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Amide bond formation is one of the most important reactions in organic chemistry because of the widespread presence of amides in pharmaceuticals and biologically active compounds. Existing methods for amides synthesis are reaching their inherent limits. Described herein is a novel rhodium‐catalyzed three‐component reaction to synthesize amides from organic azides, carbon monoxide, and (hetero)arenes via nitrene‐intermediates and direct C−H functionalization. Notably, the reaction proceeds in an intermolecular fashion with N2 as the only by‐product, and either directing groups nor additives are required. The computational and mechanistic studies show that the amides are formed via a key Rh‐nitrene intermediate. [ABSTRACT FROM AUTHOR]

Abstract: Heteroscorpionate ligands of the bis(pyrazolyl)methane family have been applied in the stabilisation of terminal copper tosyl nitrenes. These species are highly active intermediates in the copper‐catalysed direct C−H amination and nitrene transfer. Novel perfluoroalkyl‐pyrazolyl‐ and pyridinyl‐containing ligands were synthesized to coordinate to a reactive copper nitrene centre. Four distinct copper tosyl nitrenes were prepared at low temperatures by the reaction with SO2tBuPhINTs and copper(I) acetonitrile complexes. Their stoichiometric reactivity has been elucidated regarding the imination of phosphines and the aziridination of styrenes. The formation and thermal decay of the copper nitrenes were investigated by UV/Vis spectroscopy of the highly coloured species. Additionally, the compounds were studied by cryo‐UHR‐ESI mass spectrometry and DFT calculations. In addition, a mild catalytic procedure has been developed where the copper nitrene precursors enable the C−H amination of cyclohexane and toluene and the aziridination of styrenes. [ABSTRACT FROM AUTHOR]

The chemistry of aryl azides and aryl nitrenes is rich and varied in nature with different products being obtained with minor changes in reaction conditions. Thermolysis of azido- dimethylsuccinylosuccinate has been carried out to study the behaviour of this new azide during thermolysis. The products obtained have been studied by various spectroscopic and DFT calculations. These results reveal formation of compound- II and compound- III from the nitrene intermediate ( 1 ) generated during the thermolysis process. DFT results rationalized the formation of thermodynamically stable compound- II and compound- III from the stable intermediates 2 and 4 formed during the thermolysis process. Further, DFT results suggest that the reaction between 4 and 2 is thermodynamically more favourable compared to the further thermal degradation of the intermediate 4 to pyridylcarbene ( 4b ) and carbene intermediate ( 5 ), which corroborates that such products were not formed during thermolysis. [ABSTRACT FROM AUTHOR]

We report herein three new modes of reactivity between arylazides N3Ar with a bulky copper(I) β-diketiminate. Addition of N3ArX3 (ArX3=2,4,6-X3C6H2; X=Cl or Me) to [iPr2NN]Cu(NCMe) results in triazenido complexes from azide attack on the β-diketiminato backbone. Reaction of [iPr2NN]Cu(NCMe) with bulkier azides N3Ar leads to terminal nitrenes [iPr2NN]Cu]=NAr that dimerize via formation of a C−C bond at the arylnitrene p-position to give the dicopper(II) diketimide 4 (Ar=2,6-iPr2C6H3) or undergo nitrile insertion to give diazametallocyclobutene 8 (Ar=4-Ph-2,6-iPr2C6H2). Importantly, reactivity studies reveal both 4 and 8 to be 'masked' forms of the terminal nitrenes [iPr2NN]Cu=NAr that undergo nitrene group transfer to PMe3, tBuNC, and even into a benzylic sp3 C−H bond of ethylbenzene. [ABSTRACT FROM AUTHOR]

A new sextet ground state molecule, the 2,4,6-trichloro-1,3-dinitrenophenoxyl radical, was obtained upon UV of the corresponding diazido precursor in argon at 5 K. The sextet molecule is formed stepwise with the triplet nitrene, the quartet nitreno radical, and the quintet dinitrene as intermediates that were detected by EPR spectroscopy. IR and UV-Vis measurements only allowed us to observe the main product, the quintet dinitrene. The coupling between the two nitrene centers and the oxygen centered radical in the sextet state results in zero-field splitting (zfs) parameters of |D/hc| = 0.088 cm−1 and |E/hc| = 0.009 cm−1, considerably larger than in previously reported organic sextet molecules. An analogous sextet dinitrene formed by replacing the oxygen centered radical by a carbon centered radical was also studied by EPR spectroscopy, and in this case the zfs parameters |D/hc| = 0.125 cm−1 and |E/hc| = 0.023 cm−1 indicate even larger spin localization. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

As the prototype Curtius rearrangement reaction, carbamoyl azide decomposes into aminoisocyanate and molecular nitrogen. However, the key intermediate carbamoylnitrene was previously undetected, even though the decomposition of carbamoyl azides has been studied frequently since its discovery in the 1890s. Upon ArF laser (λ=193 nm) photolysis, the stepwise decomposition of the two simplest carbamoyl azides H2NC(O)N3 and Me2NC(O)N3, isolated in solid noble gas matrices, occurs with the formation of the corresponding carbamoylnitrenes H2NC(O)N and Me2NC(O)N. Both triplet species are characterized for the first time by combining matrix-isolation IR spectroscopy and quantum-chemical calculations. Subsequent visible-light irradiations cause efficient rearrangement of these nitrenes into the respective aminoisocyanates. [ABSTRACT FROM AUTHOR]

The RhII-catalyzed oxyamination and diamination of alkenes generate 1,2-amino alcohols and 1,2-diamines, respectively, in good to excellent yields and with complete regiocontrol. In the case of diamination, the intramolecular reaction provides an efficient method for the preparation of pyrrolidines, and the intermolecular reaction produces vicinal amines with orthogonal protecting groups. These alkene difunctionalizations proceed by aziridination followed by nucleophilic ring opening induced by an Rh-bound nitrene generated in situ, details of which were uncovered by both experimental and theoretical studies. In particular, DFT calculations show that the nitrogen atom of the putative [Rh]2=NR metallanitrene intermediate is electrophilic and support an aziridine activation pathway by N ⋅⋅⋅N=[Rh]2 bond formation, in addition to the N ⋅⋅⋅[Rh]2=NR coordination mode. [ABSTRACT FROM AUTHOR]

