Vinylidene Carbene Research Articles

Unexpected chemistry from the homogeneous thermal decomposition of acetylene: An ab initio study

The formation of the aromatic ring during the formation of polycyclic aromatic hydrocarbons (PAHs) remains controversial and the experimental evidence is still lacking. Moreover, the formation mechanism of benzene from acetylene in the gas phase has also puzzled organic chemists for decades. Here, ab initio molecular dynamics simulations and electronic structure calculations provide compelling evidence for an unexpected competitive reaction pathway in which the aromatic ring is formed through successive additions of vinylidene. Moreover, no collisions cause bond dissociation of the acetylene molecule during the formation of benzene in this work. This study reveals the key role for the vinylidene carbene and determines the lifetime of vinylidene.

ChemInform Abstract: Synthesis of Homopropargylamines from 2‐Cyanoazetidines.

AbstractThe tin‐catalyzed reaction of 2‐cyanoazetidines with trimethylsilyl azide gives rise to homopropargylamines via tetrazole formation, azetidine ring opening, extrusion of two molecules of dinitrogen from tetrazol moiety, and Fritsch—Buttenberg—Wiechell rearrangement of carbene to alkyne.

Synthesis of homopropargylamines from 2-cyanoazetidines.

2-Cyanoazetidines, easily accessible from β-amino alcohols, undergo ring-cleavage upon reaction with trimethylsilylazide and catalytic amounts of Bu2SnO, to give the corresponding homopropargylamines which are isolated as their N-Boc protected derivatives. The scope of this reaction, which constitutes a new way to access these highly relevant building blocks, is examined in detail. The proposed mechanism involves a tin-catalyzed cycloaddition of the nitrile moiety with the azide to give the corresponding tetrazole, which decomposes with the extrusion of two molecules of dinitrogen to produce an intermediate vinylidene carbene that finally evolves to give the alkyne.

Energy Barriers of Vinylidene Carbene Reactions from the Anti-Hermitian Contracted Schrödinger Equation

Computational studies of carbenes must take into account the possibility of multireference correlation because the highest occupied and lowest unoccupied molecular orbitals can be nearly energetically degenerate. We apply the anti-Hermitian contracted Schrodinger equation (ACSE) [Mazziotti, D. A. Phys. Rev. Lett. 2006, 97, 143002] to compute two-electron reduced density matrices (2-RDMs) and their energies for two carbene reactions: (i) the acetylene-vinylidene rearrangement and (ii) the rearrangement of pent-1-en-4-yn-3-one to acryloylvinylidene, which then cyclizes to cyclopenta-2,4-dienone. The ACSE has some unique advantages in the treatment of carbene reactions and more general families of reactions in which the importance of multireference correlation is not known a priori: (i) the ACSE is more reliable than single-reference methods for confirming the presence or absence of multireference correlation and (ii) in the absence of multireference correlation, unlike multireference second-order perturbation theory (MRPT2), the ACSE recovers more single-reference correlation energy than similarly scaling coupled-cluster methods. Because MRPT2 does not recover as much single-reference correlation as the coupled-cluster or ACSE methods, it tends to underestimate reaction barriers within the carbene reactions. For example, in the rearrangement of pent-1-en-4-yn-3-one, the ACSE and CCSD(T) methods produce cyclization barriers of 18.9 and 18.7 kcal/mol with the 6-31G(d) basis set, whereas MRPT2 predicts this barrier to be 12.1 kcal/mol; furthermore, both the ACSE and CCSD(T) determine the energy of the transition state for acryloylvinylidene formation to be 6.6-6.7 kcal/mol above that of the carbene, and yet, MRPT2 does not predict a transition state.

