis of three-, five-, six-, and seven-membered rings from Fischer carbene complexes and 4-unsubstituted 1-amino-1,3-dienes

Fischer carbene complexes react with 4-unsubstituted 1-amino-1,3-dienes to give different carbocyclization products depending on the nature of the carbene complex and on the substitution pattern of the aminodiene. Thus, the reaction of arylcarbene chromium complexes and 1-aminodienes diastereoselectively affords cyclopropane derivatives by means of a formal [2+1] carbocyclization reaction. In particular, pentacarbonyl[(2-furyl)(methoxy)methylene]chromium complex furnishes formal [4+1] carbocyclization products. Starting from beta-substituted alkenylcarbene complexes, formal [4+1] reactions occur and cyclopentenamine derivatives are diastereoselectively formed. However, when the alpha,beta-disubstituted alkenylcarbene complex pentacarbonyl[(5,6-dihydro-2H-pyran-2-yl)(methoxy)methylene]tungsten is used, the outcome of the reaction depends on the substitution on the carbon atom at the 3-position of the aminodiene, generating the [3+2] or [4+3]-cyclization products if the substituent is or is not a hydrogen atom, respectively. Finally, when the reaction is performed with alkynylcarbene complexes, benzaldehyde derivatives are obtained if the triple-bond substituent is a phenyl group or indene derivatives if the group is an alkenyl moiety.     

Schwefel(IV)-Verbindungen als Liganden. II. Die Kristall- und Molekülstruktur von Pentacarbonyl-(schwefeldioxid)chrom

Sulfur(IV) Compounds as Ligands. II. The Crystal and Molecular Structure of Pentacarbonyl--(sulfur dioxide)chromium The structure of pentacarbonyl(sulfurdioxide)chromium ( 1 ) has been determined from single crystal X-ray data. The compound crystallizes with eight formula units in the rhombic unit cell (space group Pbn2₁) of the dimensions a = 657.8(2) pm, b = 1245.2(4) pm, c = 2177.4(5) pm (at 180 K). The sulfur dioxide is η¹-coplanar coordinated, the Cr? S distance is 219 pm, the shortest bond reported so far between chromium(0) and sulfur. The Cr? C(ax) bond (189 pm) was found only marginally shorter than the Cr? C(eq) bonds (190 pm) providing proof of the high π-acceptor capacity of SO₂.     

A chromium(III)-superoxo complex in oxygen atom transfer reactions as a chemical model of cysteine dioxygenase

Metal-superoxo species are believed to play key roles in oxygenation reactions by metalloenzymes. One example is cysteine dioxygenase (CDO) that catalyzes the oxidation of cysteine with O(2), and an iron(III)-superoxo species is proposed as an intermediate that effects the sulfoxidation reaction. We now report the first biomimetic example showing that a chromium(III)-superoxo complex bearing a macrocyclic TMC ligand, [Cr(III)(O(2))(TMC)(Cl)](+), is an active oxidant in oxygen atom transfer (OAT) reactions, such as the oxidation of phosphine and sulfides. The electrophilic character of the Cr(III)-superoxo complex is demonstrated unambiguously in the sulfoxidation of para-substituted thioanisoles. A Cr(IV)-oxo complex, [Cr(IV)(O)(TMC)(Cl)](+), formed in the OAT reactions by the chromium(III)-superoxo complex, is characterized by X-ray crystallography and various spectroscopic methods. The present results support the proposed oxidant and mechanism in CDO, such as an iron(III)-superoxo species is an active oxidant that attacks the sulfur atom of the cysteine ligand by the terminal oxygen atom of the superoxo group, followed by the formation of a sulfoxide and an iron(IV)-oxo species via an O-O bond cleavage.     

