Carbene Dimerization Research Articles

Absolute kinetics of mesitylmethylchlorocarbene reactions

R. A. Moss and D. C. Merrer, Chem. Commun., 1997, 617 DOI: 10.1039/A607552E

Tetra-tert-butylethylene: An Elusive Molecule with a Highly Twisted Double Bond. Can It Be Made by Carbene Dimerization?

A theoretical evaluation of tetra-tert-butylethylene (1) at the BLYP/DZd level confirms that it should be a stable molecule with a singlet ground state. The synthesis of 1 from two molecules of di-tert-butylcarbene (6) is unlikely. Although the formation of singlet 1 from the triplet 3B ground state of 6 (singlet 6 is only 1−3 kcal/mol higher in energy) is highly exothermic (ΔH = −73.7 kcal/mol), the barrier ΔG⧧ = 25 kcal/mol (298 K, 1 atm, BLYP/DZd) for the dimerization is too large to compete with the barrier for intramolecular carbene insertion. The barrier for singlet 6 to yield 1,1-dimethyl-2-tert-butylcyclopropane (12) is only 5 kcal/mol. The CC double bond in singlet 1 is twisted by 45°, and the strain energy is ∼93 kcal/mol in agreement with molecular mechanics results. Triplet 1 has a nearly perfectly perpendicular conformation at the central CC bond (87° torsional angle), but it is still strained by 42 kcal/mol and is 12 kcal/mol higher in energy than singlet 1. Alkyl substitution decreases the S−T separation of carbenes due to the greater hyperconjugative stabilization of the singlet than the triplet.

ChemInform Abstract: Coupling Reactions. Part 15. The Reaction of 1‐Halogeno‐1‐ lithiocyclopropanes with CuCl2: Competition Between “Carbene Dimerization” and Oxidative Coupling.

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Die Reaktion von 1‐Halogeno‐1‐Lithiocyclopropanen mit CuCl2: Konkurrenz zwischen ‘Carben‐Dimerisierung’ und oxidativer Kupplung

The Reaction of 1‐Halogeno‐1‐lithiocyclopropanes with CuCl2: Competition between ‘Carbene Dimerization’ and Oxidative CouplingThe 1‐chloro‐1‐lithiocyclopropanes 2a–d react at low temperature with CuCl2 to give diastereoisomeric mixtures of oxidative‐coupling products 5a–d and of ‘carbene dimers’ 6a–d. The relative amount of 5a–d increases with CuCl2 concentration and reaction time. Diastereoselectivity of the reaction seems to be low, and separation as well as spectroscopic structure assignment of single diastereoselectivity of the reaction seems to be low, and separation as well as spectroscopic structure assignment of single diastereoisomers are difficult. The conformational behavior of 1,1′‐dichloro‐1,1′‐bi(cyclopropyls) 5c and 5d is discussed. Contrary to 2a–d, 1‐bromo‐1‐lithiocyclopropanes normally react with CuCl2 to give ‘carbene dimers’ 6 and no coupling products 5. So far the only exception is 1‐bromo‐1‐lithio‐2‐phenylcyclopropane 2e which in the presence of CuCl2 gives some percents of coupling products 5e besides carbene dimers 6b as main products. An X‐ray structure analysis of the predominant diastereoisomer 5e was performed.

Kupfer(II)‐chlorid‐katalysierte ‘Carben‐Dimerisierung’ von 1‐Halogeno‐1‐Lithiocyclopropanen: Ein einfacher Zugang zu Bi(cyclopropylidenen)

Copper(II)‐Chloride Catalyzed ‘Carbene Dimerization’ of 1‐Halogeno‐1‐lithiocyclopropanes: A Simple Access to Bi(cyclopropylidenes)A series of 13 bi(cyclopropylidenes) 11 are prepared in a simple one‐pot reaction by halogeno‐lithio exchange between 1,1‐dibromocyclopropanes 1a–n and BuLi, in most cases at −95°, to give 1‐bromo‐1‐lithiocyclopropanes 2a–n, followed by treatment with CuCl2 at low temperature and a simple workup at room temperature (Scheme 3c and Table 1). The yields of bi(cyclopropylidenes) 11 strongly depend on reaction parameters, as explicitly shown for the conversion 1f →→ 11f (Tables 2–8). Mixed couplings between two different carbenoids are possible (Scheme 4), while diastereoselectivity of the active transition‐metal complex seems to be low. The structures of bi(cyclopropylidenes) 11 are confirmed by spectroscopic data as well as by X‐ray analysis of an isolated crystalline diastereoisomer of 11k (Fig. 1).

Synthese und Röntgenstruktur einer Triafulvalen-Vorstufe

Triafulvalene precursors 3b and 3c have been synthesized by CuII-catalyzed 'carbene dimerization' of cyclopropyl carbenoids (obtained by halogen-lithium exchange of 1,1-dibromo-2-(phenylthio)-3-(trimethylsilyl)cyclopropane (2b; see Scheme 2) in moderate yields. Diastereoselectivity of the central step 2b → 3b is low. An X-ray analysis of the predominantly formed trans-anti isomer has been performed.

Carbene addition to the 2,3-bond of naphthalene and thermal Wolff rearrangement of bis(methoxycarbonyl)carbene

Carbene addition to the 2,3-bond in naphthalene produced 9 and Wolff rearrangement/cycloaddition gave a new carbene dimer 11 .