Generation of allenylthioketene S, S-dioxides through [3,3] sigmatropic rearrangement of alkynyl propargyl sulfones

Thioketene S, S-dioxides 2 were successfully generated through [3,3] sigmatropic rearrangement of alkynyl propargyl sulfones 1 and the formation of 2 was confirmed by trapping experiment using cyclohexene or allyltrimethylsilane affording a [2+2] cycloadduct 5. In situ generated thioketene S, S-dioxides 2 underwent facile conversion into allenynes 3 in moderate yields, via formation and subsequent [1,2] shift of vinylidene carbenes.

Density Functional Study of Mo-Carbonyl-Catalyzed Alkynol Cycloisomerization: Comparison with W-Catalyzed Reaction

Mo-catalyzed endo-cycloisomerizations of alkynes tethered to alcohols have been studied using density functional theory, and comparisons were made with the W-catalyzed reaction. The cycloisomerization is initiated with the formation of metal alkyne pi complex and is followed by the rate-determining step, which transforms the pi complex to a vinylidene carbene complex, considered to be critical for endo-mode cyclization. Several different alkynols have been selected to investigate five- and six-membered ring endo-cycloisomerizations in the presence of Mo(CO)(5) catalyst. The energy barriers calculated for five- and six-membered ring cycloisomerizations are within a range of 25-30 kcal/mol for most cases studied, showing no significant energy difference between the two metals. The stabilization effect of THF and Et(3)N solvents and the substitution reaction of THF by alkynol substrates in the reaction process with Mo and W complexes are studied as well. The principal difference between Mo- and W-catalyzed cycloisomerization processes appears to be the initial formation of a pi complex, which is more stabilizing for formation of the W-alkyne vs Mo-alkyne complexes.

A Complete Active Space Self-Consistent Field (CASSCF) Study of the Reaction Mechanism of theα-Alkynone Rearrangement

The pyrolytic rearrangement of α-alkynones has been discovered by Karpf and Dreiding [1] in 1979. The mechanism of this reaction, which involves an acetylene-vinylidene rearrangement followed by cyclization of the intermediate vinylidene carbene by insertion into a β-C−H bond, has been debated in a couple of theoretical investigations. Restricted Hartree-Fock (RHF) and single-point Møller-Plesset 2 (MP2) calculations at the RHF geometries apparently indicate the carbene cyclization to be the rate-determining step, contrary to chemical intuition. However, larger-scale correlated calculations with completely optimized molecular geometries ((8,8) CASSCF/6-311G**), augmented with a perturbative account for the dynamic correlation contribution to the electronic energy, show vanishing energy barriers to the cyclization step and large activation energies for the acetylene-vinylidene rearrangement, which is thus confirmed as the rate-determining step of the title reaction.

Nucleophilic additions of anionic Group 6 carbene complexes on cationic indenyl–ruthenium(II) allenylidene derivatives: an easy entry to bimetallic complexes containing σ-alkynyl–carbene and vinylidene–carbene bridges †

