CHC CH Research Articles

Reactivity of the Substituted Butadienes, Isoprene and Myrcene, with Decamethylsamarocene

The interaction of the substituted diene monomers isoprene, C5H8, and myrcene, C10H16, with a lanthanide was probed by examining their chemistry with (C5Me5)2Sm. CH2CHC(Me)CH2 reacts with (C5Me5)2Sm to form the bimetallic [(C5Me5)2Sm]2[μ-η2:η4-CH2CHC(Me)CH2], 1. Both (C5Me5)2Sm components in 1 exhibit trivalent metrical parameters. One Sm is oriented toward all four of the dienyl carbon atoms at distances of 2.604(9)−2.799(8) A, and the other Sm interacts with only two carbons at distances of 2.544(9) and 2.674(9) A. CH2CHC(CH2)CH2CH2CHCMe2 reacts with (C5Me5)2Sm to form [(C5Me5)2Sm]2[μ-η2:η4-CH2CHC(CH2)CH2CH2CHCMe2], 2, which is similar in structure to 1. The double bond of the pendant olefinic substituent attached to the diene in myrcene does not coordinate. The structures of 1 and 2 are compared to the (C5Me5)2Sm/PhC⋮CPh bimetallic reaction product [(C5Me5)2Sm]2[μ-η1:η1-PhCCPh], 3, which also contains two (C5Me5)2Sm units attached to an unsaturated hydrocarbon, but has equivalent trivalent (C5Me5)2Sm u...

Kinetics of OH radical reaction with allyl alcohol (H 2CCHCH 2OH) and propargyl alcohol (HCCCH 2OH) studied by LIF

The rate constants for the reactions of hydroxyl radical (OH) with two unsaturated alcohols (ROH) namely, allyl alcohol (H 2CCHCH 2OH) and propargyl alcohol (HCCCH 2OH) in the gas phase have been measured. The kinetic measurements were carried out using laser photolysis (LP) combined with laser induced fluorescence (LIF) technique at room temperature over a pressure range of 10–20 Torr. The bimolecular rate constants for the reactions OH+ROH→products, are determined at room temperature to be (3.7±0.5)×10 −11, (9.2±1.4)×10 −12 cm 3 molecule −1 s −1 , respectively, for allyl alcohol and propargyl alcohol. The measured rate constants in combination with ab initio molecular orbital calculation provide a better understanding of the structure-reactivity rules.

Regiospecific substitution of the 4-nitro group in 3-amino-4,6-dinitrobenzo[ b]thiophene-2-carboxylates: unexpected activating effect of the amino group

The cyclocondensation of 2,4,6-trinitrobenzonitrile with the esters of thioglycolic acid results in the formation of 3-amino-4,6-dinitrobenzo[ b]thiophene-2-carboxylates 3 . The interaction of 3 with anionic nucleophiles RO − (R=CF 3CH 2, CHCCH 2), RS − (R=Ph, PhCH 2, (CH 3) 2CHCH 2), N 3 − in NMP or DMF leads to the substitution of only the 4-NO 2 group. The replacement of the electron-donating NH 2 group in 3 with hydrogen unexpectedly and significantly hampers nucleophilic substitution of the nitro group. It is assumed that increased reactivity of the 4-NO 2 in 3 is connected with the twist of this group with respect to the plane of the aromatic ring under the influence of the NH 2 group as indicated by semi-empirical quantum chemical calculations.

Interconversion of gaseous bicyclo[3.2.1]oct-2-en-4-yl cations and protonated 7-alkylcycloheptatrienes: [5 + 2] cycloreversion in competition with fragmentation by way of alkylbenzenium ions

