cas 593-75-9, METHYL ISOCYANIDE | Articles data

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Microwave spectrum and geometry of the methyl isocyanide-argon complex
The rotational spectrum of a complex formed between methyl isocyanide and argon has been observed using pulsed-nozzle, Fourier-transform microwave spectroscopy. The spectrum and geometry of the complex are very similar to those found for CH3CN...Ar (R. S. Ford et al., J. Chem. Phys., 1991, 94, 5306). The complex is T-shaped, with the argon atom located 3.64 A from the centre of mass of the methyl isocyanide molecule. There appears to be almost free internal rotation of the methyl isocyanide molecule about its symmetry axis in the complex.
Blanco, Susana,Lister, David G.,Legon,Rego, Christopher A.
p. 1287 - 1290
(1997)
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Tunneling Model for Hydrogen Abstraction Reactions in Low-Temperature Solids. Applications to Reactions in Alcohol Glasses and Acetonitrile Crysals
A simple and internally consistent quantitative model for hydrogen-abstraction reactions in low-temperature solids, which implicitly incorporates zero point energy effects which allow for finite reaction rates at T=0 K, is derived and applied to new measurements of H-abstraction rate constants by methyl radicals in methanol and ethanol glasses at T=13-99 K and in acetonitrile and methyl isocyanide crystals at 69-128 K.Nonlinear least-squares fits of the model to the experimental data yield effective one-dimensional barriers to reaction whose heights are virtually independent of the analytic form used for the potential energy barrier, and are somewhat larger than the activation energies measured for the corresponding reactions in the gas phase.This model predicts that values of the isotopic rate constant ratio kH/KD will be larger than 1012 at T=0 K.
Roy, Robert J. Le,Murai, Hisao,Williams, Ffrancon
p. 2325 - 2334
(1980)
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Isomers of C2H4N+ and the Proton Affinities of CH3CN and CH3NC
The relative proton affinities of CH3CN (acetonitrile) and CH3NC (methyl isocyanide were determined by using the Selected Ion Flow Tube technique.Two distinct species were observed for the C2H4N+ ion: one produced from CH3CN and one from CH3NC.The two C2H4N+ isomers were readily distinguished in the flow tube by their different reactivity.The association product, C2H4N+, of the ion-molecule reaction between CH3+ and HCN was shown to be present in both isomeric forms in the ratio 85percent protonated acetonitrile and 15percent protonated methyl isocyanide.
Knight, J. S.,Freeman, C. G.,McEwan, M. J.
p. 1404 - 1408
(1986)
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Single photon ionization of methyl isocyanide and the subsequent unimolecular decomposition of its cation: Experiment and theory
Methyl isocyanide, CH3NC, is a key compound in astrochemistry and astrobiology. A combined theoretical and experimental investigation of the single photon ionization of gas phase methyl isocyanide and its fragmentation pathways is presented. Vacuum ultraviolet (VUV) synchrotron radiation based experiments are used to measure the threshold photoelectron photoion coincidence (TPEPICO) spectra between 10.6 and 15.5 eV. This allowed us to experimentally determine the adiabatic ionization energy (AIE) and fragment ion appearance energies (AE) of gas-phase methyl isocyanide. Its AIE has been measured with a precision never achieved before. It is found to be AIEexp = 11.263 ± 0.005 eV. We observe a vibrational progression upon ionization corresponding to the population of vibrational levels of the ground state of the methyl isocyanide cation. In addition, four fragment ion appearance energies (AEs) were measured to be AE (m/z 40) = 12.80 ± 0.05 eV, AE (m/z 39) = 13.70 ± 0.05, AE (m/z 15) = 13.90 ± 0.05 eV, AE (m/z 14) 13.85 ± 0.05 eV, respectively. In order to interpret the experimental data, we performed state-of-the-art computations using the explicitly correlated coupled cluster approach. We also considered the zero-point vibrational energy (ZPVE), core-valence (CV) and scalar relativistic (SR) effects. The results of theoretical calculations of the AIE and AEs are in excellent agreement with the experimental findings allowing for assignment of the fragmentations to the loss of neutral H, H2, CN and HCN upon ionization of CH3NC. The computations show that in addition to the obvious bond breakings, some of the corresponding ionic fragments result from rearrangements-upon photon absorption-either before or after electron ejection.
Bellili,Gouid,Gazeau,Bénilan,Fray,Guillemin,Hochlaf,Schwell
p. 26017 - 26026
(2019)
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Potentially prebiotic activation chemistry compatible with nonenzymatic RNA copying
The nonenzymatic replication of ribonucleic acid (RNA) may have enabled the propagation of genetic information during the origin of life. RNA copying can be initiated in the laboratory with chemically activated nucleotides, but continued copying requires a source of chemical energy for in situ nucleotide activation. Recent work has illuminated a potentially prebiotic cyanosulfidic chemistry that activates nucleotides, but its application to nonenzymatic RNA copying had not been demonstrated. Here, we report a novel pathway that activates RNA nucleotides in a manner compatible with template-directed nonenzymatic copying. We show that this pathway, which we refer to as bridge-forming activation, selectively yields the reactive imidazolium-bridged dinucleotide intermediate required for copying. Our results will enable more realistic simulations of RNA propagation based on continuous in situ nucleotide activation.
Zhang, Stephanie J.,Duzdevich, Daniel,Szostak, Jack W.
p. 14810 - 14813
(2020)
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Pressure Dependence of the Laser-Initiated Isomerization of Methyl Isocyanide
The infrared laser-induced isomerization of methyl isocyanide has been investigated and found to exhibit a marked pressure dependence; i.e., for a given set of conditions, there exists a sharp threshold pressure above which there is massive isomerization.In the subthreshold region, it has been determined that the yield depends exponentially on the pressure for a multimode beam.Since other authors have suggested that this laser-induced reaction is a thermal explosion, we have also carried out a numerical simulation of this system as a thermal explosion.Both the experimental and theoretical results are presented, and the results show that the thermal explosion model does not fit the experimental data.
Shultz, M. J.,Rock, Elizabeth J.,Tricca, Robert E.,Yam, Loretta M.
p. 5157 - 5162
(1984)
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A Light-Releasable Potentially Prebiotic Nucleotide Activating Agent
Investigations into the chemical origin of life have recently benefitted from a holistic approach in which possible atmospheric, organic, and inorganic systems chemistries are taken into consideration. In this way, we now report that a selective phosphate activating agent, namely methyl isocyanide, could plausibly have been produced from simple prebiotic feedstocks. We show that methyl isocyanide drives the conversion of nucleoside monophosphates to phosphorimidazolides under potentially prebiotic conditions and in excellent yields for the first time. Importantly, this chemistry allows for repeated reactivation cycles, a property long sought in nonenzymatic oligomerization studies. Further, as the isocyanide is released upon irradiation, the possibility of spatially and temporally controlled activation chemistry is thus raised.
Mariani, Angelica,Russell, David A.,Javelle, Thomas,Sutherland, John D.
supporting information
p. 8657 - 8661
(2018/07/15)

