On the possibility of isolating diazirine N-oxides

Ab initio molecular orbital calculations at the 6-31G level predict that diazirine N-oxide is more stable with respect to its constituent fragments, singlet CH₂ and N₂O₂, than diazirine is with respect to singlet CH₂ and N₂. In view of these results and the many diazirines which have been reported, it is suggested that it may be possible to detect a suitably substituted diazirine N-oxide.     

Diazirines as Potential Molecular Imaging Tags: Probing the Requirements for Efficient and Long‐Lived SABRE‐Induced Hyperpolarization

Diazirines are an attractive class of potential molecular tags for magnetic resonance imaging owing to their biocompatibility and ease of incorporation into a large variety of molecules. As recently reported, ¹⁵N₂‐diazirine can be hyperpolarized by the SABRE‐SHEATH method, sustaining both singlet and magnetization states, thus offering a path to long‐lived polarization storage. Herein, we show the generality of this approach by illustrating that the diazirine tag alone is sufficient for achieving excellent signal enhancements with long‐lasting polarization. Our investigations reveal the critical role of Lewis basic additives, including water, on achieving SABRE‐promoted hyperpolarization. The application of this strategy to a ¹⁵N₂‐diazirine‐containing choline derivative demonstrates the potential of ¹⁵N₂‐diazirines as molecular imaging tags for biomedical applications.     

Kinetics of OH reactions with N2H4, CH3NHNH2 and (CH3)2NNH2 in the gas phase

The gas phase reaction kinetics of OH with three di‐amine rocket fuels—N₂H₄, CH₃NHNH₂, and (CH₃)₂NNH₂—was studied in a discharge flow tube apparatus and a pulsed photolysis reactor under pseudo‐first‐order conditions in [OH]. Direct laser‐induced fluorescence monitoring of the [OH] temporal profiles in a known excess of the [diamine] yielded the following absolute second‐order OH rate coefficient expressions; k₁ = (2.17 ± 0.39) × 10^?11 e^(160±30)/T, k₂ = (4.59 ± 0.83) × 10^?11 e^(85±35)/T and k₃ = (3.35 ± 0.60) × 10^?11 e^(175±25)/T cm³ molec^?1 s^?1, respectively, for reactions with N₂H₄, CH₃NHNH₂ and (CH₃)₂NNH₂ in the temperature range 232–637 K. All three reactions did not show any discernable pressure dependence on He or N₂ buffer gas pressure of up to 530 torr. The magnitude of the weak temperature and the lack of pressure effects of the OH + N₂H₄ reaction rate coefficient suggest that a simple direct metathesis of H‐atom may not be important compared to addition of the OH to one of the N‐centers of the diamine skeleton, followed by rapid dissociation of the intermediate into products. Our findings on this reaction are qualitatively consistent with a previous ab initio study [ 3 ]. However, in the alkylated diamines, direct H‐abstraction from the methyl moiety cannot be completely ruled out. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 354–362, 2001     

Glycosylidene Carbenes a new approach to glycoside synthesis. Part 1. Preparation of glycosylidene-derived diaziridines and diazirines

A new approach towards the synthesis of glycosides based upon a (formal) insertion of glycosylidene carbenes into O? H bonds is presented. The synthesis and characterization of the glycosylidene-derived diazirines 25 – 28 , precursors of glycosylidene carbenes, are described. The diazirines were prepared by the rapid, high-yielding oxidation of the diaziridines 20 and 22 – 24 with I₂/Et₃N. The diaziridines, the first examples of C- alkoxy-diaziridines, were formed in high yields by the reaction of the [(glycosylidene)-amino]methanesulfonates 14 and 17 – 19 with a saturated solution of NH₃ in MeOH. The diazirines are highly reactive compounds, losing N₂ at room temperature or below. The reaction of the gluco-configurated diazirine 25 with i-PrOH yielding a mixture of the α- and β-D -glucosides 29 and 30 illustrates the potential of glycosylidene-derived diazirines as a new type of glycosyl donors.     

