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Bis(pyrazolyl)borate complexes [BBN(pzR)2]Cu(I) were evaluated as catalysts in the reaction of carbene/nitrene transfer and addition to C=C bonds of a wide range of aromatic, heterocyclic and aliphatic olefins. The complexes exhibit high catalytic efficiency and selectivity in both processes. [ABSTRACT FROM AUTHOR]

The VIth International Symposium "The Chemistry of Diazo Compounds and Related Systems" (DIAZO 2021) was held at the St. Petersburg State University from 6 to 10 September 2021. At the symposium, the advances in diazo chemistry over the past decade were summed up, and promising directions for further research were discussed. The review contains brief annotations of the plenary, keynote, invited and oral presentations and includes references to the relevant works of the speakers. [ABSTRACT FROM AUTHOR]

Insertion reactions of donor/donor carbenes have emerged from obscurity to become a versatile method for the synthesis of a variety of cyclic structures with excellent control of diastereo- and enantio-selectivity. This Account describes the origin of this project as part of a natural product synthesis and the ensuing decade of reaction development that has resulted in new asymmetric methods as well as intriguing tangential observations. [ABSTRACT FROM AUTHOR]

Aziridination reactions represent a powerful tool in aziridine synthesis. Significant progress has been achieved in this field in the last decades, whereas highly functionalized aziridines including 3-arylated aziridine-2-carbonyl compounds play an important role in both medical and synthetic chemistry. For the reasons listed, in the current review we have focused on the ways to obtain 3-arylated aziridines and on the recent advances (mainly since the year 2000) in the methodology of the synthesis of these compounds via aziridination.

Graphical abstract Theoretical advances on the mechanistic study of Ag-catalyzed carbene/nitrene/silylene transfer reactions were summarized in this review, which could be considered to involve two major steps: Ag–carbene/nitrene/silylene complex formation and the subsequent transformation of these complexes. Highlights • DFT studies on the mechanism of Ag-catalyzed group transfer reactions are summarized. • The mechanism consists of Ag–carbene/nitrene/silylene formation and transformation. • The mechanism is related to the electronic behaviors of Ag–carbene/nitrene/silylene. Abstract Carbene and its isoelectronic species nitrene and silylene, have long been considered reactive intermediates in organic synthesis. Ag-catalyzed carbene/nitrene/silylene transfer reactions have emerged as an important topic because they have made remarkable progress in organic synthesis. A series of theoretical investigations on the mechanism of these reactions is important to ensure their thorough understanding and aid design of new synthetic methodologies. Here, a mechanistic overview of Ag-catalyzed carbene/nitrene/silylene transfer reactions is given, which can be separated into two major steps including Ag–carbene/nitrene/silylene complex formation and the subsequent transformation of these complexes. Theoretical studies revealed that Ag–carbene and Ag–silylene complexes can be considered as typical Fischer-type complexes, in which the carbene/silylene moiety behaves as both a sp σ donor and p π acceptor. Conversely, the triplet Ag–nitrene complexes are usually more stable than the singlet ones because of the higher electronegativity of nitrogen than those of carbon and silicon. Density functional theory calculations have indicated that the triplet state of an Ag–nitrene complex has two unpaired electrons that are mainly localized on nitrogen. In this review, theoretical studies on the generation of Ag–carbene/nitrene/silylene complexes are systematically summarized. Moreover, the nucleophilic functionalization of Ag–carbene/nitrene/silylene complexes with halogen, hydroxyl, carbonyl, alkane, or arene groups are also considered theoretically. We believe that the mechanistic details discussed here will be of great importance for rational design of desired catalytic cycles and reactions. [ABSTRACT FROM AUTHOR]

