Cyclopentadiene Derivatives Research Articles

Synthesis of Cp−Re Complexes via Olefinic C−H Activation and Successive Formation of Cyclopentadienes

Treatment of an alpha,beta-unsaturated ketimine with an alpha,beta-unsaturated carbonyl compound in the presence of a rhenium complex, Re2(CO)10, gave a cyclopentadienyl-rhenium complex. This reaction proceeds via rhenium-catalyzed C-H bond activation of an olefinic C-H bond, insertion of an alpha,beta-unsaturated carbonyl compound into a Re-C bond of the alkenylrhenium intermediate, intramolecular nucleophilic cyclization, reductive elimination, elimination of aniline to give a cyclopentadiene derivative, followed by the formation of a cyclopentadienyl-rhenium complex from the cyclopentadiene derivative and the rhenium complex.

Theoretical Study of Solvent and Substituent Effects on the Reactions of 1,4-Benzoquinone with Cyclopentadiene and Cyclohexadiene

Ab initio quantum mechanics and ONIOM calculations were used to study solvent and substituent effects on the reactions of 1,4-benzoquinone with cyclopentadiene and cyclohexadiene derivatives in tetrahydrofuran and greater water solvents. These calculations revealed (i) that increasing the number of electron donating methyl group substituents and (ii) the proximity of substituents to the reacting carbons (carbon atoms which contribute to the forming C—C bonds) on the diene, promote charge transfer from the diene to the dienophile in the transition state. These effects increase the negative charge on the oxygen atoms, destabilize the transition state in the organic solvent by increasing steric interactions, and stabilize the transition state in water solvent by increasing the strength of hydrogen bonding. These results, along with consideration of variations in the solvent-accessible surface area (SASA) confirmed that the dramatic acceleration in the rate of the studied reactions in water solvent arise in part from hydrophobic association of the reactants, but predominantly arise from hydrogen bonding between water molecules and the polarized transition state.

Rhodium-Catalyzed Intramolecular Cycloaddition of Cyclopropene-ynes Triggered by Carbon-Carbon Bond Cleavage

In the presence of a catalytic amount of RhCl(PPh 3 ) 3 , an intramolecular cycloaddition of cyclopropene-yne proceeded along with carbon-carbon bond cleavage of cyclopropene ring to give various bicyclic cyclopentadiene derivatives in good to high yield.

Direct Coupling of Bromine‐Mediated Methane Activation and Carbon‐Deposit Gasification

The direct bromination of methane offers a quite selective (>98 %) route towards methane activation but shifts the problem of fuel production to converting and handling corrosive methyl bromide. The direct conversion of methyl bromide, at about 200 degrees C, into light hydrocarbons can be catalyzed under pressure by AlBr(3) resulting in the formation of propane-rich mixtures of light hydrocarbons, carbonaceous deposits, and HBr. After releasing the gaseous products, the addition of hydrogen at 260 degrees C allows a quantitative conversion of the carbonaceous deposits into the same range of light hydrocarbons. These second-stage products efficiently contribute to the overall process yield while enabling a full regeneration of the catalyst's activity. This oxygen-free process is compared to the conversion of methyl bromide on zeolites and the currently used methanol-to-gasoline (MTG) process in terms of product distributions and apparent energy of activation. A detailed chemical analysis of the intermediates revealed the presence of a carbon pool consisting of highly substituted benzene and cyclopentadiene derivatives, as observed on zeolites used in the MTG process. This similarity suggests that the currently used oxygen-based syngas/MTG process for methane conversion may be extended to a bromine-mediated process by using methyl bromide as an intermediate instead of methanol.

Biscarbene complexes from the reactions of O-ethyl lactim and 1-alkynyl Fischer carbene complexes of chromium and tungsten

Reactions of O-ethyl lactim ∼(CH 2) 3–N C(OEt)∼ with 1-alkynyl Fischer carbene complexes (OC) 5M C(OEt)C CPh (M = Cr, W) afforded biscarbene complexes with an azabicyclo[3.2.0]heptene core. Under a nitrogen atmosphere, the resultant chromium biscarbene complex gave a SiO 2-promoted rearrangement complex in 86% yield. Thermal annelation of the rearrangement product followed by hydrolysis over SiO 2 formed a cyclopentenone derivative. A cyclopentadiene derivative was obtained as a rare example of intermediate Fischer carbene species, suggesting a possible reaction pathway for the thermal annelation of the rearrangement complex. Stepwise oxidation of the chromium biscarbene complexes with an azabicyclo[3.2.0]heptene core with pyridine- N-oxide (PNO) under mild controlled conditions generated partially and completely demetalated carbonyl products, respectively. The key carbene complexes and demetalated compounds were structurally characterized by X-ray crystallographic studies.