1-硫代-1-磷杂-2,6,7-三氧杂双环[2.2.2]辛烷基-4-亚甲基硫醚及其亚砜的合成

本文通过Williamson反应,合成了9个双环笼状硫代磷酸酯的硫醚衍生物3a～i。以3b,3c为例研究了硫醚衍生物的还原性,并合成相应的亚砜化合物4b,4c。讨论了亚砜化合物的立体化学。     

Synthesis of fluorinated geminal diisocyanides stabilized on a transition metal

Chromium complexes of the geminal diisocyanides bis(pentacarbonyl)-μ-2,2-diisocyano-1,1,1,3,3,3-hexafluoropropane)dichromium 1a and bis(pentacarbonyl)-μ-2,2-diisocyano-1,1,1,3,3-pentafluorobutane)dichromium 1b were obtained by radical alkylation of pentacarbonylcyanochromate besides pentacarbonyl(2-isocyano-1,1,1,3,3,3-hexafluoropropane)chromium 2a and pentacarbonyl(2-isocyano-1,1,1,3,3-pentafluorobutane)chromium 2b, respectively. Pentacarbonyl(2-isocyano-1,1,1,2,3,3,3-heptafluoropropane)chromium 2c was prepared analogously. The crystal and molecular structures of 1a and b were determined by X-ray diffraction.     

Chemistry of the phenoxathiins and isosterically related heterocycles. XXXIII . The influence of intramolecular sulfur-nitro group interactions on the reactivity at sulfur

Nitro-groups positioned ortho to thio-esters have been shown to engage in strong, non-bonded intramolecular interactions between the sulfur atom and one of the nitro-group oxygens. The effect of the sulfur-nitro group oxygen interaction on the chemical reactivity at the sulfur atom of 9-nitro-1-azaphenoxathiin is reported. Conditions which normally produce the sulfone exclusively have been shown to yield the sulfoxide with only a minimal quantity of the sulfone produced. Protracted periods of reflux are required to produce the sulfone from the sulfoxide.     

Stepwise Oxidation of Thiophene and Its Derivatives by Hydrogen Peroxide Catalyzed by Methyltrioxorhenium(VII)

The oxidation of thiophene derivatives by hydrogen peroxide is catalyzed by methyltrioxorhenium(VII) (CH(3)ReO(3)). This compound reacts with hydrogen peroxide to form 1:1 and 1:2 rhenium peroxides, each of which transfers an oxygen atom to the sulfur atom of thiophene and its derivatives. Complete oxidation to the sulfone occurs readily by way of its sulfoxide intermediate. The rates for each oxidation step of dibenzothiophenes, benzothiophenes, and substituted thiophenes were determined. The rate constants for the oxidation of the thiophenes are 2-4 orders of magnitude smaller than those for the oxidation of aliphatic sulfides, whereas the rate constants are generally the same for the oxidation of the thiophene oxides and aliphatic sulfoxides. The rate constant for conversion of a sulfide to a sulfoxide (thiophene oxide) increases when a more electron-donating substituent is introduced into the molecule, whereas the opposite trend was found for the reaction that converts a sulfoxide to a sulfone (thiophene dioxide). Mechanisms consistent with this are proposed. The first trend reflects the attack of the nucleophilic sulfur atom of a thiophene center on a peroxide that has been electrophilically activated by coordination to rhenium. The second, more subtle, trend arises when both sulfoxide and peroxide are coordinated to rhenium; the inherently greater nucleophilicity of peroxide then takes control.     

Combining planar and central chirality in ferrocene thiophosphine-sulfoxides

Novel chiral ferrocenylthiophosphine–sulfoxide and phosphine–sulfoxide derivatives possessing planar chirality for the ferrocene moiety and central chirality at the sulfur atom have been synthesized. These ligands can be obtained as pure diastereoisomers in both racemic and enantiomerically pure forms. Complete characterization by XRD analysis has allowed the assignment of the absolute configuration in each case. Preliminary coordination studies of the phosphine–sulfoxide ligands on platinum are also reported. These show chelating complexation by the phosphorous and sulfur atoms.     

Pentacarbonyl(2,6-diaminopyridine)chromium(0): synthesis and molecular structure

Photolysis of hexacarbonylchromium(0) in the presence of 2,6-diaminopyridine in toluene solution at 10 °C yields pentacarbonyl(2,6-diaminopyridine)chromium(0), which could be isolated from solution as plate-like crystals and fully characterized by using the single crystal X-ray diffractometry and MS, IR, ¹H and ¹³C NMR spectroscopy. The complex was found to have the 2,6-diaminopyridine ligand bonded to the chromium atom through one of the NH₂ groups. A single crystal X-ray structure of the complex reveals that the coordination sphere around the chromium atom is a slightly distorted octahedron, involving five carbonyls and one 2,6-diaminopyridine ligand. Because of the steric requirement of 2,6-diaminopyridine the four equatorial carbonyl groups are bended away from the N-donor ligand. The pyridine plane makes an angle of 112.9(3)° with the OC-Cr-N bond axis. The Cr-C distances have values between 1.833(7) and 1.935(7) Å. The Cr-N distance is 2.236(5) Å.     