Synthesis and structure–activity relationship of α-keto amides as enterovirus 71 3C protease inhibitors
α-Keto amide derivatives as enterovirus 71 (EV71) 3C protease (3Cpro) inhibitors have been synthesized and assayed for their biochemical and antiviral activities. structure–activity relationship (SAR) study indicated that small moieties were primarily tolerated at P1' and the introduction of para-fluoro benzyl at P2 notably improved the potency of inhibitor. Inhibitors 8v, 8w and 8x exhibited satisfactory activity (IC50= 1.32 ± 0.26 μM, 1.88 ± 0.35 μM and 1.52 ± 0.31 μM, respectively) and favorable CC50values (CC50> 100 μM). α-Keto amide may represent a good choice as a warhead for EV71 3Cproinhibitor.
Zeng, Debin,Ma, Yuying,Zhang, Rui,Nie, Quandeng,Cui, Zhengjie,Wang, Yaxin,Shang, Luqing,Yin, Zheng
supporting information
p. 1762 - 1766
(2016/12/22)

2,3-Dihydroimidazol-2-ylidene
Irradiation of imidazole-2-carboxylic acid (3) - matrix-isolated in argon at 10 K - with a wavelength of 254 nm leads to decarboxylation and the formation of a complex between 2,3-dihydroimidazol-2-ylidene and carbon dioxide (1·CO2). Upon irradiation of 2,3-dihydroimidazol-2-ylidene (1) with λ = 254, 193, and 185 nm no imidazole can be detected. On the other hand flash vacuum pyrolysis of imidazole-2-carboxylic acid (3) produces imidazole and carbon dioxide. 2,3-Dihydroimidazol-2-ylidene (1) - the possible intermediate - cannot be trapped under these conditions.
Maier, Guenther,Endres, Joerg
p. 1517 - 1520
(2007/10/03)

Internal excitation in the products of nucleophilic substitution from the dissociation of metastable ion complexes
The relative kinetic energy distributions for the products of the dissociation of four metastable gasphase ion clusters have been analyzed by means of ion kinetic energy spectroscopy, and the results modeled using statistical phase space theory. The systems studied represent reaction intermediates in bimolecular nucleophilic substitutions (S(N)2). These studies build on previous investigations that demonstrated vibrational excitation in the products of the substitution reactions of halide ions with methyl halides. The present studies explore the effects of molecular structure, reaction exothermicity, and nucleophile and leaving group variation. The experimental kinetic energy distributions are compared with theoretical distributions calculated for statistical partitioning of energy among internal modes and relative kinetic energy of the products. In each reaction, the calculated distributions agree with the experimental distributions only if a significant fraction of the energy released in the exothermic reactions is assumed to be unavailable for randomization in the dissociation. The results suggest that the products of these S(N)2 reactions are internally excited.
Graul, Susan T.,Carpenter, Catherine J.,Bushnell, John E.,Van Koppen, Petra A. M.,Bowers, Michael T.
p. 6785 - 6796
(2007/10/03)

A Novel Route to Racemic and Nonracemic Products of the Ugi Reaction: Synthesis of Ugi's Labile α-Adducts from Iminoaziridines and Carboxylic Acids, and Their Transformations
Iminoaziridines (11) are highly reactive synthetic equivalents for three of the four components in the Ugi four-component condensation.Thus, iminoaziridines react rapidly with carboxylic acids at temperatures as low as -20 deg C to afford α-amino isoimides (14), which are identical to the elusive α-adducts of isocyanides in the Ugi reaction. 1,4-Migration of the acyl group (O -> α-N) in 14 furnishes the α-acylamino amides 15.Very little, if any, racemisation is observed when carboxylic acids react with nonracemic iminoaziridines , which are readily available.Mumm rearrangement by O -> N-acyl 1,3-migration to afford α-amino imides (16e,f) competes if the O -> α-N 1,4-shift is slowed down by steric hindrance.The latter acyl shift is catalysed by carboxylic acids while the former is not.The iminoaziridines (R)-11a,c react quantitatively and without racemisation with hydrazoic acid to produce the 5-aminoalkyltetrazoles (R)-21a,c. - Keywords: aziridines; imides; isoimides; rearrangements; Ugi reaction
Quast, Helmut,Aldenkortt, Sven
p. 462 - 469
(2007/10/03)

