Alkyne Fragment Research Articles

C–H vs. N–H Bond Activation in Aminophosphane Ligands: Reaction of [Cp*Ru(MeCN)2(PR12NHR2)]+ (R1 = Ph, iPr; R2 = Ph, C6F5) with Alkynes

AbstractThe reaction of the complexes [Cp*Ru(MeCN)2(PR12NHR2)]+ (R1 = R2 = Ph 1; R1 = iPr, R2 = C6F5 2; R1 = iPr, R2 = Ph 3) with 1‐alkynes HC≡CR (R = H, nBu, SiMe3) or diynes HC≡CCH2XCH2C≡CH (X = O, CH2, CH2CH2) yields different products depending on the nature of the aminophosphane ligand. In some cases, alkyne coupling involving migration of the phosphane and N–H activation occurs, yielding amidobutadiene complexes of the type [Cp*Ru{η4‐C4H3(R)2PR12NR2‐κ1N}]+ or [Cp*Ru{η4‐C4H3(CH2XCH2)PR12NR2‐κ1N}]+. The complexes [Cp*Ru{η4‐C4H3(CH2OCH2)PPh2NPh‐κ1N}][PF6] (1a) and [Cp*Ru{η4‐C4H3(CH2OCH2)PiPr2NC6F5‐κ1N}][PF6] (2a) have been structurally characterized by X‐ray crystallography. In other cases, for example the reaction of 3 with HC≡CR (R = nBu, SiMe3), C–H bond activation at the ortho‐position of the phenyl ring of the phenylamino moiety and coupling to the alkyne fragment takes place. This results in the formation of the novel π‐alkene complexes [Cp*Ru(MeCN){η2‐RCH=CH(C6H4)NHPiPr2‐κ1P}]+ (R = nBu 4, SiMe3 5), formally derived from the insertion of the alkyne into the ortho‐C–H bond of the phenyl ring. The derivative [Cp*Ru(MeCN){η2‐nBuCH=CH(C6H4)NHPiPr2‐κ1P}][BPh4] has been structurally characterized by X‐ray crystallography. These compounds are related to the also structurally characterized olefin complex [Cp*Ru(MeCN)(η2‐MeOOCCH=CH2)(PPh2NHPh)][PF6] (6), generated by reaction of 1 with methyl acrylate. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

Mechanism of Enyne Metathesis Catalyzed by Grubbs Ruthenium−Carbene Complexes: A DFT Study

The complete catalytic cycle of the reaction of alkenes and alkynes to dienes by Grubbs ruthenium carbene complexes has been modeled at the B3LYP/LACV3P**+//B3LYP/LACVP level of theory. The core structures of the substrates and the catalyst were used as models, namely, ethene, ethyne, hept-1-en-6-yne, (Me(3)P)(2)Cl(2)Ru=CH(2), and [C(2)H(4)(NMe)(2)C](Me(3)P)Cl(2)Ru=CH(2). Insight into the electronically most preferred mechanistic pathways was gained for both intermolecular as well as for intramolecular enyne metathesis. Alkene metathesis is predicted to proceed fast and reversible, while the insertion of the alkyne substrate is slower, irreversible, and kinetically regioselectivity determining. Ruthenacyclobut-2-ene structures do not exist as local minima in the catalytic cycle. Instead, vinylcarbene complexes are formed directly. The alkyne insertion step and the cycloreversion of 2-vinyl ruthenacyclobutanes feature comparable predicted overall barriers in intermolecular enyne metathesis. For intramolecular enyne metathesis, a noncyclic alkene fragment of the enyne substrate is first incorporated into the Grubbs catalyst by an alkene metathesis reaction. The subsequent insertion of the alkyne fragment then proceeds intramolecularly. Alkene association, cycloaddition, and cycloreversion to the diene product complex close the catalytic cycle. Rate enhancement by an ethene atmosphere (Mori's conditions) originates from a constantly higher overall alkene concentration that is necessary for the rate-limiting [2 + 2] cycloreversion step to the diene product complex.