1-硫代-1-磷杂-2,6,7-三氧杂双环[2.2.2]辛烷基-4-亚甲基硫醚及其亚砜的合成

本文通过Williamson反应, 合成了9个双环笼状硫代磷酸酯的硫醚衍生物3a～i. 以3b,3c为例研究了硫醚衍生物的还原性, 并合成相应的亚砜化合物4b,4c. 讨论了亚砜化合物的立体化学.     

Selective reaction of amino acid sulfoximines with nitrous acid; facile stereospecific conversion to amino acid sulfoxides

N-Unsubstituted sulfoximines of amino acids can he readily converted to the corresponding amino acid sulfoxides in high yields by treatment with stoichiometric quantities of nitrous acid. Under the conditions employed, reaction with L-methionine-S (or R)-sulfoximine is specific for the sulfoximine nitrogen atom, and no reaction occurs at the α-amino group. Conversion to the sulfoxide proceeds with complete retention of configuration at the sulfur atom.     

The solvent dimethyl sulfoxide

The dipolar aprotic solvent dimethyl sulfoxide is liquid over a wide range of temperatures, is a strong electron donor, and has a high polarity. It is therefore an excellent and selective solvent for many organic and even polymeric compounds, and can enter into H-bonding and dipole-dipole association. The structure of dimethyl sulfoxide, with a “hard” oxygen atom and a “soft” sulfur atom, leads to good solvation of cations and poor solvation of anions. Mixtures of alkoxides with dimethyl sulfoxide are therefore among the most strongly basic systems in organic chemistry, and are excellently suited for the deprotonation of weakly acidic OH, NH, and CH bonds, for eliminations, and for the initiation of polymerizations.     

Theoretical study on the mechanism of the oxygen activation process in cysteine dioxygenase enzymes

Cysteine dioxygenase (CDO) is a vital enzyme for human health involved in the biodegradation of toxic cysteine and thereby regulation of the cysteine concentration in the body. The enzyme belongs to the group of nonheme iron dioxygenases and utilizes molecular oxygen to transfer two oxygen atoms to cysteinate to form cysteine sulfinic acid products. The mechanism for this reaction is currently disputed, with crystallographic studies implicating a persulfenate intermediate in the catalytic cycle. To resolve the dispute we have performed quantum mechanics/molecular mechanics (QM/MM) calculations on substrate activation by CDO enzymes using an enzyme monomer and a large QM active region. We find a stepwise mechanism, whereby the distal oxygen atom of the iron(II)-superoxo complex attacks the sulfur atom of cysteinate to form a ring structure, followed by dioxygen bond breaking and the formation of a sulfoxide bound to an iron(IV)-oxo complex. A sulfoxide rotation precedes the second oxygen atom transfer to the substrate to give cysteine sulfinic acid products. The reaction takes place on several low-lying spin-state surfaces via multistate reactivity patterns. It starts in the singlet ground state of the iron(II)-superoxo reactant and then proceeds mainly on the quintet and triplet surfaces. The initial and rate-determining attack of the superoxo group on the cysteinate sulfur atom involves a spin-state crossing from singlet to quintet. We have also investigated an alternative mechanism via a persulfenate intermediate, with a realignment of hydrogen bonding interactions in the substrate binding pocket. However, this alternative mechanism of proximal oxygen atom attack on the sulfur atom of cysteinate is computed to be a high-energy pathway, and therefore, the persulfenate intermediate is unlikely to participate in the catalytic cycle of CDO enzymes.     

Reaktionen von komplexliganden : XIX. Einschiebung von inaminen in chrom-alkenylcarben- und chrom-aminocarber-bindungen

1-Diethylaminopropyne reacts with pentacarbonyl[methoxy(2,2-diphenylethenyl)carbene]chromium in a stereoselective way to give pentacarbonyl-[diethylamino-E-(2-methoxy-1-methyl-4,4-diphenyl-1,3-butadienyl)carbene]-chromium via insertion of the alkyne into the metal-carbene bond. The reaction of the ynamine with pentacarbonyl[methylamino(phenyl)carbene]chromium results in insertion of the alkyne and loss of carbon monoxide to give cis-tetracarbonyl[3-aza-1-methyl-2-phenyl-2-butenyl)diethylaminocarbene]-chromium. Its structure was established by oxidative degradation in an aqueous medium to give 2-benzoyl-N,N-diethylpropanamide and finally confirmed by an X-ray analysis. The new compounds are characterized spectroscopically.     