The recently formulated multiconfiguration-based unitary coupled electron pair approximation (UCEPA) is compared with multireference configuration interaction (MR-CISD) calculations, including all single and double excitations, for the molecules in this study. The electronic states of the molecules in this study are not only of experimental interest, but represent a challenge to any formalism to accurately predict the energy separations of the low-lying electronic states. The equilibrium geometries and fundamental vibrational frequencies of the three lowest electronic states (i.e., 1A1, 3A‘, and 1A‘) of aminonitrene H2N2, and phosphinonitrene, H2PN, have been determined using a split-valence basis with polarization functions on the heavy atoms and a small complete active space self-consistent-field (CASSCF) description of the active space. Both MR-CISD and UCEPA calculations have been performed at the equilibrium structures using larger basis sets to accurately determine the relative energetics of the electronic states. The equilibrium geometries and vibrational frequencies of the two lowest electronic states (i.e., 1A’ and 3A‘) of phosphinocarbene, H2PCH, have been determined using a larger than double zeta basis set, augmented with polarization and diffuse functions, and a CASSCF description of the active space. Both MR-CISD and UCEPA calculations were performed on the equilibrium structures and predict that the singlet lies between 10.4 and 11.8 kcal/mol lower in energy than the triplet. The use of a generalized valence bond (GVB) reference function within UCEPA is introduced and is shown to be a useful approximation. [ABSTRACT FROM AUTHOR]

Abstract: Carbenes and nitrenes can exist in both singlet and triplet states, sometimes equally stable and interconverting either thermally or photochemically. Many carbene and nitrene reactions proceed via tunneling at low temperatures. Numerous singlet and triplet states have been characterized spectroscopically, and a detailed understanding of the chemical and physical properties of carbenes and nitrenes is emerging. There has been significant progress in the direct observation of carbenes, nitrenes, and many other reactive intermediates in recent years through the application of matrix photolysis and flash vacuum pyrolysis linked with matrix isolation at cryogenic temperatures. Our understanding of singlet and triplet states has improved through the interplay of spectroscopy and computations. Bistable carbenes and nitrenes as well as many examples of tunneling have been discovered and numerous rearrangements and fragmentations have been documented. The correlation of the zero‐field splitting parameter D with calculated spin densities on nitrenes and carbenes is discussed. This Minireview gives an overview of some of these developments. [ABSTRACT FROM AUTHOR]

The functionalization of C(sp3)−H bonds streamlines chemical synthesis by allowing the use of simple molecules and providing novel synthetic disconnections. Intensive recent efforts in the development of new reactions based on C−H functionalization have led to its wider adoption across a range of research areas. This Review discusses the strengths and weaknesses of three main approaches: transition-metal-catalyzed C−H activation, 1, n-hydrogen atom transfer, and transition-metal-catalyzed carbene/nitrene transfer, for the directed functionalization of unactivated C(sp3)−H bonds. For each strategy, the scope, the reactivity of different C−H bonds, the position of the reacting C−H bonds relative to the directing group, and stereochemical outcomes are illustrated with examples in the literature. The aim of this Review is to provide guidance for the use of C−H functionalization reactions and inspire future research in this area. [ABSTRACT FROM AUTHOR]

• Establishing mechanisms for mesoionic carbene iron-catalyzed nitrene transfer reactions. • First predicting amination-to-aziridination chemoselectivity. • Suggesting that the substrate scope of this novel catalytic system expands to alkenes to greatly broaden its applications in constructing N-heterocyclic compounds. The mesoionic carbene iron complex is a new catalyst, and its catalytic mechanisms for the nitrene transfer reactions were investigated via density functional theory calculations. Especially, the amination-to-aziridination chemoselectivity is predicted for the first time. The origin of the chemoselectivity toward C(sp3)–H amination has been revealed. Based on our calculated results, it can be suggested that the substrate scope of this novel catalytic system may be expanded to alkenes to greatly broaden its potential applications in constructing N-heterocyclic compounds. The chemoselectivity of mesoionic carbene iron‐catalyzed intramolecular nitrene transfer reactions is predicted for the first time. [Display omitted] [ABSTRACT FROM AUTHOR]

Functionalization of C-H bonds has received significant attention in organic chemistry during the last decade and it is still a 'hot' topic. In particular, C-H modification of natural products has benefitted from this development. Carbohydrates are densely functionalized natural products, and methods for their functionalization are therefore very attractable. This review presents methods from the last five decades and gives an overview of the developments in C-H functionalization of carbohydrates. It covers all methods in which a C-H bond is broken: from radical abstractions and carbene insertion to new metal-catalyzed approaches. The review systematically covers the carbohydrates position-by-position and hence gives a quick overview. [ABSTRACT FROM AUTHOR]

The formally CoIV carbene Co(OR)2( = CPh)2) is formed upon the reaction of diphenyldiazomethane with the cobalt bis(alkoxide) precursor Co- (OR))2(THF))2. Structural, spectroscopic, and theoretical studies demonstrate that Co(OR))2(=CPh)2) has significant high-valent CoIV= CPh)2 character with non-negligible spin density on the carbene moiety. [ABSTRACT FROM AUTHOR]