The novel indenyl–ruthenium(II) allenylidene complexes [Ru{CCC(R)Ph}(η5-C9H7)(PPh3)L][PF6] (L = PMePh2, R = Ph 4a, H 4b; L = PMe2Ph, R = Ph 5) have been prepared by reaction of [RuCl(η5-C9H7)(PPh3)L] (L = PMePh22, PMe2Ph 3) with HCCC(OH)(R)Ph and NaPF6 in methanol. These allenylidene derivatives as well as [Ru{CCC(R)Ph}(η5-C9H7)(PPh3)2][PF6] (R = Ph 1a, H 1b) undergo regioselective nucleophilic additions of anionic Fischer type carbene complexes [Li][(CO)5M{C(OMe)CH2}] (M = Cr, W, Mo) at the Cγ atom of the unsaturated chain to afford the neutral bimetallic σ-alkynyl derivatives [Ru(CCC(R)Ph{CH2C(OMe)M(CO)5})(η5-C9H7)(PPh3)L] (L = PPh3, R = Ph, M = Cr 6a, W 6b, Mo 6c; L = PPh3, R = H, M = Cr 7a, W 7b; L = PMePh2, R = Ph, M = Cr 8a, W 8b; L = PMePh2, R = H, M = Cr 9a, W 9b; L = PMe2Ph, R = Ph, M = Cr 10a, W 10b). Protonation of these derivatives with HBF4·Et2O yields cationic vinylidene complexes [Ru(CC(H)C(R)Ph{CH2C(OMe)M(CO)5})(η5-C9H7)(PPh3)L][BF4] 11a–c, 12–15a,b which represent the first examples of bimetallic species containing a vinylidene–carbene bridge. Heating under reflux solutions of vinylidene complexes 11b and 12b in acetonitrile affords the carbene derivatives [(CO)5W{C(OMe)CH2C(R)Ph(CCH)}] (R = Ph 16a, H 16b) and the nitrile complex [Ru(NCMe)(η5-C9H7)(PPh3)2][BF4] 17. The diphenylallenylidene complex 1a regioselectively reacts with NaCN to yield the σ-alkynyl derivative [Ru{CCCPh2(CN)}(η5-C9H7)(PPh3)2] 18. Treatment of 18 with one equivalent of [M(CO)5(THF)] leads to the formation of the bimetallic σ-alkynyl complexes [Ru(CCCPh2{CN–M(CO)5})(η5-C9H7)(PPh3)2] (M = Cr 20a, W 20b, Mo 20c).

Synthesis of 2,5-dihydrofurans via alkylidene carbene insertion reactions

The insertion of vinylidene carbenes into CH bonds is an efficient method for the synthesis of 2,5-dihydrofurans. The methodology provides a convenient entry to the core structure of squalestatin/zaragozic acid natural products.

ChemInform Abstract: Group VI Metal‐Promoted endo‐Azacyclizations via Alkyne‐Derived Metal Vinylidene Carbenes.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform Abstract: Group VI Metal‐Promoted endo‐Carbocyclizations via Alkyne‐Derived Metal Vinylidene Carbenes.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Group VI metal-promoted endo-carbocyclizations via alkyne-derived metal vinylidene carbenes

The molybdenum-promoted cycloisomerization of terminal alkynes tethered to β-dicarbonyl nucleophiles is described, providing a novel synthesis of 1,1-disubstituted-2-cyclopentenes.

Group VI metal-promoted endo-azacyclizations via alkyne-derived metal vinylidene carbenes

The molybdenum-promoted cycloisomerization of terminal alkynes tethered to nitrogen nucleophiles is described. Reaction of N-carbamoyl alkynylamines with (Et 3N)Mo(CO) 5 affords cyclic enecarbamates. Similarly, cyclization of 2-ethynylaniline gives the isomeric indole heterocycle, although N-3-butynylaniline affords the cyclic metal azacarbene product.

Allenylidene indenyl ruthenium(II) complexes as sources of highly functionalized alkynyl complexes: synthesis of the first bimetallic derivatives containing a vinylidene–carbene bridge

The alkynylphosphonioruthenium(II) complex [Ru{–CC–C(PMe3)(H)Ph}(PPh3)2(η–C9H7)][PF6] reacts with aldehydes, ketones and phenylisocyanate via a Wittig process to afford either enynyl or keteniminyl complexes; [Ru(CCCPh2)(P-Ph3)2(η-C9H7)][PF6] undergoes regioselective necleophilic attacks at Cγ by the anionic species [M(CO5)C(OMe)CH2]-(M Cr, Mo, W) to yield binuclear alkynyl-carbene complexes [(η-C9H7)(PPh3)2Ru-CC-CPh2-CH2-C(OMe)M(CO)5] which are the precursors of the first vinylidene–carbene bimetallic cationic derivatives [(η-C9H7)(PPh3)2RuCC(H)–CPh2–CH2–C(OMe)M(CO)5]+.