Synthesis and Thermal Reorganisations of Iminoaziridines. Ab Initioo Calculations of Their Transition States, of Diazatrimethylenemethanes, and Some Cyclic Members of the C2H4N2 Potential-Energy Hypersurface
2-Iminoaziridine 19 and the pairs of isomers 22/23 and 32/33 can be obtained in high yields by base-induced 1,3-dehydrohalogenation of the corresponding α-halo amidines.Regioselectivity of the ring closure reaction of 21 is achieved by treatment with potassium hydride as base in the presence of 18-crown-6 to afford almost exclusively 23.At low temperatures, the cyclisation of 21a under the influence of potassium tert-butoxide occurs diastereoselectively yielding (Z)-22 and (Z)-23 (87:13).Resolution of racemic 21a can be attained by single recrystallisation of the nicely crystallised mandelates of the like configuration, thus providing an efficient route to (R)- and (S)-23 of high enantiomeric purity.Chiroptical data are reported for 21a and 23. - (E)- and (Z)-22 equilibrate faster by more than one order of magnitude than (E)- and (Z)-23 but almost the same preference for the E diastereomer is found in both cases. - Only first-order decomposition into isocyanides 6 and imines is observed on thermolysis of 19, 22, 23, and 32 with activation parameters depending on the substitution pattern.In contrast, the thermal valence isomerisation 35 -> 36 is fast enough to complete with the cycloreversion of 35.Thermal racemisation of (R)-23 does not occur.Quantum-chemical calculations were performed on the parent iminoaziridines (E)- and (Z)-38, 3-amino-2H-azirine (39), the methylenediaziridines cis- and trans-40, and diastereomeric closed-shell and open-shell planar (41) and (open-shell) "mono-orthogonal" diazatrimethylenemethanes 42, 43.Complete geometry optimisations were appropriately performed with the RHF/6-31+G** and the UHF/6-31+G** basis sets.Energies of the closed-shell states were calculated on the RHF, MP2, MP4SDTQ, and CCSD(T) levels, those of open-shell states on the UHF, UMP2, UMP4SDTQ, and CCSD(T)/UHF levels. - (E)-38, being lowest in energy of the parent iminoaziridines (Erel = 0.0), equilibrates with (Z)-38 via an almost linear transition state (Erel = 113.4 kJ mol-1) and decomposes into hydrogen isocyanide and formaldimine in a one-step cheletropic process rel = 179.8 kJ mol-1, CCSD(T)/RHF> with a highly unsymmetrical transition state in which the N1-C2 bond is almost completely broken whereas the C2-C3 bond is still strong.The same is true for the cheletropic decomposition of (Z)-38 the transition state of which (Erel = 168.2 kJ mol-1) is even lower by 11.6 kJ mol-1. - Energy-rich zwitterionic transition states are found with the RHF method among which 1A'-(E,Z)-41 is lowest in energy rel = 203.0 ... - Keywords: Aziridines, 2-imino-, chiral, non-racemic; Amidines, N,N'-dialkyl-2-halo-; 1,3-Dehydrohalogenation, regioselectivity and diastereoselectivity of; E/Z Diastereomerisation; Cycloreversion of isocyanides and imines; Valence isomerisation; Calculations, high-level ab initio, RHF, UHF, MPn, CCSD(T); 2H-Azirine, 3-amino; Diaziridine, 3-methylene; Diazatrimethylenemethanes, diastereomeric, closed-shell and open-shell; Reorganisations, transition states of thermal
Quast, Helmut,Aldenkortt, Sven,Schaefer, Peter,Schmitt, Edeltraud,Wuerthwein, Ernst-Ulrich
p. 2171 - 2188
(2007/10/03)

Chemistry of α-Amino Nitriles. Exploratory Experiments on Thermal Reactions of α-Amino Nitriles
The paper extends a previously published report on chemical properties of α-amino nitriles and of members of the C3H4N2 ensemble (Scheme 1) as observed in experiments carried out under non-aqueous conditions.The reactions investigated and the observations made are summarized in some detail in the English footnotes (*) referring to Schemes 1-17 and Fig. 1.
Xiang, Yi-Bin,Drenkard, Susanne,Baumann, Karl,Hickey, Deirdre,Eschenmoser, Albert
p. 2209 - 2250
(2007/10/02)

REACTION OF 1,1,3,3-TETRACHLORO-2-METHYL-2-AZAPROPANE WITH o-PHENYLENEDIAMINE
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Guseinov, F. I.,Khairullin, R. A.,Kharlamova, A. G.,Moskva, V. V.
p. 847 - 848
(2007/10/03)