Several bicyclo[3.2.1]oct-2-en-3-yl cations, as isomers of protonated 7-methyl- and 7-ethylcycloheptatriene and of the protonated C8H10 and C9H12 alkylbenzenes, respectively, have been studied by deuterium labeling and mass-analyzed ion kinetic energy (MIKE) and collision-induced dissociation/MIKE spectrometry. Labeling reveals that the bicyclic framework undergoes fast and apparently complete hydrogen equilibration prior to fragmentation, involving a series of skeletal and hydrogen rearrangements (1,2-C and 1,2-H shifts). Fragmentation of the bicyclic ions C8H11+ and C9H13+ is manyfold: It occurs in part by way of the isomeric alkylbenzenium ions, e.g. CH3CH2C6H6+ and CH3C6H5CH3+, and C2H5C6H5CH3+ and CH3CH2CH2C6H6+, respectively, with the corresponding 7-alkyldihydrotropylium ions as intermediates. Another fraction of the bicyclic ions does not fragment by way of alkylbenzenium ions but apparently by [5 + 2] cycloreversion of bicyclo[3.2.1]octenyl framework itself. This process is indicated by ethene expulsion associated with an unusually large kinetic energy release (T∗ ≈ 300 meV). The characteristic high-KER ethene loss was also found for protonated 7-ethylcycloheptatriene but not for protonated 7-methylcycloheptatriene, suggesting a delicate balance of the activation energies and confirming, in turn, that bicyclo[3.2.1]oct-2-en-yl cations are intermediates during the fragmentation of higher alkyldihydrotropylium ions.

Calculation of static mean polarisability and polarisability anisotropy. Statistical comparison with the results of gases and influence of the geometrical parameters

The static mean polarisabilities α ̄ and polarisability anisotropies Δ α of nine molecules have been computed at the B3LYP level by using 6-311++G(3df,2pd), aug-cc-pVDZ and Sadlej basis sets, experimental r e or optimised geometries. These molecules are either linear (CO 2, CS 2, OCS, HCCH) or symmetric top (CH 3CCH, CH 3Cl, CHCl 3, CH 3CN, C 6H 6). A statistical comparison with accurate experimental data has shown that 6-311++G(3df,2pd) basis set gives slightly better results than the two other sets. More precisely, for α ̄ (0), Sadlej basis set has the best statistical indicators to experiment, but a 0.98 scale factor should be applied to calculated values to improve agreement with experimental values, wherefore no scale factor is needed with 6-311++G(3df,2pd) basis set. For Δ α(0), B3LYP/6-311++G(3df,2pd) method clearly performs the best results, however, a 0.96 scale factor is necessary to fit experiment. Also, computed polarisabilities are better when the experimental microwave geometry is used instead of the geometry computed by optimisation.

Dicobalt cluster functionalized 2,2′:6′,2″-terpyridine ligands and their ruthenium(II) complexes

A series of 2,2′:6′,2″-terpyridine (tpy) ligands functionalized in the 4′-position with alkyne substituents has been prepared and characterized. Treatment of these ligands with [RuCl 3(tpy)] yields complexes with pendant alkyne groups which then readily react with Co 2(CO) 8 to give novel compounds containing both cluster and classical coordination motifs. The new compounds are characterized by mass spectrometric and spectroscopic methods, and the single crystal structure of [Ru(tpy)(4′-HCCCH 2Otpy)][PF 6] 2 is reported.

Laboratory investigation on the formation of unsaturated nitriles in Titan’s atmosphere

Crossed molecular beam experiments of ground state cyano radicals, CN(X 2Σ +), with hydrocarbons acetylene (C 2H 2), ethylene (C 2H 4), methylacetylene (CH 3CCH), allene (H 2CCCH 2), dimethylacetylene (CH 3CCCH 3), and benzene (C 6H 6,) were performed to investigate the formation of unsaturated nitriles in Titan’s atmosphere. These radical–neutral reactions have no entrance barrier, depict an exit barrier well below the energy of the reactant molecules, and are all exothermic. The CN radical attacks the π electron density at the olefine, alkyne, and aromatic molecules; the formation of an initial addition complex is a common pathway on the involved potential energy surfaces for all reactions. A subsequent carbon–hydrogen bond rupture yields the unsaturated nitriles HCCCN, C 2H 3CN, CH 3CCCN, H 2CCCH(CN), H 2CCCH 2CN, and C 6H 5CN as detected in our experiments. The explicit identification of this CN vs H atom exchange pathway under single collision, makes this reaction-class a compelling candidate to synthesize unsaturated nitriles in Titan’s atmosphere. This versatile concept makes it even possible to predict the formation of nitriles once the corresponding unsaturated hydrocarbons are identified in Titan. Here, the C 2H 2 as well as cyanoacetylene, HCCCN, have been already identified unambiguously in Titan’s troposphere. Those nitriles as sampled in our crossed beam experiments resemble an ideal challenge to be detected in the framework of the NASA–ESA Cassini–Huygens mission to Titan.