Evidence for partial quenching of orbital angular momentum upon complex formation in the infrared spectrum of OH-acetylene.

The entrance channel leading to the addition reaction between the hydroxyl radical and acetylene has been examined by spectroscopic characterization of the asymmetric CH stretching band of the pi-hydrogen bonded OH-acetylene reactant complex. The infrared action spectrum observed at 3278.6 cm(-1) (origin) consists of seven peaks of various intensities and widths, and is very different from those previously reported for closed-shell HF/HCl-acetylene complexes. The unusual spectrum arises from a partial quenching of the OH orbital angular momentum in the complex, which in turn is caused by a significant splitting of the OH monomer orbital degeneracy into (2)A(') and (2)A(") electronic states. The magnitude of the (2)A(')-(2)A(") splitting as well as the A rotational constant for the OH-acetylene complex are determined from the analysis of this b-type infrared band. The most populated OH product rotational state, j(OH)=9/2, is consistent with intramolecular vibrational energy transfer to the nu2 C triple bonded C stretching mode of the departing acetylene fragment. The lifting of the OH orbital degeneracy and partial quenching of its electronic orbital angular momentum indicate that the electronic changes accompanying the evolution of reactants into products have begun to occur in the reactant complex.

Synthesis, Structure, and Dynamics of Molybdenum Imido Alkyne Complexes

The monomeric alkyne complexes (η2-alkyne)Mo(NPh)(o-(Me3SiN)2C6H4) (3) have been synthesized by the displacement of isobutylene from (η2-isobutylene)Mo(NPh)(o-(Me3SiN)2C6H4) (2). The alkyne fragment in these complexes is oriented perpendicular to the MoN bond of the cis imido ligand, as confirmed by an X-ray structural analysis of 3e. The deshielded nature of the chemical shifts of the α-carbons and terminal protons of the alkyne fragments in these complexes strongly suggests the participation of the alkyne π⊥ electrons in the Mo−alkyne interaction. The alkyne fragment in 3 rotates freely about the Mo−alkyne bond, resulting in the fluxional behavior of these complexes at room temperature. An activation barrier of 13.2 kcal/mol for the alkyne rotation was measured using VT NMR spectroscopy. Computational studies using a two-layer ONIOM model, and the B3LYP hybrid functional, provided insight into the Mo−alkyne bonding. The transition state for alkyne rotation has been calculated and is characterized by a parallel orientation of the alkyne fragment to the cis imido ligand. A natural bond orbital (NBO) population analysis reveals that alkyne π⊥ donation to Mo is more extensive in the transition state than in the ground state. Weaker Mo−N(imido) bonds are also observed in the transition state, because π donation from the alkyne ligand competes with imido π donation.

Efficient and general approach to eremophilanes using siloxyalkyne-alkene metathesis.

An efficient skeletal reorganization of a terminal alkene armed with an appropriate siloxy alkyne fragment is a pivotal step in our novel and general strategy for the construction of a bicyclic core of eremophilanes with complete diastereocontrol and high synthetic efficiency. Our approach features three significant strategic elements. First, the enyne metathesis precursor is assembled via a highly endo-selective Diels-Alder reaction. Second, installation of the siloxy group at the alkyne terminus enables the regioselective assembly of the ensuing enone fragment via intramolecular enyne cyclization. Third, the common enone precursor offers the necessary flexibility of accessing several natural products of the eremophilane family.

Molecular Structures of Acetylene Derivatives of Tin. VIII Trimethylstannylacetylene: Use of Results of Quantum-Chemical Calculations and Spectroscopic Measurements in Analysis of Gas-Phase Electron Diffraction Data

