Artur Mardyukov, André K. Eckhardt, and Peter R. Schreiner
Angew. Chem. Int. Ed. 2020, 58, in press.
Chelladurai Ganesamoorthy, Juliane Schoening, Christoph Wölper, Lijuan Song, Peter R. Schreiner, and Stephan Schulz
Nat. Chem. 2020, in press.
Spectroscopic Identification of the Phenyltelluryl Radical and its Reactivity Toward Molecular Oxygen
Felix Keul, Artur Mardyukov and Peter R. Schreiner
PCCP 2019, 21, 25797–25801.
Artur Mardyukov, Felix Keul, and Peter R. Schreiner
J. Phys. Chem. A 2019, 123, 4937–4941.
Formation of Glyoxylic Acid (HCOCOOH) in Interstellar Ices – A Key Entry Point for Prebiotic Chemistry
André K. Eckhardt, Alexandre Bergantini, Santosh K. Sing, Peter R. Schreiner and Ralf I. Kaiser
Angew. Chem. Int. Ed. 2019, 58, 5663–5667.
With nearly 200 molecules detected in interstellar and circumstellar environments, the identification of the biologically relevant α‐keto carboxylic acid, glyoxylic acid (HCOCOOH), is still elusive. Herein, the formation of glyoxylic acid via cosmic‐ray driven, non‐equilibrium chemistry in polar interstellar ices of carbon monoxide (CO) and water (H2O) at 5 K via barrierless recombination of formyl (HCO) and hydroxycarbonyl radicals (HOCO) is reported. In temperature‐programmed desorption experiments, the subliming neutral molecules were selectively photoionized and identified based on the ionization energy and distinct mass‐to‐charge ratios in combination with isotopically labeled experiments exploiting reflectron time‐of‐flight mass spectrometry. These studies unravel a key reaction path to glyoxylic acid, an organic molecule formed in interstellar ices before subliming in star‐forming regions like SgrB2(N), thus providing a critical entry point to prebiotic organic synthesis.
Zhuang Wu, Changyun Chen, Jie Liu, Yan Lu, Jian Xu, Jian, Xiangya Liu, Ganglong Cui, Tarek Trabelsi, Joseph Francisco, Artur Mardyukov, André K. Eckhardt, Peter R. Schreiner, Xiaoqing Zeng
J. Am. Chem. Soc. 2019, 141, 3361–3365.
Zhenpin Lu, Julia Ruhl, Henrik Quanz, Georg Albrecht, Christian Logemann, Derck Schlettwein, Peter R. Schreiner and Hermann A. Wegner
Angew. Chem. Int. Ed. 2019, 58, 4259–4263.
Preparation and Characterization of Phenyl Phosphine Diselenide – The Monomeric Form of Woollins' Reagent
Artur Mardyukov, Felix Keul and Peter R. Schreiner
Eur. J. Org. Chem. 2019, 46, 387-390.
We report the preparation, matrix‐isolation, and IR and UV/Vis spectroscopic characterization of phenyl phosphine diselenide, thus providing the first experimental evidence of the monomeric form of Woollins' reagent. Phenyl phosphine diselenide was prepared by thermal dissociation of Woollins' reagent and was identified by matching its spectroscopic data with density functional theory [B3LYP‐D3/6‐311++G(3df,3pd)] computations. The title compound proved to be highly photolabile and irradiation with light at λ = 334 nm results in the formation of hitherto unknown phenyldiselenyl phosphirane. Upon λ = 465 nm irradiation it rearranges back to phenyl phosphine diselenide.
André K. Eckhardt, Raffael C. Wende and Peter R. Schreiner
J. Am. Chem. Soc. 2018, 140,12333–12336. . Highlight: Cover picture of this issue.
We report the spontaneous gas-phase formation of 1,3-dioxolane-4-ol, a mixed hemiacetal resulting from the addition of glycolaldehyde to formaldehyde. It was spectroscopically characterized by matching matrix IR spectra with coupled cluster computations. The formation of the hemiacetal must be surface-catalyzed owing to the very high computed reaction barrier of 39.8 kcal mol–1. The reaction barrier is lowered by almost 20 kcal mol–1 when a single water molecule acts as a proton shuttle in a favorable six-membered transition state. We characterized the hemiacetal in solution via NMR spectroscopy and followed its decomposition into its constituents within a few hours; it also dissociates upon contact with water. Sugars form in the presence of Ca(OH)2, in line with formose-type reactivity. 1,3-Dioxolane-4-ol may be considered a storage form for formaldehyde and glycolaldehyde that is rather stable in the gas-phase.
