Carbene Center Research Articles

Photochemistry of (2-nitrophenyl)diazomethane studied by a matrix isolation technique. (Nitrophenyl)carbene to (carboxylphenyl)nitrene rearrangement by successive reduction of nitro group with carbenic center

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTPhotochemistry of (2-nitrophenyl)diazomethane studied by a matrix isolation technique. (Nitrophenyl)carbene to (carboxylphenyl)nitrene rearrangement by successive reduction of nitro group with carbenic centerHideo Tomioka, Naoki Ichikawa, and Kazunori KomatsuCite this: J. Am. Chem. Soc. 1992, 114, 21, 8045–8053Publication Date (Print):October 1, 1992Publication History Published online1 May 2002Published inissue 1 October 1992https://doi.org/10.1021/ja00047a012RIGHTS & PERMISSIONSArticle Views1104Altmetric-Citations45LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (1 MB) Get e-Alerts Get e-Alerts

Ein neuartiger Einstieg in Wittig‐Umlagerungen – Eine stereoselektive [1,2]‐Wittig‐Umlagerung mit Konfigurationsumkehr am Carbanion‐Zentrum

A Novel Entry into Wittig Rearrangements – A Stereoselective [1,2]‐Wittig Rearrangement with Inversion of Configuration at the Carbanion CenterThe O,Se‐ketal 10, through lithium naphthalenide induced reductive cleavage of its C–Se bond, was converted into the α‐lithio ether 11a with an equatorially oriented CO bond. At ‐78°C, 11a undergoes a rapid [1,2]‐Wittig rearrangement to provide stereoselectively the homoallylic alcohol 12a with an axial OH group. Thus, the rearrangement proceeds with inversion of configuration at the carbanion center.

Sterically congested molecules. 5. Trimeric [.alpha.-(1,1,3,3-tetramethyl-2-indanylidene)benzyl]lithium: structural example of an unsolvated vinyllithium derivative

The X-ray structure of this compound discloses the stabilization of a vinylic carbanion by two lithium cations in a hydrocarbon milieu. Each lithium cation is in turn coordinated to two carbanion centers and additionally to one aromatic CC bond as well as to one CH bond of a methyl group. These bonding interactions result in an unsolvated trimer with pseudo-C 3 symmetry.

Electronic stabilization of nucleophilic carbenes

Four new stable nucleophilic carbenes have been synthesized and structurally characterized. The remarkable ability of the imidazole nucleus to stabilize a carbene center at the C-2 position is demonstrated by the isolation of 1,3,4,5-tetramethylimidazol-2-ylidene. The isolation of three imidazol-2-ylidenes that bear aryl substituents is counter to speculations based on previous reports

Reaction of Tri-2-thienylmethyllithium with Alkyl Halides. Substitution on Carbanion Center vs. Thiophene Ring

Abstract Tri-2-thienylmethyllithium, produced by treatment of tri-2-thienylmethane with butyllithium in the presence of N,N,N′,N′-tetramethylethylenediamine at −78 °C in tetrahydrofuran, reacts with primary alkyl halides to give the alkylated products on the carbanion center nearly quantitatively, while the reaction with secondary and tertiary alkyl halides affords not only the substitution products at the carbanion center but also those at the 3-position of the thiophene ring.

E Effect of Alkyl Groups on Carbanion Stability Part I. Interaction of Small Rings with Adjacent Carbanion Centers

AbstractRelative kinetic acidity measurements have shown that the cyclobutyl group has the ability to stabilize an adjacent carbanion center similar to vinyl and cyclopropyl groups, although to a lesser extent. The results of semiempirical calculations (MNDO) covering all the mentioned substituents, including the isopropyl group correlate well with the experimentally determined relative kinetic acidities.

Clusters containing carbene ligands. 14. Further studies of the reactivity of the carbene centers in the dicarbene cluster complex Os3(CO)9[.mu.3-C(Et)N(Me)CH](.mu.-H)2 with diphenylacetylene

Six products were obtained from the reaction of Os{sub 3}(CO){sub 9}[{mu}{sub 3}-C(Et)N(Me)CH]({mu}-H){sub 2}: (1) with PhC{sub 2}Ph at 125 {degrees}C. They have been identified as the two previously reported compounds Os{sub 3}(CO){sub 8}[{mu}{sub 3}-{eta}{sup 2}-C(H)N-(Me)C(Et)][{eta}{sup 2}-CPhC(H)Ph]({mu}-H) (2) (3%) and Os{sub 3}(CO){sub 8}({mu}{sub 3}-C[C(Ph)CH(Ph)]N(Me)C(Et))({mu}-H){sub 2} (3) (39%) and four new compounds Os{sub 3}(CO){sub 8}({mu}-{eta}{sup 3}-C[N(Me)C(Et)]C(Ph)C(Ph))({mu}-H) (4) (4%), Os{sub 3}(CO){sub 8}({mu}{sub 3}-CEt)[{mu}-N(Me)C(H)C(Ph)CPh] (5) (6%), Os{sub 3}(CO){sub 8}[C(Et)N(Me)CH{sub 2}][{mu}{sub 3}-C(Ph)C(Ph)]({mu}-H) (6) (3%), and Os{sub 3}-(CO){sub 7}({mu}{sub 3}-C[C(Ph)CH(Ph)]N(Me)C(Et))[{eta}{sup 2}-C(Ph)C(H)Ph]({mu}-H) (7) (3%). Compounds 4-7 were characterized by IR, {sup 1}H NMR, and single-crystal X-ray diffraction analyses. 19 refs., 5 figs., 17 tabs.