The intramolecular benzylic C−H amination catalyzed by bimetallic paddlewheel complexes was investigated by using density functional theory calculations. The metal-metal bonding characters were investigated and the structures featuring either a small HOMO-LUMO gap or a compact SOMO energy scope were estimated to facilitate an easier one-electron oxidation of the bimetallic center. The hydrogen-abstraction step was found to occur through three manners, that is, hydride transfer, hydrogen migration, and proton transfer. The imido N species are more preferred in the Ru-Ru and Pd-Mn cases whereas coexisting N species, namely, singlet/triplet nitrene and imido, were observed in the Rh-Rh and Pd-Co cases. On the other hand, the triplet nitrene N species were found to be predominant in the Pd-Ni and Pd-Zn systems. A concerted asynchronous mechanism was found to be modestly favorable in the Rh-Rh-catalyzed reactions whereas the Pd-Co-catalyzed reactions demonstrated a slight preference for a stepwise pathway. Favored stepwise pathways were seen in each Ru-Ru- and Pd-Mn-catalyzed reactions and in the triplet nitrene involved Pd-Ni and Pd-Zn reactions. The calculations suggest the feasibility of the Pd-Mn, Pd-Co, and Pd-Ni paddlewheel complexes as being economical alternatives for the expensive dirhodium/diruthenium complexes in C−H amination catalysis. [ABSTRACT FROM AUTHOR]

Alkene aziridination by azides through uncatalyzed thermal gas phase routes has been studied using the DFT B3LYP/6-31G(d,p) method, where the possible role of discrete nitrene intermediates is emphasized. The thermal decomposition of azides is studied using the MP2/aug-cc-pVDZ strategy as well. The MP2 (but not the B3LYP) results discount the existence of singlet alkylnitrenes where the alkyl group has an α-hydrogen. Addition of the lowest lying singlet and triplet nitrenes R-N (R = H, Me, Ac) to four different alkene substrates leading to aziridine formation was studied by the B3LYP method. Singlet nitrenes with alkenes can yield aziridines via a concerted mechanism, where H-N insertion takes place without a barrier, whereas Me-N shows larger barriers than Ac-N. Methyl substitution in the alkene favors this reaction. Triplet nitrene addition to alkenes is studied as a two-step process, where the initially formed diradical intermediates cyclize to form aziridines by ISC (intersystem crossing) and collapse. Scope for C-C bond rotation in the diradical leads to loss of stereochemical integrity for triplet nitrene addition to cis- and trans-2-butenes. Geometries of the transition states in the various reaction steps studied here are described as 'early' or 'late' in good accordance with the Hammond postulate. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

A facile and efficient one-pot synthesis of isoxazol-3(2 H)-ones has been developed starting from α-acyl cinnamides and tosyliminophenyliodinane catalyzed by copper(II) acetate [Cu(OAc)2] under very mild conditions involving a tandem aza-Michael addition and intramolecular cyclization sequence. [ABSTRACT FROM AUTHOR]

N-Acyl nitrenes have been generated from a range of heterocyclic precursors, and their applications in light-induced ruthenium-catalyzed sulfur imidations have been studied. Analyzing the reaction scope and determining the structural requirements of the in situ formed electrophilic nitrogen species for effective nitrene transfer allowed a mechanistic scheme to be proposed. The mechanistic conclusions were substantiated by the identification of potential intermediates. [ABSTRACT FROM AUTHOR]

The mechanism of the nitrene-group transfer reaction from an organic azide to isonitrile catalyzed by a ZrIV d0 complex carrying a redox-active ligand was studied by using quantum chemical molecular-modeling methods. The key step of the reaction involves the two-electron reduction of the azide moiety to release dinitrogen and provide the nitrene fragment, which is subsequently transferred to the isonitrile substrate. The reducing equivalents are supplied by the redox-active bis(2-iso-propylamido-4-methoxyphenyl)-amide ligand. The main focus of this work is on the mechanism of this redox reaction, in particular, two plausible mechanistic scenarios are considered: 1) the metal center may actively participate in the electron-transfer process by first recruiting the electrons from the redox-active ligand and becoming formally reduced in the process, followed by a classical metal-based reduction of the azide reactant. 2) Alternatively, a non-classical, direct ligand-to-ligand charge-transfer process can be envisioned, in which no appreciable amount of electron density is accumulated at the metal center during the course of the reaction. Our calculations indicate that the non-classical ligand-to-ligand charge-transfer mechanism is much more favorable energetically. Utilizing a series of carefully constructed putative intermediates, both mechanistic scenarios were compared and contrasted to rationalize the preference for ligand-to-ligand charge-transfer mechanism. [ABSTRACT FROM AUTHOR]

The group 6 MIV terminal oxo complexes, Cp*M[N(iPr) C(Me)N(iPr)](O) (Cp* = η5-C5Me5) where M = Mo (1) and W (2) react with N3SiMe3 to provide the MVI terminal nitrido complexes, Cp*M[N(iPr)C(Me)N(iPr)](N)(OSiMe3) where M = Mo (5) and W (7), respectively. A mechanism involving nitrene group transfer to generate a MVI oxo, imido intermediate, followed by inter-ligand silyl group transfer is proposed to account for formation of 5 and 7. Compound 7 was alternatively prepared through an orthogonal route to the same proposed intermediate involving oxygen atom transfer from N2O to the WIV terminal imido complex Cp*W[N(iPr)C(Me)N(iPr)](NSiMe3) (4). The nucleophilicity of the terminal nitride 7 was further established through methylation to provide cationic {Cp*W[N(iPr)C(Me) N(iPr)](NMe)(OSiMe3)}{I} (8). [ABSTRACT FROM AUTHOR]