Water Soluble Gold(I)‐diacetyl‐1,3,5‐triaza‐7‐phosphaadamantane‐arylazoimidazole Complexes: Synthesis and Spectroscopic Study

Reaction of [Au(DAPTA)(Cl)] with RaaiR’ in CH2Cl2 medium following ligand addition leads to [Au(DAPTA)(RaaiR’)](Cl) [DAPTA＝diacetyl-1,3,5-triaza-7-phosphaadamantane, RaaiR’＝p-R-C6H4-N＝N- C3H2-NN-1-R’, (1—3), abbreviated as N,N’-chelator, where N(imidazole) and N(azo) represent N and N’, respectively; R＝H (a), Me (b), Cl (c) and R’＝Me (1), CH2CH3 (2), CH2Ph (3)]. The 1H NMR spectral measurements in D2O suggest methylene, CH2, in RaaiEt gives a complex AB type multiplet while in RaaiCH2Ph it shows AB type quartets. 13C NMR spectrum in D2O suggest the molecular skeleton. The 1H-1H COSY spectrum in D2O as well as contour peaks in the 1H-13C HMQC spectrum in D2O assign the solution structure.     

8‐Aza‐7‐deaza‐7‐propynyladenosine methanol solvate

In the title compound, 4‐amino‐3‐propynyl‐1‐(β‐d ‐ribofur­anosyl)‐1H‐pyrazolo[3,4‐d]pyrimidine methanol solvate, C₁₃H₁₅N₅O₄·CH₃OH, the torsion angle of the N‐glycosylic bond is between anti and high‐anti [χ = −101.8 (5)°]. The ribofuranose moiety adopts the C3′‐endo (³T₂) sugar conformation (N‐type) and the conformation at the exocyclic C—C bond is +sc (gauche, gauche). The propynyl group is out of the plane of the nucleobase and is bent. The compound forms a three‐dimensional network which is stabilized by several hydrogen bonds (O—H·O and O—H·N). The nucleobases are stacked head‐to‐tail. The methanol solvent mol­ecule forms hydrogen bonds with both the nucleobase and the sugar moiety.     

Synthesis,Thermal Behavior,and Dehydrogenation Kinetics Study of Lithiated Ethylenediamine

The lithiation of ethylenediamine by LiH is a stepwise process to form the partially lithiated intermediates LiN(H)CH₂CH₂NH₂ and [LiN(H)CH₂CH₂NH₂][LiN(H)CH₂CH₂N(H)Li]₂ prior to the formation of dilithiated ethylenediamine LiN(H)CH₂CH₂N(H)Li. A reversible phase transformation between the partial and dilithiated species was observed. One dimensional {Li_nN_n} ladders and three‐dimensional network structures were found in the crystal structures of LiN(H)CH₂CH₂NH₂ and LiN(H)CH₂CH₂N(H)Li, respectively. LiN(H)CH₂CH₂N(H)Li undergoes dehydrogenation with an activation energy of 181±8 kJ mol^?1, whereas the partially lithiated ethylenediamine compounds were polymerized and released ammonia at elevated temperatures. The dynamical dehydrogenation mechanism of the dilithiated ethylenediamine compounds was investigated by using the Johnson‐Mehl‐Avrami equation.     

CH Bond Activation with Triel Metals: Indium and Gallium Zwitterions through Internal Hydride Abstraction in Rigid Salan Ligands

The hydropyrimidine salan (salan=N,N′‐dimethyl‐N,N′‐bis[(2‐hydroxyphenyl)methylene]‐1,2‐diaminoethane) proteo‐ligands with a rigid backbone {ON^(CH₂)^NO}H₂ react with M(CH₂SiMe₃)₃ (M=Ga, In) to yield the zwitterions {ON^(CH⁺)^NO}M^?(CH₂SiMe₃)₂ (M=Ga, 2 ; In, 3 ) by abstraction of a hydride from the ligand backbone followed by elimination of dihydrogen. By contrast, with Al₂Me₆, the neutral‐at‐metal bimetallic complex [{ON^(CH₂)^NO}AlMe]₂ ( [1]₂ ) is obtained quantitatively. The formation of indium zwitterions is also observed with sterically more encumbered ligands containing o‐Me substituents on the phenolic rings, or an N (CHPh) N moiety in the heterocyclic core. Overall, the ease of C?H bond activation follows the order Al?Ga<In. Experimental data based on model complexes, XRD studies, and ²H NMR spectroscopy show that the formation of the Ga/In zwitterion involves rapid release of SiMe₄ followed by evolution of H₂, and suggest the formation of a transient metal‐hydride species. DFT calculations indicate that the systems {ON^(CH₂)^NO}H₂+M(CH₂SiMe₃)₃ (M=Al, Ga, In) all initially lead to the formation of the neutral monophenolate dihydrocarbyl species through a single protonolysis. From here, the thermodynamic product, the model neutral‐at‐metal complex 1 , is formed in the case of aluminum after a second protonolysis. On the other hand, lower activation energy pathways lead to the generation of zwitterionic complexes 2 and 3 in the cases of gallium and indium, and the formation of these zwitterions obeys a strict kinetic control; the computations suggest that, as inferred from the experimental data, the reaction proceeds through an instable metal‐hydride species, which could not be isolated synthetically.     

