Cis Compound Research Articles

Cis- and trans-influences in [PtCl2(SPh2)2

Both cis- and trans-dichlorobis(diphenyl sulfide)platinum(II), [PtCl(2)(C(12)H(10)S)(2)], crystallize as mononuclear pseudo-square-planar complexes. In the cis compound, the Pt-Cl distances are 2.295 (2) and 2.319 (2) A, and the Pt-S distances are 2.280 (2) and 2.283 (2) A. In the trans compound, Pt is located on a centre of inversion and the Pt-Cl and Pt-S distances are 2.2786 (15) and 2.3002 (12) A, respectively.

Sulphur-terminated silicon surfaces for the epitaxial growth of chalcopyrite semiconductors

As an alternative to wet chemical treatments and hydrogen termination, we propose the sulphur-termination of silicon surfaces in order to obtain favourable starting conditions for epitaxial growth of chalcopyrite semiconductors. We show that a high-temperature treatment of Si(001) and Si(111) in ultra-high vacuum under continuous exposure to a reactive sulphur molecular beam from a cracker source leads to new well-defined ordered surfaces. We identify the ideal sulphur termination of Si(001) with (1×1) structure and a quasi-ideal termination of Si(111) with a (4×4) surface structure. We propose structural models and discuss these surfaces also in the light of former experimental effort and theoretical predictions. Furthermore, we elucidate the implications of sulphur termination for epitaxial growth of the CIS compound.

CIS film growth by metallic ink coating and selenization

A novel technique was demonstrated for the growth of CuInSe 2 (CIS) thin films. The technique used an ink formulation containing sub-micron size particles of Cu–In alloys. A metallic precursor layer was first formed by coating this ink onto the substrate by spraying. The precursor film was then made to react with Se to form the CIS compound. The morphology of the CIS layers depended on the initial composition of the Cu–In particles as well as the post-deposition treatments. Solar cells were fabricated on CIS absorber layers prepared by this low-cost ink-coating approach and devices with a conversion efficiency of over 10.5% were demonstrated.

Nucleoside Analogues with a Novel Glycone Based on the Benzo[C]Furan Core

Routes to novel nucleoside analogues based on 1, 3-dihydrobenzo[c]furan have been investigated. Thus l-(1, 3-dihydro-3-hydroxymethylbenzo[c]furan-1-yl)-thymine, an analogue of d4T, was obtained as two diastereoisomers. The cis compound (quasi β-D/α-L stereochemistry) was obtained pure but the trans compound was only 90% pure. A purine analogue with a four atom spacer group between base and glycone was also prepared. The conformation of these constrained nucleosides was studied by molecular modelling.

Bis(acetylacetonato)bis(cyclooctene)ruthenium(II), cis-[Ru(acac)2(η2-C8H14)2]: a synthetic precursor to trans- and cis-bis(acetylacetonato)ruthenium(II) complexes †