The yield of the Lewis acid adducts of a copper-tosylnitrene intermediate and their decay are dependent on the Lewis acidity of the redox innocent metal ions. Surprisingly, however, their spectroscopic properties and reactivity in nitrene transfer reaction with PPh3 are independent of the nature of the Lewis acid used. The result provides some new insights into the structure and reactivity of the Lewis-acid bound copper nitrene complexes. [ABSTRACT FROM AUTHOR]

1,4,2-Dioxazol-5-ones are five-membered heterocycles known to decarboxylate under thermal or photochemical conditions, thus yielding N-acyl nitrenes. Described herein is a light-induced ruthenium-catalyzed N-acyl nitrene transfer to sulfides and sulfoxides by decarboxylation of 1,4,2-dioxazol-5-ones at room temperature, thus providing direct access to N-acyl sulfimides and sulfoximines under mild reaction conditions. In addition, a one-pot sulfur imidation/oxidation sequence catalyzed by a single ruthenium complex is reported. [ABSTRACT FROM AUTHOR]

The details of reaction mechanism of imidogen (NH) and hydroxyl radicals are explored at the UMP2(FC)/cc-pVDZ and PMP4(FC,SDTQ)/cc-pVQZ//UMP2 + ZPE levels, theoretically. The initial association between NH and OH radicals leads to the formation of the intermediates, NH...OH, HN...HO, cis HNOH, and trans HNOH, through the barrierless and exothermic processes. By starting from the initial intermediates, all possible paths for the formation of H + HNO, H + NO, HO + N, HN + O, and H + HON products are investigated on potential energy surface. The results reveal that HO + N is the main product involved in the mechanism of hydrogen atom abstraction of NH by OH radical through the intermediate NH...OH. [ABSTRACT FROM AUTHOR]

1-Azidophthalazine 9A is generated in trace amount by mild FVT of tetrazolo[5,1-α]phthalazine 9T and is observable by its absorption at 2121 cm-1 in the Ar matrix 1R spectrum. Ar matrix photolysis of 9T/9A at 254 nm causes ring opening to generate two conformers of (o-cyanophenyl)diazoniethane 11 (2079 and 2075 cm-1), followed by (o-cyanophenyl)carbene ³12, cyanocycloheptatetraene 13, and finally cyano(phenyl)carbene ³14 as evaluated by IR spectroscopy. The two carbenes ³12 and ³14 were observed by ESR spectroscopy (D\hc = 03078, E\hc = 0.0236 and D\hc = 0.6488, E\hc = 0.0195 cm-1, respectively). The rearrangement of 12 ... 2 13 ... 14 constitutes a carbene--carbene rearrangement. 1-Phthalazinylnitrene ³10 is observed by means of its UV--vis spectrum in Ar matrix following FVT of 9 above 550 °C. Rearrangement to cyanophenylcarbenes also takes place on FVT of 9 as evidenced by observation of the products of ring contraction, viz., fulvenallenes and ethynylcydopentadienes 16-18. Thus the overall rearrangement 10 → 11 → 12 ... 13 ... 14 can be formulated. [ABSTRACT FROM AUTHOR]

Organoazides and their nitrogen expulsion chemistry have attracted the attention of many scientists because they serve as a useful source of nitrene fragments and interesting nitrene rearrangement products. Gold-mediated reactions are also of significant current interest. This manuscript describes several important discoveries based at the intersection of these fields. In particular, we report the first isolable gold organoazides ([(SIPr)AuN(1-Ad)NN][SbF6], [(SIPr)AuN(2-Ad)NN][SbF6] and [(SIPr)AuN(Cy)NN]- [SbF6]; SIPr = a N-heterocyclic carbene; 1-AdNNN = 1- azidoadamantane; 2-AdNNN = 2-azidoadamantane; CyNNN = azidocyclohexane), and their gold-mediated nitrogen expulsion chemistry, and the isolation of formal nitrene rearrangement products of “1-AdN”, “2-AdN” and “CyN” (including the elusive 4- azahomoadamant-3-ene) as their gold complexes. We have also performed a computational study to understand and explain the observed structure of gold-coordinated 1-AdNNN and 2-AdNNN and their nitrogen elimination pathways, which implies that the conversion of the organoazide complex to the imine is a concerted process without a nitrene/nitrenoid intermediate. Kinetic studies of [(SIPr)AuN(2-Ad)NN][SbF6] from 30 to 50 °C indicate that nitrogen elimination is a first-order process. The experimentally determined activation parameters are in good agreement with the calculated values. [ABSTRACT FROM AUTHOR]

We examine important reactivity pathways relevant to stoichiometric and catalytic C-H amination via isolable β-diketiminato dicopper alkylnitrene intermediates {[Cl2NN]Cu}2(μ-NR). Kinetic studies involving the stoichiometric amination of ethylbenzene by {[Cl2NN]Cu}2(μ-NtBu) (3) demonstrate that the terminal nitrene [Cl2NN]Cu NtBu is the active intermediate in C-H amination. Initial rates exhibit saturation behavior at high ethylbenzene loadings and an inverse dependence on the copper species [Cl2NN]Cu, both consistent with dissociation of a [Cl2NN]Cu fragment from 3 prior to C-H amination. C-H amination experiments employing 1,4-dimethylcyclohexane and benzylic radical clock substrate support a stepwise H-atom abstraction/radical rebound pathway. Dicopper nitrenes [Cu]2(μ-NCHRR') derived from 1° and 2° alkylazides are unstable toward tautomerization to copper(I) imine complexes [Cu](HN CRR'), rendering 1° and 2° alkylnitrene complexes unsuitable for C-H amination. [ABSTRACT FROM AUTHOR]