A computational study using both density functional and correlated wavefunction methods on the reaction between ethylene and model zinc carbenoid, nitrenoid and oxenoid complexes (L–Zn–E–X, E = CH 2 , NH or O, L = X = I or Cl) is reported. An investigation at DFT and MP2 levels of theory predicts that the epoxidation of ethylene with ClZnOCl oxenoid proceeds through a two-step mechanism involving an initial oxometalation and subsequent ring-closure, the latter being the rate determining step (RDS). Among all DFT methods applied in this study, BP86/CEP-31G(d) method produced the most similar geometries and energy barrier for the second step to those derived from MP2 simulations with correlation consistent basis sets. Interestingly, the mechanism of the cyclization reaction of ethylene with LZnEX is dependent on both E and X groups. Cyclopropanation of ethylene with IZnCH 2 I and aziridination of ethylene with IZnNHI proceed via a single-step mechanism with an asynchronous transition state. The reaction barrier for the aziridination with IZnNHI is 5.4 kcal/mol lower than that of cyclopropanation. Changing the leaving group of IZnNHI from I to Cl changes the mechanism of the aziridination reaction to a two-step pathway, with the second step as the RDS. The calculation results from the epoxidation with IZnOI and ClZnOCl oxenoids suggest a two-step mechanism for both oxenoids. The epoxidation reaction barriers for the RDS for both IZnOI and ClZnOCl is ∼15 kcal/mol, which is ∼6 kcal/mol less than that calculated for aziridination of ethylene with ClZnNHCl nitrenoid. [ABSTRACT FROM AUTHOR]

The room-temperature stable phosphinonitrene 1 undergoes a thermal rearrangement into heterocycle 2 through a process involving a nitrene insertion into a CH bond. In the presence of acetonitrile, a nitrene-acetonitrile adduct has been isolated; then it first rearranges into a ketenimine and subsequently into a rare example of diazaphosphete. Compound 1 also splits water, carbon dioxide, carbon disulfide, and elemental sulfur, although it reacts with white phosphorus, leading to a P5N cluster formally resulting from the insertion of the PN moiety into a P-P edge of the P4 tetrahedron. [ABSTRACT FROM AUTHOR]

Copper complexes with chiral iminopyridine ligands were screened for their catalytic efficiency in carbene () and nitrene transfer reactions (, CH ). Both pre-formed and in situ formed complexes were considered. The results highlighted the poor catalytic efficiency of these complexes in employing methyl phenyldiazoacetate as the carbene source, whereas better results were obtained in nitrene transfer reactions, particularly in the of CH bonds, albeit the of the reactions was negligible in nearly all cases. Finally, copper complexes were also found to promote an interesting oxidative of alkynes with PhI(OAc)2 at room temperature. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Bis(NHC)ruthenium(II)-porphyrin complexes were designed, synthesized, and characterized. Owing to the strong donor strength of axial NHC ligands in stabilizing the trans MCRR′/MNR moiety, these complexes showed unprecedently high catalytic activity towards alkene cyclopropanation, carbene CH, NH, SH, and OH insertion, alkene aziridination, and nitrene CH insertion with turnover frequencies up to 1950 min−1. The use of chiral [Ru( D4-Por)(BIMe)2] ( 1 g) as a catalyst led to highly enantioselective carbene/nitrene transfer and insertion reactions with up to 98 % ee. Carbene modification of the N terminus of peptides at 37 °C was possible. DFT calculations revealed that the trans axial NHC ligand facilitates the decomposition of diazo compounds by stabilizing the metal-carbene reaction intermediate. [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]

This paper illustrates the research on the photochemistry of reactive intermediates that was (and still is) carried out in the author's research group on three typical examples: the photochemistry of arylcarbenes, arylnitrenes, and organic radical cations.