Structural analysis of electron diffraction data on trimethylstannylacetylene, (CH3)3SnC≡CH (1), obtained in the previous investigation (the nozzle temperature being 22°C), has been performed with consideration of nonlinear kinematic effects at the first-order level of perturbation theory (h1). The geometry and force field of 1 have been calculated by the RHF and MP2 (“frozen core”) methods. The effective core potential in SBK form and the optimized 31G* valence basis set have been applied in the case of Sn atom. The 6-311G** basis set have been used for carbon and hydrogen atoms. Vibrational spectra of the light and two deuterated isotopomers of 1 have been interpreted using the C 3v equilibrium molecular symmetry. For this purpose, the procedure of scaling the quantum-chemical force field by fitting the calculated frequencies to the experimental ones has been employed. The root-mean-square (RMS) vibrational amplitudes and shrinkage corrections used in the electron diffraction analysis have been calculated from the scaled quantum-chemical force field. It has been shown that flexibility of the linear fragment in 1 decreases considerably compared to that of the symmetrically substituted acetylene fragment in the (CH3)3SnC≡CSn(CH3)3 molecule (2). Using these data, we refined the geometrical parameters of 1 in terms of a static C 3v symmetry molecular model. The following r h1 values have been obtained (the bond distances are given in A and the valence angles in degrees): Sn—CMe 2.147(7), Sn—C≡2.096(17), C≡C 1.237(11), CMe—H (av.) 1.091(4), CMe—Sn-C≡107.1(7), Sn—CMe—H (av.) 113.4(6). The values in parentheses are experimental total errors including least-squares standard deviation values and scale uncertainties. The structural parameters of linear fragments in both ethynyl derivatives of Sn 1 and 2 are found to be virtually equal.

(‐)‐(R)‐ and (+)‐(S)‐Carvone in the Synthesis of Optically Active Acetylenic Alcohols, Ethers, and Dichlorosilyl Derivatives.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Detection of reactive intermediates during laser pyrolysis of cellulose char by molecular beam mass spectroscopy, implications for the formation of polycyclic aromatic hydrocarbons

We report here the use of infrared laser pyrolysis as both an analytical tool, at low power, for the determination of pendant polycyclic aromatic hydrocarbons (PAH) in chars and as a means, at high power, for the generation of the reactive intermediate precursors of PAH. Cellulose, in the form of pelletized Avicel, was charred under argon for various times at 375 °C up to 3 h. The char formed in this way was pyrolyzed using a 65W carbon dioxide laser at powers corresponding to peak char surface temperatures, T max, of up to approximately 1000 °C in a helium atmosphere and the products detected by molecular beam mass spectroscopy (MBMS). Relatively fast scanning of the mass spectrum allowed useful information to be gathered before the sample reached peak temperatures, <1 s. Low laser power, T max≈850 °C, experiments produced PAH from pendant groups on the char surface corresponding to the molecular weight growth of the aromatic species with charring time. At long charring times the size of the PAH detected diminished as the chars became more intractable. In addition propargyl and formyl methyl radicals were observed as the PAH was ablated from the char surface. Additional evidence for these radicals comes from simulating the mass spectrum and low electron-energy ionization measurements. At high laser powers, T max≈1700 °C, significant quantities of propargyl radical and acetylene were observed as the PAH was broken into fragments. By increasing the effective distance from hot char to the MBMS inlet we were able to observe moderate molecular weight growth of the propargyl radical to hexadiene and PAH. Only very small amounts of the cyclopentadienyl radical were observed and its condensation product, the naphthalene precursor, dihydrofulvalene. We, therefore, conclude that the important reactive intermediates in the fast pyrolysis of cellulose char are: acetylene, propargyl, formyl methyl and PAH fragment radicals.

(-)-(R)- and (+)-(S)-Carvone in the Synthesis of Optically Active Acetylenic Alcohols, Ethers, and Dichlorosilyl Derivatives

Reaction of butyllithium with acetylene and 1-hexyne gave the corresponding lithium acetylides which reacted with (-)-(R)- and (+)-(S-carvone in a stereospecific fashion to give lithium (1-ethynyl- or 1-hexynyl)-5-isopropenyl-2-methyl-2-cyclohexenolates. Hydrolysis of the latter gave individual optically active tertiary terpene alcohols having both acetylenic and p-menthene fragment. Their treatment with methyl iodide in the presence of hexamethylphosphoric triamide afforded the corresponding methyl ethers. The reaction of 3-ethynyl-5-isopropenyl-3-methoxy-2-methylcyclohexene with butyllithium and trichloro(vinyl)silane yielded optically active dichlorosilyl-containing acetylenic compounds.

