Carbodiimide Production from Cyanamide by UV Irradiation and Thermal Reaction on Amorphous Water Ice

Zinc catalyzed chemoselective hydrofunctionalization of cyanamides

The zinc-catalyzed hydrosilylation and hydroboration of cyanamides have been described. Chemoselective reduction of cyanamides with Ph2SiH2 and partial or complete hydroboration of cyanamides with pinacolborane (HBpin) have been successfully carried out. The active catalyst/intermediate in the catalytic reactions, i.e., the bis-guanidinate zinc amidinate compound, has been isolated and structurally characterized.

Structure, Spectra and Photochemistry of 2-Amino-4-Methylthiazole: FTIR Matrix Isolation and Theoretical Studies

The structure, tautomerization pathways, vibrational spectra, and photochemistry of 2-amino-4-methylthiazole (AMT) molecule were studied by matrix isolation FTIR spectroscopy and DFT calculations undertaken at the B3LYP/6-311++G(3df,3pd) level of theory. The most stable tautomer with the five-membered ring stabilized by two double C=C and C=N bonds, was detected in argon matrices after deposition. When the AMT/Ar matrices were exposed to 265 nm selective irradiation, three main photoproducts, N-(1-sulfanylprop-1-en-2-yl)carbodiimide (fp1), N-(1-thioxopropan-2-yl)carbodiimide (fp2) and N-(2-methylthiiran-2-yl)carbodiimide (fp3), were photoproduced by a cleavage of the CS–CN bond together with hydrogen atom migration. The minor photoreaction caused by the cleavage of the CS–CC bond and followed by hydrogen migration formed 2-methyl-1H-azirene-1-carbimidothioic acid (fp15). We have also found that cleavage of the CS–CN bond followed by disruption of the N–C bond produced cyanamide (fp11) and the C(CH3)=CH–S biradical that transformed into 2-methylthiirene (fp12) and further photoreactions produced 1-propyne-1-thiole (fp13) or methylthioketene (fp14). Cleavage of the CS–CC bond followed by disruption of the N–C bond produced propyne (fp22) and the S–C(NH₂)=N biradical that transformed into 3-aminethiazirene (fp23); further photoreactions produced N-sulfanylcarbodiimide (fp25). As a result of these transformations, several molecular complexes were identified as photoproducts besides new molecules in the AMT photolysis process.

Realizing Fast Charge Diffusion in Oriented Iron Carbodiimide Structure for High-Rate Sodium-Ion Storage Performance

Iron carbodiimide (FeNCN) belongs to a type of metal compounds with a more covalent bonding structure compared to common transition metal oxides. It could provide possibilities for various structural designs with improved charge-transfer kinetics in battery systems. Moreover, these possibilities are still highly expected for promoting enhancement in rate performance of sodium (Na)-ion battery. Herein, oriented FeNCN crystallites were grown on the carbon-based substrate with exposed {010} faces along the [001] direction (O-FeNCN/S). It provides a high Na-ion storage capacity with excellent rate capability (680 mAh g^-1 at 0.2 A g^-1 and 360 mAh g^-1 at 20 A g^-1), presenting rapid charge-transfer kinetics with high contribution of pseudocapacitance during a typical conversion reaction. This high rate performance is attributed to the oriented morphology of FeNCN crystallites. Its orientation along [001] maintains preferred Na-ion diffusion along the two directions in the entire morphology of O-FeNCN/S, supporting fast Na-ion storage kinetics during the charge/discharge process. This study could provide ideas toward the understanding of the rational structural design of metal carbodiimides for attaining high electrochemical performance in future.

Theoretical Study of Possible Reaction Mechanisms for the Formation of Carbodiimide in the Interstellar Medium (ISM) and Polarizabilities of Carbodiimide

The Structure of carbodiimide has been studied by using quantum chemical methods. Carbodiimide (HNCNH) has been detected towards Sagittarius B2 (N) in interstellar medium (ISM). Two reaction mechanisms have been proposed to study the formation of interstellar Carbodiimide. The first reaction mechanism is based on molecule-radical and the second one is a radical-radical mechanism, through previously detected interstellar molecules or radicals. Quantum chemical calculations have been performed by using density functional theory (DFT) and Moller-Plesset second order perturbation (MP2) theory, in gas phase as well as in polarizable continuum model (PCM). The proposed reaction paths are exothermic and barrierless which indicates the possibility of carbodiimide formation in ISM. Several basis sets have been used to verify the validity and accuracy of the results. The isotropic and anisotropic polarizabilities of carbodiimide have been calculated from relevant tensor components for both reaction mechanisms with the help of data obtained by DFT/B3LYP and MP2 methods using aug-cc-pVTZ basis sets in gaseous phase as well as in PCM.