Dearomatizing Anionic Cyclization of 1‐Lithio‐4‐naphthyl‐1,3‐butadienes Leading to the Formation of Spiro Cyclopentadiene Derivatives.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

A Novel Acid-Assisted Transformation of Cyclopentadiene Endoperoxides to Pyrylium Cations

The substituted cyclopentadiene endoperoxides were observed to form their corresponding substituted pyrylium cations in the presence of perchloric acid. Keywords: photooxygenation, cyclopentadiene derivatives, HPLC, pyrylium cations, perchloric acid

New cyclopentadiene derivatives as novel pH indicators

(Triphenylphosphoranylidene)cyclopenta-1,3-dienes with stabilized zwitterionic resonance structures showed the application feasibility as new pH indicators. In terms of absorption intensity occurring from the acid–base reactions, (triphenylphosphoranylidene)cyclopenta-1,3-dienes displayed strong colors with high extinction coefficients in the alkali pH range. Resonance structures of (triphenylphosphoranylidene)cyclopenta-1,3-dienes in alkali media stabilize anionic ions. Three derivatives of (triphenylphosphoranylidene)cyclopenta-1,3-dienes 1a– c, are used as pH indicators in the range 10–12. For these compounds color change in the pH range 10–12 was extremely sharp, clear and reversible. But there are not many indicators in the pH range 10–14.

Reaction of 4-methyl, 4-phenyl, and 4-hydrogen substituted 1-lithio-1,3-butadienes with aldehydes: preparation of multiply substituted cyclopentadienes

Abstract Reaction of aldehydes with 1-lithio-1,3-butadiene reagents possessing a methyl substituent, a phenyl substituent or a hydrogen at position 4 of the butadienyl skeletons was studied. Polysubstituted cyclopentadiene derivatives were obtained in high yields upon hydrolysis using strong acidic solution. Reaction mechanism study revealed that these cyclopentadienes were formed via an acid-promoted cyclization of conjugated dienols. Thus, stereodefined all-cis substituted dienols or a wide diversity of substituted cyclopentadienes can be obtained from the same 1-lithio-1,3-butadiene reagent and aldehyde by adjusting the hydrolysis conditions.

Dearomatizing Anionic Cyclization of 1-Lithio-4-naphthyl-1,3-butadienes Leading to the Formation of Spiro Cyclopentadiene Derivatives

On treatment with t-BuLi, 1-iodo-4-naphthyl-1,3-butadiene derivatives cyclize with dearomatization to give spiro compounds bearing a moiety of allyllithium, which reacts further with electrophiles to yield spiro tricyclic systems.

Can Substituted Cyclopentadiene Become Aromatic or Antiaromatic?

Cyclopentadiene derivatives with electronegative (F, Cl) or electropositive (H(3)Si, Me(3)Si) bis-5,5-substituents were studied at the B3LYP/6-311G* level of theory. It was found that there is no special stabilization or destabilization for any of the derivatives; the energetic effects that were previously attributed to aromatic stabilization or antiaromatic destabilization are the result of interactions in the reference systems. A nucleus-independent chemical shift (NICS) scan study at the HF-GIAO/6-311+G* theoretical level of these and similar derivatives suggest that they all show different magnitudes of diamagnetic ring current. None of the derivatives shows a paramagnetic ring current. Thus, cyclopentadienes are neither aromatic nor antiaromatic. It is also concluded that a diamagnetic ring current is perhaps necessary but certainly not a sufficient condition for aromaticity. The NICS scan procedure describes the type of ring current in the system, whereas a single isotropic NICS value (i.e., NICS(1)) may wrongly assign the type of ring current. It is shown that neither NICS(1) nor the NICS scan procedure can be used as a single aromaticity criterion.