Crossed beam investigation of elementary reactions relevant to the formation of polycyclic aromatic hydrocarbon (PAH)-like molecules in extraterrestrial environments

The reactions of ground state carbon atoms, C( 3P j), with benzene, C 6H 6, and phenyl radicals, C 6H 5, with methylacetylene, CH 3CCH, were investigated in crossed beam experiments at collision energies of 21.8 and 140 kJ mol −1 to investigate elementary reactions relevant to the formation and chemistry of polycyclic aromatic hydrocarbons (PAHs) in extraterrestrial environments. The C( 3P j) reaction proceeds via complex formation and gives a cyclic, seven-membered C 7H 5 doublet radical plus atomic hydrogen. This pathway has neither an entrance nor exit barrier, and is exothermic. Together with the experimental verification of the carbon versus hydrogen exchange under single collision conditions, the findings have an important impact on the chemistry of aromatic molecules in interstellar clouds and outflow of carbon stars. Even in the coldest molecular clouds ( T=10 K), the benzene molecule can be destroyed upon reaction with carbon atoms, whereas they are resistant toward an attack of oxygen and nitrogen atoms. Since the aromatic benzene unit is ubiquitous in extraterrestrial, PAH-like material, our results suggest that PAHs might react with carbon atoms as well. On the other side, the reaction of C 6H 5 radicals with methylacetylene to form phenylmethylacetylene is direct. Since an entrance barrier inhibits the reaction in cold molecular clouds and in the atmospheres of hydrocarbon rich planets like Jupiter and Saturn and satellites such as Titan, this reaction is expected to play a role in PAH synthesis only in high temperature interstellar environments, such as circumstellar outflows of carbon stars.

Synthesis and characterization of [ trans-di(μ-acetato)(μ-bis(diphenylphosphino)methylamine)bis(pyridine)dimolybdenum(II)]bis(tetrafluoroborate) and derivatives

Reaction of trans-[Mo 2(μ-O 2CCH 3) 2(μ-dppma) 2(MeCN) 2](BF 4) 2 ( 1, dppma=diphenylphosphinomethylamine) with a variety of pyridine derivatives leads to axially substituted complexes of formula trans-[Mo 2(μ-O 2CCH 3) 2(μ-dppma) 2(NC 5H 4-R) 2](BF 4) 2 (R=H, 2; C(CH 3) 3, 3; C 6H 5, 4; CHCHC 6H 5, 5; CCH, 6; CN, 7). The obtained complexes were characterized by 1H-, 13C- and 31P{ 1H}-NMR, IR, Raman spectroscopy and elemental analyses. Raman spectroscopy shows a weakening of the metal–metal interaction due to the axially coordinated pyridine ligands in all examined cases. Compound 2 was additionally examined by single-crystal X-ray analysis, revealing a Mo–Mo distance of 215.04(2) pm, which is slightly longer than that in compound 1 (213.15(3) pm).

Thermal reaction of 2-methyl-2-butene in the presence of azomethane: enthalpy of formation of the radicals (CH3)2ĊCH(CH3)2 and tert-Ċ4H9

The reaction of ĊH3 and 2-methyl-2-butene (2MB2) was investigated in the temperature range 540610 K. Azomethane was used as the source of ĊH3. The addition of ĊH3 to 2MB2 was concluded to be an equilibrium process: ĊH3+(CH3)2C2CHCH3(CH3)2ĊCH(CH3)2. The equilibrium constant of this reaction was determined from the rates of formation of the combination products (E)- and (Z)-CH3CH2C(CH3)2CHCH3 and (E)- and (Z)-(CH3)2CHC(CH3)2CH2C(CH3)2CHCH3. Finally, the enthalpy of formation of the adduct radical, ΔfH298°[(CH3)2ĊCH(CH3)2] = (3±10) kJ mol−1, was obtained from the temperature dependence of the equilibrium constant. On the assumption that the group additivity rule was valid for the adduct radical, the following group value was obtained: ΔfH298°[Ċ–(C)3] = (179±12) kJ mol−1. Through use of this datum ΔfH298°(tert-Ċ4H9) = (53±12) kJ mol−1.