Reactivity of Diynes with a 1-Azavinylidene-Bridged Triruthenium Carbonyl Cluster. Insertion Reactions of Diynes into Ru−H, Ru−C, and Ru−N Bonds

The reactivity of the 1-azavinylidene cluster complex [Ru3(μ-H)(μ-NCPh2)(CO)10] (1) with diynes has been studied. The nonconjugated diyne 1-trimethylsilyl-1,4-pentadiyne affords the binuclear ynenyl derivative [Ru2(μ-NCPh2)(μ-η2-CH2CCH2C⋮CSiMe3)(CO)6] (2), which results from cluster fragmentation and from the insertion of the terminal alkyne fragment of the diyne into a Ru−H bond. The reactions of 1 with the internal conjugated diynes 1,6-diphenoxy-2,4-hexadiyne, 2,4-hexadiyne, and diphenylbutadiyne have allowed the isolation of the trinuclear derivatives [Ru3{μ-η2-NCPh(C6H4)}(μ3-η4-PhOCH2CHCCCHCH2OPh)(CO)8] (3), [Ru3{μ3-η4-NCPh(C6H4)CH(Me)CHCCMe}(CO)9] (4), [Ru3{μ-η2-NCPh(C6H4)}(μ3-η4-PhCHCHC⋮CPh)(CO)8] (5), and [Ru3{μ3-η4-PhCHCHC(CPh)NCPh(C6H4)}(CO)9] (6). The four compounds have been characterized by X-ray diffraction methods. They all arise from the orthometalation of a phenyl ring of the 1-azavinylidene ligand and from the transfer of two hydride ligands (the original plus that coming from the orthometalation) to the coordinated diyne. This hydrogenation process can proceed as a 1,4-addition to give a 1,2,3-triene fragment (as occurs in 3) or as a 1,2-addition to give an enyne fragment (as occurs in 5). In the cases of 4 and 6, a 1,2-addition of hydrogen is accompanied by the insertion of the unsaturated hydrocarbon fragment into the Ru−C bond associated with the orthometalated ring (4, 6) and into a Ru−N bond (6). The precise order by which these processes lead to the corresponding products has not been established. The reactions involved in the formation of compounds 2−6 represent excellent examples of insertion of diynes into M−H, M−C, and M−N bonds of metal clusters and have allowed the characterization of substituted 1-yn-3-enyl (in 2), 1,2,3-triene (in 3), 1,2-dienyl (in 4), 1-en-3-yne (in 5), and 2-(N-imido)-1,2,3-allyl-1-yl (in 6) ligands.

Molecular structures of acetylene derivatives of tin

The electron diffraction data on bis(trimethylstannyl)acetylene, Me3SnC≡CSnMe3, were analyzed in the framework of the one-dimensional dynamic model of free internal rotation of the SnMe3 group about the axis of the Sn−C≡C−Sn linear fragment. The root-mean-square amplitudes and harmonic shrinkage corrections used in the analysis were calculated from the scaled quantum-chemical force field (i) taking into account nonlinear relations between Cartesian and internal vibrational coordinates at the first-order level of perturbation theory (h1) and (ii) using a conventional approach (h0). Therh1 parameters of internuclear distances describe the equilibrium geometry of the Me3SnC≡CSnMe3 molecule much better than the commonly accepted parametersrα≡rh0. Substituent effects on the geometry of the acetylene fragment are discussed.