Oberflächen-Reaktionen, 9 Dehydrohalogenierungen von Halogenkohlenwasserstoffen an Raney-Nickel / Surface Reactions, 9 Dehydrohalogenation of Halohydrocarbons at Raney Nickel

Raney nickel, a highly reactive and air-sensitive solid, if prepared and investigated under oxygen-free conditions, exhibits interesting catalytic properties. Using photoelectron spectroscopy for real-time gas analysis in a flow reactor, the following results are obtained with alkyl and acylhalides: Dehydrohalogenation temperatures are lowered relative to thermal HHal elimination up to 350 K. Monochloro and bromo propanes and butenes yield propene and butadiene, respectively. 1,1-Dichloro ethane or 1,1-dibromo propane only split off one HHal and form chloroethene or 1-bromopropene-2. HCl elimination from 2-methyl propionic acid chloride, expectedly, produces dimethyl ketene. Most interesting, however, is the ring opening of monobromo cyclobutane to 1-bromo-butene-3, observed already at room temperature, which strongly suggests the intermediate formation of a chemisorbed surface carbene at Raney nickel. The formation of hexadiene-1,5 as a by-product in the HCl elimination of 1-chloropropane, i. e. a surface carbene dimer, indicates their presence also in other dehydrohalogenations heterogeneously catalyzed by Raney nickel.

Modification of polybutadienes by catalytic and photochemical decomposition of dimethyldiazomalonate

AbstractModifications of polybutadienes via catalytic and photolytic decomposition of dimethyldiazomalonate (dmdm) are described. This method pertains to the generation of highly reactive carbenes which give rise to the formation of addition and insertion products. Chemical structures of the modified polymers were confirmed by NMR spectroscopy. It was found that carbene dimers were also formed in a significant extent depending on the molecular weight and microstructure of the initial polymers.

ChemInform Abstract: Study of Chlorine Atom Abstraction Reactions of Phenylchlorocarbene by Laser Flash Photolysis.

AbstractPhotolysis of 3‐phenyl‐3‐chlorodiazirine in CCl4 gives, via phenylchlorocarbene (see foregoing ref.), a mixture of products consistent with the occurrence of some chlorine atom abstraction/radical recombination in addition to products formed by carbene dimerization and reaction with its precursor (kinetics, mechanism).

MOLECULAR ORBITAL (MO) THEORY FOR MAGNETICALLY INTERACTING ORGANIC COMPOUNDS. AB-INITIO MO CALCULATIONS OF THE EFFECTIVE EXCHANGE INTEGRALS FOR CYCLOPHANE-TYPE CARBENE DIMERS

Abstract A generalized molecular orbital (GMO) theory for magnetically interacting organic compounds has been presented. The theory is applied to the calculations of the effective exchange integrals (Jab) for the cyclophane-type carbene dimers whose para and ortho-isomers have the high-spin ground state. The calculated Jab-values are consistent with observations.

Dimerization of carbene to ethylene

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTDimerization of carbene to ethyleneL. M. Cheung, K. R. Sundberg, and K. RuedenbergCite this: J. Am. Chem. Soc. 1978, 100, 25, 8024–8025Publication Date (Print):December 1, 1978Publication History Published online1 May 2002Published inissue 1 December 1978https://doi.org/10.1021/ja00493a050RIGHTS & PERMISSIONSArticle Views197Altmetric-Citations50LEARN 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 (233 KB) Get e-Alerts Get e-Alerts

Unrestricted Hartree-Fock Studies on the Dimerization Reactions of the Carbenes CH2, CHF and CF2

UHF theoretical analyses are carried out on the olefin forming dimerization reactions of the carbenes CH2 , CHF and CF,. It is shown that the UHF singlet ground state of the carbene dimer in coplaner symmetric conformations may enter into five distinct configura­ tions; two closed shell states, two ASDW states and one TSDW state. These five states appear at different regions of the nuclear configuration space depending on the substituents of the carbenes. A singlet olefin may dissociate into two singlet carbenes or two triplet carbenes depending on the bond angle of the carbene moieties. The two ASDW states correspond to the two different spin states of the carbene moieties, the triplet and singlet diradical states. The TSDW ground state appears at the region where the interconversion of the spin states of the carbene moieties takes place. The adiabatic potentials of the UHF configurations are calculated on various reaction paths. The distinction between the least and the non-least motion approaches is discussed.

Metal salt catalyzed carbenoides—XIV: The mechanisms of carbene dimer formation from diazoacetic ester and dimethyl diazomalonate in the presence of some soluble copper catalysts

An examination of partial rate data for the decomposition of diazo acetic ester and dimethyl diazomalonate, in the presence of soluble copper salts and cyclohexene, revealed the existence of two paths to carbene dimer formation, one with a unimolecular dependence upon catalyst, the other with a bimolecular dependence. Assuming carbenoid formation, this is taken as indicative of dimer formation occurring by carbenoid + diazo compound and carbenoid + carbenoid paths. Conformational analyses indicate a preference for diethyl maleate formation by the carbenoid-diazo ester path for the case of diazoacetic ester and a preference for diethyl furmate formation by the carbenoid + carbenoid path.

Thermolysis of 1,2-dithiolylium salts in the ion source of the mass spectrometer

1,2-Dithiolylium salts are thermolysed in the ion source of a mass spectrometer; some salts (group I) undergo thermolysis to give a stable dithiolyl radical where subsequent ionization gives rise to a mass spectrum in which the parent ion corresponds to the dithiolyl ion. The radical may be stabilized before ionization by expulsion of a hydrogen atom to form a neutral dithiole derivative, and then mass spectra exhibit abundant molecular ions corresponding to such dithiole derivatives. Other salts (group II) may expel a proton with formation of a carbene and subsequent dimerization to a tetrathiafulvalene. The thermolytic behaviour of 1,2-dithiolylium salts is compared with their electrochemical behaviour and several analogies are found.