Cation, carbene, and radical centers in a [4.4.4.5]Fenestrane

Carbocation 2a, formed on photolysis of iodide 3a in methanol is captured by solvent to yield 4d exclusively. Carbene 2b, formed on photolysis of salt 1b in methanol, also yields only 4d. Radical 2c, formed on photochemical initiation of reaction between 3a and tributylstannane, abstracts hydrogen without rearrangement to give only 3c. These reactions and relevant MNDO calculations are discussed.

Approaches from High-Spin Organic Molecules to Organic Ferromagnets

ABSTRACTPseudo-two dimensional branched polycarbenes 1, 3, 5-[H(m-C6H4C:)n/3]3C6H3 (2)(n = 6, 9) were prepared. The measurement of their magnetization on a Faraday balance equipped with a light guide has revealed that 2(n = 6) has a tridecet ground state (S = 6.0). The m-phenylene skeleton as a dependable ferromagnetic coupling unit has also been applied with success to the synthesis of persistent systems, i.e., 5, by replacing each carbene center in linear polycarbenes 1 with a nitroxide. A necessary degree of steric protection of the radical centers was disclosed. Extension to real polymers 4 gave an only partly successful result.

Correlation of singlet‐triplet gaps for aryl carbenes calculated by MINDO/3, MNDO, AM1, and PM3 with Hammett‐type substituent constants

AbstractHeats of formation, atomic charges, and geometries of some 110 structures involving substituted singlet and triplet phenyl and 4,4‐dimethyl‐1,4‐dihydronaphthalene carbenes and the corresponding diazomethanes were calculated by MINDO/3, MNDO, AM1, and PM3 semiempirical molecular orbital methods. The singlet‐triplet gaps for AM1 and PM3 calculations for the para derivatives in both systems have been successfully correlated with Brown σ+ constants. Good correlations with σ+ were found for the charges on the carbenic centers of the singlets as well as with the energy barrier for rotation of the aryl group about the C‐C single bond in substituted singlet phenylcarbenes. Comparisons of these results with experimental data indicate that AM1 and PM3 are much better than MNDO and MINDO/3 in predicting the intrinsic substituent effects in singlet carbenes.

Clusters containing carbene ligands. 12. The synthesis and transformations of Os3(CO)11[C(Et)NMe2], the first simple carbene derivative of Os3(CO)12

The carbonylation of Os2(CO)10[μ-CH2N(Me)C(Et)](μ-H),1 at 110°C/1300 psi has yielded the carbene complex Os3(CO)11[C(Et)NMe2],2, the first simple carbene derivative of Os3(CO)12, in 68% yield. Compound2 was characterized by a single crystal structure analysis which showed the position of a dimethylaminocarbene ligand in an equatorial coordination site. Compound2 is decarbonylated at 97°C to reform1 in 59% yield. Compound1 can be decarbonylated further at 125°C to yield the new compound Os3(CO)9 [μ3-η2-C(H)N(Me)C(Et)](μ-H)2,3 in 94% yield. Compound3 was characterized by a crystal structure analysis and was shown to possess a triply bridging C(H)N(Me)C(Et) ligand containing two carbene centers. Compounds1 and2 can be regenerated from3 by carbonylation with CO at 110°C/800 psi. The facile activation of the N-methyl CH bonds of the carbene ligand of2 is produced by the metal atoms adjacent to the carbene coordination site, and may be a characteristic feature of the chemistry of carbene ligands in clusters. For2: space group=P $$\bar 1$$ ,a=11.407(2) A,b=12.332(2) A,c=8.602(1) A, α=103.92(1), β=110.56(1)°, γ=82.57(1),Z=2, 2627 reflections,R=0.031; for3: space group=C2/c,a=17.160(3) A,b=8.947(2) A,c=27.034(6) A, β=97.82(1)°,Z=8, 2044 reflections,R=0.038.