Pentacarbonyl(organylphenoxycarben)-Komplexe des Chrom(0) und Wolfram(0)

Pentacarbonyl(acetoxyorganylcarbene) complexes of chromium(0) and tungsten(0) react with sodium phenolate to give pentacarbonyl(organylphenoxycarbene)chromium(0) and tungsten(0).     

Oxidation of l-methionine with aqueous chromic acid: a kinetic study

The kinetics of oxidation of l-methionine by chromic acid in acidic medium (pH=0.83–2.2) has been studied spectrophotometrically. The effect of l-methionine and chromium(VI) concentrations on the rate of the reaction was determined. The reaction rate decreases with increasing the pH of the medium. The kinetics of the formation of a chromium(III) complex conform to the rate law:with k1=7.5×10–2s–1 and Kes1=43.85 at constant [H+]=1.9×10–2moldm–3 and [l-methionine]T= 2.0×10–2moldm–3. The same values were found with [l-methionine]T variation at constant [H+]. The reaction proceeds through formation of chromium(VI)-l-methionine ester in a rapid pre-equilibrium step, followed by a slower redox reaction of the ester. The present study provides kinetic evidence for formation of a complex ion (ester). One mole of Cr2O72– oxidizes four moles of l-methionine, which acts as a monodentate ligand and binds to chromium(VI) through the sulfur atom. The coordinated sulfur atom of l-methionine–chromium(VI) ester is responsible for the oxidative degradation (breaking of the C1-C2 bond) of l-methionine. Coordinated oxygen of the carboxylate group inhibits the cleavage of the C1-C2 bond.     

CHIRAL VARIANTS OF ARYLALKYL SULFUR REAGENTS. (R)-CAMPHOR KETIMINES OF OGIOVANNA AMINOTHIOETHERS AND OXIDES

Abstract

Ketimines la-d derived from ortho-aminosubstituted phenylthioethers were prepared in order to determine the degree of chirality transfer from the chiral auxiliary to the sulfur atom in the formation of the sulfoxide or to the α-carbon atom in the reaction of the anion with alkyl halides or benzaldehyde. Oxidation to the sulfoxide occurred with little or no asymmetric induction. The crystalline benzyl sulfone 4c was deprotonated by alkyllithium or Grignard reagents and reacted with alkyl halides and benzaldehyde, in all cases with little to fair transfer of chirality. The major diastereoisomer from methylation of the anion of 4c with methyl iodide, was isolated, and afforded the enantiomerically pure amine 5 after removal of the chiral auxiliary. An X-ray structure determination of 4d allowed the assignment of the absolute configuration of the asymmetric carbon and revealed that the conformation of the ketimine in the crystal state is not homogeneous.     

Electrochemical approaches to generation of phosphinidene complexes of tungsten pentacarbonyl

An alternative approach to synthesis of electrophilic terminal phosphinidene complexes of tungsten pentacarbonyl with various substituents at the phosphorus atom has been developed. The approach is based on the reaction of the electrochemically generated tungsten pentacarbonyl ion with trivalent phosphorus acyl chlorides. Electrochemical reduction of ethyldichlorophosphines in the presence of α-diimines is a one-step process that forms 1,3,2-diazaphospholenes containing an exocyclic P-C bond.     

Polymers with electron-deficient olefin moieties by oxidation of precursors containing “push–pull” olefin (β-alkylmercaptoenoate) moieties in the main chain

Oxidation of a polymer (1) having β-alkylmercaptoenoate moieties in the main chain by m-chloroperbenzoic acid (MCPBA) is described. Oxidation of 1 proceeded selectively to give polymers having vinyl sulfoxide or vinyl sulfone moieties in the main chain by using an appropriate amount of MCPBA. In the case of 1.1 equiv of MCPBA (relative to the sulfur atom), a polymer (4) having vinyl sulfoxide moieties selectively in the main chain was obtained in quantitative yield without side reactions. Likewise, a polymer (5) having vinyl sulfone moieties was obtained in quantitative yield by using 2.6 equiv of MCPBA. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2589–2592, 1998