Synthesis and Thermolysis of a Chiral, Non-Racemic Iminoaziridine
The 2-halo imidoyl chlorides 7 are obtained from the amide 5 and the 2-halo amides 6 by the action of phosphorus pentachloride and thionyl chloride, respectively.Non-racemic (S)-6a is converted into 7a which is racemic, however.The reaction of Lawesson's reagent with 6a furnishes the diasteromeric 1,3,2-thiazaphospholidine derivatives 15.Treatment of (S)-6a (98percent ee) with methyl triflate affords 2-chloro imidate 8 (95percent ee) which reacts with methanamine in the presence of methanammonium chloride to yield the 2-chloro amidine (S)-9a (90percent ee).The 2-halo imidoyl halides 7a and b react with methanamine to produce the 2-halo amidines 9a and b. - Strong bases, e.g. potassium tert-butoxide or sodium hydride in the presence of catalytic amounts of tert-butyl alcohol, eliminate hydrogen chloride or bromide from the 2-halo amidines 9a and b and (S)-9a to yield mixtures of the 2-iminoaziridines (E)- and (Z)-4, and (E,R)- and (Z,R)-4 (83percent ee), respectively.The 1,3-elimination of hydrogen bromide from 9b is diastereoselective at -30 to -40 deg C 90>.The diastereomers equilibrate at 36 deg C with (kEZ + kZE) = (5.92+/-0.08)*1E-5 s-1 (K = kEZ/kZE = 0.428 +/- 0.013). - The thermolysis of (E)- and (Z)-4 in 6>benzene solution yields the imine 16 and methyl isocyanide (17).The decomposition follows the first-order rate law.The following Arrhenius and Eyring parameters are calculated from five rate constants obtained in the temperature range of 70-110 deg C.Ea = (115.2 +/-0.4) kJmol-1, lgA = (12.06 +/- 0.28), ΔH(excit.) = (112.1 +/- 0.4) kJmol-1, ΔS(excit.) = (-23.9 +/- 0.7) JK-1 mol-1, ΔG(excit.) 373K = 121 kJmol-1.The enantiomeric excess of the surviving fraction of (E,R)- and (Z,R)-4 is unchanged after two half-lives at 80 deg C. - Key Words: Aziridines, 2-imino-, chiral, non-racemic / Imidoyl halides, 2-halo / Imidates, 2-chloro / 1,3,2-Thiazaphospholidines / Amidines, 2-halo / 1,3-Elimination, inversion of configuration in / E/Z Diastereomerization / Cycloreversion, kinetics of thermal
Quast, Helmut,Aldenkortt, Sven,Heller, Eberhard,Schaefer, Peter,Schmitt, Edeltraud
p. 1699 - 1706
(2007/10/02)

Synthesis of L-histidine specifically labelled with stable isotopes
(2'-13C)-, (1'-15N)- and (3'-15N)-L-Histidine were prepared according to a synthetic scheme that allows the 13C or 15N labelling of all carbon and nitrogen positions or any combination of positions.A 1,5-disubstituted imidazole ring was constructed via condensation of tosylmethyl isocyanide with 3-phenylpropenal and subsequent cycloaddition of benzylamine.The imidazole intermediate was converted into 1-benzyl-5-(chloromethyl)-imidazolium chloride which was coupled to a glycine moiety via an enantioselective coupling with the bislactim ether of cyclo-D-valylglycine.Deprotection of the coupling product afforded L-histidine in high optical purity.Syntheses for the isotopically labelled synthons were developed starting from simple, comercially available, highly enriched compounds.The labelled L-histidines were characterized by mass spectrometry and 1H-, 13C- and 15N-NMR spectroscopy.
Cappon, J. J.,Witters, K. D.,Baart, J.,Verdegem, P. J. E.,Hoek, A. C.,et al.
p. 318 - 328
(2007/10/02)

Hydrogen Cyanide N-Methylide: Preparation, Spectroscopic Identification, and Its Relationship to Other C2H3N Isomers
With the intention of isolating 1H-azirene (8) we studied several precursors which should offer an entry into the C2H3N potential energy hypersurface.It was found that in addition to the known isomers 1, 2, 3, and 6 hydrogen cyanide N-methylide (5) - and probably aminoacetylene (4) - can be detected in an argon matrix at 10 K.No spectroscopic evidence for the formation of 1H-azirene (8) was found.In other words, the first six members 1-6 are now all identified.The elucidation of the structure of the new C2H3N species is based on the comparison of the observed IR spectra with those calculated by ab initio methods. - Key Words: Matrix isolation/ Calculations, ab initio/ Flash pyrolysis/ Photochemistry/ Hydrogen cyanide N-methylide
Maier, Guenther,Schmidt, Christiane,Reisenauer, Hans Peter,Endlein, Edgar,Becker, Dieter
p. 2337 - 2352
(2007/10/02)

Photooxygenation of 1,4-Diaza-1,3-butadienes (α-Diimines): Formation of Isonitriles
Dye-sensitized photooxygenations of cyclic and acyclic 1,4-diaza-1,3-butadienes (α-Diimines), carrying a methyl or an ethyl group in the 2-position, yield isonitriles and amides, as well as formaldehyde or acetaldehyde.Thus, cyclic α-diimines such as 5,6-dimethyl- (1a), 5-methyl-6-phenyl- (1b), 5-methyl-6-(p-tolyl)- (1c), and 5,6-diethyl-2,3-dihydropyrazine (1d) yield the respective 1-isocyano-2-(acylamino)ethanes 2a-d, whereas 5-isopropyl-6-phenyl- (1e) and 5,6-diphenyl-2,3-dihydropyrazine (1f) are inert toward photooxygenation.Acyclic α-diimines such as 1,8-bis(acetylamino)-3,6-diaza-4,5-dimethyl-3,5-octadiene (4a), 2,5-diaza-3,4-dimethyl-2,4-hexadiene (4b), 1,4-diaza-2,3-dimethyl-1,4-diphenyl-1,3-butadiene (4c), and N,N'-bis-2,3-butanediimine (4d) afford the respective isonitriles 5a-d and acetamides 6a-d.With retention of configuration, chiral α-diimines such as (-)-N,N'-bis-2,3-butanediimine and its R,R enantiomer , and (3S,8S)-(-)-3,8-dicarbomethoxy-4,7-diaza-2,5,6,9-tetramethyl-4,6-decadiene yield the corresponding enantiomerically pure isonitriles (S)-5e, (R)-5e, and (S)-5f and acetamides (S)-6e, (R)-6e, and (S)-6f.Evidence for a singlet oxygen reaction is presented.A working hypothesis is proposed which includes the formation of a transient hydroperoxide 7 that fragments into an isonitrile molecule, an aldehyde, and an N-alkyl- or N-arylnitrilium cation and a hydroxide ion; the latter combine to yield the amide groups in 2a-d and the amide compounds 6a-f.
Gollnick, Klaus,Koegler, Sigrid,Maurer, Dorothee
p. 229 - 234
(2007/10/02)