Multicentre hydrogen bonds in a 2:1 aryl­sulfonyl­imidazol­one ­hydro­chloride salt

The title compound, (S)‐(+)‐4‐[5‐(2‐oxo‐4,5‐di­hydro­imidazol‐1‐yl­sulfonyl)­indolin‐1‐yl­carbonyl]­anilinium chloride (S)‐(+)‐1‐[1‐(4‐amino­benzoyl)­indoline‐5‐sulfonyl]‐4‐phenyl‐4,5‐di­hydro­imidazol‐2‐one, C₂₄H₂₃N₄O₄S⁺·Cl^?·C₂₄H₂₂N₄O₄S, crystallizes in space group C2 from a CH₃OH/CH₂Cl₂ solution. In the crystal structure, there are two different conformers with their terminal C₆ aromatic rings mutually oriented at angles of 67.69 (14) and 61.16 (15)°. The distances of the terminal N atoms (of the two conformers) from the chloride ion are 3.110 (4) and 3.502 (4) Å. There are eight distinct hydrogen bonds, i.e. four N—H?Cl, three N—H?O and one N—H?N, with one N—H group involved in a bifurcated hydrogen bond with two acceptors sharing the H atom. C—H?O contacts assist in the overall hydrogen‐bonding process.     

Synthesis,Characterization, and Energetic Properties of Nitroso Compounds

Sodium and potassium methyl(nitroso)amide (M[CH₃N₂O], M = Na ( 1 ), K ( 2 )) were prepared by the reaction of monomethylhydrazine with iso‐pentyl nitrite or n‐butyl nitrite and a suitable metal ethoxide (M[CH₃CH₂O], M = Na, K) in an ethanol‐ether mixture. The reaction of monomethylhydrazine with a small excess of iso‐pentyl nitrite or n‐butyl nitrite and in the absence of a metal ethoxide led to the formation of N‐nitroso‐N‐methylhydrazine (CH₃(NO)N–NH₂, ( 3 )). Alternatively, compound 3 was prepared by the amination reaction of 1 or 2 using the sodium salt of HOSA in ethanol solution. Compounds 1–3 were characterized using elemental analysis, differential scanning calorimetry, mass spectrometry, vibrational (infrared and Raman) and UV spectroscopy and multinuclear (¹H, ¹³C and ¹⁵N) NMR spectroscopy. For compounds 1–3 , several physical and chemical properties of interest and sensitivity data were measured and for compound 3 thermodynamic and explosive properties are also given. Additionally, the solid‐state structure of compound 3 was determined by single‐crystal X‐ray analysis and the structures of the cis‐ and trans‐[CH₃N₂O]^– anions and that of 3 were optimized using DFT calculations and used to calculate the NBO charges.     

Stereospecificity of 1H, 13C and 15N shielding constants in the isomers of methylglyoxal bisdimethylhydrazone: problem with configurational assignment based on 1H chemical shifts