Copper-Catalyzed Alkenylation of Cyanamides

An efficient procedure for the copper-catalyzed cross-coupling between a broad range of cyanamides and iodoalkenes is reported. Upon reaction with catalytic amounts of copper(I) iodide and 2,2'-bisimidazole in the presence of cesium carbonate in DMF at 80 °C, a fast, regioselective, and stereoretentive cross-coupling occurs. This reaction, which was found to have a broad substrate scope, provides the first general entry to N-alkenylcyanamides, building blocks that hold great synthetic potential.

Photochemistry of 1- and 2-Methyl-5-aminotetrazoles: Structural Effects on Reaction Pathways

The influence of the position of the methyl substituent in 1- and 2-methyl-substituted 5-aminotetrazoles on the photochemistry of these molecules is evaluated. The two compounds were isolated in an argon matrix (15 K) and the matrix was subjected to in situ narrowband UV excitation at different wavelengths, which induce selectively photochemical transformations of different species (reactants and initially formed photoproducts). The progress of the reactions was followed by infrared spectroscopy, supported by quantum chemical calculations. It is shown that the photochemistries of the two isomers, 1-methyl-(1H)-tetrazole-5-amine (1a) and 2-methyl-(2H)-tetrazole-5-amine (1b), although resulting in a common intermediate diazirine 3, which undergoes subsequent photoconversion into 1-amino-3-methylcarbodiimide (H₂N-N═C═N-CH₃), show marked differences: formation of the amino cyanamide 4 (H₂N-N(CH₃)-C≡N) is only observed from the photocleavage of the isomer 1a, whereas formation of the nitrile imine 2 (H₂N-C^-═N⁺═N-CH₃) is only obtained from photolysis of 1b. The exclusive formation of nitrile imine from the isomer 1b points to the possibility that only the 2H-tetrazoles forms can give a direct access to nitrile imines, while observation of the amino cyanamide 4 represents a novel reaction pathway in the photochemistry of tetrazoles and seems to be characteristic of 1H-tetrazoles. The structural and vibrational characterization of both reactants and photoproducts has been undertaken.

B(C6F5)3-mediated transformations and hydrogenation of carbodiimides

The reactivity of a series of carbodiimides RNCNR (R=tBu (1 a), iPr (1 b), SiMe3 (1 c), and Dipp (2,6-di-iso-propylphenyl (1 d)) with B(C6 F5 )3 was investigated. After initial adduct formation, several distinct reaction pathways were identified. These pathways involve either isomerization of the carbodiimide to cyanamide derivatives or insertion of a carbodiimide into a BC bond of B(C6 F5 )3 to yield four-membered heterocycles. In the presence of dihydrogen, stepwise hydrogenation of the heteroallene moiety in the carbodiimides was achieved, which yielded the respective amidine-B(C6 F5 )3 adducts and amidinium borate salts upon reaction with one or two equivalents of H2 , respectively.

Formaldehyde chemistry in cometary ices: the case of HOCH2OH formation

Laboratory experiments devoted to simulate the chemistry occurring in interstellar and cometary ice analogues are of paramount importance to understand the formation of complex organic molecules that are detected throughout the universe.

Nitrile imines: matrix isolation, IR spectra, structures, and rearrangement to carbodiimides

The structures and reactivities of nitrile imines are subjects of continuing debate. Several nitrile imines were generated photochemically or thermally and investigated by IR spectroscopy in Ar matrices at cryogenic temperatures (Ph-CNN-H 6, Ph-CNN-CH(3)17, Ph-CNN-SiMe(3)23, Ph-CNN-Ph 29, Ph(3)C-CNN-CPh(3)34, and the boryl-CNN-boryl derivative 39). The effect of substituents on the structures and IR absorptions of nitrile imines was investigated computationally at the B3LYP/6-31G* level. IR spectra were analyzed in terms of calculated anharmonic vibrational spectra and were generally in very good agreement with the calculated spectra. Infrared spectra were found to reflect the structures of nitrile imines accurately. Nitrile imines with IR absorptions above 2200 cm(-1) have essentially propargylic structures, possessing a CN triple bond (typically PhCNNSiMe(3)23, PhCNNPh 29, and boryl-CNN-boryl 39). Nitrile imines with IR absorptions below ca. 2200 cm(-1) are more likely to be allenic (e.g., HCNNH 1, PhCNNH 6, HCNNPh 43, PhCNNCH(3)17, and Ph(3)C-CNN-CPh(3)34). All nitrile imines isomerize to the corresponding carbodiimides both thermally and photochemically. Monosubstituted carbodiimides isomerize thermally to the corresponding cyanamides (e.g., Ph-N═C═N-H 5 → Ph-NH-CN 8), which are therefore the thermal end products for nitrile imines of the types RCNNH and HCNNR. This tautomerization is reversible under flash vacuum thermolysis conditions.