The electronic states of propyne studied by optical (VUV) absorption, near-threshold electron energy-loss (EEL) spectroscopy and ab initio multi-reference configuration interaction calculations

The VUV absorption and EELS spectra of propyne (CH 3CCH) have been reinvestigated, and reassigned in the light of multi-reference multi-root CI calculations of quadruple zeta quality containing both valence and Rydberg type functions. While the Rydberg states were considered as linear, and hence studied as vertical excitations, the known bending of valence states in alkynes led to a parallel investigation of the equilibrium structures of the lowest singlet and triplet valence states of cis and trans type in C s symmetry, by GVB calculations. Some of the rotamers from these bent states are clearly saddle-points. The calculated vibration frequencies of the ground state have been compared with experiment.

Solution thermochemical study of ligand substitution reactions of hybrid alkyl/fluoroalkoxy phosphorus ligands in the L 2Fe(CO) 3 system

The enthalpies of reaction of (BDA)Fe(CO) 3 (BDA=(C 6H 5)CHCHC(O)CH 3, benzylideneacetone) with a series of novel fluorinated phosphine ligands, PR 2OR f (R=Ph, iPr, Cy; R f=(CH 2) 2(CF 2) 5CF 3) and (R fO) 2PCH 2CH 2P(OR f) 2 (dOR fpe), leading to the formation of L 2Fe(CO) 3 complexes (L=PR 2OR f) have been measured by solution calorimetry in THF at 50°C. Remarkably, reaction enthalpies are essentially invariant over this series of ligands, despite the differing steric and electronic properties of the phosphorus ligands. Carbonyl stretching frequencies help in the estimation of useful electronic parameters associated with the novel phosphorus ligand series.

C–S, C–H, and N–H bond cleavage of heterocycles by a zero-valent iron complex, Fe(N 2)(depe) 2 [depe=1,2-bis(diethylphosphino)ethane

Treatment of Fe(N 2)(depe) 2 [depe=1,2-bis(diethylphosphino)ethane] ( 1) with benzo[ b]thiophene at room temperature results in the regioselective C–S and C–H bond cleavages giving Fe(SC 6H 4CHC H)(depe) 2 ( 2a) and trans-FeH( CCHC 6H 4S )(depe) 2 ( 3a) in 72 and 19% yields, respectively. Complex 1 also reacts with thiophene, 2- and 3-acetylthiophenes and 2- and 3-methylthiophenes to give both C–S and C–H bond oxidative addition products: Fe(SCHCHCHC H)(depe) 2 ( 2b) and trans-FeH( CCHCHCHS )(depe) 2 ( 3b), Fe[SC(COMe)CHCHC H](depe) 2 ( 2c) and trans-FeH[ CCHCHC(COMe)S ](depe) 2 ( 3c), Fe[SC(Me)CHCHC H](depe) 2 ( 2d) and trans-FeH[ CCHCHC(Me)S ](depe) 2 ( 3d), and Fe[SCHC(Me)CHC H](depe) 2 ( 2e) and trans-FeH[ CCHC(Me)CHS ](depe) 2 ( 3e), respectively. On the other hand, only C–H bond cleavage takes place in the reactions of 1 with furans such as furan, benzo[ b]furan, and 2,3-dihydrofuran to give trans-FeH( CCHCHCHO )(depe) 2 ( 4a), FeH( CCHC 6H 4O )(depe) 2 ( 4b) and trans-FeH( CCHOCH 2C H 2)(depe) 2 ( 4c) and N–H bond is exclusively cleaved by the reaction of 1 with pyrroles such as pyrrole, indole and 2-acetylpyrrole to give trans-FeH( NCHCHCHC H)(depe) 2 ( 5a), trans- and cis-FeH( NCHCHC 6H 4)(depe) 2 ( 5b) and FeH[ NC(COMe)CHCHC H](η 2-depe)(η 1-depe) ( 6). Treatment of 2a with MeI results in the Fe–S bond cleavage of the thiaferracycle giving trans-FeI[( E)-CHCHC 6H 4-2-SMe](depe) 2 ( 7) whose structure is unequivocally characterized by X-ray analysis. In contrast, hydrogenolysis of 2a with H 2 (50 atm) leads to the cleavage of the Fe–C bond of the thiaferracycle to yield cis- and trans-FeH(SC 6H 4-2-Et)(depe) 2 ( 8).