In the ¹³C NMR spectra of methylglyoxal bisdimethylhydrazone, the ¹³C‐5 signal is shifted to higher frequencies, while the ¹³C‐6 signal is shifted to lower frequencies on going from the EE to ZE isomer following the trend found previously. Surprisingly, the ¹H‐6 chemical shift and ¹J(C‐6,H‐6) coupling constant are noticeably larger in the ZE isomer than in the EE isomer, although the configuration around the –CH═N– bond does not change. This paradox can be rationalized by the C–H?N intramolecular hydrogen bond in the ZE isomer, which is found from the quantum‐chemical calculations including Bader's quantum theory of atoms in molecules analysis. This hydrogen bond results in the increase of δ(¹H‐6) and ¹J(C‐6,H‐6) parameters. The effect of the C–H?N hydrogen bond on the ¹H shielding and one‐bond ¹³C–¹H coupling complicates the configurational assignment of the considered compound because of these spectral parameters. The ¹H, ¹³C and ¹⁵N chemical shifts of the 2‐ and 8‐(CH₃)₂N groups attached to the –C(CH₃)═N– and –CH═N– moieties, respectively, reveal pronounced difference. The ab initio calculations show that the 8‐(CH₃)₂N group conjugate effectively with the π‐framework, and the 2‐(CH₃)₂N group twisted out from the plane of the backbone and loses conjugation. As a result, the degree of charge transfer from the N‐2– and N‐8– nitrogen lone pairs to the π‐framework varies, which affects the ¹H, ¹³C and ¹⁵N shieldings. Copyright © 2012 John Wiley & Sons, Ltd.     

Synthesis,Spectroscopic Characterization,and Oxidative C–C Coupling in New Copper(II) Salicylaldiminates Containing Sterically Hindered Phenol

New bis[N‐(2,6‐di‐tert‐butyl‐1‐hydroxyphenyl)salicylideneminato]copper(II) complexes bearing HO and CH₃O substituents on the salicyaldehyde moiety were prepared, and have been characterized by elemental analyses, IR, UV/Vis, ESR spectroscopy, and magnetic moments. It has been found that in the synthesis of CH₃O substituted complexes unlike HO bearing, the oxidative C–C coupling of coordinated salicylaldimine ligands take place. It has been suggested that the intermolecular H‐bonding is a dominant factor in controlling of oxidative C–C coupling conversion. The powder ESR spectra of CH₃O substituted compounds unlike of HO are typical of a triplet state Cu^II dimers with a half‐field forbidden (δM = ± 2) and the allowed (δM = ± 1) transitions at 300 and 113 K.     

Kinetics and mechanisms for reactions of HNO with CH3 and C6H5 studied by quantum‐chemical and statistical‐theory calculations

Kinetics and mechanisms for the reactions of HNO with CH₃ and C₆H₅ have been investigated by ab initio molecular orbital (MO) and transition‐state theory (TST) and/or Rice‐Ramsperger‐Kassel‐Marcus/Master Equation (RRKM/ME) calculations. The G2M(RCC, MP2)//B3LYP/6‐31G(d) method was employed to evaluate the energetics for construction of their potential energy surfaces and prediction of reaction rate constants. The reactions R + HNO (R = CH₃ and C₆H₅) were found to proceed by two key product channels giving (1) RH + NO and (2) RNO + H, primarily by direct abstraction and indirect association/decomposition mechanisms, respectively. As both reactions initially occur barrierlessly, their rate constants were evaluated with a canonical variational approach in our TST and RRKM/ME calculations. For practical applications, the rate constants evaluated for the atmospheric‐pressure condition are represented by modified Arrhenius equations in units of cm³ mol^?1 s^?1 for the temperature range 298–2500 K: κ_1A = 1.47 × 10¹¹ T ^0.76 exp[?175/ T ], κ_2A = 8.06 × 10³ T ^2.40 exp[?3100/ T ], κ_1B = 3.78 × 10⁵ T ^2.28 exp[230/ T ], and κ_2B = 3.79 × 10⁹ T ^1.19 exp[?4800/ T ], where A and B represent CH₃ and C₆H₅ reactions, respectively. Based on the predicted rate constant at 1 atm pressure for R + HNO → RNO + H, we estimated their reverse rate constants for R + HNO production from H + RNO in units of cm³ mol^?1 s^?1: κ_?2A′ = 7.01 × 10¹⁰ T ^0.84 exp[120/ T ] and κ_?2B′ = 2.22 × 10¹⁹ T ^?1.01 exp[?9700/ T ]. The heats of formation at 0 K for CH₃NO, CH₃N(H)O, CH₃NOH, C₆H₅N(H)O, and C₆H₅NOH have been estimated to be 18.6, 18.1, 22.5, 47.2, and 50.7 kcal mol^?1 with an estimated ±1 kcal mol^?1 error. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 261–274, 2005     