Jian Xu, Zhuang Wu, Huabin Wan, Guohai Deng, Bo Lu, André K. Eckhardt, Peter R. Schreiner, Tarek Trabelsi, Joseph S. Francisco and Xiaoqing Zeng
J. Am. Chem. Soc. 2018, 140, 9972–9978.
Arylsulfinyl radicals are key intermediates in sulfoxide chemistry. The parent molecule, phenylsulfinyl radical PhSO•, has been generated for the first time in the gas phase through high-vacuum flash pyrolysis of PhS(O)R (R = CF3 and Cl) at about 1000 K. Upon UV light irradiation (365 nm), PhSO• isomerizes to novel oxathiyl radical PhOS• in cryogenic matrices (2.8 K). Prolonged irradiation causes further isomerization of PhOS• to 2-hydroxyphenylthiyl radical, the formation of which has been also observed in the 193 nm laser photolysis of matrix-isolated 2-hydroxybenzenethiol. Concomitantly, ring-opening occurs during the UV photolysis of PhOS• and 2-hydroxybenzenethiol and forms an acyclic thioketoketene radical. Phenylsulfinyl radical reacts partially with molecular oxygen in the gas phase and yields phenyl radical Ph• and OSOO. Upon irradiation (365 nm), the isomeric oxathiyl radical also combines O2 with immediate dissociation to phenoxy radical PhO• and SO2. The identification of the intermediates with IR and UV–vis spectroscopy is supported by quantum chemical computations at the B3LYP/def2-TZVPP and UCCSD(T)/aug-cc-pV(D+d)Z levels of theory. The isomerization of PhSO• has been discussed based on the computed potential energy profile and the comparison with the intensively explored photochemistry of phenylperoxy radical PhOO•.
Dennis Gerbig, Sarina Desch and Peter R. Schreiner
Chem. Eur. J. 2018, 24, 11904-11907.
André K. Eckhardt, Michael M. Linden, Raffael C. Wende, Bastian Bernhardt and Peter R. Schreiner
Nature Chem. 2018, 10, 1141–1147.
Zhuang Wu, Huabin Wan, Jian Xu, Bo Lu, André K. Eckhardt, Peter R. Schreiner, Changjian Xie, Hua Guo and Xiaoqing Zeng
Chem. Commun. 2018, 54, 4517–4520.
Disulfur dioxide, OSSO, has been proposed as the enigmatic “near-UV absorber” in the yellowish atmosphere of Venus. However, the fundamentally important spectroscopic properties and photochemistry of OSSO are scarcely documented. By either condensing gaseous SO or 266 laser photolysis of an S2⋯O2 complex in Ar or N2 at 15 K, syn-OSSO, anti-OSSO, and cyclic OS(O)S were identified by IR and UV/Vis spectroscopy for the first time. The observed absorptions (λmax) for OSSO at 517 and 390 nm coincide with the near-UV absorption (320–400 nm) found in the Venus clouds by photometric measurements with the Pioneer Venus orbiter. Subsequent UV light irradiation (365 nm) depletes syn-OSSO and anti-OSSO and yields a fourth isomer, syn-OSOS, with concomitant dissociation into SO2 and elemental sulfur.
Artur Mardyukov, Dominik Niedek and Peter R. Schreiner
Chem. Commun. 2018, 54, 2715–2718.
Highlights: a) Front cover of corresponding issue; b) “HotChem” article featured by the Royal Society of Chemistry.
We describe the isolation as well as IR and UV/Vis spectroscopic characterization of (4-methoxyphenyl)phosphine disulfide in argon matrices at 10 K. The title compound proved to be highly photolabile; irradiation with UV light (λ = 334 nm) led to rearrangement to the equally unreported 3-(4-methoxyphenyl)-1,2,3-dithiaphosphirane. Photoreversion can be achieved upon irradiation at λ = 465 nm.