The 7-coordinate complex [Fe(qpy)(MeCN)2](ClO4)2 (1, qpy = 2,2':6',2'':6'',2''':6''',2''''-quinquepyridine) is a highly active nonheme iron catalyst for intra- and intermolecular amination of C(sp3)-H bonds. This complex effectively catalyzes the amination of limiting amounts of not only benzylic and allylic C(sp3)-H bonds of hydrocarbons but also the C(sp3)-H bonds of cyclic alkanes and cycloalkane/linear alkane moieties in sulfamate esters, such as those derived from menthane and steroids cholane and androstane, using PhI-NR or "PhI(OAc)2 + H2NR" [R = Ts (p-toluenesulfonyl), Ns (p-nitrobenzenesulfonyl)] as nitrogen source, with the amination products isolated in up to 93% yield. Iron imide/nitrene intermediates [Fe(qpy)(NR)(X)]n+ (CX, X = NR, solvent, or anion) are proposed in these amination reactions on the basis of experimental studies including ESI-MS analysis, crossover experiments, Hammett plots, and correlation with C-H bond dissociation energies and with support by DFT calculations. Species consistent with the formulations of [Fe(qpy)(NTs)2]2+ (CNTs) and [Fe(qpy)(NTs)]2+ (C) were detected by high-resolution ESI-MS analysis of the reaction mixture of 1 with PhI=NTs (4 equiv). DFT calculations revealed that the reaction barriers for H-atom abstraction of cyclohexane by the ground state of 7-coordinate CNTs and ground state of C are 15.3 and 14.2 kcal/mol, respectively, in line with the observed high activity of 1 in catalyzing the C-H amination of alkanes under mild conditions. [ABSTRACT FROM AUTHOR]

C-H amination by iron-imido/nitrene species has attracted increasing research interest in recent years because of its potential use in economical and environmentally benign syntheses of amino compounds. With the aim of providing a comprehensive overview of this field, which is of interest to both the synthetic organic and inorganic communities, this paper reviews the status quo of C-H amination chemistry by iron-imido/nitrene intermediates, as well as by well-defined iron-imido/nitrene compounds, with special emphasis on their structure/reactivity correlations. Achievements, problems, and perspectives in this growing field are discussed. [ABSTRACT FROM AUTHOR]

High-valent copper-nitrene intermediates have long been proposed to play a role in copper-catalyzed aziridination and amination reactions. However, such intermediates have eluded detection for decades, preventing the unambiguous assignments of mechanisms. Moreover, the electronic structure of the proposed copper-nitrene intermediates has also been controversially discussed in the literature. These mechanistic questions and controversy have provided tremendous motivation to probe the accessibility and reactivity of CuIII-NR/CuIIN•R species. In this paper, we report a breakthrough in this field that was achieved by trapping a transient copper-tosylnitrene species, 3-Sc, in the presence of scandium triflate. The sufficient stability of 3-Sc at −90 °C enabled its characterization with optical, resonance Raman, NMR, and X-ray absorption near-edge spectroscopies, which helped to establish its electronic structure as CuIIN•Ts (Ts = tosyl group) and not CuIIINTs. 3-Sc can initiate tosylamination of cyclohexane, thereby suggesting CuIIN•Ts cores as viable reactants in oxidation catalysis. [ABSTRACT FROM AUTHOR]

The analytical possibilities of portable photocolorimeter, reflectometer and scanner have been compared by the example of different test systems, involving Co(II) and Fe(III) complexes with thiocyanate and nitrite ions adsorbed onto polyurethane foams. The performance characteristics of Co(II), Fe(III) and nitrite ion determination in water using portable instruments have been determined. The reproducibility and the area of possible application of the instruments have been assessed. [ABSTRACT FROM AUTHOR]

The tetrahydrido complex [WH4(κ4-P4)] (P4= meso-o-C6H4(PPhCH2CH2PPh2)2) reacted with aliphatic nitrilesAkCN at 80 °C in toluene to afford a series of the imido complexes,[W(NCH2Ak)(κ4-P4)] (2). Similar reactions with aromatic nitriles ArCN proceededstepwise, leading to formation of the hydrido–alkylideneamidocomplexes [WH(NCHAr)(κ4-P4)](3) at the first stage and a subsequent isomerizationinto the imido complexes [W(NCH2Ar)(κ4-P4)] (4). Conversion of 3into 4was accelerated by electron-rich Ar groups suchas p-CH3OC6H4, whileit was completely inhibited when Ar was the considerably electron-deficient p-CF3C6H4. An X-ray crystallographicstudy on 2(Ak = p-ClC6H4CH2) and 4(Ar = p-tolyl) has disclosed a distorted-square-pyramidal coordination geometry,in which the apical position is occupied by the imido ligand witha WII–N triple bond. An almost linear WIINC linkage of 3(Ar = p-tolyl) has also been determined. Complex 2was capableof nitrene group transfer to isocyanide to produce carbodiimide. [ABSTRACT FROM AUTHOR]

Laser flash photolysis, phosphorescence and density functional calculations were used to characterize the triplet excited states of phenylethanol derivatives 1, 2, 3 and 4. In acetonitrile, the triplet excited states of these alcohols were formed with rate constants on the order of ~107 s-1 and decayed with rate constants between 105 and 106 s-1. The energies of these triplet excited states were between 80 and 83 kcal/mol. Furthermore, 3 can be used as a triplet sensitizer for alkyl azides to form triplet nitrene intermediates. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Rearrangements of aromatic and heteroaromatic nitrenes and carbenes can be initiated with either heat or light. The thermal reaction is typically induced by flash vacuum thermolysis, with isolation of the products at low temperatures. Photochemical experiments are conducted either under matrix isolation conditions or in solution at ambient temperature. These rearrangements are usually initiated by ring expansion of the nitrene or carbene to a seven-membered ring ketenimine, carbodiimide, or allene (that is, a cycloheptatetraene or an azacycloheptatetraene when a nitrogen is involved). [ABSTRACT FROM AUTHOR]

