Syntheses and reactions of some 4,5-dihaloimidazole-2-carboxylic acid derivatives

The preparation of 5H,10H-diimidazo[1,2-a:1′,2′-d]pyrazine-5,10-dione ( 2a ) and its 2,3,7,8-tetrabromo- and 2,3,7,8-tetrachloro- analogs ( 2b and 2c , respectively) is reported. These dimers, when allowed to react with various anilines, afford imidazole-2-carboxamides ( 3a-c ).     

PHOTOELECTRIC EFFECTS IN DYE-SENSITIZED ARTIFICIAL LIPID MEMBRANES

Using dyes of known redox potentials the specific mechanisms of dark and light potential generation is analyzed in pigmented lipid membranes. The role of the ionic and electronic conductance, as well as the redox potential gradient is specifically related to the observed open circuit voltage developed across the membrane. The results can be most easily explained by the redox electrode model.     

13C-NMR studies of marine natural products II. Total assignment of the 13C-NMR spectrum of asperdiol

¹³C-nmr spectral assignments for asperdiol are made with the aid of model compounds and T₁ relaxation behavior. Overall isotropic tumbling was inferred from the latter providing a supplemental means of multiplicity determination. Utilization of the T₁ relaxation times as an assignment criterion for select resonances in asperdiol is also described.     

Improved limits on the mass of the tau neutrino

Several methods to determine (or set an upper bound on) the mass of the tau neutrino are described. The decay spectrum of \(\tau \to e\bar \nu _e \nu _\tau \) near the high center-of-mass electron-energy end is particularly sensitive to the tau-neutrino mass. It is shown that an upper bound of 20 MeV or lower may be feasible. In addition, improved limits on the mass and mixing angle of a heavy component of the tau-neutrino may be readily obtained. We also discuss the purely leptonic decays of theD andF mesons, and show how measurements of the ratiosB(D→τν_τ/B(D→μν_μ,B(F→τν_τ/B(D→μν_μ can be sensitive to tau-neutrino masses of 30 MeV or greater.     

An Asymmetric Edge-Sharing Bioctahedral Complex: (η2-DAniF)MoIII(μ-DAniF)2(μ-O,Cl)MoVCl2 (DAniF=N,N′-di-p-anisylformamidinate)

A novel asymmetric, edge-sharing bioctahedral complex with formamidinato ligands ( ²-DAniF)Mo(-DAniF)₂(-O,Cl)MoCl₂, 1, (DAniF=N,N-di-p-anisylformamidinate) has been isolated as a byproduct from the preparation of the dimolybdenum(II,III) compound Mo₂(DAniF)₃Cl₂. An X-ray crystallographic study shows that the structure consists of edge-sharing bioctahedra, with the shared edge defined by the vector joining the: -O and -Cl ligands. Compound 1 is best formulated as a mixed-valent Mo^IIIMo^V compound, the Mo(V) ion being that with the two terminal Cl^– ligands. The cyclic voltammogram of 1 shows a reversible reduction at –0.472 V and a reversible oxidation at 1.028 V vs. the Ag/AgCl reference electrode, while the absorption spectrum of 1 reveals an intense low energy absorption at 523 nm ( _max=12 500) which is attributed to an intervalence charge transfer transition. Crystallographic data for 1 are as follows: a=13.387(1) Å, b=15.500(2) Å, c=21.855(2) Å, =98.786(2)°, V=4481.8(8) ų, P2₁/c, R1 (wR2)=0.082 (0.177).     

Donor—acceptor interactions of substituted benzenes with molecular chlorine and carbon disulfide

CNDO molecular orbital calculations have been performed to analyze donor—acceptor interactions between molecular chlorine and benzene, toluene, mesitylene and hexamethylbenzene and the, as yet, unreported chlorine—hexafluorobenzene and carbon disulfide—benzene pairs. The stabilization energy and the dipole moment and its derivative (?p/?R_CICI) calculated for the benzene—chlorine complex are in good agreement with the estimated experimental values. The trends in the experimental stabilization energies and the Cl-Cl vibrational frequencies with increasing methyl substitution appear to be well reproduced by the calculations. The charge transferred from the benzene donor is polarized toward the outer chlorine atom or sulfur atom. For hexafluorobenzene-chlorine the direction of electronic charge polarization is reversed from that of the benzene and methylbenzene complexes. The calculated results are discussed within the framework of Muliiken's simplified resonance theory for complexes.     

Synthesis of 1,2-dihydroindolo [1,7-AB] [1,5] benzodiazepines and related structures. A new heterocyclic ring system

The synthesis of the novel 1,2-dihydroindolo [1,7-ab][1,5]benzodiazepine ring system 4 is described. Condensation of 2-fluoronitrobenzene with indoline provided the starting material for the synthesis, 1-(2-nitrophenyl)indoline (1a) in high yield. The nitro group was reduced catalytically and the resulting amino function was acylated to afford the heterocycle percursor amide 3. Refluxing this amide in phosphorus oxychloride brought about a Bischler-Napieralski type cyclodehydration to form the target 1,2-dihydroindolo[1,7-ab][1,5]benzodiazepine ring system. Dehydrogenation of the latter led to the fully aromatic indolo[1,7-ab][1,5]benzodiazepine structure 5, while reduction with sodium borohydride provided the 1,2,6,7-tetrahydroindolo[1,7-ab]-[1,5]benzodiazepine tetracycle 6.     

Half-sandwich titanium(IV) complexes with Kläui's tripod ligand

Treatment of [Ti(O-i-Pr)(2)Cl(2)] with NaL(OEt) (L(OEt)(-) = [CpCo[P(O)(OEt)(2)](3)](-), Cp = eta(5)-C(5)H(5)) afforded [L(OEt)Ti(O-i-Pr)(2)Cl] that reacted with HCl in ether to give [L(OEt)TiCl(3)] (1). The average Ti-O and Ti-Cl distances in 1 are 1.975 and 2.293 A, respectively. Reaction of titanyl sulfate with NaL(OEt) in water followed by addition of HBF(4) afforded [L(OEt)TiF(3)] (2), the Ti-O and Ti-F distances of which are 2.020(2) and 1.792(2) A, respectively. The Zr(IV) analogue [L(OEt)ZrF(3)] (3) was prepared similarly from zirconyl nitrate, NaL(Oet), and HBF(4) in water. The Zr-O and average Zr-F distances in 3 are 2.139(2) and 1.938(2) A, respectively. Treatment of 1 with tetrachlorocatechol (H(2)Cl(4)cat) afforded [L(OEt)Ti(Cl(4)cat)Cl] (4). The average Ti-O(P), Ti-O(C), and Ti-Cl distances in 4 are 1.972, 1.926, and 2.334 A, respectively. Hydrolysis of 4 in the presence of Et(3)N yielded the mu-oxo dimer [(L(OEt))(2)Ti(2)(Cl(4)cat)(2)(mu-O)] (5). The average Ti-O(P), Ti-O(C), and Ti-O(Ti) distances in 5 are 2.027, 1.926, and 1.7977(9) A. Treatment of 1 with 1,1'-binaphthol (BINOLH(2)) in the presence of Et(3)N afforded [(L(OEt))(2)Ti(2)(mu-O)(2)(mu-BINOL)] x 2BINOLH(2) (6.2BINOLH(2)). Complex 1 is capable of catalyzing ring opening of epoxides with Me(3)SiN(3) under solvent-free conditions presumably via a Ti-azide intermediate.