Zhuang Wu, Bo Lu, Ruijuan Feng, Jian Xu, Yan Lu, Huabin Wan, André K. Eckhardt, Peter R. Schreiner, Changjian Xie, Hua Guo, and Xiaoqing Zeng
Chem. Commun. 2018, 54, 1690–1693.
Highlight: Inside front cover.
When mixing SO with O2 in N2, Ne, or Ar, an end-on complex OS–OO forms in the gas phase and can subsequently be trapped at cryogenic temperatures (2.8–15.0 K). Upon infrared light irradiation, OS–OO converts to SO3 and SO2 + O with the concomitant formation of a rare 1,2,3-dioxathiirane 2-oxide, i.e., cyclic OS(O)O. Unexpectedly, the ring-closure of 16OS–18O18O yields a ca. 2 : 1 mixture of cyclic 18OS(16O)18O and 16OS(18O)18O. The characterization of OS–OO and OS(O)O with IR and UV/Vis spectroscopy is supported by high-level ab initio computations.
Artur Mardyukov and Peter R. Schreiner
Acc. Chem. Res. 2018, 51, 475–483.
The large number and amounts of volatile organosulfur compounds emitted to the atmosphere and the enormous variety of their reactions in various oxidation states make experimental measurements of even a small fraction of them a daunting task. Dimethyl sulfide (DMS) is a product of biological processes involving marine phytoplankton, and it is estimated to account for approximately 60% of the total natural sulfur gases released to the atmosphere. Ocean-emitted DMS has been suggested to play a role in atmospheric aerosol formation and thereby cloud formation. The reaction of ·OH with DMS is known to proceed by two independent channels: abstraction and addition. The oxidation of DMS is believed to be initiated by the reaction with ·OH and NO3· radicals, which eventually leads to the formation of sulfuric acid (H2SO4) and methanesulfonic acid (CH3SO3H). The reaction of DMS with NO3· appears to proceed exclusively by hydrogen abstraction. The oxidation of DMS consists of a complex sequence of reactions. Depending on the time of the day or altitude, it may take a variety of pathways. In general, however, the oxidation proceeds via chains of radical reactions. Dimethyl sulfoxide (DMSO) has been reported to be a major product of the addition channel. Dimethyl sulfone (DMSO2), SO2, CH3SO3H, and methanesulfinic acid (CH3S(O)OH) have been observed as products of further oxidation of DMSO. Understanding the details of DMS oxidation requires in-depth knowledge of the elementary steps of this seemingly simple transformation, which in turn requires a combination of experimental and theoretical methods. The methylthiyl (CH3S·), methylsulfinyl (CH3SO·), methylsulfonyl (CH3SO2·), and methylsulfonyloxyl (CH3SO3·) radicals have been postulated as intermediates in the oxidation of DMS. Therefore, studying the chemistry of sulfur-containing free radicals in the laboratory also is the basis for understanding the mechanism of DMS oxidation in the atmosphere. The application of matrix-isolation techniques in combination with quantum-mechanical calculations on the generation and structural elucidation of CH3SOx (x = 0–3) radicals is reviewed in the present Account. Experimental matrix IR and UV/vis data for all known species of this substance class are summarized together with data obtained using other spectroscopic techniques, including time-resolved spectroscopy, electron paramagnetic resonance spectroscopy, and others. We also discuss the reactivity and experimental characterization of these species to illustrate their practical relevance and highlight spectroscopic techniques available for the elucidation of their geometric and electronic structures. The present Account summarizes recent results regarding the preparation, characterization, and reactivity of various radical species with the formula CH3SOx (x = 0–3).
Zhenpin Lu, Henrik Quanz, Olaf Burghaus, Jonas Hoffmann, Christian Logemann, Peter R. Schreiner, Sebastian Beeck and Hermann A. Wegner
J. Am. Chem. Soc. 2018, 139, 18488–18491.
Zhuang Wu, Jian Xu, Guohai Deng, Yan Lu, Liubov Sokolenko, Tarek Trabelsi, Joseph S. Francisco, André Kristopher Eckhardt, Peter R. Schreiner and Xiaoqing Zeng
Chem. Eur. J. 2018, 24, 1505-1508.