Retention of Configuration in Two Photochemical Reactions: Formation of Cyclopropanimines by Extrusion of Molecular Nitrogen from Tetraalkyl-4-imino-1-pyrazolines and Cycloreversion of Cyclopropanimines to Isocyanides and Alkenes
The 1-pyrazolin-4-ones 7 and 9 and the pyrazolidin-4-one 13 are condensed with alkanamines 8 to produce the imines 3, 10 and 12 in high yields.Direct irradiation of 3 with 350-nm light at 90 deg C in deuterated hydrocarbon solvents affords the cyclopropanimines 4 in almost quantitative yields besides molecular nitrogen and small amounts of the imines 12 as a result of photoreduction.In acetone, the cyclopropanimine 4b isomerizes in part of the α,β-unsaturated imine 14.Direct irradiation of 3 with the unfiltered light of the high-pressure mercury lamp results in quantitative cycloreversion of the primary photoproducts 4 into the alkene 6 and an isocyanide 5.At low temperature (10 deg C), photolysis of 3 occurs much more slowly giving rise to photoextrusion of nitrogen (-> 4) and photoreduction (-> 12) to about the same extent. - Photolysis of the stereochemically labelled iminopyrazolines cis- and trans-10 (d. e. 99percent) at 90 deg C produces the cyclopropanimines cis- and trans-16 (d. e. 94percent) with high stereospecifity.The configuration of cis- and trans-16 is established by a comparison with the corresponding methylenecyclopropanes cis- and trans-19 and the quantitative and completely stereospecfic cycloreversion into methyl isocyanide (5a) and the 3,4-dimethyl-3-hexenes (Z)- and (E)-17 on irradiation with the unfiltered light of the mercury arc.The necessity of thermal activation for efficient nitrogen extrusion from the 1(n, ?*) state of 3 and 10 is indicative of a considerable energy barrier towards the transition into a dissociative state.At low temperature, hydrogen abstraction from the solvent or other molecules becomes important for the deactivation of the 1(n, ?*) state, in addition to decay and fluorescence.The stereospecific formation of cis- and trans-16 is interpreted in terms of diastereomeric bis-orthogonal azatrimethylenemethane diradicals as intermediates which retain the configuration on cyclization.The minor non-stereospecific path may involve mono-orthogonal azatrimethylenemethane diradicals.Thus, mechanisms that involve the same types of diradical intermediates can rationalize the photolysis of the iminopyrazolines 3, 10 and of the methylenetriazoline 1 as well.The cycloreversion of cis- and trans-16 into the alkenes (Z)- and (E)-17 and methyl isocyanide (5a) demonstrates for the first time that such photoreactions can be entirely stereospecific. Key Words: 4H-pyrazoles, 3,3,5,5-tetraalkyl-4-imino-3,5-dihydro- / cyclopropanes, 2,2,3,3-tetraalkyl-1-(alkylimino)- / alkanamines, 2,2,3,3-tetraalkylcyclopropylidene- / photolysis / extrusion of molecular nitrogen / photoreduction / configuration, retention of / azatrimethylenemethanes / cycloreversion, stereospecific, photochemical
Quast, Helmut,Fuss, Andreas,Heublein, Alfred,Jakobi, Harald,Seiferling, Bernhard
p. 2545 - 2554
(2007/10/02)