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]

Abstract: A brief survey of the structure, methods of generation and reactivity of the singlet and triplet carbenes and nitrenes is given. The DFT and CCSD(T) calculations of the singlet–triplet energy gap ΔE ST for a large number of differently substituted carbenes and nitrenes are performed and the dependence of ΔE ST on the substituent(s) at the sextet center is discussed. [Copyright &y& Elsevier]

It was shown using IR spectroscopy and ESR spectroscopy that UV irradiation of 2-azido-4,6-dichloro-1,3,5-triazine isolated in solid argon resulted in triplet 4,6-dichloro-1,3,5-tri-azinyl-2-nitrene ( D = 1.384 cm, E = 0.004 cm), whose further photochemical transformation included the consecutive formation of 3-didehydro-1,2,4,6-tetraazepine, 2-chloro-1-diazochloromethyl-2-isocyanocarboimide, and presumably triplet 2-chloro-1-chloromethyl-idene-2-isocyanocarboimide and isocyanodichloroacetonitrile. The photolysis of 2-azido-4,6-dimethoxy-1,3,5-triazine and 2-azido-4,6-di(dimethylamino)-1,3,5-triazine affords photo-chemically stable triplet 4,6-dimethoxy-1,3,5-triazinyl-2-nitrene ( D = 1.436 cm, E = 0.0044 cm) and 4,6-bis(dimethylamino)-1,3,5-triazinyl-2-nitrene ( D = 1.468 cm, E = 0.0042 cm) as the final products. [ABSTRACT FROM AUTHOR]

Matrix photolysis of 4-quinolyl azide 22 affords 4-quinolylnitrene 21, identified by electron spin resonance (ESR) and infrared (IR) spectroscopy. Minor absorptions assigned to azirene 23 (1741 cm−1) were also observed. Further photolysis affords strong absorptions at 1902 and 1909 cm−1 ascribed to the cyclic ketenimine 19 as well as weaker absorptions at 2044 cm−1 ascribed to the open-chain ketenimine 26 and at 1982 cm−1 assigned to the open-chain nitrile ylide 25. Both 2-(5-tetrazolyl)quinoxaline 14 and triazolo[1,5- a]quinoxaline 16 give rise to an absorption at 2084 cm−1 because of formation of the diazo compound 15 on mild flash vacuum thermolysis (FVT) with Ar matrix isolation of the product. Matrix photolysis of 16 affords diazo compound 15, cyclic ketenimine 19 and open-chain ketenimine 26. 2-Quinoxalinylcarbene 17 was also formed in the matrix photolysis and identified by its ESR spectrum. FVT of either 22 or 15/16 afforded 4-quinolylnitrene, identified by its Ar-matrix ESR spectrum. A second nitrene ESR signal obtained in several FVT and photolysis experiments from both 22 and 16 is ascribed to the phenylnitrene derivative 24 formed by ring opening of 2-quinoxalinylcarbene 17. FVT of 14, 16, and 22 affords 3-cyanoindole 27 as the major product. Minor amounts of 2-cyanoindole 28, 4-aminoquinoline 29 and 4,4′-azoquinoline 30 are also formed. Preparative photolysis of 22 in solution in the presence of dialkylamines leads to trapping of the azirene 23 to afford 5-dialkylaminobenzo[ e]-1,4-diazepines 35. 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]

A gold-catalyzed intermolecular nitrene transfer to alkynes was developed for the first time, revealing a new mode of nitrene transfer and providing a novel access to versatile α-imino metal carbenes. Various mild nitrene-transfer reagents were examined, and iminopyridium ylides especially those based on 3,5-dichloropyridine proved be highly effective. With activated alkynes such as N-alkynyloxazolidinones as substrates, α,β-unsaturated amidines were formed in mostly good yields. [ABSTRACT FROM AUTHOR]

Metalloporphyrins are a class of versatile catalysts with the capability to functionalize saturated C–H bonds viaseveral well-defined atom/group transfer processes, including oxene, nitrene, and carbene C–H insertions. The corresponding hydroxylation, amination, and alkylation reactions provide direct approaches for the catalytic conversion of abundant hydrocarbons into value-added functional molecules through C–O, C–N, and C–C bond formations, respectively. This tutorial reviewdescribes metalloporphyrin-based catalytic systems for the functionalization of different types of sp3C–H bonds, both inter- and intramolecularly, including challenging primary C–H bonds. Additional features of metalloporphyrin-catalyzed C–H functionalization include unusual selectivities and high turnover numbers. [ABSTRACT FROM AUTHOR]