Artur Mardyukov,Yetsedaw Tsegaw, Wolfram Sander and Peter R. Schreiner
PCCP 2017, 19, 27384-27388.
Preparation and Characterization of Parent Phenylphosphinidene and its Oxidation to Phenyldioxophosphorane, the Elusive Phosphorous Analogue of Nitrobenzene
Artur Mardyukov, Dominik Niedek and Peter R. Schreiner
J. Am. Chem. Soc. 2017, 139,5019–5022.
Dominik Niedek, J. Philipp Wagner, and Peter R. Schreiner*
J. Anal. Appl. Pyrol. 2017, 124, 439–445.
Generation and Characterization of the Phenylthiyl Radical and its Oxidation to the Phenylthiylperoxy and Sulfonylbenzenyl Radical
Artur Mardyukov and Peter R. Schreiner*
PCCP 2016, 18, 26161–26165.
Roxane Vabre, Biana Island, Claudia Diehl, Peter R. Schreiner, and Ilan Marek*
Angew. Chem. Int. Ed. 2015, 54, 9996–9999. DOI: 10.1002/anie.201504756
Noted as very important paper (top 5% of all Angewandte publications)
The combined carbometalation/zinc homologation followed by reactions with α-heterosubstituted aldehydes and imines proceed through a chair-like transition structure with the substituent of the incoming aldehyde residue preferentially occupying a pseudo-axial position to avoid the two gauche interactions. The heteroatom in the axial position produces a chelated intermediate (and not a Cornforth–Evans transition structure for α-chloro aldehydes and imines) leading to a face differentiation in the allylation reaction. This method provides access to functionalized products in which three new carbon–carbon bonds and two to three stereogenic centers, including a quaternary one, were created in acyclic systems in a single-pot operation from simple alkynes.
Hans Peter Reisenauer, Jarosław Romański, Grzegorz Mlostoń, Peter R. Schreiner
Highlight: Holm Petzold, Nachr. Chem. 2015, 63, 760
The atmospherically highly relevant methylsulfinyl radical (CH3(O)S•) readily reacts with molecular triplet oxygen in cryogenic argon matrices containing small amounts of 3O2. Comparison of experimental and computed IR- and UV/Vis spectra, including isotope exchange, show that the initially formed 3O2 adduct has the structure of a peroxyl radical (CH3(O)SOO•), which upon irradiation with UV light isom-erizes to the methylsulfonoxyl radical (CH3SO3•). The latter transforms into the methansulfonic acid radical (•CH2SO3H) by irradiation with visible light. During the matrix photolysis small amounts of SO3 and methyl radical were detected indi-cating competitive direct photodissociation.
Gas Phase Generation and Matrix Isolation of the Methylsulfonyl Radical CH3SO2• from Allylmethylsulfone
Hans-Peter Reisenauer, Jaroslaw Romanski, Peter R. Schreiner, and Grzegorz Mloston
J. Phys. Chem. A 2015, Article ASAP.
Hans Peter Reisenauer, Jan Philipp Wagner, Peter R. Schreiner
Angew. Chem. Int. Ed. 2014, 53, 11766–11771 (“hot paper”), DOI: 10.1002/anie.201406969.
a) Front cover of this issue;
b) Perspective: Götz Bucher and Wolfram Sander Science 2014, 346, 544–545; c) Feature:. Jyllian N. Kemsley C & EN News 2014, 92 (41), 28–29;
e) Innovations Report:;
Carbonic acid (H2CO3), an essential molecule of life (e.g., as bicarbonate buffer), has been well characterized in solution and in the solid state, but for a long time, it has eluded its spectral characterization in the gas phase owing to a lack of convenient preparation methods; microwave spectra were recorded only recently. Here we present a novel and general method for the preparation of H2CO3 and its monomethyl ester (CH3OCO2H) through the gas-phase pyrolysis of di-tert-butyl and tert-butyl methyl carbonate, respectively. H2CO3 and CH3OCO2H were trapped in noble-gas matrices at 8 K, and their infrared spectra match those computed at high levels of theory [focal point analysis beyond CCSD(T)/cc-pVQZ] very well. Whereas the spectra also perfectly agree with those of the vapor phase above the β-polymorph of H2CO3, this is not true for the previously reported α-polymorph. Instead, the vapor phase above α-H2CO3 corresponds to CH3OCO2H, which sheds new light on the research that has been conducted on molecular H2CO3 over the last decades.
