Polymerisation von cis- und trans-8-Oxabicyclo[4.3.0]nonan

Ohne Zusammenfassung     

Room-temperature photochromism in cis- and trans-[Ru(bpy)2(dmso)2]2+

We report on phototriggered Ru-S --> Ru-O and thermal Ru-O --> Ru-S intramolecular linkage isomerizations in cis- and trans-[Ru(bpy)2(dmso)2]2+. The cis complex features only S-bonded sulfoxides (cis-[S,S]), whereas the trans isomer is characterized by S- and O-bonded dmso ligands. Both cis-[S,S] and trans-[S,O] exhibit photochromism at room temperature in dmso solution and ionic liquid (IL). Rates of reaction in IL were monitored by UV-visible spectroscopy and are similar to those reported in dmso solution (k(O-->S) ranges from approximately 10(-3) to 10(-4) s(-1)). Cyclic voltammetric measurements of cis-[S,S] and trans-[S,O] are consistent with an electrochemically triggered linkage isomerism mechanism. While both cis-[S,S] and trans-[S,O] are photochromic at room temperature, neither complex is emissive. However, upon cooling to 77 K, cis-[S,S] exhibits LMCT (ligand-to-metal charge transfer) emission typical of many ruthenium polypyridine complexes. In contrast to cis-[S,S], trans-[S,O] does not show any detectable emission even at 77 K.     

Electronic coupling mediated by stacked [Thymine-Hg-Thymine] base pairs

Very recently it has been shown that stable metal-mediated base pairs [Thymine-Hg-Thymine] can form in DNA. To estimate the effect of such pairs on the efficiency of charge transfer through DNA, we carry out quantum mechanical calculations of double-stranded pi-stacks GXG, GXXG, and GXXXG, where X = [Thymine-Hg-Thymine] and stacks GT(n)G of canonical base pairs. The charge-transfer efficiency in short duplexes GXG and GTG is found to be similar. However, the donor-acceptor coupling in GXXG and GXXXG is stronger by a factor of 2.5-3.0 than that in GT(n)G (n = 2 and 3), respectively. It is shown that the valence orbitals of Hg atoms do not essentially participate in mediating the electronic coupling for hole transfer; however, they may play an important role in excess electron transfer.     

Preparation and Properties of trans-[CoCl2(tmd>)2]Cl,and trans- and cis-[Co(NCS)2(tmd)2]NO3 (tmd: Tetramethylenediamine)

The cobalt(III) complexes [CoX₂(tmd)₂]⁺ (X: Cl^? or NCS^?, tmd: tetramethylenediamine), in which tmd forms a seven-membered chelate ring, have been prepared. Trans-[CoCl₂(tmd)₂]Cl was derived from [Co(NO₂)₂(tmd)₂]NO₃ in a fairly good yield. Two geometrical isomers, trans and cis, of [Co(NCS)₂-(tmd)₂]NO₃ were independently synthesized from trans-[CoCl₂(tmd)₂]Cl by different methods. The geometrical configurations of the isomeric pair of the NCS complex have been determined based on chromatographic behavior, electronic absorption spectra, and vibrational spectra. The d-d and CT absorption maxima of the NCS complex (18.7 x 10³cm^?1 (ε = 275) and 30.9 x 10³cm^?1 (ε = 3630) for the trans isomer, 19.3 x 10³cm^?1 (ε = 302) and 31.0 x 10³cm^?1 (ε = 4070) for the cis isomer) and the Co-N(amine) stretching frequency of trans-[CoCl₂(tmd)₂]Cl (418 cm^?1) have been compared with those of the corresponding ethylenediamine and trimethylenediamine complexes.     

Facile [3+2] dimerization and formal dehydrogenative coupling mode of a cyanophenylphosphaallene

Due to a facile head-to-tail [3+2] dimerization, even a sterically demanding group such as the Mes^∗ (2,4,6-tri-tert-butylphenyl) group around the PCC moiety did not allow us to isolate 3-(4-cyanophenyl)-1-(2,4,6-tri-tert-butylphenyl)-1-phosphaallene from the elimination reaction of 2-bromo-3-(4-cyanophenyl)-1-(2,4,6-tri-tert-butylphenyl)-1-phosphaprop-1-ene with DBU (1,8-diazabicyclo[5.4.0]undec-7-ene), and the corresponding 1,4-diphosphafulvene containing cyano groups was obtained and characterized. Theoretical studies on the [3+2] dimerization of phosphaallene characterize possible intermediates affording 1,4-diphosphafulvenes and also suggest the cyano group effect to facilitate the saturation of the PC double bonds. On the other hand, 1,2-bis(4-cyanophenyl)-3,4-bis[(2,4,6-tri-tert-butylphenyl)phosphinidene]cyclobutene was obtained from 2-bromo-3-(4-cyanophenyl)-3-trimethylsiloxy-1-(2,4,6-tri-tert-butylphenyl)-1-phosphaprop-1-ene together with the 3-(4-cyanophenyl)-1-phosphaallene.     