Coupling of a local triplet carbene with a local triplet nitrene through an acetylene linkage gives a new brand of high spin quintet minima (X - C̈ - C ≡ C - N̈, where X = H, F, Cl, Br), which are rather experimentally unreachable. Placing the same linkage between the local open-shell singlet carbene (δ¹π¹) and the local triplet nitrene (π¹π¹) gives triplet minima which are 54-56 kcal/mol more stable than their corresponding quintets. The carbenic angles in both quintets and triplets follow electropositivity of X (H > Br > Cl > F), with every divalent angle in quintet being smaller than the corresponding one in the triplet. Finally no reactive intermediate is observed through connecting singlet states of carbene and nitrene subunits which gives a neutral linear molecule with X - C ≡ C - C ≡ N formula, and show about 70 kcal/mol more stability than the corresponding triplet states. Our results are compared at B3LYP, HF, MP2, MP4(SDTQ), CCSD(T), and QCISD(T) levels using 6-311++G** basis set. [ABSTRACT FROM AUTHOR]

Middle and late transition metal imido complexes (which may also be viewed as metal—nitrene adducts) are rather rare, especially for square-pyramidal and octahedral coordination geometries. However, an iron(ll) porphyrin aminonitrene adduct, denoted here as Fe(Por)(NN), has been known for almost a quarter of a century. Unlike the corresponding S= 1 oxene and S = 0 carbene adducts, Fe(Por)(NN) exhibits an S = 2 ground slate. DFT calculations reported herein provide a molecular orbital description of this unusual species as well as a rationale for its S = 2 ground stale. The electronic configuration of Fe(Por)(NN) may be described as dπ2dxy1dze1dxe-yedπ'1, where the z direction corresponds to the Fe—NN axis. The stability and double occupancy of one of the dπ orbitals may be attributed to a π-backbonding interaction with the N-N π* orbital. The weak a-donor ability of the aminonitrene ligand results in a relatively low-energy dze orbital and an overall d orbital splitting pattern that engenders a high-spin ground state. [ABSTRACT FROM AUTHOR]

This review article summarizes C-H functionalization-based synthesis of indoles and related structures (e.g. carbazoles and indolines) with an emphasis on literature after 2000. The discussion is organized into four broadly defined sections: a) via nitrene or carbene insertion into a C-H bond; b) via direct coupling of two sp2 carbon centers; c) via transition-metal catalyzed C-H amination and d) other strategies. [ABSTRACT FROM AUTHOR]

The NHC-supported Ni(I) dimer {(IPr)Ni(μ-Cl)}2(1; IPr = 1,3-di(2,6-di-isopropylphenyl)imidazolin-2-ylidene) yields the bridging d8−d8imido complex {(IPr)NiCl}2(μ-NMes) (2; Mes = 2,4,6-Me3C6H2) upon combination with N3Mes. Tosylazide reacts with 1to give the paramagnetic, dark red complex {(IPr)Ni}2(Cl)(μ-Cl)(μ-N,κ1-O:NSO2Tol) (3). Chloride abstraction from 2with NaBArF4affords the d8−d8dimer [{(IPr)Ni}2(μ-Cl)(μ-NMes)]BArF4(4; BArF4= B[3,5-(CF3)C6H3)]4), and reduction of 2with KC8yields the neutral d8−d9mixed-valence complex {(IPr)Ni}2(μ-Cl)(μ-NMes) (5). 2undergoes stoichiometric nitrene group transfer to CO, PMe3, and CNR (R = CH2Ph, CMe3) to form MesNCO, MesNPMe3, and MesNCNR with regeneration of 1. Both 1and 2react with excess CNR to give monomeric, three-coordinate Ni(I) complexes (IPr)NiCl(CNR) (6a, R = CH2Ph; 6bR = CMe3). In the presence of excess CO, 1undergoes disproportionation to give {(IPr)NiCl}2(μ-Cl)2(7) and (IPr)Ni(CO)3. Similarly, reaction of 2with PMe3is accompanied by disproportionation of 1to (IPr)NiCl2(PMe3) (8) and [(IPr)Ni]2. Catalytic carbodiimide (MesNCNR) formation is achieved with 10 mol % 1, N3Mes, and CNR. Catalytic mesityl isocyanate (MesNCO) formation is achieved with 10 mol % 4, N3Mes, and CO. [ABSTRACT FROM AUTHOR]