Combined ab initio molecular dynamics and experimental studies show that carbon atom addition to benzene.
Michael L. McKee, Hans-Peter Reisenauer, and Peter R. Schreiner,
Car–Parrinello molecular dynamics was used to explore the reactions between triplet and singlet carbon atoms with benzene. The computations reveal that, in the singlet C atom reaction, products are very exothermic where nearly every collision yields a product that is determined by the initial encounter geometry. The singlet C atom reaction does not follow the minimum energy path because the bimolecular reaction is controlled by dynamics (i.e., initial orientation of encounter). On the other hand, in a 10 K solid Ar matrix, ground state C(3P) atoms do tend to follow RRKM kinetics. Thus, ab initio molecular dynamics (AIMD) results indicate that a significant fraction of C–H insertion occurs to form phenylcarbene whereas, in marked contrast to previous theoretical and experimental conclusions, the Ar matrix isolation studies indicate a large fraction of direct cycloheptatetraene formation, without the intermediacy of phenylcarbene. The AIMD calculations are more consistent with vaporized carbon atom experiments where labeling studies indicate the initial formation of phenylcarbene. This underlines that the availability of thermodynamic sinks can completely alter the observed reaction dynamics.
Hans Peter Reisenauer,* Jaroslav Romanski, Grzegorz Mloston,* and Peter R. Schreiner,
The atmospherically highly relevant methylsulfinyl radical CH3(O)S• was generated thermally under flash pyrolysis conditions and isolated in Ar matrices at 10 K; the allyl radical is a byproduct. CH3(O)S• and its D3- and 13C-isotopologues were characterized through the excellent agreement between experimental and computed IR and UV/Vis spectra.
Thermolysis of 3,3,5,5-Tetramethyl-1,2,4-triothiolane-1-oxide: Matrix Isolation of the HOSS•-Radical.
Hans-Peter Reisenauer,* Grzegorz Mloston,* Jaroslaw Romanski, and Peter R. Schreiner,
Flash vacuum pyrolysis of 3,3,5,5-tetramethyl-1,2,4-trithiolane 1-oxide performed at 700 °C yields the 1-oxatrisulfan-3-yl radical (HOSS·) along with disulfur monoxide (S2O) and diisopropyl sulfide, which were isolated in argon matrices at 10 K. Upon irradiation with UV light, the 1-oxatrisulfan-3-yl radical undergoes isomerization to the 1-oxatrisulfan-1-yl radical (HSSO·). Both radicals were identified by comparison of their computed and experimental IR and UV/Vis spectra. In addition, density functional theory (DFT) computations offer a plausible explanation of the most likely reaction mechanism, suggesting that the initial step is a 1,3-H shift with simultaneous ring opening. A 1-oxatrisulfane derivative formed thereby undergoes fragmentations via a radical and a competitive concerted pathway leading to the observed final products. The same mechanism also governs the thermal fragmentation of di-tert-butyl disulfide S-oxide. Its pyrolysis at 700 °C affords an analogous set of products, including the 1-oxatrisulfan-3-yl radical (HOSS·) as the key intermediate.
Udo H. Brinker, Alexander A. Bespokoev, Hans Peter Reisenauer, and Peter R. Schreiner
Bicyclo[3.2.1]oct-6-en-8-ylidene (1) can assume either the conformation of “classical” carbene 1a or that of foiled carbene 1b in which the divalent carbon bends toward the double bond. Oxadiazoline precursors for the generation of 1 were prepared, followed by photochemical and thermal decomposition as well as flash vacuum pyrolysis (FVP) of a tosyl hydrazone sodium salt precursor, to give a number of rearrangement products. Matrix isolation experiments demonstrate the presence of a diazo intermediate and methyl acetate in all photochemical and thermal precursor reactions. The major product from rearrangements of “classical” bridged carbene 1a is bicyclo[3.3.0]octa-1,3-diene as a result of an alkyl shift, while dihydrosemibullvalene formed from a 1,3-C–H insertion. In contrast, thus far unknown strained bicyclo[4.2.0]octa-1,7-diene formed by a vinyl shift in foiled carbene 1b. The experimental results are corroborated by density functional theory (DFT), MP2, and G4 computations.