Roles of bridging ligand π-acidity in determining the nature of the lowest excited states of binuclear complexes of nickel(0). Ligand-centered (M2 → μ-LCT), metal-centered (μ-L → M2CT), and intraligand (IL) lowest excited states for the series of complexes Ni2(μ-L)(CNMe)2(PPh2CH2PPh ...
Full title: Roles of bridging ligand π-acidity in determining the nature of the lowest excited states of binuclear complexes of nickel(0). Ligand-centered (M2 → μ-LCT), metal-centered (μ-L → M2CT), and intraligand (IL) lowest excited states for the series of complexes Ni2(μ-L)(CNMe)2(PPh2CH2PPh 2)2 (L = CNR, CNMe(R)+, NO+). The spectroscopy and photochemistry of the series of binuclear Ni(0) complexes Ni2(μ-L)(CNMe)2(dppm)2 (dppm = bis(diphenylphosphino)methane) with either bridging isocyanide ligands (L = CNMe (1), CNC6H5 (2), CN-p-C6H4Cl (3), CN-p-C6H4Me (4)), bridging aminocarbyne ligands (L = CNMe(C5H11)+ (5), CNMe2+ (6), CNMe(CH2Ph)+ (7), CNMe(H)+ (8), CNMe(Ph)+ (9)), or bridging NO+ (10), have been examined. Bridging-ligand substituent effects and solvent dependence of the lowest energy electronic absorption bands of the isocyanide complexes, 1-4, have been interpreted in terms of dimetal to bridging ligand charge transfer (M2 → μ-LCT). This assignment is supported by results of extended Hu?ckel calculations, which indicate a LUMO of predominantly μ-isocyanide π* character. Bridging-ligand substituent effects on the lowest energy electronic absorption spectral bands of the related aminocarbyne complexes, 5-9, indicate that the direction of charge transfer is reversed compared to the case of the isocyanide complexes. The lowest excited states of the aminocarbyne complexes, 5-9, are assigned to bridging ligand to dimetai charge transfer (μ-L → M2CT). This assignment is supported by extended Hu?ckel calculations, which indicate a LUMO of predominantly Ni-Ni antibonding character for the aminocarbyne complexes. The μ-nitrosyl complex [Ni2(μ-NO)(CNMe)2(dppm)2][PF6] (10) has also been studied. The molecule possesses a structure similar to 1 and 8. Photochemical reactivity as well as extended Hu?ckel calculations indicates an intraligand (IL) lowest excited state for 10. Only the M2 → μ-LCT excited state of the μ-isocyanide complexes was found to participate in bimolecular photochemistry. Photolysis of 1 in the presence of CO2 (1 atm) leads to the [2 + 2] photocycloaddition of CO2 to the μ-CNMe ligand of 1 and the complex Ni2(μ-CN(Me)C-(O)O)(CNMe)2(dppm)2 (11). The degree of metal-metal interaction in complexes 1, 8, and 10 was found to be related to the Lewis acidity of the bridging ligand. Extended Hu?ckel calculations indicate that the decreasing π* energies for the series of bridging ligands CNMe, CN(H)Me+, and NO+ decrease the ground-state contribution of a metal-metal dπ* orbital, resulting in increased Ni-Ni interactions. The relative μ-L π* and Ni-Ni dπ* energies also control the nature of lowest excited states as M2 → μ-LCT, μ-L → M2CT, and IL for μ-L = CNR, CNMe(R)+, and NO+, respectively.
Ratliff,DeLaet,Gao,Fanwick,Kubiak
p. 4022 - 4027
(2008/10/08)

Gas-Phase Thermolysis of 4-substituted 3,5-Dihydro-3,3,5,5-tetramethyl-4H-pyrazoles Studied by Photoelectron Spectroscopy and Flash Vacuum Pyrolysis
Gas-phase thermolysis of the 3,5-dihydro-4H-pyrazoles 1-4 have been studied by photoelectron spectroscopy and flash vacuum pyrolysis.In the PE-controlled thermolysis, 1-4 extrude molecular nitrogen, and the fragments cyclize immediately to different three-membered rings.In the case of 2 and 3, the former 4-substituent becomes part of the three-membered ring, whereas 1 and 4 afford short living oxo- and iminocyclopropanes.At higher temperatures and in flash vacuum pyrolysis, acyclic compounds and smaller molecules are formed in a second step.Based on MNDO, AM1, and PM3 calculations, the ionization potentials of 3,5-dihydro-3,3,5,5- tetramethyl-4-methylene-4H-pyrazole (3) have been assigned to molecular orbitals.To aid the identificaion of the pyrolysis products, PE spectra of the methylenethiirane 9 and the methylenecyclopropanes 11 and 13 have been measured and interpreted with the aid of SCF calculations.
Kindermann, Markus K.,Poppek, Rainer,Rademacher, Paul,Fuss, Andreas,Quast, Helmut
p. 1161 - 1168
(2007/10/02)

Synthesis and Photolysis of 1,4,4-Trialkyl-4,5-dihydro-5-imino-1H-1,2,3-triazoles. - Regio- and Diastereoselective Formation of (Z)-Aziridinimines
The novel 5-iminodihydro-1,2,3-triazoles 14 are synthesized from the 5-isopropylidenedihydrotetrazole 11 through a ring transformation involving cycloaddition and cycloreversion of alkyl azides 12.Thus, cycloaddition of 11 and 12 produces high yields of the spiro compounds 13.On thermolysis at 120-130 deg C, the latter undergo clean cycloreversion into methyl azide (12a) and the iminodihydro-1,2,3-triazoles 14, which exists as mixtures of diastereomers, e. g. (E)-/(Z)-14a = 95 : 5, or as a single stereoisomer (E)-14c.When toluene solutions of 14 are irradiated (λ >/= 280 nm) at -60 deg C, the configuration of the products is under kinetic control.Irradiation of 14a affords a quantitative yield of the aziridinimines (E)- and (Z)-15a (11 : 89) besides molecular nitrogen.In order to allow the distinction between the least-motion and the non-least-motion path of product formation, the photolysis of iminodihydro-1,2,3-triazoles is studied which are labelled at N-1 by a deuterated methyl group (14b) or a neopentyl group (14c).Neither photolysis (λ >/= 280 nm) nor heating to 120 to 130 deg C induces any scrambling of the alkyl groups attached to N-1 and the exocyclic nitrogen atom of 14b and c.The major product from (E)-/(Z)-14b (84percent) is formed by the non-least-motion path leading diastereoselectively to (Z)-15b, while the least-motion products (E)- and (Z)-17b (16percent) exhibit a diastereomeric ratio of 3 : 1.Very similar results are obtained on photolysis of (E)-14c, except that the least-motion product (15percent) arises only in a single configuration .In the non-least-motion products (Z)-15b,c, the geometry of the group, fixed by the ring in 14b,c, is completely retained.Therefore, the (Z) diastereoselectivity is interpreted in terms of a one-bond cleavage leading to diazenyl-1,3-diazaallyl diradicals 22 having lifetimes too short for changes of their configuration which is determined by the stucture of the precursor.
Quast, Helmut,Regnat, Dieter
p. 2195 - 2202
(2007/10/02)