Reduction of [Ru(acac)3] with zinc amalgam or zinc dust in hot THF containing some water in the presence of an excess of cyclooctene generated in solution cis-[Ru(acac)2(η2-C8H14)2], which cannot be isolated in solid form but has been identified on the basis of its 1H NMR spectrum. It is a useful synthetic precursor because the co-ordinated olefins are easily displaced by many ligands. Treatment with pyridine, tert-butyl isocyanide, tertiary phosphines, phosphites and triphenylarsine (L) at room temperature gave red-brown complexes trans-[Ru(acac)2L2], which isomerise in solution to the more stable cis compounds on heating. In contrast, the similarly prepared trimethylamine complex, trans-[Ru(acac)2(NMe3)2], does not undergo trans to cis isomerisation. Reaction of cis-[Ru(acac)2(η2-C8H14)2] with acetonitrile or triphenylstibine (L′) gave monosubstitution products cis-[Ru(acac)2(η2-C8H14)L′], which react on heating with an excess of L′ to give cis-[Ru(acac)2L′2]. Treatment of cis-[Ru(acac)2(η2-C8H14)2] (1 mol) with Ph2PCH2PPh2 (dppm) (2 mol) at room temperature gave trans-[Ru(acac)2(η1-dppm)2], whereas the ligands Ph2P(CH2)mPPh2 (L–L, m = 2, dppe; m = 3, dppp) under the same conditions gave oligomers [{Ru(acac)2(L–L)}n], which probably contain mutually trans-phosphorus atoms. On heating all three compounds are converted into cis-[Ru(acac)2(L–L)]. Treatment of trans-[Ru(acac)2L2] (L = NMe3 or PPh3) with CO at room temperature and pressure gave trans-[Ru(acac)2(CO)L], which, in the case of L = PPh3, isomerises to the cis compound on heating; reaction of trans-[Ru(acac)2(AsPh3)2] with CO under the same conditions gave cis-[Ru(acac)2(CO)(AsPh3)] directly. The structures of trans-[Ru(acac)2(CNBut)2], trans-[Ru(acac)2(PMePh2)2], cis-[Ru(acac)2(CNBut)2] (in the form of a molecular adduct with [Ru(acac)3]), cis-[Ru(acac)2(PMePh2)2] and trans-[Ru(acac)2(η1-dppm)2] have been determined by X-ray crystallography, and trends in the metal–ligand distances are discussed. The formation of trans-[Ru(acac)2L2] from cis-[Ru(acac)2(η2-C8H14)2] may proceed via a square-pyramidal intermediate [Ru(acac)2L].

Phase Transition in Trans and Cis-1,2-Cyclohexanediol Studied by Infrared Spectroscopy

The study of trans- and cis-1,2-cyclohexanediol by infrared spectroscopy was performed. The variation of the maximum frequency and of the bandwidth of the OH stretching vibration give evidence of the role played by hydrogen bonding in the solid and liquid phases of both isomers and allows to follow the phase transitions. A solid rotator phase is shown for the cis compound.

Theoretical Studies on the Photochemistry of the Cis-to-Trans Conversion in Dinuclear Gold Halide Bis(diphenylphosphino)ethylene Complexes

Ab initio calculations were carried out on cis- and trans-(diphosphino)ethylene digold halide, Au2X2C2H2(PH2)2 (X = Cl, Br, I), the model compounds for dinuclear gold(I) bis(diphenylphosphino)ethylene complexes, Au2X2(dppee). The calculations reveal aurophilic interactions in the cis compound, thus stabilizing the cis complex with respect to the trans species. The aurophilic interaction, caused by an interplay between relativistic and electron correlation effects, increases with increasing softness of the ligand attached to gold. Excited-state calculations show ethylene π* contributions only for the cis compound, but not for the trans compound, thus explaining why the trans complex does not isomerize to the cis compound upon UV radiation at wavelengths greater than 220 nm. The singlet excitation can be best described as a charge-transfer transition from the halogen lone pair to the Au (5d6s6p) orbitals with strong intermixing from phosphorus (sp) orbitals. Because of symmetry reasons, these orbitals mix w...

On the Stereochemistry of Diaryl-Substituted Cyclohexanones Formed by Michael Reactions. Trans to Cis Isomerization of Their Ketals under Basic Conditions

The stereochemistry of C-1-substituted 2,6-diphenylcyclohexan-4-ones 1−3 prepared by Michael reactions has been investigated. While preparations of these compounds have been reported over the past 70 years, in many instances the correct stereochemistry at C-2 (6) and, in some instances at C-1, was uncertain. We show here that in one case in which two identical substituents (CN) are present at C-1, it is possible to isomerize the initially formed trans isomer 1d to the cis isomer 3f. When a cyano group and a dissimilar substituent are present at C-1, the initially formed trans isomer may be isomerized to the cis compound. The stereochemistry is vertified by NMR spectroscopy and by X-ray analysis. Reaction of the ethylene ketals (4 and 5) of these ketones with KOH in DMSO at elevated temperatures gives rise to cis products, and deuterium-labeling studies demonstrated the acidity of the benzylic hydrogen at C-2 (6). Isomerization was evident since the trans ketal 4a and the cis ketal 4b gave the same amide 6a. 1H and 13C NMR spectra provided conclusive evidence for the cis → trans rearrangement.