Solvent and substituent effects on the reaction of phenylchlorocarbene with pyridine

The absolute rate of reaction of phenyl-chlorocarbene with pyridine is not a function of solvent polarity but does respond to placement of polar substituents para to the carbene center

Buttressing effect in carbene chemistry. Effect of 3-alkyl groups on the reactions of 2-alkoxydiphenylcarbenes

Irradiation of 2-methoxydiphenyldiazomethane 1a in diethyl ether at 10 °C gave 3-phenyldihydrobenzofuran 3a along with a small amount of the ether adduct 4a, which became the major product when the irradiation was carried out in the ether matrix at –196 °C. The reaction patterns were dramatically changed as an alkyl group was introduced into the 3-position of substrates 1. Thus, irradiation of 2-methoxy-3-alkyldiphenyldiazomethanes 1b–d in diethyl ether either at 10 °C or at –196 °C afforded the corresponding benzofurans 3b–d at the complete expense of the ether adducts 4b–d. The results are nicely explained in terms of the buttressing effect of the 3-alkyl group, which prevents the 2-methoxy group from lying in the plane of the phenyl ring in the precursor molecules and assists the methoxy group in rotating around the C–O bond toward the carbene centre after elimination of N2. Generation of carbenes 2 in methanol at 10 °C produced O–H-insertion adducts 5 as the major product at the expense of benzofurans 3. The ether 5a was formed as a major product in the reaction of carbene 2a with the alcohol matrix at –196 °C, but the benzofurans 3 became the major product in the irradiation of substrates 1b–d in methanol matrix at –196 °C. The results are again explicable in terms of the buttressing effect of 3-alkyl substituents on the relative populations of the rotational isomers of the carbenes 2.The effect of the 3-alkyl group on the reaction of 2,2′,5′-trimethoxydiphenylcarbenes 7 which form two kinds of intramolecular C–H-insertion products 8 and 9 were studied and the results are again discussed in terms of the buttressing effect.

ChemInform Abstract: A New Approach to the Construction of Novel π‐Electron Systems Using Nickel Complexes

New Synthetic methods for preparing highly unsaturated compounds are developed by using the nickel-catalyzed cyclooligomerization of cumulenes, carbenoids, and benzocyclobutadiene, and the nickel-catalyzed Ullmann coupling of organic halides. [3] Cumulenes (butatrienes), which are generated in situ from various precursors, react with nickel (0) complexes to produce [4] radialenes in benzene and THF or [6] radialenes in DMF. The formation of dimers and trimers depends on the solvent used. Reaction of [5] cumulenes (hexapentaenes) with Ni (CO)2 (PPh3)2 yields very unique compounds containing radialene frameworks. Furthermore, reaction of nickel carbenoids proceeds formally as a cyclooligomerization of the carbene center to give [3] -, [4] -, and [5] radialenes. This one-step method has been applied to the synthesis of radialenes containing functional groups. The nickel-catalyzed Ullmann coupling of vinyl halides can be also achieved to give novel π-electron systems. Nickel-mediated synthesis of trimers of benzocyclobutadiene is demonstrated with mechanistic explanation.

1,3-Migration of triorganosilyl groups from carbon to oxygen in highly crowded organosilanols

The silanol (Me 3Si)CSiMe 2OH has been shown to isomerize to (Me 3Si) 2CH(SiMe 2OSiMe 3) (which reacts further to give (Me 3Si) 2CH(SiMe 2OMe)) in 0.5 M NaOMe/MeOH, the isomerization being ca. 90% complete after 6 h under reflux. Corresponding isomerizations of (PhMe 2Si) 3CSiMe 2OH (to give (PhMe 2Si) 2CH(SiMe 2OSiMe 2Ph)), (Me 3Si) 2C(SiMePh 2)SiMe 2OH (to give (Me 3Si) 2CH(SiMe 2OSiMePh 2)), and (Me 3Si) 3CSiPh 2OH (to give (Me 3Si) 2CH(SiPh 2OSiMe 3)) take place much more readily, and are complete within ca. 2 min at room temperature in 0.10 M NaOMe/MeOH. The reactions involve 1,3-migration from carbon to oxygen within a silanolate ion to give a carbanion, which rapidly acquires a proton from the solvent. The migration is facilitated by relief of steric strain and stabilization of the forming carbanionic centre by the three attached silyl groups. The relative reactivities of the various silanols may be determined by the magnitude of the release of steric strain, by the inherent ease of nucleophilic attack at the relevant silicon centre, and, at least at low base concentrations, by the acidity of the silanol. Treatment of (Me 3Si) 3CSiPh 2OH with MeLi in Et 2O/THF gives, by the same rearrangement, the organolithium reagent (Me 3Si) 2CLi(SiPh 2OSiMe 3), which on treatment with Me 2SiHCl gives (Me 3Si) 2C(SiMe 2H)(SiPh 2OSiMe 3).

