Chloride ion promoted nucleophilic pentafluorophenylation of imines

Nucleophilic addition of the pentafluorophenyl group from (C₆F₅)₃SiF to non-activated imines affording α-C₆F₅-substituted secondary amines in high yield has been described. The reaction proceeds via simultaneous activation of imines and the silane reagent by means of a proton and chloride ion, respectively.     

Mapping the influence of molecular structure on rates of electron transfer using direct measurements of the electron spin-spin exchange interaction

The spin-spin exchange interaction, 2J, in a radical ion pair produced by a photoinduced electron transfer reaction can provide a direct measure of the electronic coupling matrix element, V, for the subsequent charge recombination reaction. We have developed a series of dyad and triad donor-acceptor molecules in which 2J is measured directly as a function of incremental changes in their structures. In the dyads the chromophoric electron donors 4-(N-pyrrolidinyl)- and 4-(N-piperidinyl)naphthalene-1,8-dicarboximide, 5ANI and 6ANI, respectively, and a naphthalene-1,8:4,5-bis(dicarboximide) (NI) acceptor are linked to the meta positions of a phenyl spacer to yield 5ANI-Ph-NI and 6ANI-Ph-NI. In the triads the same structure is used, except that the piperidine in 6ANI is replaced by a piperazine in which a para-X-phenyl, where X = H, F, Cl, MeO, and Me(2)N, is attached to the N' nitrogen to form a para-X-aniline (XAn) donor to give XAn-6ANI-Ph-NI. Photoexcitation yields the respective 5ANI(+)-Ph-NI(-), 6ANI(+)-Ph-NI(-), and XAn(+)-6ANI-Ph-NI(-) singlet radical ion pair states, which undergo subsequent radical pair intersystem crossing followed by charge recombination to yield (3)NI. The radical ion pair distances within the dyads are about 11-12 A, whereas those in the triads are about approximately 16-19 A. The degree of delocalization of charge (and spin) density onto the aniline, and therefore the average distance between the radical ion pairs, is modulated by the para substituent. The (3)NI yields monitored spectroscopically exhibit resonances as a function of magnetic field, which directly yield 2J for the radical ion pairs. A plot of ln 2J versus r(DA), the distance between the centroids of the spin distributions of the two radicals that comprise the pair, yields a slope of -0.5 +/- 0.1. Since both 2J and k(CR), the rate of radical ion pair recombination, are directly proportional to V(2), the observed distance dependence of 2J shows directly that the recombination rates in these molecules obey an exponential distance dependence with beta = 0.5 +/- 0.1 A(-)(1). This technique is very sensitive to small changes in the electronic interaction between the two radicals and can be used to probe subtle structural differences between radical ion pairs produced from photoinduced electron transfer reactions.     

Resolution of four k-region arene imines and mutagenicity of the optically pure aziridines

Racemic K-region imines of benz[a]anthracene, 7-methylbenz[a]anthracene, chrysene and benzo[a]pyrene ( 1–4 , respectively) have been resolved by high performance liquid chromatography on a column packed with amylose tris(3,5-dimethylphenylcarbamate) on silica gel. The absolute configuration of the resolved aziridines was assigned by comparison of their circular dichromism spectra to those of the corresponding enantiomerically pure arene oxides. The mutagenicity of the enantiomers of the arene imines was investigated using Salmonella typhimurium strains TA98 and TA100. Although all arene imines investigated were potent mutagens, quantitative and qualitative differences in the mutagenic activity were observed between enantiomers.     

Intermolecular alkyne hydroaminations involving 1,1-disubstituted hydrazines

[reaction: see text] Two readily prepared catalysts have been developed for the hydroamination of alkynes by 1,1-disubstituted hydrazines. The catalyses are facile with terminal alkynes and some internal alkynes. If the hydrazine bears an aryl group, Fischer cyclization can occur in a one-pot procedure. In addition, reactions with acetylene to produce a plethora of hydrazones are described. Catalytic reactions involving acetylene and substituted hydrazines are complete in less than 2 h at room temperature and 1 atm of pressure.     