UV-Vis, FT-Raman, and 1H NMR Spectroscopies of cis-trans Carotenoids from Saffron (Crocus sativus L.)

Stigmata of Crocus sativus L. were extracted in water, and the extract was analyzed by using a high-pressure liquid chromatography (HPLC) method. The carotenoids of saffron [ cis and trans glycosyl esters of crocetin or crocins (CRCs)] were isolated, and the two major isomer compounds (all- trans-digentiobiosyl crocetin and 13- cis-digentiobiosyl crocetin) were characterized spectroscopically with ultraviolet-visible (UV-vis), Fourier transform (FT)-Raman, and 1H NMR spectroscopies. The 13 -cis compound showed in a UV-vis spectrum an additional peak at 330 nm, in an FT-Raman spectrum the presence of a peak at 1138 cm−1, and in the 1H NMR downfield shifts of protons 12 and 15 and an uptield shift of proton 14, with respect to the all-trans isomer, according to differences in their skeletal structures. These features are shown also by the profile of their two-dimensional spectra.

Novel Rearrangement Reactions. 4. Thermal Rearrangement of [(η5:η5-t-BuC5H3Me2SiSiMe2C5H3-t-Bu)Fe2(CO)P(OPh)3(μ-CO)2] Containing a Bulky Phosphite Ligand

Photolysis of cis-(Me2SiSiMe2)[(η5-t-BuC5H3)Fe(CO)]2(μ-CO)2 (2c) in the presence of P(OPh)3 ligands afforded only cis-[(η5:η5-t-BuC5H3Me2SiSiMe2C5H3-t-Bu)Fe2(CO)P(OPh)3(μ-CO)2] (3c), whereas similar treatment of 2t yielded only the trans isomer 3t. When 3c and 3t were heated, in xylene, the cis compound (3c) rearranged to the trans product [{Me2Si(η5-t-BuC5H3)Fe}2(CO)3P(OPh)3] (4t), while the trans compound (3t) afforded the cis product [{Me2Si(η5-t-BuC5H3)Fe}2(CO)3P(OPh)3] (4c); thus, the rearrangement is stereospecific.

INVESTIGATIONS ON KINETICS AND MECHANISMS OF REACTIONS OF MONOCYCLIC OXYPHOSPHORANES WITH ETHYLENE GLYCOL

The reaction of monocyclic oxyphosphorane compounds 1a, 1b, 1c, with ethylene glycol in pyridine was studied by 31P NMR. The results showed that compound 1a, with an unsaturated five-membered ring reacts slightly faster than compound lb with a saturated ring attached by two trans p-nitro phenyl groups, which reacts 100 times faster than the cis compound lc. To interpret the mechanism, hexacoordinated intermediates 3, and 4, were proposed. The properties of 3b, and 3c, as well as 1b, and 1c, were investigated on the basis of PM3 calculations. The calculations showed that there was about 2.9 kcal/mol difference between the active energy of the ester exchange reaction for compound 1b, and 1c, which matched well with our experimental results and provided more support to the proposed mechanism.

The vibrational spectra and ab initio calculations of trans- and cis-1,3-dibromo-1,3-dimethylcyclobutane

Infrared spectra of the title compounds were recorded as vapours, as solutes in various solvents, and as solids at ambient temperature and at 80 K. Raman spectra of the solids were obtained at various temperatures between ambient and 80 K. While trans-1,3-dibromo-1,3-dimethylcyclobutane exists in one puckered conformer only, the cis compound can be present as a mixture of diequatorial and diaxial bromine conformers. In the trans compound a large majority of the IR and Raman bands of the crystal did not coincide, suggesting C 2h molecular symmetry. Accordingly, this cyclobutane ring appears to be planar or very close to planar in the crystal, as observed for certain cyclobutanes. However, no significant changes between the IR spectra of the vapour, melt and crystal were detected. No additional IR or Raman bands of the cis compound were detected in the vapour phase, in the melt or in saturated solutions compared to the solid state spectra, suggesting the presence of negligible amounts of the diaxial bromine conformer. The IR and Raman spectra of the trans and cis compounds were assigned and compared with the results of ab initio quantum chemical calculations employing the basis sets STO-3G, HF/3-21G∗ and HF/6-31G∗.