ChemInform Abstract: A Stable 6‐Metalated 1‐Azafulvene: Synthesis and Reactions of Cyclic Ru(C(C4H3N)SCNMe2S)(η2‐S2CNMe2)(CO)(PPh3) and Crystal Structure of Cyclic (Ru(=C(SCNMe2S)(2‐pyrrolyl))(η2‐S2CNMe2)(CO)(PPh3))+.

AbstractDimethyldithiocarbamate displaces chloride from both the carbene center and the metal in the carbene‐Ru complex (I) to give the stable Ru‐substituted 1‐azafulvene (III).

ChemInform Abstract: Catecholate Spanning a Metal‐Carbon Double Bond. Synthesis and Crystal Structure of Cyclic Ru(=C(OC6H4O)(2‐N‐methylpyrrolyl))I(CO)(PPh3)2.

AbstractCatecholate displaces chloride from both the carbene center and the metal in the carbene‐Ru complex (I) to give the complex (III).

Clusters containing carbene ligands. 8. Formation of ligands containing (dialkylamino)carbene centers by a novel 1,1-hydrogenation of ynamine ligands

Each compound consists of a sulfur-bridged triangular triosmium cluster. Compound 3 contains a bridging EtCN(Me)CH{sub 2} ligand. The ethyl-substituted carbon is a carbene center. Compound 4 contains a terminally coordinated carbene, EtC(NMe{sub 2}). Compound 5 contains a chelating EtCN(Me)CH{sub 2}. The ethyl-substituted carbon is a carbene center. Compound 6 contains a {eta}{sup 2}-H{sub 2}CC(H)C(H)NMe{sub 2} ligand. The carbene centers in compounds 3-5 were formed by 1,1-hydrogenations at the methyl-substituted carbon atom of the ynamine ligand in 1. In compounds 3 and 5 one of the N-methyl groups was metalated. The (dimethylamino)allyl ligand in 6 was formed by a 1,2-dihydrogenation of the ynamine ligand in 1 plus a CH activation on the methyl group on the carbon atom. Crystal data: for 3, space group Pbca, a = 12.884 (3) {angstrom}, b = 23.897 (5) {angstrom}, c = 12.522 (3) {angstrom}, 1,858 reflections, R = 0.034, R{sub w} = 0.033; for 4, space group P{anti 1}, a = 9.955 (1) {angstrom}, b = 13.971 (2) {angstrom}, c = 8.227 (1) {angstrom}, {alpha} = 102.91 (1){degree}, {beta} = 113.134 (9){degree}, {gamma} = 92.06 (1){degree}, 2,606 reflections, R = 0.027, R{sub w} = 0.031; for 5, space group P2{sub 1}/n, a = 9.260 (2)more » {angstrom}, b = 12.784 (3) {angstrom}, c = 16.734 (3) {angstrom}, {beta} = 90.60 (2){degree}, 2,163 reflections, R = 0.025, R{sub w} = 0.026; for 6, space group P2{sub 1}/n, a = 10.226 (3) {angstrom}, b = 12.589 (5) {angstrom}, c = 15.990 (7) {angstrom}, {beta} = 106.88 (3){degree}, 2,129 reflections, R = 0.036, R{sub w} = 0.039.« less

Catecholate spanning a metal-carbon double bond. Synthesis and crystal structure of -(2- N-methylpyrrolyl)]I(CO)(PPh 3) 2

Catecholate displaces chloride from both the carbene centre and the metal in Ru[CCl(2-pyrrolyl)]Cl 2(CO)L 2 (L = PPh 3) to give Ru[C(OC 6H 4O )(2-pyrrolyl)]Cl(CO)L 2 ( A). Cations derived from A can be deprotonated to ruthenium-substituted 1-azafulvene intermediates which undergo further reactions including methylation at nitrogen to give Ru[C(OC 6H 4O )(2- N-methylpyrrolyl)]I(CO)L 2 ( E). The crystal structure of E is reported.

A stable 6-metallated 1-azafulvene: synthesis and reactions of [formula omitted])(η 2-S 2CNMe 2)(CO)(PPh 3) and crystal structure of [ [formula omitted])(2-pyrrolyl)}(η 2-S 2CNMe 2)(CO)(PPh 3)] +

Dimethyldithiocarbamate displaces chloride from both the carbene centre and the metal in Ru[CCl(2-pyrrolyl)]Cl 2(CO)(PPh 3) 2 to give the stable ruthenium-substituted 1-azafulvene Ru(C[C 4H 3N]SCNMe 2S )(η 2-S 2CNMe 2)(CO)(PPh 3) ( A). Compound A can be protonated (reversibly) or methylated at the nitrogen of the 1-azafulvene to give compounds B and C respectively. The structure of B has been determined by a single crystal X-ray study.