Using spin dynamics of covalently linked radical ion pairs to probe the impact of structural and energetic changes on charge recombination

We have synthesized a series of structurally related, covalently linked electron donor-acceptor triads having highly restricted conformations to study the effects of radical ion pair (RP) structure, energetics, and solvation on charge recombination. The chromophoric electron acceptor in these triads is a 4-aminonaphthalene-1,8-dicarboximide (6ANI), in which the 4-amine nitrogen atom is part of a piperazine ring. The second nitrogen atom of the piperazine ring is part of a para-substituted aniline donor, where the para substituents are X = H, OMe, and NMe(2). The imide group of 6ANI is linked to a naphthalene-1,8:4,5-bis(dicarboximide) (NI) electron acceptor across a phenyl spacer in a meta relationship. The triads undergo two-step photoinduced electron transfer to yield their respective XAn(*)(+)-6ANI-Ph-NI(*)(-) RP states, which undergo radical pair intersystem crossing followed by charge recombination to yield (3)NI. Time-resolved electron paramagnetic resonance experiments on the spin-polarized RPs and triplet states carried out in toluene and in E-7, a mixture of nematic liquid crystals (LCs), show that for all three triads, the XAn(*)(+)-6ANI-Ph-NI(*)(-) RPs are correlated radical pairs and directly yield values of the spin-spin exchange interaction, J, and the dipolar interaction, D. The values of J are all about -1 mT and show that the LC environment most likely enforces the chair conformation at the piperazine ring, for which the RP distance is larger than that for the corresponding boat conformation. The values of D yield effective RP distances that agree well with those calculated earlier from the spin distributions of the radical ions. Within the LC, changing the temperature shows that the CR mechanism can be changed significantly as the energy levels of the RPs change relative to that of the recombination triplet.     

Tight‐binding molecular dynamics simulation of Si?H bond dissociation in silicon clusters

New model of Si? H bond dissociation is proposed and tested in the cluster Si₁₀H₁₆ by the simulation approach that combines classic molecular dynamics method and the self‐consistent tight‐binding electronic and total energy calculation one. It is shown that the monohydride Si? H bond is unstable with respect to silicon dangling bond and bend‐bridge Si? H? Si bond formation when this cluster traps the single positive charge and that hydrogen migrates through a path involving rather rotation around the Si? Si bond than the center of this bond (the bond‐centered position). These results can be useful for understanding hydrogen‐related phenomena at surfaces, interfaces, and internal voids of various hydrogenated silicon systems: electronic devices, silicon solar cells, and nanocrystalline and porous silicon. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 93: 351–359, 2003     

Photochemically induced fluorescence investigation of aβ-cyclodextrin: Azure A inclusion complex and determination of analytical parameters

The photooxidation of Azure A and fluorescence properties of Azure A and its photoproduct have been investigated in aqueous media and in the presence of-cyclodextrin (-CD). The fluorescence intensity of the complex formed between the photoproduct and -CD was found to be three times higher than that of the uncomplexed Azure A photoproduct. A complex formation constant of 110±40 M^–1 was calculated using the Benesi-Hildebrand treatment of the fluorescence emission data. Although the stoichiometry of the Azure A photoproduct: -CD complex was found to be 1: 1, it seems that the Azure A structure is only partially included. Calibration graphs were plotted for the free Azure A photoproduct and the photogenerated product included in -CD. The analytical parameters and quantification limits were determined.     

Photochemical,thermal, and thermocatalytic reactions of diphenyldiazomethane with dimethyl thiophosphite

Conclusions The direct photolysis of diphenyldiazomethane in dimethyl thiophosphite gave the product of P-H insertion. The thermal reaction leads to the N-dimethoxythiophosphorylhydrazone of benzophenone and O,O-dimethyl S-(diphenylmethyl) thiophosphate. Carbenoid P-H insertion occurred in the thermocatalytic decomposition.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 726–727, March, 1989.