Thermolysis of 5-Alkylidene-1,4-dihydro-5H-tetrazoles
In benzene solution at 100 deg C, the isopropylidenedihydrotetrazole 1a decomposes mainly (80percent) into molecular nitrogen and the aziridinimines (E)- and (Z)-2a which are thermally unstable and afford methyl isocyanide and the imine 3a.In addition, the novel spirocyclic tetrahydropyrimidine 7a is formed (18percent yield) in a cycloaddition of 1a and the hypothetical intermediate 1,3-diazabutadiene 19a generated from 1a through a hydrogen shift and loss of molecular nitrogen.The thermolysis of the neopentylidenedihydrotetrazole 1b at 100 deg C is more complex.Only small amounts of the aziridinimines (E)- and (Z)-2b and their decomposition products 3b and methyl isocyanide are observed.A major product is the spirocyclic tetrahydropyrimidine 7b which exhibits moderate thermal stability.Slow thermolysis of 7b affords the tetrahydropyrimidinimine 8b and methyl azide.The latter reacts with 1b in a cycloaddition furnishing the spiro compound 5b which partially decomposes into the amino-1,2,3-triazole 16, thus regenerating methyl azide.This catalyzed isomerization 1b -> 16 which is initiated through the thermal cycloreversion of 7b involves a total of 19percent of 1b.The structures of the products are elucidated by means of mass spectra and high-field NMR spectra.The mechanism of formation of the 1,3-diazabutadienes 19 from 1 is discussed.
Quast, Helmut,Bieber, Lothar,Regnat, Dieter
p. 1739 - 1747
(2007/10/02)

Gas- Phase Ion Chemistry of Siloxide and Silamide Ions by Using the Flowing Afterglow. Unusual Rearrangements Involving SiO and SiS Bond Formation
Siloxide ions undergo O/S exchange reactions with suitable sulfur-containing neutrals, e.g.H3SiO- + CS2 -> H3SiS- + COS.Silamide ions similarly undergo NR/O and NR/S exchange reactions together with nucleophilic displacement reactions, e.g.: .No simple correlation between rate and mechanism is observed for all the studied reactions.
O'Hair, Richard A.J.,Sheldon, John C.,Bowie, John H.,Damrauer, Robert,DePuy, Charles H.
p. 489 - 496
(2007/10/02)

Reaction of the Metallacycle n)S>(1+) with Nucleophiles. X-Ray Crystal Structures of the Comlexes n)S>SO3CF3 and SC(FeLn)S>n = Fe(cp)(CO)2, cp = η-C5H5>
Reactions of the metallacyclic cation n)S>(1+)n = Fe(cp)(CO)2, cp = η-C5H5> with nucleophilic agents have been investigated.The results indicate that the carbene carbon atom bonded to the endocyclic iron is the site of addition of all the nucleophiles examined.Primary amines NH2R (R = Me, C6H11, or n-Bu) form neutral isocyanide derivatives n> with opening of the FeC2S2 ring, whereas secondary amines such as NHR2 (R = Me or Et) or HN(CH2)nCH2 (n = 3 or 4) produce stable cationic cyclic aminothiocarbenes.The structure of one of these, n)S>SO3CF3, has been determined by X-ray diffraction a = 11.570(2), b = 12.242(2), c = 10.552(2) Angstroem, α = 104.60(2), β = 87.51(1), γ = 117.24(2) deg, Z = 2, and space group P1>.The cation contains the five-membered planar ring FeSCSC with the Fe(cp)(CO)2 and NC5H10 groups bonded to the carbon atoms.The C(carbene)-N interaction exhibits strong double-bond character , typical for an iminium cation.Methanethiol, Li(BHEt3), and KCN yield neutral n)S> (X = SMe, H, or CN).In the hydride addition an isomeric mixture has been ascertained by i.r. and n.m.r. spectra, whereas the cyanide ion adds steroselectively at the prochiral carbene centre to form only one diastereoisomer whose steric nature has been determined by X-ray diffraction a = 6.894(2), b = 10.057(1), c = 14.520(2) Angstroem, α = 96.00(2), β = 96.17(1), γ = 106.31(1) deg, Z = 2, and space group P1>.In this derivative the FeSCSC ring undergoes substantial changes because the iron-bonded carbon atom becomes four-co-ordinate with loss of its carbenic character and significant out-of-plane displacement.A comparative analysis of the relevant geometric features of all the members of this family is reported.Propane-1,3-dithiol produces the neutral spirocyclic SC(FeLn)S> which shows equivalence of the two diastereotopic SCH2 carbons in the high-temperature 13C n.m.r. spectrum and splitting of ν(CO) in the i.r. spectrum.These spectroscopic features are discussed and interpreted.
Busetto, Luigi,Zanotti, Valerio,Albano, Vincenzo G.,Braga, Dario,Monari, Magda
p. 1067 - 1074
(2007/10/02)