The π-(Hydroxyalkenyl)germane Complexes Rh(acac){η2-(E)-Et3GeCHCHC(OH)R2}(PCy3) (R = Me, Ph) as Intermediates in the Hydrogermylation of Alkynols Catalyzed by Rh(acac)(cyclooctene)(PCy3)

The (hydroxyalkenyl)germanes (E)-R3GeCHCHC(OH)R‘2 (R = Et, Ph; R‘ = Me, Ph) are prepared in quantitative yield, and in a catalytic manner, by addition of germanes to the alkynols HC⋮CC(OH)R‘2 (R‘ = Me, Ph) in the presence of the complex Rh(acac)(cyclooctene)(PCy3). During the reactions four cycles are evident. They have as a common point the intermediates Rh(acac){η2-(E)-CH(GeR3)CHC(OH)R‘2}(PCy3), which have been isolated for R = Et and R‘ = Me, Ph.

Flow tube and theoretical study of proton transfer reactions of C 3H 5+ ions

The allyl, CH 2CHCH 2 +, and 2-propenyl, CH 3CCH 2 +, ions have been observed as distinct isomeric species in a flowing afterglow/selected ion flow drift tube (FA/SIFDT). Reaction with methanol is used as a diagnostic for distinguishing the two isomers. The isomeric ratio of allyl:2-propenyl formed via protonation of allene or propyne by a protonated base BH +, is shown to be dependent on the proton affinity of the base B. Proton transfer from H 3O + to allene produces the 2-propenyl cation only, whereas proton transfer from SO 2H + to allene generates a mixture of allyl and 2-propenyl cations, enabling us to estimate the barrier height for the rearrangement allyl → 2-propenyl as 110 ± 30 kJ mol −1. This is in accord with ab initio calculations performed at the G2(MP2) level of theory. The C 3H 5 + product of the reaction between C 2H 4 ·+ and C 2H 4 was identified as the 2-propenyl cation. Rate coefficients are also reported for reactions of the allyl and 2-propenyl cations with several neutrals.

On the heats of formation of methylketene, dimethylketene and related cations

Ab initio MO and DFT calculations up to the CCSD(T)/6-311++G(3df, 2p) level have been applied to the disagreement between theory and experiment concerning the standard enthalpies of formation of methylketene and dimethylketene. Our results confirm previous theoretical (G2) values, as well as the experimental proton affinities and ionization energies of both alkylketenes. A set of consistent values for Δ H f, 298 o are estimated as follow (kJ mol −1): CH 3CHCO: −68; CH 3CHCO ⋅+: 795; CH 3CH 2CO +: 618; (CH 3) 2CCO: −92; (CH 3) 2CCO ⋅+: 723 and (CH 3) 2CHCO +: 583. The proton affinities (kJ mol −1) are: PA(methylketene)=842 and PA(dimethylketene)=855. The persistent disagreement between the theoretical and experimental values appears to arise from an overestimation of the experimental heats of formation of CH 3CH 2CO +, CH 3CHCO ⋅+ and (CH 3) 2CCO ⋅+.

Kinetic study of the reaction of OH with a series of acetals at 298 � 4 K

Rate coefficients have been measured at 298 ± 4 K and 1000 mbar total pressure for the reactions of OH with a series of symmetrical acetals (ROCH2OR, R = C1 to C4) using a relative kinetic technique. The investigations have been performed in a laboratory photoreactor and also in the large outdoor EUPHORE simulation chamber facility in Valencia, Spain. The following rate coefficients (in units of 10−11 cm3 molecule−1 s−1) have been obtained: dimethoxy methane (R = CH3), 0.49 ± 0.02; diethoxy methane (R = CH3CH2), 1.84 ± 0.18; di-n-propoxy methane (R = CH3CH2CH2), 2.63 ± 0.49; di-iso-propoxy methane (R = (CH3)2CH), 3.93 ± 0.48; di-n-butoxy methane (R = CH3CH2CH2CH2), 3.47 ± 0.42; di-iso-butoxy methane (R = (CH3)2CHCH2), 3.68 ± 0.57; di-sec-butoxy methane (R = CH3CH2C(CH3)H), 4.68 ± 0.05. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 797–803, 1999