Collision induced dissociations of carbanions in the gas phase: the formation of vinylidene carbene intermediates from deprotonated prop-2-ynyl ethers

Evidence is presented which suggests that the anionic isomers MeO–CH2–CC– and CH2CC––OMe, upon collision activation in the gas phase, fragment through the vinylidene carbene intermediate [(CH2CC:)MeO–]. In particular, the intermediate eliminates CH2O and MeOH to form C3H3– and C3H–, respectively. Ab initio calculations indicate that the latter ion has a ground state triplet structure with ‘allenic’ type geometry.

ChemInform Abstract: X-RAY CRYSTALLOGRAPHIC CHARACTERIZATION OF AN IRON PORPHYRIN WITH A VINYLIDENE CARBENE INSERTED INTO AN IRON-NITROGEN BOND

Chemischer InformationsdienstVolume 14, Issue 8 Physical Organic Chemistry ChemInform Abstract: X-RAY CRYSTALLOGRAPHIC CHARACTERIZATION OF AN IRON PORPHYRIN WITH A VINYLIDENE CARBENE INSERTED INTO AN IRON-NITROGEN BOND M. M. OLMSTEAD, M. M. OLMSTEADSearch for more papers by this authorR.-J. CHENG, R.-J. CHENGSearch for more papers by this authorA. L. BALCH, A. L. BALCHSearch for more papers by this author M. M. OLMSTEAD, M. M. OLMSTEADSearch for more papers by this authorR.-J. CHENG, R.-J. CHENGSearch for more papers by this authorA. L. BALCH, A. L. BALCHSearch for more papers by this author First published: February 22, 1983 https://doi.org/10.1002/chin.198308071AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume14, Issue8February 22, 1983 RelatedInformation

Regioselective insertion of vinylidene carbene into α CH bond of aalkoxides

Dimethylvinylidene carbene inserted regioselectively into α CH bond of various alkoxides gave allenylcarbinols in 17–68% yields.

X-ray crystallographic characterization of an iron porphyrin with a vinylidene carbene inserted into an iron-nitrogen bond

X-ray crystallographic characterization of an iron porphyrin with a vinylidene carbene inserted into an iron-nitrogen bond

Stability and bonding of disilyne and its isomers: A generalized valence bond‐effective potential study

AbstractWe have employed an effective potential and a single‐zeta basis in SCF–MO computations to estimate the relative stability of linear disilyne HSiSiH and five isomeric structures defined in earlier all‐electron ab initio SCF–MO computations. The effect of electron correlation has been estimated by generalized valence‐bond (GVB) computations for the five valence electron pairs of these structures. All our computations indicate that linear disilyne is the least stable structure and that H2SiSi, the silicon analog of vinylidene carbene, is the most stable structure. In these structures silicon occurs in divalent and tetravalent states. The nature of silicon bonding in these valence states is illustrated by contour diagrams of the GVB orbital pairs.

On the nature and reactivity towards substrates of the active oxygen hemoprotein complexes involved in the reaction of peroxidases and cytochrome P- 450 with two-electron oxidants

Two sets of results are presented which contribute to the understanding of the nature and reactivity of the active oxygen complexes formed during reactions of catalase, horseradish peroxidase, and cytochrome P- 450 with two-electron oxidants. The one-electron oxidation of vinylidene carbene complexes of iron porphyrins [Fe II→ CCAr 2] ← [Fe IVCCAr 2], by FeCl 3 or CuCl 2, leads to stable complexes which exhibit visible spectra very similar to those of catalase and horseradish peroxidase compounds I. This suggests a common formulation [porphyrin Fe = X] +· for the carbene complexes, X = CAr 2, and for the hemoprotein compounds I, X = O. From model studies, evidence has been obtained in favor of the formation of a stable iron-carbene bond after oxidation of 1,3-benzodioxole by the active oxygen cytochrome P-450 complex. From these data, a stepwise mechanism for substrate oxidation by two-electron oxidants, catalyzed by cytochrome P-450, involving the possible formation of unstable iron—carbon α bond, is proposed. This mechanism exhibits a close similarity with that of hydrocarbon oxidations by peroxy-compounds catalyzed by copper or iron salts.