Gas-Phase Ionic Syntheses of Amino Acids: β versus α

Both theoretical and experimental studies are reported for the gas-phase reactions of protonated hydroxylamine with acetic and propanoic acids which yield protonated glycine and alanine, GlyH+ and AlaH+, respectively. The key step for these reactions is an insertion of the amino group into a C-H bond. For the formation of AlaH+, the reaction barrier for insertion into a Cbeta-H bond is ca. 5 kcal.mol-1 lower than that for the insertion into a Calpha-H bond; the product beta-AlaH+ is ca. 6 kcal mol-1 lower in energy than alpha-AlaH+. Thus, both kinetics and thermodynamics favor formation of the beta-form. The energetic preference for the beta-form is due to more efficient hydrogen bonding between the amino group and the carbonyl oxygen in the limiting transition structure and in the beta-AlaH+ product. These theoretical results are in excellent accord with selected ion flow tube measurements of the gas-phase synthesis which show striking specificity for the beta-isomer according to multi-collision-induced dissociation of the AlaH+ product ion. The results suggest that Gly and beta-Ala found in carbonaceous chondrite meteorites are products of interstellar chemistry.

Water-Catalyzed Hydrolysis of the Radical Cation of Ketene in the Gas Phase: Theory and Experiment

Both theoretical and experimental investigations are reported for the gas-phase hydrolysis of the radical cation of ketene, H(2)CCO(*+). Density functional theory (DFT) with the B3LYP/6-311++G(d,p) method indicates that a second water molecule is required as a catalyst for the addition of water across the C=O bond in H(2)CCO(*+) by eliminating the activation barrier for the conversion of [H(2)CCO.H(2)O](*+) to [H(2)CC(OH)(2)](*+). Theory further indicates that [H(2)CC(OH)(2).H(2)O](*+) may recombine with electrons to produce neutral acetic acid. Experimental results of flow-reactor tandem mass spectrometer experiments in which CH(2)CO(*+) ions were produced either directly from ketene by electron transfer or by the chemical reaction of CH(2)(*+) with CO are consistent with formation of an (C(2),H(4),O(2))(*+) ion in a reaction second-order in H(2)O. Furthermore, comparative multi-CID experiments indicate that this ion is likely to be the enolic CH(2)C(OH)(2)(*+) cation. The results suggest a possible mechanism for the formation of acetic acid from ketene and water on icy surfaces in hot cores and interstellar clouds.

Vacuum Ultraviolet (VUV) Photodecomposition of Urea Isolated in Cryogenic Matrix: First Detection of Isourea

Vacuum ultraviolet (VUV) irradiation at wavelengths of lambda > 160 nm of urea-h4 (NH2CONH2) and urea-d4 (ND2COND2) has been monitored by Fourier transform infrared spectroscopy in argon and xenon matrixes. Several primary photoproducts, such as HNCO:NH3 (isocyanic acid:ammonia), CO:N2H4 (carbon monoxide:hydrazine) molecular complexes, and isourea (H2N(OH)C=NH), which is reported for the first time, were characterized. The assignment of complexes was achieved by co-depositing the pairs of respective species, whereas the isourea identification was based on the comparison between the experimental and theoretical (B3LYP) infrared spectra. Isourea is found in the argon matrix in its most stable (s-Z)-(E) configuration. It is an intermediate in the VUV decomposition process; its dehydration leads to the NH2CN:H2O complex. In the xenon matrix, the photochemistry of urea yields the HNCO:NH3 complex as a major product, whereas the CO:N2H4 complex is observed in trace amounts. The observed differences between the argon and xenon matrixes suggest the crossing between S1 and T1 potential surfaces of urea to be responsible for the formation of the HNCO:NH3 complex. A comparison is also performed with other carboxamides, such as formamide (HCONH2) or acetamide (CH3CONH2).