Nickelocene adsorption on single-crystal surfaces

Nickelocene adsorption onto Ag(100), Ni(100), and NiO(100)/Ni(100) surfaces was studied with x-ray photoelectron spectroscopy and high-resolution electron energy loss spectroscopy at 135 K for monolayer and multilayer coverages of NiCp2. On the relatively inert Ag(100) surface, nickelocene physisorbs molecularly, with its molecular axis perpendicular to the surface plane. Exposure to the reactive Ni(100) surface results in the decomposition of nickelocene into acetylene and acetylene-like fragments and, when this surface is warmed to 273 K, carbide contamination is observed. There is evidence for double-bond carbon on nickelocene-exposed NiO(100), and vinyl and propenyl fragments are the most likely decomposition products on this surface. At very large exposures, adsorbed nickelocene is molecularly condensed and, therefore, produces similar thin films on all three surfaces.

Synthesis of areneacetylenic chelate complexes of chromium with a terminal triple bond, their reversible rearrangements to areneallenic chelates, and addition at the triple bond

New areneacetylenedicarbonylchromium chelate complexes containing the terminal acetylene fragment in the side chain of the arene ligand were synthesized. The rearrangement of these chelates to the previously unknown areneallenedicarbonylchromium chelate complexes was found and studied. It was demonstrated that this rearrangement is in principle reversible. For areneallenedicarbonylchromium chelates, a new example of metallotropic rearrangement was found and both isomers, namely, with the coordination either at the substituted or at the nonsubstituted double bond of the allene ligand, were detected for the first time. The coupled addition of the proton and the nucleophile at the coordinated triple bond afforded the corresponding areneolefin chelates.

Alkyl alkynylphosphonites in the Kabachnik-Fields reaction

O-Ethyl alkynylphosphonites [EtOP(O)(H)CэCR] (1 and2) react withp-bromobenzaldehyde and benzylamine to form the usual acyclic products of the Kabachnik-Fields reaction or phosphorus-containing heterocycles depending on the nature of the substituent R at the β-carbon atom of the acetylene fragment of phosphonite. In the case of R=But,O-ethyl (α-benzylamino-p-bromobenzyl)(3,3-dimethylbut-1-ynyl)phosphinate (3) was obtained. In the case of R=Me, 1-benzyl-2-p-bromophenyl-3-ethoxy-5-methyl-3-oxo-Δ4-1,3-λ5-azaphospholine (4) was formed. Compounds3 and4 were also synthesized by the reactions of the above-mentioned phosphonites with the corresponding azomethines.

Laser Irradiation of Monomeric Acetylene and the T-Shaped Acetylene Dimer in Xenon and Argon Matrices

Irradiation of acetylene (4) in an argon matrix with an ArF laser (λ = 193 nm) yields the ethynyl radical C2H· (5) and C2 (6). If the same wavelength is used to irradiate 4 in a xenon matrix, only the infrared signal of the compound Xe–C2 (7) can be detected. The same band is found on irradiation at λ = 248 nm (KrF laser) in a xenon matrix, despite the fact that acetylene (4) does not absorb light of this wavelength. Irradiation of the T-shaped acetylene dimer 9 in an argon or xenon matrix at λ = 193 nm yields butadiyne (11) and vinylacetylene (12). However, irradiation with a KrF laser (λ = 248 nm) in a xenon matrix additionally yields cyclobutadiene (13). The dependence of the mechanisms of the fragmentation and dimerization of acetylene (4) on the matrix material is discussed.

Laser Irradiation of Monomeric Acetylene and the T-Shaped Acetylene Dimer in Xenon and Argon Matrices

Irradiation of acetylene (4) in an argon matrix with an ArF laser (λ = 193 nm) yields the ethynyl radical C2H· (5) and C2 (6). If the same wavelength is used to irradiate 4 in a xenon matrix, only the infrared signal of the compound Xe–C2 (7) can be detected. The same band is found on irradiation at λ = 248 nm (KrF laser) in a xenon matrix, despite the fact that acetylene (4) does not absorb light of this wavelength. Irradiation of the T-shaped acetylene dimer 9 in an argon or xenon matrix at λ = 193 nm yields butadiyne (11) and vinylacetylene (12). However, irradiation with a KrF laser (λ = 248 nm) in a xenon matrix additionally yields cyclobutadiene (13). The dependence of the mechanisms of the fragmentation and dimerization of acetylene (4) on the matrix material is discussed.