Peter R. Schreiner, Hans Peter Reisenauer, Jaroslaw Romanski, and Grzegorz Mloston
J. Am. Chem. Soc. 2010, 132, 7240–7241.
We describe the first preparation of the long sought after parent oxathiirane from sulfine through photochemical rearrangement with light at 313 ± 10 nm in an Ar-matrix at 11 K. Oxathiirane was characterized by the extraordinarily good agreement of experimentally measured and CCSD(T)/cc-pVTZ (unscaled) computed vibrational frequencies both for the perhydrogenated and perdeuterated species. The title molecule is about 10 kcal mol–1 less stable than sulfine, in marked contrast to the isomer energy difference of dioxirane vs. carbonyl oxide (ca. –25 kcal mol–1). This is due to the strong positive polarization (blue potential) vs. the highly electronegative oxygen atom (red). The stability ordering and the relative energy differences of carbonyl vs. thiocarbonyl groups underlines the likely role oxathiiranes play in sulfur transfer reactions.
Grzegorz Mloston, Jaroslaw Romanski, Michael L. McKee, Hans-Peter Reisenauer, and Peter R. Schreiner
Eur. J. Org. Chem. 2010, 2132–2137.
The products of the gas phase pyrolysis of two regioisomeric 1,2,4-trithiolane S-oxides were collected in an argon matrix at 10 K and studied by means of spectroscopic as well as computational methods. Whereas the main products of the pyrolysis of the ‘symmetrical’ S-oxide were identified as thioformaldehyde S-oxide and thioformaldehyde S-sulfide, the ‘non-symmetrical’ S-oxide gave predominantly dithioformic acid, which exists as a mixture of s-cis and s-trans conformers. We present a rationalization of the reaction pathways including density functional theory computations.
Peter R. Schreiner, Hans Peter Reisenauer, Jaroslaw Romanski, and Grzegorz Mloston
Angew. Chem. Int. Ed. 2009, 48, 8133–8136. ; Highlight: Neil Withers Nature Chem. 2009. ; Robert Berger Nachr. Chem. 2010, 58, 7.
Extremely rare: a CS triple bond can be assigned to HCSOH, a new molecule prepared through a photochemical [1,3]H-shift of sulfine H2C=S=O. But does this formal description agree with analyses on the basis of IR vibrations, bond lengths, bond orders, molecular orbitals, and compliance constants? Such types of molecules challenge and refine our current understanding of chemical bonding.
Peter R. Schreiner, Hans Peter Reisenauer, Edit Mátyus, Attila G. Császár, Ali Siddiqi, Andrew C. Simmonett, and Wesley D. Allen
Phys. Chem. Chem. Phys. 2009, 11, 10385-10390.
The first definitive infrared signatures of the elusive NCCO radical have been measured using a microwave discharge technique combined with low-temperature matrix-isolation spectroscopy, resulting in a consistent set of vibrational assignments for six isotopologues. The infrared spectra of these NCCO isotopologues were concomitantly established by rigorous variational nuclear-motion computations based on a high-level coupled-cluster quartic vibrational force field [ROCCSD(T)/cc-pCVQZ] and cubic dipole field [ROCCSD/cc-pCVTZ]. Our experimental and theoretical results for NCCO overturn the vibrational assignments in a NIST-JANAF compilation and those from a recent two-dimensional cross-spectral correlation analysis. For the parent isotopologue at 11 K in a nitrogen matrix, we find the signature bands n2(CO str.) = 1889.2 cm-1 and n3(CC str.) = 782.0 cm-1. Our variational vibrational computations reveal strong mixing of the n3 stretching fundamental and the n4+n5 bending combination level for all isotopologues. These Fermi resonances manifest a clear breakdown of the simple normal-mode picture of molecular vibrations at low energies.