In high-spin chemistry, random-orientation fine-structure (FS) electron spin resonance (ESR) spectroscopy entertains advantages as the most facile and convenient method to identify high-spin systems, as frequently reported in the literature. Random-orientation ESR spectroscopy applicable to organic high-spin entities can date back to the Wasserman and co-workers’ attempt on the first spin-quintet dicarbene, m-phenylenebis(phenylmethlene) (m-PBPM), in the 2-MTHF glass in 1963 and 1967, following their successful work on randomly oriented triplet-state ESR spectroscopy. The FS ESR spectrum of m-PBPM in the 2-MTHF glass, however, has never fully been analyzed due to a peculiar line-broadening appearing at many canonical peaks. Organic high-spin spectra from most quintet dinitrenes also suffer from similar phenomena. Seemingly intrinsic line-diffusing or -broadening phenomena adversely affect the reliable determination of FS parameters for organic high-spin entities in rigid glasses. In high-spin chemistry, the line-broadening has been an obstacle that masks key FS transitions in many cases. Thus, both the origin of the broadening and the comprehensive spectral analysis have been a long-standing issue. In this report, we examine the origin of the line-broadening appearing in the FS ESR spectra, illustrated by a comprehensive spectral analysis for m-PBPM in the quintet ground state and the first-documented quintet-state dinitrene, m-phenylenebis(nitrene) (m-PBN) in the 2-MTHF glass. A complete analysis of the random-orientation FS spectra from m-PBPM diluted in the benzophenone crystal has shown that the g-anisotropy of m-PBPM is not prominent. Also the higher-order FS terms such as Si2Sj2group-theoretically allowed for S= 2 are not necessary in spite of the argument for a hydrocarbon-based tetraradical (S= 2) in the ground state. Our new approach to the line-broadening analysis invokes both exact analytical solutions for the resonance fields of canonical peaks and the magnetic-parameters gradient method. The D- and E-values of m-PBPM acquired by the spectral simulation in this study give different molecular structures of the quintet dicarbene in the benzophenone crystal lattice (D= +0.07030cm−1, E= +0.02120cm−1) and in the 2-MTHF glass (D= +0.07800cm−1, E= +0.02210cm−1). Microscopic origins of the line-broadening observed for high-spin oligocarbenes or oligonitrenes generated by photolysis in organic glasses have been proposed. [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]

The first α-difluoromethyl sulfoximine compound, 2, was successfully prepared by using the copper(II)-catalyzed nitrene transfer reaction. Compound 2was found to be a novel and efficient difluoromethylation reagent for transferring the CF2H group to S-, N-, and C-nucleophiles. Deuterium-labeling experiments suggest that a difluorocarbene mechanism is involved in the current difluoromethylation reactions. [ABSTRACT FROM AUTHOR]

Photolysis of 3-azidoquinoline 6 in an Ar matrix generates 3-quinolylnitrene 7, which is characterized by its electron spin resonance (ESR), UV, and IR spectra in Ar matrices. Nitrene 7 undergoes ring opening to a nitrile ylide 19, also characterized by its UV and IR spectra. A subsequent 1,7-hydrogen shift in the ylide 19 affords 3-(2-isocyanophenyl)ketenimine 20. Matrix photolysis of 1,2,3-triazolo[1,5-c]quinoxaline 26 generates 4-diazomethylquinazoline 27, followed by 4-quinazolylcarbene 28, which is characterized by ESR and IR spectroscopy. Further photolysis of carbene 28 slowly generates ketenimine 20, thus suggesting that ylide 19 is formed initially. Flash vacuum thermolysis (FVT) of both 6 and 26 affords 3-cyanoindole 22 in high yield, thereby indicating that carbene 28 and nitrene 7 enter the same energy surface. Matrix photolysis of 3-quinolyldiazomethane 30 generates 3-quinolylcarbene 31, which on photolysis at >500 nm reacts with N2to regenerate diazo compound 30. Photolysis of 30 in the presence of CO generates a ketene (34). 3-Quinolylcarbene 31 cyclizes on photolysis at >500 nm to 5-aza-2,3-benzobicyclo[4.1.0]hepta-2,4,7-triene 32. Both 31 and 32 are characterized by their IR and UV spectra. FVT of 30 yields a mixture of 2- and 3-cyanoindenes via a carbene–carbene–nitrene rearrangement 31 → 2-quinolylcarbene 39 → 1-naphthylnitrene 43. The reaction mechanisms are supported by density functional theory calculations of the energies and spectra of all relevant ground and transition state structures at the B3LYP/6–31G*level. [ABSTRACT FROM AUTHOR]