2‐Amino‐8‐(2‐deoxy‐2‐fluoro‐β‐d‐arabinofuranosyl)imidazo[1,2‐a][1,3,5]triazin‐4(8H)‐one monohydrate,a 2′‐deoxyguanosine analogue with an altered Watson–Crick recognition site

The title compound, C₁₀H₁₂FN₅O₄·H₂O, shows an anti glycosyl orientation [χ = −123.1 (2)°]. The 2‐deoxy‐2‐fluoroarabinofuranosyl moiety exhibits a major C2′‐endo sugar puckering (S‐type, C2′‐endo–C1′‐exo, ²T₁), with P = 156.9 (2)° and τ_m = 36.8 (1)°, while in solution a predominantly N conformation of the sugar moiety is observed. The conformation around the exocyclic C4′—C5′ bond is −sc (trans, gauche), with γ = −78.3 (2)°. Both nucleoside and solvent molecules participate in the formation of a three‐dimensional hydrogen‐bonding pattern via intermolecular N—H...O and O—H...O hydrogen bonds; the N atoms of the heterocyclic moiety and the F substituent do not take part in hydrogen bonding.     

Gas‐phase reactions of Cl atoms with propane,n‐butane,and isobutane

Using the relative kinetic method, rate coefficients have been determined for the gas‐phase reactions of chlorine atoms with propane, n‐butane, and isobutane at total pressure of 100 Torr and the temperature range of 295–469 K. The Cl₂ photolysis (λ = 420 nm) was used to generate Cl atoms in the presence of ethane as the reference compound. The experiments have been carried out using GC product analysis and the following rate constant expressions (in cm³ molecule^?1 s^?1) have been derived: (7.4 ± 0.2) × 10^?11 exp [‐(70 ± 11)/ T], Cl + C₃H₈ → HCl + CH₃CH₂CH₂; (5.1 ± 0.5) × 10^?11 exp [(104 ± 32)/ T], Cl + C₃H₈ → HCl + CH₃CHCH₃; (7.3 ± 0.2) × 10^?11 exp[?(68 ± 10)/ T], Cl + n‐C₄H₁₀ → HCl + CH₃ CH₂CH₂CH₂; (9.9 ± 2.2) × 10^?11 exp[(106 ± 75)/ T], Cl + n‐C₄H₁₀ → HCl + CH₃CH₂CHCH₃; (13.0 ± 1.8) × 10^?11 exp[?(104 ± 50)/ T], Cl + i‐C₄H₁₀ → HCl + CH₃CHCH₃CH₂; (2.9 ± 0.5) × 10^?11 exp[(155 ± 58)/ T], Cl + i‐C₄H₁₀ → HCl + CH₃CCH₃CH₃ (all error bars are ± 2σ precision). These studies provide a set of reaction rate constants allowing to determine the contribution of competing hydrogen abstractions from primary, secondary, or tertiary carbon atom in alkane molecule. © 2002 Wiley Periodicals, Inc. Int J Chem Kinet 34: 651–658, 2002     

7‐Amino‐1‐(2‐deoxy‐β‐erythro‐pentofuranosyl)‐1H‐1,2,3‐triazolo[4,5‐d]pyrimidine: an 8‐azaadenine nucleoside with the nucleobase in a syn conformation

The title compound, C₉H₁₂N₆O₃, shows a syn‐glycosylic bond orientation [χ = 64.17 (16)°]. The 2′‐deoxyfuranosyl moiety exhibits an unusual C1′‐exo–O4′‐endo (₁T⁰; S‐type) sugar pucker, with P = 111.5 (1)° and τ_m = 40.3 (1)°. The conformation at the exocyclic C4′—C5′ bond is +sc (gauche), with γ = 64.4 (1)°. The two‐dimensional hydrogen‐bonded network is built from intermolecular N—H...O and O—H...N hydrogen bonds. An intramolecular bifurcated hydrogen bond, with an amino N—H group as hydrogen‐bond donor and the ring and hydroxymethyl O atoms of the sugar moiety as acceptors, constrains the overall conformation of the nucleoside.     