Diene condensation of cis- and trans-2-cyclododecenone

Conclusions In the diene condensation of the cis- and trans-2-cyclododecenones with butadiene only the transisomer reacts, with the formation of trans-bicyclo [10. 4. 0]-14(15)-hexadecen-2-one, which when treated with t-C₄H₃OK is isomerized completely to cis-bicyclo[10. 4. 0]-14(15)-hexadecen-2-one.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 2157–2159, September, 1973.     

Reaction of cis- and trans-3,4-epoxy-3-methylbicyclo-[4.1.0] heptanes with hydrogen halides

Conclusions The reaction of cis- and trans-3,4-epoxy-4-methylbicyclo[4.1.0]heptanes with hydrochloric and hydrobromic acids was studied. The reactions of the trans-epoxide yield products derived from rupture of the epoxide ring both on the secondary and tertiary carbon atoms. The reaction of the cis-epoxide results in preferential rupture of the tertiary bond with HC1 and the secondary bond with HBr.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 829–831, April, 1979.     

Factors controlling the relative stabilities of cis- and trans-[PtX2L2] isomers: Chatt and Wilkins--50 years on

DFT computations reveal that cis-trans preferences in [PtX2(PR3)2] species are due to a combination of electrostatics, pi-backbonding, antisymbiosis, and solvation effects.     

Carbon-13 chemical shifts and coupling constants in cis- and trans-1,2-di-tert-butylethylene

The spectral parameters of the title compounds were redetermined to resolve discrepancies between data reported in the literature.     

Dehydrohalogenations of cis- and trans-1-bromo-2-flourocyclohexanes

Reactions of both diastereomeric vicinal bromofluorocyclohexanes with sodamide, sodium methoxide, potassium tert-butoxide, and triethylamine were studied. cis-1-Bromo-2-fluorocyclohexane eliminated almost exclusively hydrogen bromide giving mainly 1-fluorocyclohexene and a small amount of 3- fluorocyclohexene. trans-1-Bromo-2-fluorocyclohexane eliminated preferentially hydrogen fluoride on treatment with sodamide. Potassium tert- butoxide eliminated hydrogen bromide and yielded 3-fluorocyclohexene and a small amount of 1,3-cyclohexadiene, whereas sodium methoxide converted trans-1-bromo-2-fluorocyclohexane to 3-fluorocyclohexene and 3-methoxycyclohexene. Possible mechanisms and stereochemistry of the preferential elimination of hydrogen fluoride are discussed and new interpretations are offered.     

Synthesis of cis- and trans-1,3-dicarbomethoxy-2-aminoisoindoline

The title compounds ( 4a,b ) were synthesized starting with dimethyl α,α'-dibromo-o-benzenediacetate and t-butyl carbazate. Alternate approaches to 4 involving reduction of the appropriate 2-nitrosoisoindoline were found unsuitable because of predominant side reactions.     

A facile,stereoselective [2 + 2] photoreaction mediated by curcurbit[8]uril

The [2 + 2] photoreaction of (E)-diaminostilbene dihydrochloride proceeds with large rate acceleration and high stereoselectivity via formation of a stable 1:2 host-guest complex with curcurbit[8]uril in solution.     

Synthesen von cis- und trans-1,2,3,4,4a, 10a-Hexahydro-1,4-benzodioxino[2,3-c]-pyridinen

Cis- and trans-1,2,3,4,4a,10a-hexahydro-1,4-benzodioxino[2,3-c]pyridines have been synthetised and their structures established by NMR.-spectroscopy.     

Boron fluorides of cis- and trans-2-aryl-3-aroylaziridines

The reaction of boron trifluoride etherate with cis- and trans-2-aryl-3-aroylaziridines yields the respective complexes in high yield. According to PMR spectral data the methyl group of boron trifluoride trans-1-methyl-3-aroylaziridines is located in syn-position, and in the cis-aziridine complexes in anti-position, to the carbonyl group.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1047–1049, August, 1987.     

The cis-effect in trans-[PtCl2XY] compounds

The cis-influence observed in chlorine NQR data of X, Y affecting the Pt-Cl bonds in compounds of type trans-[PtCl₂XY] is interpreted. -bonding differences in Pt-Cl bonds are suggested to account for the trends in NQR frequencies. Pt-Cl -bonding is negligibly small for both d (Pt)–p (Cl) and p –p (Cl) interactions.     

Ring[bond]chain tautomerism of 2-Aryl-substituted cis- and trans-decahydroquinazolines

In CDCl(3) at 300 K, 2-aryl-substituted cis- and trans-3-isopropyldecahydroquinazolines and trans-3-phenyldecahydroquinazolines proved to be three-component (r(1)[bond]o[bond]r(2)) ring[bond]chain tautomeric mixtures, whereas only ring-closed tautomers could be detected for the 3-methyl-substituted analogues. The proportions of the ring-chain tautomeric forms at equilibrium were strongly influenced by the N-substitutents and the cis-trans ring junction and could be described by the equation log K(X) = rho sigma(+) + log K(X=H). These are the first examples among 2-aryl-1,3-N,N-heterocycles of a three-component ring-chain tautomeric equilibrium characterized by a Hammett-type equation. The stabilities of the ring-closed forms of cis- and trans-2-aryldecahydroquinazolines and the corresponding 3,1-benzoxazines were found to increase in the following sequence of the heteroatom at position 3: NPh < N-i-Pr < O < NMe.