The geometries and energies of the electronic states of phenyloxenium ion 1 (Ph-O+) were computed at the multireference CASPT2/pVTZ level of theory. Despite being isoelectronic to phenylnitrene 4, the phenyloxenium ion 1 has remarkably different energetic orderings of its electronic states. The closed-shell singlet configuration (1A1) is the ground state of the phenyloxenium ion 1, with a computed adiabatic energy gap of 22.1 kcal/mol to the lowest-energy triplet state (3A2). Open-shell singlet configurations (1A2, 1B1, 1B2, 21A1) are significantly higher in energy (>30 kcal/mol) than the closed-shell singlet configuration. These values suggest a revision to the current assignments of the ultraviolet photoelectron spectroscopy bands for the phenoxy radical to generate the phenyloxenium ion 1. For para-substituted phenyloxenium ions, the adiabatic singlet-triplet energy gap (ΔEST) is found to have a positive linear free energy relationship with the Hammett-like σ+R/σ+ substituent parameters; for meta substituents, the relationship is nonlinear and negatively correlated. CASPT2 analyses of the excited states of p-aminophenyloxenium ion 5 and p-cyanophenyloxenium ion 10 indicate that the relative orderings of the electronic states remain largely unperturbed for these para substitutions. In contrast, meta-donor-substituted phenyloxenium ions have low-energy open-shell states (open-shell singlet, triplet) due to stabilization of a π,π* diradical state by the donor substituent. However, all of the other phenyloxenium ions and larger aryloxenium ions (naphthyl, anthryl) included in this study have closed-shell singlet ground states. Consequently, ground-state reactions of phenyloxenium ions are anticipated to be more closely related to closed-shell singlet arylnitrenium ions (Ar-NH+) than their isoelectronic arylnitrene (Ar-N) counterparts. [ABSTRACT FROM AUTHOR]

Organic molecules with a strong preference for triplet ground states, in which the triplet state is below the lowest singlet state by ⩾10 kcal/mol, are typically short-lived and mostly detected as reactive intermediates. We now report a triplet ground state derivative of aza-m-xylylene diradical with a large singlet-triplet energy gap (ΔEST) of ~10 kcal/mol, which is comparable to ΔEST for the well-known reactive intermediate m-xylylene diradical. The aminyl diradical persists in solution at room temperature on the time scale of minutes. [ABSTRACT FROM AUTHOR]

Abstract: The thermal reactions of fluoroalkanesulfonyl azides RfSO2N3 with pyrazine and its derivatives are studied in detail. All the reactions involved the fluoroalkanesulfonyl nitrene intermediates RfSO3N: which was captured by pyrazine to give the pyrazinium N-fluoroalkanesulfonyl ylides C4NH4N+–−NSO2Rf and hydrogen abstraction product RfSO2NH2, but no corresponding N-pyrazinyl fluoroalkanesulfonyl amide derivatives RfSO2NHC4N2H3 were isolated. Excess azides did not afford the bisN-ylide product RfSO2N−–+NC4H4N+–−NSO2Rf. [Copyright &y& Elsevier]

Septet 3,5-dicyanopyridyl-2,4,6-trinitrene was synthesized together with quintet 2-azido-3,5-dicyanopyridyl-4,6-dinitrene, quintet 4-azido-3,5-dicyanopyridyl-2,6-dinitrene, triplet 2,6-diazido-3,5-dicyanopyridyl-4-nitrene, and triplet 2,4-diazido-3,5-dicyanopyridyl-6-nitrene by photolysis of 2,4,6-triazido-3,5-dicyanopyridine in solid argon at 4 K. The electronic and magnetic properties of the matrix-isolated nitrenes were studied using electron paramagnetic resonance (EPR) spectroscopy in combination with density functional theory (DFT) calculations. The fine-structure parameters of the nitrenes were determined with high accuracy from spectral simulations. All signals in the EPR spectra of the nitrenes, randomly oriented in the solid phase, were unambiguously assigned based on eigenfield calculations of the Zeeman energy levels and angular dependences of resonance fields. Copyright © 2009 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The enthalpies for H-atom abstraction reactions by triplet imidogen as well as ethyl, alkoxycarbonyl, acyl, phenyl, and vinyl nitrenes were calculated using density functional theory calculations. These calculations show that H-atom abstraction reactions are only feasible for triplet imidogen, alkoxycarbonyl, and acyl nitrenes in solution. The calculated charges on the N-atoms (QNPA) in the nitrene correlate with the magnitude of the transition state barrier for the H-atom abstraction reactions from methanol as a model reactant. Electron-withdrawing substituents on these nitrenes make them less stable but do not affect the transition state barrier significantly. Thus, as the electron deficiency of the N-atom in the nitrenes is increased, the H-atom abstraction reaction becomes more feasible. Copyright © 2010 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The photochemistry of a series of fluorinated p-iodophenyl azides 2 has been investigated using matrix isolation IR and EPR spectroscopy. In all cases, the corresponding phenylnitrenes 1 were formed as primary photoproducts. Further irradiation of the nitrenes 1 resulted in the formation of azirines 3, ketenimines 4, and nitreno radicals 5. The yield of 5 depends on the number of ortho fluorine substituehts: with two ortho fluorine atoms the highest yield is observed, whereas without fluorine atoms the yield is too low for JR spectroscopic detection. The interconversion between the isomers 1, 3, and 4 proved to be rather complex. If the fluorine atoms are distributed unsymmetrically, two isomers of azirines 3 and ketenimines 4 can be formed. The yields of these isomers depend critically on the irradiation conditions. [ABSTRACT FROM AUTHOR]

Nitrene transfer reactions represent a useful methodology to synthesize in a few steps high added-value compounds used as organic intermediates. Herein, we describe the catalytic activity of metal porphyrin complexes in a wide range of reactions such as C–H hydrocarbon amination and olefin aziridination to synthesize nitrogen containing molecules. All the most important nitrene sources have been reviewed stressing the potentiality and limits of each one in the particular class of chemical transformation. [ABSTRACT FROM AUTHOR]

