Percycloalkylated cyclohexanes: attempted synthesis of a trispropellane

The acid catalyzed rearrangement of two cyclohexanols of spiroannelated four-membered rings has been studied. In accordance with molecular mechanics calculations, far-reaching reorganizations with formation of unsaturated hexacyclic systems, including a fully cycloalkylated cyclohexene with a bispropellane partial structure, were observed. Attempts to convert this bispropellane to a trispropellane failed.     

Lead structures for applications in photodynamic therapy. Part 2: Synthetic studies for photo-triggered release systems of bioconjugate porphyrin photosensitizers

Photodynamic therapy (PDT) selectivity and specificity can be improved by binding the photosensitizers to target receptors. One approach is to cross-link porphyrins to a biological target receptor via the photocleavable o-nitrobenzyl linker, where a controlled released of the porphyrin can be monitored upon irradiation. The synthetic pathways involved esterification of a porphyrin-carboxylic acid and a unit containing the o-nitrobenzyl alcohol moiety and the bioconjugate. Reactions of a model porphyrin and o-nitrobenzyl alcohol using the carbonyl activating carbodiimide reagent DCC gave a stable N-acyl urea porphyrin, whereas use of EDAC (1-ethyl-3-(3-dimethyl aminopropyl)carbodiimide hydrochloride) gave the desired compounds. Further studies were carried out on the attachment of carbohydrates (i.e., potentially receptor binding ligands) through such a linker to porphyrins. Preliminary irradiation experiments of such a compound show that upon UV irradiation (350 nm) for 80 min, approximately 50% of the porphyrin was cleaved to release the carboxylic acid porphyrin photosensitizer indicating the utility of such systems as photosensitizers delivery systems.     

First synthesis of 4-(arylsulfonyl)phenols by regioselective [3+3] cyclocondensations of 1,3-bis(silyloxy)-1,3-butadienes with 2-arylsulfonyl-3-ethoxy-2-en-1-ones

The formal [3+3] cyclization of 1,3-bis(silyloxy)-1,3-butadienes with readily available 2-arylsulfonyl-3-ethoxy-2-en-1-ones resulted in regioselective formation of 4-(arylsulfonyl)phenols.     

Polychloride Monoanions from [Cl3]− to [Cl9]−: A Raman Spectroscopic and Quantum Chemical Investigation

Polychloride monoanions stabilized by quaternary ammonium salts are investigated using Raman spectroscopy and state‐of‐the‐art quantum‐chemical calculations. A regular V‐shaped pentachloride is characterized for the [N(Me)₄][Cl₅] salt, whereas a hockey‐stick‐like structure is tentatively assigned for [N(Et)₄][Cl₂???Cl₃^?]. Increasing the size of the cation to the quaternary ammonium salts [NPr₄]⁺ and [NBu₄]⁺ leads to the formation of the [Cl₃]^? anion. The latter is found to be a pale yellow liquid at about 40 °C, whereas all the other compounds exist as powders. Further to these observations, the novel [Cl₉]^? anion is characterized by low‐temperature Raman spectroscopy in conjunction with quantum‐chemical calculations.     

Reactions with Oleum under Harsh Conditions: Characterization of the Unique [M(S2O7)3]2− Ions (M=Si,Ge, Sn) in A2[M(S2O7)3] (A=NH4, Ag)

The reactions of group 14 tetrachlorides MCl₄ (M=Si, Ge, Sn) with oleum (65 % SO₃) at elevated temperatures lead to the unique complex ions [M(S₂O₇)₃]^2?, which show the central M atoms in coordination with three chelating S₂O₇^2? groups. The mean distances M? O within the anions increase from 175.6(2)–177.5(2) pm (M=Si) to 186.4(4)–187.7(4) pm (M=Ge) to 201.9(2)–203.5(2) pm (M=Sn). These distances are reproduced well by DFT calculations. The same calculations show an increasing positive charge for the central M atom in the row Si, Ge, Sn, which can be interpreted as the decreasing covalency of the M? O bonds. For the silicon compound (NH₄)₂[Si(S₂O₇)₃], ²⁹Si solid‐state NMR measurements have been performed, with the results showing a signal at ?215.5 ppm for (NH₄)₂[Si(S₂O₇)₃], which is in very good agreement with theoretical estimations. In addition, the vibrational modes within the [MO₆] skeleton have been monitored by Raman spectroscopy for selected examples, and are well reproduced by theory. The charge balance for the [M(S₂O₇)₃]^2? ions is achieved by monovalent A⁺ counter ions (A=NH₄, Ag), which are implemented in the syntheses in the form of their sulfates. The sizes of the A⁺ ions, that is, their coordination requirements, cause the crystallographic differences in the crystal structures, although the complex [M(S₂O₇)₃]^2? ions remain essentially unaffected with the different A⁺ ions. Furthermore, the nature of the A⁺ ions influences the thermal behavior of the compounds, which has been monitored for selected examples by thermogravimetric differential thermal analysis (DTA/TG) and XRD measurements.     