Reaction of stabilised arsonium ylides with acetylenic esters: convenient ring synthesis of a tetrasubstituted benzene

Reaction of stabilised arsonium ylides such as 24 with methyl and ethyl propiolate in benzene gives the β,γ-unsaturated arsonium ylides 25 and 27 resulting from net insertion of the alkyne fragment into the CAs bond, but the isomeric ylides 26 and 28 corresponding to net insertion into the C–H bond when the reaction is carried out in methanol. The assignment of the structures is confirmed in the case of 25 by an X-ray structure determination. The corresponding phosphonium ylide 29 reacts with methyl propiolate to give 31 in either benzene or methanol in contrast to an earlier report. Further reaction of 25 with DMAD proceeds with net insertion of the alkyne into the CC double bond and spontaneous intramolecular cyclisation to give the tetrasubstituted benzene derivative 39.

Synthesis, structure and reactivity of acetylenic Co2(CO)6 pyrylium salts. Electronic influence of the Co2(CO)6 acetylenic fragment

Abstract The formation of new pyrylium salts bearing in the γ position an acetylenic Co2(CO)6 fragment is described. X-ray analysis showed that the γ carbon of the pyrylium ring does not interact with a cobalt atom. However, IR values, relating to the carbonyl stretching band, suggested that a part of the positive charge is delocalized on the cluster core. Finally, the reactivity of these cationic complexes towards nucleophiles is reported.

Reactions between ruthenium cluster carbonyls and 1,4-diphenylbuta-1,3-diyne

The complexes RuC(CCPh)CPhC(CCPh)CPh(CO) 3(NMe 3) ( 3), Ru 2μ-C(CCPh)CPhC(CCPh)CPh(CO) 6 ( 1), Ru 2μ-[C(CCPh)CPh] 2CO(CO) 6 ( 2), Ru 3( μ 3-PhC 2 CCPh)( μ-CO)(CO) 9 ( 4) and Ru 4( μ 4-PhC 2 C CPh)(CO) 12 ( 5) have been isolated from reactions between PhC 2C 2Ph and Ru 3(CO) 12 or RU 3(CO) 10(NCMe) 2. The molecular structures of complexes 1, 2, 3 and 5 have been determined from single-crystal X-ray studies. All complexes have precedents in similar products obtained from reactions involving mono-ynes; in the present cases, each alkyne fragment retains a phenylethynyl (PhCC) group as a non-coordinated substituent.

Reactions of 1,4-difeffocenylbuta-1,3-diyne and 1,4-diphenylbut-l-en-3-yne with Ru3(CO)12. Crystal structure of Ru3(CO)8(?3-?-1-?1-?4-?2-C4Ph2(CH=CHPh)2)

Diyne FcCmCC.CFc (Fc is ferrocenyl) reacts with Ru3(CO)12 in boiling hexane to yield binuclear complexes Ru2 and Ru2(CO)6(C4Fc2(C=CFc)2C=O) containing ruthenacyclopentadiene and diruthenacycloheptadienone rings, respectively. The isomerism of the complexes is due to the different ways of coupling of the alkyne fragments of the diyne, namely, “head-to-head”, “head-to-tail” or “tail-to-tail”. The reaction of enyne PhC=CCH=CHPh with Ru3(CO)12 under similar conditions gives isomeric binuclear complexes Ru2(CO)6(C4Ph2(CH=CHPh)2) and trinuclear clusters Ru3(CO)6(w-CO)2(C4Ph2(CH=CHPh)2) and Ru3(CO)8(μ3-,η1-η1-η4-η2 C4Ph2(CH=CHPh)2). The structure of the latter was determined by X-ray diffraction analysis. The Ru3 triangle coordinates eight terminal CO groups and the organic ligand resulting from the “head-to-head” dimerization of enyne molecules; the ruthenacyclopentadiene moiety is η4-coordinated to the Ru(CO)2 group, and the third ruthenium atom is η2-bound to one of the PhCH=CH groups.