Abstract: Carbonaceous dolomites and shales of the 1.64 billion years (Ga) old Barney Creek Formation (BCF), McArthur Basin, northern Australia contain the oldest, clearly indigenous biomarkers. We describe three new series of regularly branched aryl isoprenoids with base ions at m/z 119, 161 and 175. The m/z 119 compounds were identified as a complete series of C15–C40 oligoprenyl-perhydro-ar-curcumenes (oligoprenyl-curcumanes). Their likely biogenic precursors are oligoprenyl-β-curcumenes that occur in a wide range of bacterial phyla. [Copyright &y& Elsevier]

We performed a detailed study of the NH + O2potential energy surface by means of a number of multireference (CASSCF, MC-QDPT2, MR-AQCC, MR-CISD(18;13)+Q with 6-311+G(d,p), and aug-cc-pVTZ basis sets) and composite (G3B3, G3MP2B3, CBS-QB3, W1U) methods. Parent nitroso oxide, HNOO, was found to be the key intermediate of this process. In its ground state, 1A′, HNOO exists in two conformations, where the cisform is 8.1−10.9 kJ·mol−1more stable than the trans-nitroso oxide. The mechanism of nitrene oxidation by dioxygen may be represented as a set of various transformations of vibrationally excited HNOO, namely, decomposition into NO and OH radical pair, O−O dissociation reaction, and a number of thermal deactivation processes. We localized all stationary points of these transformations on both the singlet and the triplet reaction PES. The energies of reactants, products, and transition states were calculated at the RI-MR-CISD(18;13)+Q/aug-cc-pVTZ level of theory; the vibrational analysis of these species was done by means of CASSCF(18;13)/6-311+G(d,p). Apparent rate constants of the NH + O2reaction were calculated using RRKM theory. The total rate constant ktotalcorresponds well to available experimental data. The temperature dependence of ktotalis rather nontrivial and consists of three quasi-linear intervals. At low temperatures (up to room temperature) the slope of log(ktotal) vs 1/Tis negative due to prevailing stabilization of HNOO. The rate-determining channel of the “NH + O2” reaction in the medium-temperature interval (up to ∼1000 K) was found to be formation of the NO + OH radical pair via H transfer to the terminal oxygen atom. This reaction is accelerated by a factor of 4.2 (214 K) and 1.2 (2500 K) due to tunnel effect. The distinctive feature of the NH + O2high-temperature chemistry is the increase of the effective activation energy due to prevailing dissociation of the HNOO peroxide bond. [ABSTRACT FROM AUTHOR]

A critical review is presented of the results of (experimental) quantitative structural studies of molecular reaction intermediates at surfaces; i.e. molecular species that do not exist naturally in the gas phase and, in most cases, are implicated in surface catalytic processes. A brief review of the main experimental methods that have contributed to this area is followed by a summary of the main results. Investigated species include: carboxylates, RCOO– (particularly formate, but also deprotonated amino acids); methoxy, CH3O–; carbonate, CO3; ethylidyne, CH3C–; NHx and SOx species; cyanide, CN. As far as possible in the limited range of systems studied, a few general trends are identified (108 references). [ABSTRACT FROM AUTHOR]

Mndoped ZnO were synthesized by solid state reaction and solgel method respectively. It was found that samples synthesized by solid state reaction containing Mn2O3and MnO2are a mixture of ferromagnetic and paramagnetic phases. Contrary, samples without second phases were found to be paramagnetic at room temperature. According to previous report, interface effects between Znrich Mn2O3and MnO2interfaces may be the origin of the ferromagnetic behavior observed in our samples prepared by solid reaction, so the alloy of Zn1?xMnxO may be paramagnetic at room temperature. Prepared by solgel technique, the samples without second phases in the XRD patterns are also roomtemperature paramagnetic. Therefore we believe that the magnetism of Zn1?xMnxO is paramagnetic at room temperature. © 2008 WILEYVCH Verlag GmbH & Co. KGaA, Weinheim [ABSTRACT FROM AUTHOR]

In the present work, the effects of sulphate ions on the iron precipitation from aqueous solution were investigated. It was shown that sulphate ions delayed the iron precipitation when this ion was added in form of Na2SO4. This effect became less significant in presence of magnesium or calcium. The iron precipitates were characterized by Xray diffraction XRD, scanning electron microscopy SEM and differential scanning calorimetry DSC. In all experiments iron oxide hydroxide FeOOH precipitates were obtained. The sulphate ions were adsorbed on the surfaces of the iron precipitates. The effect of temperature on these precipitates was also studied. At 237 °C, the iron oxide hydroxide precipitates obtained from NaCl solution was transformed in crystallized hematite, Fe2O3. At 793 °C, the hematite was partially transformed into magnetite Fe3O4. In presence of sulphate ions, this transformation was not detected. © 2008 WILEYVCH Verlag GmbH & Co. KGaA, Weinheim [ABSTRACT FROM AUTHOR]

1,3-Bis(2-formylphenoxy)-2-propanol (BFPP) was first synthesized and then grafted to 3-(triethoxysilyl)propyl isocyanate (TESPIC) to achieve a molecular precursor BFPP−Si through the hydrogen-transfer nucleophilic addition reaction between the hydroxyl group of BFPP and the isocyanate group of TESPIC. Then, a chemically bonded lanthanide/inorganic/organic hybrid material (BFPP−Si−Ln) was constructed using BFPP−Si as a bridge molecule that can both coordinate to lanthanide ions (Eu 3+or Tb 3+) and form an inorganic Si−O network with tetraethoxysilane (TEOS) after cohydrolysis and copolycondensation processes. Furthermore, two types of ternary rare-earth/inorganic/organic hybrids (BFPP−Si−Dipy−Ln and BFPP−Si−Phen−Ln) were assembled by the introduction of the second ligands (4,4′-bipyridyl and 1,10-phenanthroline) into the above system. All of these hybrid materials exhibit homogeneous microstructures and morphologies, suggesting the occurrence of self-assembly of the inorganic network and organic chain. Measurements of the photoluminescent properties of these materials show that the ternary rare-earth/inorganic/organic hybrids present stronger luminescent intensities, longer lifetimes, and higher luminescent quantum efficiencies than the binary hybrids, indicating that the introduction of the second ligands can sensitize the luminescence emission of the lanthanide ions in the ternary hybrid systems. [ABSTRACT FROM AUTHOR]