New copper(i) complexes with tris(2-pyridyl)methane (TPC), tris(2-pyridyl)methoxymethane (TPM) and tris(2-pyridyl)amine (TPN) ligands have been synthesized and characterized, including structural determinations by X-ray diffraction of some examples. Their activity as catalysts in carbene and nitrene transfer reactions was studied. [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]

We have carried out molecular dynamics (MD) simulations of the aggregation of FeCl 2clusters in supercritical water. The particle formation in systems of 2048 water molecules (rigid SPC/E-model) and 120 Fe 2+ions and 240 Cl −ions has been investigated for 250 ps at five different state points at temperatures from 798 to 873 K and system densities from 0.18 g/cm 3to 0.13 g/cm 3. We describe the particle growth by means of properties of the largest cluster in a system as well as cluster size averaged and time averaged observables. From preexisting or immediately formed units of Fe 2+−Cl −, Fe 2+−Cl −2, Fe 2+−Cl −3etc., the further growth of clusters is dominated by aggregation of such small building blocks. Clusters up to 10 ions in size with large charge imbalances are found during the growth process while a balanced positive to negative charge ratio is found on the average with time and cluster size development. Water molecules are found within the FeCl 2clusters during the whole time interval covered by the simulations, which is in agreement with the existence of crystal water in FeCl 2crystals grown from aqueous solutions. The radial distribution functions obtained from the simulation data are in good agreement with experimental results of slightly distorted FeCl 2·4H 2O crystals. [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]

Abstract  Results of a systematic study of the chemical sensitization of cubic-faceted AgBr emulsion microcrystals with complex compounds K2[XY4] and Na6[XZ4] [X = Pd, Pt; Y = Br−, Cl−, SCN−; Z =(SO3)2−] were considered. The role of secondary dissociation of complex ions during the chemical sensitizing was established. Conditions were determined in which the compounds specified can be used as chemical sensitizers of AgBr. The effect of these complexes on the basic photographic characteristics was demonstrated. [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]

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]

The fragmentation of a 5-membered heteroaromatic ring to afford a conjugated ene–ene–yne skeleton, and the corresponding reverse process, cyclization of the hetero-ene–ene–yne motif to generate a variety of heterocyclic systems, are the subject of this review. These synthetically useful reactions, which proceed through a coarctate/pseudocoarctate mechanistic pathway, are unique in that they involve the generation of either a carbene or nitrene intermediate, and provide access to hard to obtain heterocyclic or ene–ene–yne structures. While fragmentation of heteroaromatic rings containing a exocyclic carbene or nitrene has been well documented in the literature for over 40 years, the use of hetero-ene–ene–yne precursors to synthesize heterocycles is a relatively new approach that is generating much interest in the literature. This review highlights both the synthetic and mechanistic aspects of these unique reactions. [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: 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]

Abstract: The relationship between the adiabatic singlet–triplet gap, electrophilicity, nucleophilicity, spin-philicity and spin-donicity indices is investigated for a large number of carbenes, silylenes, germylenes, nitrenes and phosphinidenes. In accordance with the experimental findings, it is shown that with increasing stability of the singlet state of the molecule the electrophilicity decreases in the case of silylenes and germylenes. The electrophilicity index of nitrenes and phosphinidenes shows no direct correlation to their adiabatic singlet–triplet gap. However, a good correlation is found between the adiabatic singlet–triplet gap and the spin-philicity and spin-donicity indices, and this correlation is universal for all investigated molecules independent of their ground state spin multiplicity. The correlation between spin-philicity and electrophilicity indices for silylenes and germylenes is explained in terms of the stability and the electron distribution of the molecule. [Copyright &y& Elsevier]

Abstract: A β-beam with maximum (for 6He ions) or (for 18Ne) could be achieved at the CERN-SPS. We study the sensitivity to and δ of such a beam as function of γ, optimizing with the baseline constrained to CERN–Frejus (130 km), and also with simultaneous variation of the baseline, for a fixed ion flux. These results are compared to the standard scenario previously considered, with lower , and also with a higher option that requires a more powerful accelerator. We conclude that the sensitivity to CP violation and increases significantly with γ if the baseline is increased proportionally, while for the CERN–Frejus scenario the dependence on γ is mild provided γ is above 100. [Copyright &y& Elsevier]