The Oxidation of ReCl5 with Oleum: Synthesis and Crystal Structure of Re2O4Cl4(SO4)

The reaction of ReCl₅ and fuming sulfuric acid (25 % SO₃) in a sealed glass tube at 200 °C led to red, needle shaped single crystals of Re₂O₄Cl₄(SO₄) (monoclinic, C2/c, a = 1501.8(2) pm, b = 1545.9(2) pm, c = 945.18(8) pm, β = 98.761(9)°, Z = 8). In the crystal structure the [ReO₂] moieties are linked by [SO₄]^2– tetrahedra to chains along the [101] direction. Each sulfate ion connects four rhenium atoms, additional two chloride ions complete the octahedral coordination sphere of each rhenium atom according to $\rm^1_\infty$ [ReO_2/1Cl_2/1(SO₄)_2/4].     

The [Au(CH3SO3)4]– Anion in the Crystal Structures of M[Au(CH3SO3)4] (M = Li,Na, Rb)

The reactions of Au(OH)₃, M₂CO₃ (M = Li, Na, Rb), and methanesulfonic acid at elevated temperatures in sealed glass ampoules lead to single crystals of M[Au(CH₃SO₃)₄] (M = Li, Na, Rb). In the crystal structures of Li[Au(CH₃SO₃)₄] (tetragonal, I$\bar{4}$ , Z = 2,a = 938.64(2) pm, c = 917.01(3) pm, V = 807.93(4) ų) and Rb[Au(CH₃SO₃)₄] (tetragonal, P$\bar{4}$ 2₁c, Z = 2, a = 946.7(1) pm,c = 889.9(1) pm, V = 797.6(2) ų) the complex aurate anions are linked by the M⁺ ions in three dimensions. Contrastingly, in the structure of Na[Au(CH₃SO₃)₄] (triclinic, P$\bar{4}$ , Z = 1, a = 540.04(2) pm,b = 863.75(2) pm, c = 973.29(3) pm, α = 72.694(2)°, β = 75.605(2)°, γ = 77.687(2)°, V = 415.05(2) ų) the complex anions are connected into layers that are further connected by weak hydrogen bonds. The thermal decomposition of Li[Au(CH₃SO₃)₄] was monitored up to 500 °C and leads in a multi‐step process to elemental gold and Li₂SO₄.     

Selenium(IV) fluoride and oxofluoride anions

The [((C₆H₅)₃P)₂N]⁺, [(C₆H₅)₄P]⁺ and [N(CH₃)₄]⁺ salts of SeF₅⁻, SeF₆²⁻ and SeOF₃⁻ and CsSeO₂F were prepared and characterized. Crystal structures were obtained for [((C₆H₅)₃P)₂N][SeF₅] and [((C₆H₅)₃P)₂N][SeOF₃] CH₂Cl₂. In contrast to oxygen-bridged dimeric TeOF₃⁻, the SeOF₃⁻ anion in [((C₆H₅)₃P)₂N][SeOF₃] CH₂Cl₂ is monomeric and represents the first experimentally well determined molecular structure of a monomeric trifluoro-chalcogenite anion. Similarly, [((C₆H₅)₃P)₂N][SeF₅] represents the first example of a structure containing a well-isolated undistorted SeF₅⁻ anion. The NMR and the vibrational spectra and their assignments were re-examined and corrected by comparison with high-level theoretical calculations. Whereas the previously published normal coordinate analysis of SeF₅⁻ is correct, that for SeOF₃⁻ needs major revision.     

Generalized CC-TDSCF and LCSA: The system-energy representation

Typical (sub)system-bath quantum dynamical problems are often investigated by means of (approximate) reduced equations of motion. Wavepacket approaches to the dynamics of the whole system have gained momentum in recent years and there is hope that properly designed approximations to the wavefunction will allow one to correctly describe the subsystem evolution. The continuous-configuration time-dependent self-consistent field (CC-TDSCF) and local coherent-state approximation (LCSA) methods, for instance, use a simple Hartree product of bath single-particle-functions for each discrete variable representation (DVR) state introduced in the Hilbert space of the subsystem. Here we focus on the above two methods and replace the DVR states with the eigenstates of the subsystem Hamiltonian, i.e., we adopt an energy-local representation for the subsystem. We find that stable and semiquantitative results are obtained for a number of dissipative problems, at the same (small) computational cost of the original methods. Furthermore, we find that both methods give very similar results, thus suggesting that coherent-states are well suited to describe (local) bath states. As a whole, present results highlight the importance of the system basis-set in the selected-multiconfiguration expansion of the wavefunction. They suggest that accurate and yet computationally cheap methods may be simply obtained from CC-TDSCF/LCSA by letting the subsystem states be variationally optimized.