Photogeneration and characterization of group 6 metal carbonyl derivatives on alumina

The photochemically-induced CO substitution reactions of [M (CO) 6] (M = Cr, Mo, W) have been investigated in the presence of triphenylphosphine (PPh 3) and γ-alumina. The metal loading was determined by Rutherford backscattering spectrometry (RBS) and the generated species were analysed by Fourier transform IR spectroscopy (FT-IR) and 13C NMR spectroscopy. The metal loading on alumina surface was seen to increase with the irradiation time reaching 0.6, 0.8 and 3.4% for Cr, W and Mo, respectively. The ligand cone angle plays an important role in the case of Cr, where only the trans disubstituted species was found on the alumina surface. However, it is less important for the two other metals, where the cis compound was formed preferentially and the electronic cis-labilization factor seems more important. After grafting, only the disubstituted species was seen to remain on alumina evidencing a stronger interaction with the support than in the case of the monosubstituted and the hexacarbonyl compounds.

Digitalis-like compounds: Synthesis and biological evaluation of seco-D and D-homo derivatives

The synthesis of seco-D and D-homo digitalis derivatives, from the carda-14,20(22)-dienolide 1, is described. Selective ozonolysis gave the seco-D 14-ketoaldehyde 2a. Modification of the two carbonyl groups and of the α, β-unsaturated lactone ring of the seco-D 14-ketoaldehyde 2a allowed preparation of derivatives with a broad range of binding affinity to the Na +, K +-ATPase receptor. Some of the seco-D derivatives ( 10, 11b, and 13b) showed a binding affinity similar to that of digitoxigenin, demonstrating that the D-ring is not essential for recognition by the digitalis receptor. In the class of D-homo derivatives the highest binding value, about 15 times lower than that of digitoxigenin, was that of the C >D cis compound 29b; the C D trans analog 28b showed a 7-fold decrease in binding affinity, indicating that the C D configuration plays an important role in D-homo derivatives as in the classical digitalis compounds.

Time‐resolved EPR studies of covalently linked porphyrin—crown ether—quinones, dissolved in liquid crystals

AbstractTime‐resolved EPR spectra are reported for photoexcited porphyrin—quinones with butylene and cis‐ or trans‐ cyclohexylene spacers between porphyrin donors and crown ether—quinone acceptors. In the nematic phases of liquid crystals, polarized triplet EPR spectra of the porphyrin moiety could be observed at early delay times (0.1–0.6 μs) after laser flash irradiation. At later delay times (1–2 μs) the triplet EPR spectra of the charge‐separated radical pair state, created by intramolecular electron transfer from the porphyrin donor to the crown ether quinone acceptor, could be detected. The similarity of the zero‐field splitting parameters D of the cyclohexylene‐ and butylene‐linked compounds shows that the radical pair of the flexible butylene‐linked compound is in a stretched conformation. However, longer laser irradiation of the species with the flexible bridge results in the formation of a novel triplet radical pair species with a shorter porphyrin—quinone separation indicating a photoinduced backfolding of the quinone over the porphyrin plane. Comparison of the cis‐ and trans‐cyclohexylene‐linked compounds reveals a distortion of the cyclohexylene spacer in the cis compound.