Time-resolved infrared (TRIR) spectroscopy, product studies, and computational methods were applied to the photolysis of sulfilimines derived from dibenzothiophene that were expected to release acetylnitrene, trifluoroacetylnitrene, mesylnitrene, and tosylnitrene. All three methods provided results for acetylnitrene consistent with literature precedent and analogous experiments with the benzoylnitrene precursor, i.e., that the ground-state multiplicity is singlet. In contrast, product studies clearly indicate triplet reactivity for trifluoroacetylnitrene, though TRIR experiments were more ambiguous. Product studies suggest that these sulfilimines are superior sources for sulfonylnitrenes, which have triplet grounds states, to the corresponding azides, and computational studies shed light on the electronic structure of the nitrenes. [ABSTRACT FROM AUTHOR]

Linkages between vinylidene (=C:) and nitrenes (-N:), through methyne and its derivatives (CX), give allylic carbenonitrenes, C=(X)C–N, as a new brand of reactive intermediates, with conceivable singlet, triplet, or quintet ground states (X=H, 1, X=CH3, 2, X=COOH, 3, X=F, 4, X=OH, 5, XX=OMe, 6, XX=CF3, 7, XX=CN, 8, and XX=NH2, 9). High-spin quintet (5A″) ground states are found for 1 and 2 at eight ab initio and DFT levels of theory. At the same levels, triplet (3A″) ground states prevail for 3–8. Low-spin singlet (1A') input structures of 1, 2, and 4–9 cyclize spontaneously through optimization to their corresponding aromatic X-azacyclopropenylidenes, with multiplicities irrelevant to allylic carbenonitrenes. Researchers may aim for generating 3–8 with triplet states, or even 1 and/or 2 with quintet states, but we do not recommend going for generation of 9 with any multiplicity, and/or formation of 1–8 with singlet states. [ABSTRACT FROM AUTHOR]

Linkages between vinylidene (=C:) and nitrenes (-N:), through methyne and its derivatives (CX), give allylic carbenonitrenes, C=(X)C–N, as a new brand of reactive intermediates, with conceivable singlet, triplet, or quintet ground states (X=H, 1, X=CH3, 2, X=COOH, 3, X=F, 4, X=OH, 5, XX=OMe, 6, XX=CF3, 7, XX=CN, 8, and XX=NH2, 9). High-spin quintet (5A″) ground states are found for 1 and 2 at eight ab initio and DFT levels of theory. At the same levels, triplet (3A″) ground states prevail for 3–8. Low-spin singlet (1A') input structures of 1, 2, and 4–9 cyclize spontaneously through optimization to their corresponding aromatic X-azacyclopropenylidenes, with multiplicities irrelevant to allylic carbenonitrenes. Researchers may aim for generating 3–8 with triplet states, or even 1 and/or 2 with quintet states, but we do not recommend going for generation of 9 with any multiplicity, and/or formation of 1–8 with singlet states. [ABSTRACT FROM AUTHOR]

Abstract: A model of the active transport of ions in a cardiac muscle cell, which takes into account the active transport of Na+, K+, Ca2+, Mg2+, HCO3 − and Cl− ions, has been constructed. The model allows independent calculations of the resting potential at the biomembrane and concentrations of basic ions (sodium, potassium, chlorine, magnesium and calcium) in a cell. For the analysis of transport processes in cardiac cell hierarchical algorithm “one ion–one transport system” was offered. The dependence of the resting potential on concentrations of the ions outside a cell has been established. It was shown, that ions of calcium and magnesium, despite their rather small concentration, play an essential role in maintenance of resting potential in cardiac cell. The calculated internal concentrations of ions are in good agreement with the corresponding experimental values. [Copyright &y& Elsevier]

The trichloro derivatives [MCl 3(NR)(py) 2] reacted with LiOAr to give the imido aryloxo complexes [MCl 2(NR)(OAr)(py) 2] (M = Nb, R = tBu ( 1a), Ar ( 1b); M = Ta, R = tBu ( 2a); Ar = 2,6- iPr 2C 6H 3) and were alkylated with [BzMgCl], affording the tribenzyl derivatives [NbBz 3(NR)] (R = tBu ( 3a), Ar ( 3b)). Similar alkylations of the aryloxo derivatives 1and 2gave the dibenzyl complexes [MBz 2(NR)(OAr)(THF)] (M = Nb, R = tBu ( 5a); M = Ta, R = tBu ( 6a), Ar ( 6b)). The zwitterionic imido complexes [MBz 2(N tBu){η 6-C 6H 5CH 2E(C 6F 5) 3}] (M = Nb, E = B (7a-B ), Al ( 7a-Al); M = Ta, E = Al ( 8a-Al)) were obtained upon addition of 1 equiv of E(C 6F 5) 3(E = B, Al) to the tribenzyl derivatives [MBz 3(N tBu)] (M = Nb ( 3a), Ta ( 4a)). The aryloxo compound 6areacted with 2 equiv of the Lewis acids E(C 6F 5) 3(E = B, Al) to give the corresponding zwitterionic imido complexes [TaBz(N tBu)(OAr){η 6-C 6H 5CH 2E(C 6F 5) 3}] (E = B ( 11a-B), Al ( 11a-Al)) and the adduct (THF)·E(C 6F 5) 3, through two different intermediates, the ionic [TaBz(N tBu)(OAr)(THF)][BzB(C 6F 5) 3] ( 9a) for E = B and the neutral [TaBz 2(N tBu)(OAr)] ( 10a) for E = Al. The related monocyclopentadienyl complex [ZrCpBz 2{η 6-C 6H 5CH 2Al(C 6F 5) 3}] ( 12-Al) was also isolated by reaction of [ZrCpBz 3] with Al(C 6F 5) 3. DFT calculations were carried out to further understand this type of zwitterionic imido derivative in comparison with the isolobal zirconium cyclopentadienyl compound [ZrCpBz 2{η 6-C 6H 5CH 2B(C 6F 5) 3}]. MMA polymerization was investigated for the [MBz 2X(N tBu)]/E(C 6F 5) 3(X = Bz, OAr) and [ZrCpBz 3]/E(C 6F 5) 3(E = B, Al) systems. [ABSTRACT FROM AUTHOR]