An unusual reaction of Rh(SbPh 3) 3(CO)Cl with propargyl halides: the formation of rhodiacyclopent-3-ene-2-one complexes

Reactions of Rh(SbPh 3) 3(CO)Cl ( 1) with PhCCCH 2X (X = Cl, Br, p-TolSO 3) and with HCCCH 2X (X = p-TolSO 3, PhSO 3) in CH 2Cl 2 at room temperature result in the formation of the propargyl complexes Rh(SbPh 3) 2( η 1-CH 2CCPh) (CO) (C1)X and the allenyl complexes Rh(SbPh 3) 2( η 1-CHCCH 2)(CO)(Cl)X, respectively. However, treatment of 1 with unsubstituted propargyl halides under similar conditions unexpectedly affords the rhodiacyclopent-3-ene-2-one complexes Rh(SbPh 3) 3( η 2-C(O)CHCXCH 2) Cl (X = Cl ( 5), Br ( 6)). The molecular structure of 5 was elucidated by an X-ray diffraction analysis of 5 · 1 /2CH 2Cl 2.

Synthesis and characterisation of alkynylacetal and alkynylaldehyde derivatives of Ni (II) and Fe(II) ; the X-ray crystal structure of Ni (η 5-C 5H 5) (PPh 3) CCCH (OEt) 2

Alkynylacetal derivatives of Ni(II) and Fe(II) were synthesised using CuI in Et 3N from equimolar amounts of HCCCH(OEt) 2 with Ni( η 5-C 5H 5)(PPh 3)Br or Fe( η 5-C 5H 5) (CO) 2Cl, respectively. Deprotection of the Ni(II) complex Ni( η 5-C 5H 5)(PPh 3)CCCH(OEt) 2 ( 1) with oxalic acid conveniently yields the alkynylaldehyde complex Ni( η 5-C 5H 5) (PPh 3)CCCHO ( 2), whereas the Fe(II) complex could not be isolated from Fe( η 5-C 5H 5)(CO) 2CCCH(OEt) 2 ( 3) under similar conditions. The crystal structure of 1 has been determined and represents the first structural characterisation of a metalloalkynylacetal. Principal dimensions include NiP, 2.1301 (10), 2.1376(10) Å, Ni C alkyne, 1.853(4), 1.840(4) Å, CC 1.194(5), 1.193(4) Å and PNiC alkyne 90.27(11), 90.90(10) °, in the two independent molecules A and B, respectively.

CH activation of methyl vinyl ketone in Ir(acac){ η2-CH 2CHC(O)CH 3}(PCy 3)

The cyclooctene complex Ir(acac)(cyclooctene)(PCy 3) ( 1) reacts with methyl vinyl ketone to give Ir(acac){ η 2-CH 2CHC(O)CH 3}(PCy 3) ( 2) and cyclooctene. In benzene at 70°C, complex 2 affords by means of an intramolecular CH activation process the thermodynamically favored alkenyl derivative I r(acac)H{(Z)-CHCHC(O )CH 3}(PCy 3) ( 3), which was isolated as a mixture of the isomers 3a (PCy 3 trans to carbonyl group of alkenyl ligand) and 3b (PCy 3 trans to acac). Isomers 3a and 3b do not react with tricyclohexylphosphine. However, the complex Ir(acac)H{( E)-CHCHC(O)CH 3}(PCy 3) 2 ( 4) can be obtained by treatment of 2 with the phosphine in benzene at 70°C. Complex 2 also reacts with HBF 4 at -78°C, to give the five-coordinate hydrido derivative [Ir(acac)H{ η 2-CH 2CHC(O)CH 3}(PCy 3)]BF 4 ( 5). In solution, complex 5 is only stable at temperatures lower than −40°C. At room temperature and in the presence of acetonitrile, it evolves into the alkyl compound [I r(acac){CH 2CH 2C(O )CH 3}(NCCH 3)(PCy 3)]BF 4 ( 6), as a result from the selective anti-Markovnikov insertion of the carboncarbon bond of the activated olefin into the IrH bond of the 5.