Syntheses and structures of dicyanobis(oxazolidin-2-ylidene)palladium(II) and platinum(II) complexes

(2-Trimethylsiloxy)ethyl isocyanide reacts with Pd(CN) 2 and Pt(CN) 2 to give trans-[Pd(CN) 2( CN(H)CH 2CH 2O) 2 ] ( 1), trans-[Pt(CN) 2( CN(H)CH 2CH 2O) 2 ] ( 2) and cis-[Pt(CN) 2( CN(H)CH 2CH 2O) 2 ] ( 3), respectively. Complexes 1–3 have been characterized by crystal structure determinations. In the cis compound 3, the carbene ligands are linked by NH…O hydrogen bonds. A measured Pt…Pt distance of 3.2828(6) Å in this crystal structure indicates a weak Pt…Pt interaction.

Fluorinated pyrimidines. Part 4. Synthesis, properties and stereochemical conversion of the cis and trans isomers of 6-alkoxy-5-fluoro-5,6-dihydrouracils

The reaction of 6-acetoxy-5-fluoro-5,6-dihydrouracil with ROH (R = Me, Et, Pr, Pri, Bu, But) under acidic conditions has been investigated using 18F as a tracer. The quantitative replacement of the OAC-group proceeded predominantly with cisoid(gauche) stereochemistry, but upon prolonged heating the amount of the trans compound increased. This isomerization did not originate from epimerization at C5. The trans compounds—apart from being more stable towards substitution and elimination than the corresponding cis compounds—gave invariably substitution products with inversion of configuration, while the cis compounds mainly retained their configuration. Within the concept of the unifying ion-pair mechanism it is proposed that the trans compound reacts via an intimate protonated intermediate and the cis compound via a solvent-separated protonated intermediate. As a result, it was not the gauche attraction between the fluorine atom and the incoming nucleophile, but the poor π-donor ability of the C–F bond that was the determining factor in the cisoid stereochemistry of 5-fluoro-5,6-dihydrouracil adducts.

Synthesis of vinylcyclopropanes by intramolecular epoxide ring opening. Application for an enantioselective synthesis of dictyopterene A

The reaction of functionalized oxiranes 1 with the sulfur- or silicon-stabilized anions 2 provides β-heteroatom-substituted γ,δ-unsaturated epoxides 5 with, for 5e,f, a trans C=C moiety. A cis compound 9 is obtained using acetylide anion 2c via 7 and subsequent partial hydrogenation of the C≡C bond in the intermediate oxirane 8. Regiospecific anion generation in 5,9is achieved by deprotonation, reductive desulfurization, and desilylation, respectively.The resulting anions 10 cyclize to 1-(hydroxyalkyl)-2-vinylcyclopropanes 11 by a stereochemically controlled S N i process.Starting from the optically active epoxide 1b,the approach allows synthesis of cyclopropane 11b with (1S,2R) configuration at the ring carbon atoms.This compound can be further elaborated to be algae sex pheromone dictyopterene A which is obtained along with the unnatural Z diastereomer

Cis--Trans Influences in Pt Complexes. Crystal Structures of cis-[PtCl2(1,4-thioxane)2] and trans-[PtCl2(1,4-thioxane)2

The cis compound crystallizes in the space group P2 1 /n with a=10.614, b=11.283, c=11.015A, β=93.33°, Z=4. The refinement converged to R=0.057. The trans compound crystallizes in Pbca with a=7.959, b=8.972, c=18.590A, Z=4. The refinement converged to R=0.031. The coordination geometry is sqaure-planar in both compounds. In the cis compound the Pt-Cl distances are in the range 2.321-2.327A and the Pt-S distances are both 2.273A. In the trans compound the Pt-Cl and Pt-S distances are 2.300 and 2.298A

Synthesis of Derivatives of 1, 2, 6-Trisubstttuted-4-Piperidones

Abstract Robinson-Schöpf cyclisation was used to prepare several 1, 2, 6-trisubstituted-4-piperidones: 1, 2, 6-trimethyl-4-piperidone, tricyclic ketones 2 and 3 derivatives of coccinelline. In the case of 1, 2, 6-trimethyl-4-piperidone, a mixture of the trans and cis compounds 4 and 1 was obtained. The pure cis compound was prepared by another route.