SYNTHESE D'IMINES CYCLIQUES NON-STABILISEES PAR REACTIONS GAZ-SOLIDE SOUS VIDE ET THERMOLYSE-ECLAIR (1,2).
Unstabilized cyclic imines 1-4 were synthetized in gram-scale by vacuum dehydrochlorination of N-chlorocycloamines.Azirine 5 was prepared by flash vacuum thermolysis of the corresponding vinylazide 19.All the new compounds were characterized at low temperature by 1H, 13C NMR and IR spectroscopy.
Guillemin, Jean-Claude,Denis, Jean-Marc,Lasne, Marie-Claire,Ripoll, Jean-Louis
p. 4447 - 4456
(2007/10/02)

Gas-Phase Negative Ion Chemistry of Methyl Isocyanide
The gas-phase negative ion chemistry of methyl isocyanide (CH3NC) has been studied at 0.4 Torr in a flowing afterglow apparatus and compared with that of its isomer acetonitrile (CH3CN).Methyl isocyanide has been determined to be 1.8 +/- 0.4 kcal/mol less acidic than acetonitrile in the gas phase, yielding ΔH0 acid(CH3NC) = 374 +/- 3 kcal/mol.The isocyano group has been found to stabilize an adjacent radical site better than does the cyano group.Methyl isocyanide reacts with bases by competing proton abstraction and SN2 processes.The reaction of the isocyanomethyl anion with a number of neutral reagents has also been studied.It undergoes hydrogen-deuterium exchange with D2O while cyanide ion is a major product upon reaction with O2, SO2, N2O, COS, CS2, and C6H5CHO.Other ions are also produced in smaller amounts with many of these reagents.The rates of reaction of the isomeric anions with CH3Br have also been determined.
Filley, Jonathan,DePuy, Charles H.,Bierbaum, Veronica M.
p. 5992 - 5995
(2007/10/02)

Trapping of a Stable Complex in the Reaction between C(3P) and Trimethylamine
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McPherson, Daniel W.,McKee, Michael L.,Shevlin, Philip B.
p. 2712 - 2713
(2007/10/02)

The Question of Tautomerism of Alkylnitrile and Isonitrile Cations
The isomeric pairs+. and +. and +. and +. have been established as stable, noninterconverting structures.The conclusion derives from studies of collision induced decomposition spectra.The same conclusion pertains for the ions +. and +., and for +., +. and HNCCHCHCNH>+..The energy barrier of a -hydrogen shift, a possible isomerization mechanism, is determined to be at least 163kJ mol-1 for the +. and +. pair, and the barrier may be as high as 318kJ*mol-1.The C3H5N and C4H4N2 radical cations decompose before they can be activated with 318 kJ mol-1 of internal energy.
Chess, Edward K.,Lapp, R. L.,Gross, Michael L.
p. 475 - 480
(2007/10/02)

Coordination Chemistry of Metal Surfaces. 2. Chemistry of CH3CN and CH3NC on Nickel Surfaces
The coordination chemistry of the isomeric molecules CH3CN and CH3NC on a nickel has been studied as a function of surface crystallography and surface composition by electron spectroscopic and diffraction techniques, by chemical displacement reactions, by thermal desorption spectrometry, and by isotopic labeling experiments.The surfaces studied were the low Miller index planes (111), (110), and (100) and also the stepped and stepped-kinked planes 9(111)x(111) and 7(111)x(310), respectively.Effects of surface carbon, sulfur, and oxygen contaminant atoms on the chemistry were examined for these surfaces.Acetonitrile was weakly and reversibly bound on the (111), stepped, and stepped-kinked surface and was probably oriented with the CN vector normal to the flat surface sections.The thermal desorption temperature was about 90 deg C.Some irreversible decomposition, probably focused at step or kink sites, was observed in the thermal desorption experiments.Consistently then, acetonitrile on the super-stepped (110) surface largely underwent decomposition on heating; very little reversible chemisorption was observed.Binding of the nitrile on the (100) surface was a significantly different than for the more closely packed (111) surface; the thermal desorption temperature maximum was about 20 deg C higher than for Ni(111)-NCCH3.The Ni(100)-NCCH3 state was ordered, c(2x2); here the nitrile nitrogen atom may lie in the fourfold sites.Labeling studies of the acetonitrile chemisorption showed there was no reversible bond breaking process from 20 to ca. 100 deg C.Neither carbon nor sulfur contaminant atoms quantitatively altered this nickel surface-acetonitrile chemistry.In sharp contrast to acetonitrile, methyl isocyanide was strongly bound to all the nickel surfaces and essentially could not be thermally desorbed from the clean surfaces; decomposition to H2(g) and N2(g) prevailed.Sulfur contaminant atoms on the nickel surfaces did not alter this chemistry but carbon did.Methyl isocyanide chemisorbed on carbon containing Ni(111), Ni, and Ni surfaces rearranged on heating and desorbed as acetonitrile at ca. 90 deg C.The chemistry was similar on the carbon-containing (110) and (100) surfaces to that for acetonitrile on the respective Ni(110)-C and Ni(100)-C surfaces.Thus, isomerization of the isocynide also appeared to prevail on these surfaces.Structural aspects of this surface chemistry are discussed.Experiments with "real" nickel surfaces on which isomerization of CH3NC to CH3CN was demonstrated are also described.Oxygen (oxide) contamination of all the nickel surfaces drastically reduced the sticking coefficient of the two isomeric molecules; essentially no chemisorption was observed at 10-8-10-10 torr and 20 deg C.
Friend, C. M.,Stein, Judith,Muetterties, E. L.
p. 767 - 772
(2007/10/02)