Ruthenium‐Catalyzed Cycloisomerization of cis‐3‐En‐1‐ynes to Cyclopentadiene and Related Derivatives Through a 1,5‐Sigmatropic Hydrogen Shift of Ruthenium—Vinylidene Intermediates.

AbstractFor Abstract see ChemInform Abstract in Full Text.

A Controllable Synthesis of Homoallyl Ketones and Multiply Substituted Cyclopentadienes by Direct Insertion of Aroyl Cyanides to Zirconacyclopentenes.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Controlled nucleophilic activation of different sites in [Mo 2Cp 2L 2(μ-SMe) 2(μ-L′)] + cations (L = Bu tNC, xylNC, CO; L′ = SMe or PPh 2)

The thiolato-bridged binuclear molybdenum complexes [Mo 2Cp 2L 2(μ-SMe) 2(μ-L′)]Y (Cp = η 5-C 5H 5; L′ = SMe, L = Bu t NC ( 1a), xylNC ( 1b) or CO ( 3); L′ = PPh 2, L = Bu t NC ( 16); Y = BF 4, Cl) react with the anionic reagents NaBH 4, NaBD 4, LiR (R = Me, Bu n ), R′MgCl (R′ = Me, Pr i , Bu n or Ph). The products are unsubstituted ( 5, 7) or substituted ( 8– 12) η 4-cyclopentadiene derivatives, [Mo 2(η 5-C 5H 5)(η 4-C 5H 5R)L 2(μ-SMe) 3] (L = xylNC, CO), or μ-formimidoyl dinuclear products, [Mo 2Cp 2L 2(μ-SMe) 2(μ-L′)(μ-CHNR)] (L′ = SMe, L = Bu t NC ( 4) or xylNC ( 6); L′ = PPh 2, L = Bu t NC ( 17)). Since the reduced dinuclear species [Mo 2Cp 2(CO) 2(μ-SMe) 2] and the related oxo-compound [Mo 2Cp 2(CO)(O)(μ-SMe) 2] are sometimes isolated as minor products, the anionic reagent can play a secondary role as a reductant in these reactions in addition to its main role as a nucleophile. The electronic properties of the donor carbon atoms of the cyclopentadienyl rings and of the terminal ligands L, together with the nature of the anionic reagent, are the dominant factors controlling selective formation of 4– 12 and 17. Tetrafluoroboric acid reacts with the substituted cyclopentadiene derivatives 9, 11 and 12 to form new functionalised cyclopentadienyl derivatives, [Mo 2(η 5-C 5H 5)(η 5-C 5H 4R)(CO) 2(μ-SMe) 3](BF 4) (R = Me ( 13), Bu n ( 14) or Ph ( 15)). New complexes have been characterised by spectroscopic and chemical methods, supplemented for 5, 6 and 12 by X-ray diffraction studies at 100 K.

Ruthenium-Catalyzed Cycloisomerization of cis-3-En-1-ynes to Cyclopentadiene and Related Derivatives through a 1,5-Sigmatropic Hydrogen Shift of Ruthenium−Vinylidene Intermediates

We report a new ruthenium-catalyzed cycloisomerization of unactivated cis-3-en-1-ynes, which produces substituted cyclopentadiene and related derivatives. The mechanism of this cyclization is proposed to involve a [1,5]-sigmatropic hydrogen shift of ruthenium-vinylidene intermediates on the basis of deuterium-labeling experiments.

New Methods for the Preparation of Multiply Substituted Cyclopentadienes and Related Compounds