More Than 12 % Polarization and 20 Minute Lifetime of 15N in a Choline Derivative Utilizing Parahydrogen and a Rhodium Nanocatalyst in Water

Hyperpolarization techniques are key to extending the capabilities of MRI for the investigation of structural, functional and metabolic processes in vivo. Recent heterogeneous catalyst development has produced high polarization in water using parahydrogen with biologically relevant contrast agents. A heterogeneous ligand‐stabilized Rh catalyst is introduced that is capable of achieving ¹⁵N polarization of 12.2±2.7 % by hydrogenation of neurine into a choline derivative. This is the highest ¹⁵N polarization of any parahydrogen method in water to date. Notably, this was performed using a deuterated quaternary amine with an exceptionally long spin‐lattice relaxation time (T₁) of 21.0±0.4 min. These results open the door to the possibility of ¹⁵N in vivo imaging using nontoxic similar model systems because of the biocompatibility of the production media and the stability of the heterogeneous catalyst using parahydrogen‐induced polarization (PHIP) as the hyperpolarization method.     

Alkoxy-1,3,5-triazapentadien(e/ato) copper(II) complexes: template formation and applications for the preparation of pyrimidines and as catalysts for oxidation of alcohols to carbonyl products

Template combination of copper acetate (Cu(AcO)₂?H₂O) with sodium dicyanamide (NaN(C≡N)₂, 2 equiv) or cyanoguanidine (N≡CNHC(=NH)NH₂, 2 equiv) and an alcohol ROH (used also as solvent) leads to the neutral copper(II)–(2,4‐alkoxy‐1,3,5‐triazapentadienato) complexes [Cu{NH?C(OR)NC(OR)?NH}₂] (R=Me ( 1 ), Et ( 2 ), nPr ( 3 ), iPr ( 4 ), CH₂CH₂OCH₃ ( 5 )) or cationic copper(II)–(2‐alkoxy‐4‐amino‐1,3,5‐triazapentadiene) complexes [Cu{NH?C(OR)NHC(NH₂)?NH}₂](AcO)₂ (R=Me ( 6 ), Et ( 7 ), nPr ( 8 ), nBu ( 9 ), CH₂CH₂OCH₃ ( 10 )), respectively. Several intermediates of this reaction were isolated and a pathway was proposed. The deprotonation of 6 – 10 with NaOH allows their transformation to the corresponding neutral triazapentadienates [Cu{NH?C(OR)NC(NH₂)?NH}₂] 11 – 15 . Reaction of 11 , 12 or 15 with acetyl acetone (MeC(?O)CH₂C(?O)Me) leads to liberation of the corresponding pyrimidines NC(Me)CHC(Me)NC NHC(?NH)OR, whereas the same treatment of the cationic complexes 6 , 7 or 10 allows the corresponding metal‐free triazapentadiene salts {NH₂C(OR)?NC(NH₂)?NH₂}(OAc) to be isolated. The alkoxy‐1,3,5‐triazapentadiene/ato copper(II) complexes have been applied as efficient catalysts for the TEMPO radical‐mediated mild aerobic oxidation of alcohols to the corresponding aldehydes (molar yields of aldehydes of up to 100 % with >99 % selectivity) and for the solvent‐free microwave‐assisted synthesis of ketones from secondary alcohols with tert‐butylhydroperoxide as oxidant (yields of up to 97 %, turnover numbers of up to 485 and turnover frequencies of up to 1170 h^?1).     

Die Kristallstruktur von cis‐ und trans‐N‐iso‐Propylamidodimethylindium, [(CH3)2In‐N(H)iC3H7]2

The Crystal Structure of cis‐ and trans‐N‐iso‐Propylamidodimethyl Indium, [(CH₃)₂In‐N(H)ⁱC₃H₇]₂ According to the X‐ray structure determination [(CH₃)₂In‐N(H)ⁱC₃H₇]₂ (prepared from InMe₃ (Me = CH₃) and H₂NⁱPr (ⁱPr = CH(CH₃)₂) crystallizes in the monoclinic space group P2₁/n with 3 dimeric trans as well as 3 dimeric cis isomers per unit cell. The centrosymmetric form has a planar In₂N₂ core with In—N bonds of 222.1(4) and 222.9(5) pm, respectively, the skeleton of the cis isomer with In—N bonds of 221.4(4) pm is slightly folded (13.7°). Some ¹H, ¹³C NMR, IR, and Raman data are reported.