Adelina Nemirowski, Hans Peter Reisenauer, Jaroslaw Romanski, Grzegorz Mloston, and Peter R. Schreiner,
J. Phys. Chem. A, 2008, 50, 13244.
Abstract. The current case study focuses on the generation, identification, and characterization of two representative mono- and disubstituted alkyl phosphonatocarbenes by means of matrix isolation techniques in conjunction with density functional theory [B3LYP/6-311++G(d,p)] and coupled cluster [CCSD(T)/cc-pVXZ, X = D, T] computations. The EPR measurements identify both carbenes as triplet ground-state species with D values of 0.660 and 0.623 cm–1 respectively, exhibiting persistency toward intramolecular reactions (the EPR signal observable in perfluoromethylcyclohexane up to around 70 K for the disubstituted molecule). While the reaction of the carbene center of the conformationally rich tetramethyl bisphosphonatocarbene with the CH bonds of the methyl groups leads to phosphaoxetane at room temperature, its fragmentation via a Wittig-type reaction during high vacuum flash pyrolysis (HVFP) results in dimethyl vinylphosphonate and methyl metaphosphate. The latter has been observed for the first time as an isolated entity.
Adelina Nemirowski and Peter R. Schreiner, J. Org. Chem. 2007, 72, 9533.
Abstract. Based on systematic ab initio (CCSD(T)/cc-pVDZ) studies of substituent effects, we present a concept for the construction of electronically stabilized triplet ground state carbenes with singlet−triplet energy separations (∆EST) exceeding that of methylene. Sterically demanding and conjugating substituents were excluded from the selection of model compounds under investigation, as these either destabilize both the singlet and the triplet states or delocalize unpaired spins away from the carbene carbon. Negative partial charges on the carbene center allow for the prediction of the electronic stabilization of substituted carbenes. To decrease carbene reactivity, we chose b-substituents with strong polar bonds. Among them, highly electronegative elements such as fluorine and oxygen enlarge the ∆EST value with respect to hydrogen, while chlorine does not due to p-orbital participation.
Hans Peter Reisenauer, Jaroslaw Romanski, Grzegorz Mloston, and Peter R. Schreiner,
Eur. J. Org. Chem. 2006, 4813.
Abstract. Dimethoxycarbene was prepared from an oxadiazoline precursor under high-vacuum flash pyrolysis (HVFP) conditions and was trapped at low temperatures by matrix isolation techniques (Ar, 10 K). The excellent agreement between the computed [CCSD(T)/cc-pVDZ] IR spectrum of the mixture of conformers of dimethoxycarbene and the experimentally measured IR absorptions allows a detailed analysis ofthe conformational preference of dimethoxycarbene. ItsUV spectrum is in agreement with earlier studies and our TD-B3LYP/6-311+G(d,p) computations. The computed [CCSD(T)/cc-pVDZ] rotational profile is rather steep and separates the s-trans,s-trans and s-cis,s-trans conformers by a 16 kcal mol-1 barrier, whilst the s-cis,s-cis conformer is too high-lying to be observable (+17 kcal mol-1). In marked contrast with the gauche,gauche minimum of dimethoxymethane, the s-trans,s-trans conformer of dimethoxycarbene is slightly preferred (0.5 kcal mol-1). The s-cis,s-trans conformer equilibrates at the high temperatures required during HFVP generation and both conformers can be identified in the IR spectrum of the argon matrix at 10 K. The conformational preference is partly due to the minimization of the overall dipole moment in the s-trans,s-trans conformer.
Peter R. Schreiner, Hans Peter Reisenauer, Kurt W. Sattelmeyer, and Wesley D. Allen,
J. Am. Chem. Soc. 2005, 127, 12156.
Abstract. Ground-state triplet silaethylidene, generated directly by the reaction of 3P carbon atoms with silane under matrix isolation conditions in solid Ar (10–12 K), has been thoroughly characterized by the EPR and IR spectra of both the parent and perdeuterated isotopologs. A theoretical anharmonic vibrational analysis based on a CCSD(T)/cc-pVTZ complete quartic force field gave remarkable agreement with the experimental IR fundamentals, generally within 10 cm–1 and without any empirical scaling of the ab initio frequencies. Silaethylidene exhibits a CS minimum with a H–C–Si angle near 153 °, but the barrier to H–C–Si linearity (C3v symmetry) is only 0.24 kcal mol–1. This minuscule barrier can be surmounted by zero-point vibrations, as evident from the EPR data. The triplet stabilizing effect of the electropositive SiH3 group amounts to about 15 kcal mol–1.