Substituents on cyclopentadienyl ligands significantly influence the reactivity and catalytic efficiency of their transition metal complexes. Therefore, development of synthetic methods for cyclopentadiene derivatives possessing different substituents has been in great demand. In this paper, we report new synthetic methods for multiply substituted cyclopentadienes recently developed in this group. In principle, three types of preparative methods are described. Firstly, zirconacyclopentadienes in the presence of Lewis acids react with aldehydes to afford multiply substituted cyclopentadienes, thus providing a one-pot procedure from two molecules of identical or different alkynes and one molecule of aldehyde; reaction of aluminacyclopentadienes with aldehydes also result in high-yield formation of multiply substituted cyclopentadienes. Secondly, 1,2,3,4-tetrasubstituted 1,4-dilithio- and 1,4-bis(magnesiobromo)-1,3-diene derivatives react with aldehydes or ketones via deoxygenation of the C=O moieties to afford cyclopentadiene derivatives. Thirdly, monolithio reagents, 1,2,3,4-tetrasubstituted 1-lithio-1,3-butadienes, and Grignard reagents, 1,2,3,4-tetrasubstituted 1-magnesiobromo-1,3-butadienes react with aldehydes or ketones to afford cyclopentadiene derivatives upon hydrolysis.

Synthesis of pentavalent imidovanadium complexes and their catalyses for the polymerization of ethylene and propylene

AbstractImidovanadium complexes with cyclopentadienyl (Cp) ligands—(Cp)V(NC6H4Me‐4)Cl2 (1), (Cp)V(NtBu)Cl2 (2), and (tBuCp)V(NtBu)Cl2 (3; tBuCp = tert‐butylcyclopentadienyl)—were synthesized through the reaction of imidovanadium trichloride with (trimethylsilyl)cyclopentadiene derivatives. The molecular structure of 3 was determined by X‐ray crystallography. The monocyclopentadienyl complex 1 exhibited moderate activity in combination with methylaluminoxane [MAO; 10.3 kg of polyethylene (mol of V)−1 h−1 atm−1], whereas similar complexes with bulky tBu groups, 2 and 3, were less active. (2‐Methyl‐8‐quinolinolato)imidovanadium complexes, V(NR)(O ˆN)Cl2 (R = C6H3iPr2‐2,6 (4) or n‐hexyl (5), O ˆN = 2‐methyl‐8‐quinolinolato), were obtained from the reaction of imidovanadium trichloride with 2‐methyl‐8‐quinolinol. Upon activation with modified MAO, complex 4 showed moderate activities for the polymerization of ethylene at room temperature. The complex 5/MAO system also exhibited moderate activity at 0°C. The polyethylenes obtained by these complexes had considerably high melting points, which indicated the formation of linear polyethylene. Moreover, the 5/dried MAO system showed propylene polymerization activities and produced polymers with considerably high molecular weights and narrow molecular weight distributions. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1008–1015, 2005

A Controllable Synthesis of Homoallyl Ketones and Multiply Substituted Cyclopentadienes by Direct Insertion of Aroyl Cyanides to Zirconacyclopentenes

[reaction: see text] The direct reaction of aroyl cyanides with zirconacyclopentenes was achieved cleanly under controlled reaction conditions. This methodology provided an extremely efficient, one-pot, and high-yield route for the synthesis of homoallyl ketones when the reaction was carried out at -50 degrees C. Trapping of the zirconium intermediate by a variety of electrophiles afforded functionalized homoallyl ketones. Remarkably, the insertion reaction occurred with complete chemoselectivity, that means, the Zr-sp3 carbon bond reacted preferentially, which is different from Cu-mediated elaboration of zirconacycles. Surprisingly, when the reaction was done at room temperature, 1,2,3-trisubstituted cyclopentadiene derivatives were readily formed in high yields. The direct insertion reaction of zirconacyclopentanes with acyl cyanides was also described. When bicyclic zirconacyclopentanes were used, cyclopentanol derivatives were obtained with high stereoselectivity.

Reaction Chemistry of 1,4‐Dilithio‐1,3‐diene and 1‐Lithio‐1,3‐diene Derivatives

AbstractFor Abstract see ChemInform Abstract in Full Text.

Synthesis of a tin-functionalized cyclopentadiene derivative

A 3- tert-butyl-1-(stannylpropyl)-functionalized cyclopentadienyl ligand precursor 6 is readily available in 64% overall yield from allylic alcohol 1 by a three-step reaction sequence including Pd-catalyzed hydrostannylation with Ph 3SnH. Treatment with FeCl 2 and ZrCl 4 · 2THF afforded corresponding ferrocene and zirconocene derivatives. Transmetallation of Sn–Ph with Li–Bu was observed under these reaction conditions by using BuLi as a base.