Novel reactions that can selectively functionalize carbon–hydrogen bonds are of intense interest to the chemical community because they offer new strategic approaches for synthesis. A very promising ‘carbon–hydrogen functionalization’ method involves the insertion of metal carbenes and nitrenes into C–H bonds. This area has experienced considerable growth in the past decade, particularly in the area of enantioselective intermolecular reactions. Here we discuss several facets of these kinds of C–H functionalization reactions and provide a perspective on how this methodology has affected the synthesis of complex natural products and potential pharmaceutical agents. [ABSTRACT FROM AUTHOR]

‘Tritopic’ picolinic dihydrazone ligands with tridentate coordination pockets are designed to produce homoleptic [3 × 3] nonanuclear square grid complexes on reaction with transition-metal salts, and many structurally documented examples have been obtained with Mn(ll), Cu(ll), and Zn(ll) ions. However, other oligomeric complexes with smaller nuclearities have also been discovered and identified structurally in some reactions involving Fe(ll), Co(ll), Ni(ll), and Cu(ll), with certain tritopic ligands. This illustrates the dynamic nature of the metal-ligand interaction and the conformationally flexible nature of the ligands and points to the possible involvement of some of these species as intermediates in the [3 × 3] grid formation process. Examples of mononuclear, dinuclear, hexanuclear, heptanuclear, and nonanuclear species involving Fe(ll), Co(II), Ni(ll), and Cu(ll) salts with a series of potentially heptadentate picolinic dihydrazone ligands with pyrazine, pyrimidine, and pyridine end groups are described in the present study. Iron and cobalt complexation reactions are complicated by redox processes, which lead to mixed-oxidation-state Co(ll)/Co(lll) systems when starting with Co(lI) salts, and reduction of Fe(lll) to Fe(lI) when starting with Fe(lll). Magnetic exchange within the polynuclear structural frameworks is discussed and related to the structural features. [ABSTRACT FROM AUTHOR]

Abstract: Tb-activated scintillating glasses with Ln2O3 (Ln=Y, Gd, Lu) concentrations up to 40mol% have been prepared. The effects of Ln3+ ions on the density, thermal properties, transmission, and luminescence properties under both UV and X-ray excitation have been investigated. Glasses containing Gd2O3 or Lu2O3 exhibit a density of more than 6.0g/cm3. Energy transfer from Gd3+ to Tb3+ takes place in Gd-containing glass and as a result the Gd-containing glass shows a light yield 2.5 times higher than the Y- or Lu-containing glass. The effect of the substitution of fluorine for oxygen on the optical properties was also investigated. [Copyright &y& Elsevier]

Abstract: A new highly sensitive and selective colorimetric method for fluoride determination in water is described. The novel reagent used is a hemicyanine dye (HC), which forms a stable complex with Zr–EDTA, the fluoride-binding site, through the hydroxyl groups. The hemicyanine-chelating Zr–EDTA complex (HC–Zr–EDTA) is ready to react with fluoride ion to release HC. This result in remarkable color change of the sensing solutions from red (λ max =513nm) to yellow (λ max =427nm) at pH 4.40. When applied to the colorimetric determination of fluoride ions, a linear range from 3.0×10−6 to 5.0×10−5 mol/L and a detection limit of 2.8×10−6 mol/L with a correlation coefficient of 0.9993 can be achieved under the optimized conditions. Because of the specific affinity of fluorides for the [Zr–EDTA], there is little interference by other ions. This method has been successfully applied to the determination of fluorides in toothpaste samples. [Copyright &y& Elsevier]

Photoderivatized polymer-coated gold surfaces have been developed following a perfluorophenylazide-based double ligation strategy. Gold-plated quartz crystal microbalance (QCM) crystals were initially covalently functionalized with a monolayer of poly(ethylene glycol) (PEG), using photo- or thermolytic nitrene formation and insertion. The polymer surfaces were subsequently used as substrates for photoinsertion of carbohydrate-derivatized photoprobes, yielding different recognition motifs for selective protein binding. The resulting robust and biocompatible sensor surfaces were applied to a flow-through QCM instrument for monitoring lectin—carbohydrate interactions in real time. The results clearly show the predicted lectin selectivity, demonstrating the applicability of the approach. [ABSTRACT FROM AUTHOR]

Abstract: In this study the separation of cadmium(II) from iron(III) has been successfully realized by a hybrid liquid membrane (HLM) containing tri-n-octylamine (TNOA, R3N)–secondary octylalcohol (ROH)–kerosene. The effect of different variable on the separation has been carefully studied. The apparatus composed of three compartments, including a reservoir of organic solution, with double solid supports was used in this study. The experiments show that the transport of Cd(II) ions is coupled by the co-transport flow of protons and the nitric acid in the feed phase of the HLM system can apparently improve the separation efficiency of cadmium(II) from iron(III). The loss of TNOA in the membrane phase was determined. The experiments demonstrated that the HLM can automatically and continuously replenish the membrane supports pores by the membrane solution (organic phase). [Copyright &y& Elsevier]