Solvent-Driven Supramolecular Wrapping of Self-Assembled Structures

Self‐assembly relies on the ability of smaller and discrete entities to spontaneously arrange into more organized systems by means of the structure‐encoded information. Herein, we show that the design of the media can play a role even more important than the chemical design. The media not only determines the self‐assembly pathway at a single‐component level, but in a very narrow solvent composition, a supramolecular homo‐aggregate can be non‐covalently wrapped by a second component that possesses a different crystal lattice. Such a process has been followed in real time by confocal microscopy thanks to the different emission colors of the aggregates formed by two isolated Pt^II complexes. This coating is reversible and controlled by the media composition. Single‐crystal X‐ray diffraction and molecular simulations based on coarse‐grained (CG) models allowed the understanding of the properties displayed by the different aggregates. Such findings could result in a new method to construct hierarchical supramolecular structures.

Photochemical Synthesis of cis,trans,cis-1,2,3,4-Tetrakis(diphenylphosphanyl)buta-1,3-diene and Its Metal Coordination

The new bis(bidentate) tetraphosphane cis,trans,cis‐1,2,3,4‐tetrakis(diphenylphosphanyl)buta‐1,3‐diene (dppbd) (7) was obtained by applying a photochemical synthetic protocol. The key step of the photochemical reaction consisted of an intramolecular [2+2] cycloaddition involving a C–C double and triple bond of the Pt‐dimer species of the formula [Pt₂Cl₄(dppa)(trans‐dppen)] (2) {dppa = 1,2‐bis(diphenylphosphanyl)acetylene and dppen = 1,2‐bis(diphenylphosphanyl)ethene} leading to [Pt₂Cl₄(dppbd)] (5). The asymmetrically bridged precursor complex 2 was obtained by combinatorial chemistry. Single crystal X‐ray structure analyses of 2 and 5 proved that the intramolecular photochemical reaction occurred. Cyanolysis of 5 gave 7, which was oxidized to dppbdO4 (8). Compounds 7, 8, and the Pd^II dimer complex [Pd₂Cl₄(dppbd)] (9) were characterized in the solid state by a single‐crystal X‐ray structure analysis. Interesting photophysial properties emerged from the UV/Vis spectra acquired for 7 and the dimer Os complexes meso‐Δ,Λ/Λ,Δ‐[Os₂(bpy)₄(dppbd)](PF₆)₄ (10) and rac‐Δ,Δ/Λ,Λ‐[Os₂(bpy)₄(dppbd)](PF₆)₄ (11).

Exploration into the Syntheses of Gallium- and Indiumborates under Extreme Conditions: M5 B12 O25 (OH): Structure, Luminescence, and Surprising Photocatalytic Properties

Explorative solid-state chemistry led to the discovery of the two new compounds Ga₅ B₁₂ O₂₅ (OH) and In₅ B₁₂ O₂₅ (OH). Extreme synthetic conditions within the range of 12 GPa and a temperature of 1450 °C realized in a Walker-type multianvil apparatus resulted in the formation of an unprecedented tetragonal structure with the exclusive presence of condensed BO₄ tetrahedra, forming cuboctahedral cavities. Doping of these cavities with Eu³⁺ in In₅ B₁₂ O₂₅ (OH) yielded in an orange-red luminescence. Photocatalytic tests of In₅ B₁₂ O₂₅ (OH) revealed a hydrogen production rate comparable to TiO₂ but completely co-catalyst free.

Stabilisation effects of phosphane ligands in the homogeneous approach of sunlight induced hydrogen production

Most of the systems for photochemical hydrogen production are not stable and suffer from decomposition. With bis(bidentate) tetraphosphane ligands the stability increases enormously, up to more than 1000 h. This stability was achieved with a system containing osmium(ii) as a light harvesting antenna and palladium(ii) as a water reduction catalyst connected with a bis(bidentate) phosphane ligand in one molecule with the chemical formula [Os(bpy)₂(dppcb)Pd(dppm)](PF₆)₄. With the help of electrochemical measurements as well as photophysical data and its single crystal X-ray structure, the electron transfer between the two active metal centres (light harvesting antenna, water reduction catalyst) was analysed. The distance between the two active metal centres was determined to be 7.396(1) Å. In a noble metal free combination of a copper based photosensitiser and a cobalt diimine-dioxime complex as water reduction catalyst a further stabilisation effect by the phosphane ligands is observed. With the help of triethylamine as a sacrificial donor in the presence of different monophosphane ligands it was possible to produce hydrogen with a turnover number of 1176. This completely novel combination is also able to produce hydrogen in a wide pH-range from pH = 7.0 to 12.5 with the maximum production at pH = 11.0. The influence of monophosphane ligands with different Tolman cone angles was investigated. Monophosphane ligands with a large Tolman cone angle (>160°) could not stabilise the intermediate of the cobalt based water reduction catalyst and so the turnover number is lower than for systems with an addition of monophosphane ligands with a Tolman cone angle smaller than 160°. The role of the monophosphane ligand during sunlight-induced hydrogen production was analysed and these results were confirmed with DFT calculations. Furthermore the crystal structures of two important Co(i) intermediates, which are the catalytic active species during the catalytic pathway, were obtained. The exchange of PPh₃ with other tertiary phosphane ligands can have a major impact on the activity, depending on the coordination properties. By an exchange of monophosphane ligands with functionalised phosphane ligands (hybrid ligands) the hydrogen production was raised 2.17 times.

Unusual stability of dyads during photochemical hydrogen production

Heterodimetallic dyads containing Os and Pd are connected by a bis(bidentate) phosphine and show an excellent stability for the water splitting application.

Das JerJ-Butyl-Kation in Lösungen von Aluminiumbromid in Mono-, Di- und Tribrommethan / The terf-Butyl-Cation in Solutions of Aluminium Bromide in Mono-, Di- and Tribromomethane

The tert-butyl cation is formed from tert-BuBr in concentrated solutions of AlBr3 in CH3Br, CH2Br2 and CHBr3 and was characterized by 1H NMR spectroscopy. Stabilization of the cation depends strongly on the AlBr3 concentration: in CH3Br saturated with AlBr3, C(CH3)3+ is formed in 80% yield; in dilute solutions of AlBr3 in CH3Br the usual de-composition occurs. In saturated solutions of AlBr3 in CH2Br2 and CHBr3 the C(CH3)3+ yield is 60 and 40%, resp. The concentration of the cation decreases in all three solvents by 20 to 30% within 10 days at room temp. In concentrated solutions of AlBr3 in CH3Br the formation of the methyl-tert-butylbromonium ion as a rapidly equilibrating species is suggested. The 1H NMR chemical shift of C(CHs)3+ in the presence of AlBr3 (δ = 5.19 in CHsBr, δ = 5.23 in CH2Br2, δ = 5.35 in CHBr3) indicates strong deshielding in comparison with shifts in SbF5 and SbF5/SO2

(Dimethylphosphito-P){tris[2-(diphenylphosphino)ethyl]-phosphine-P,P′,P″,P″′}platinum(II)-chloride: Synthesis and Structural Characterization

Controlled hydrolysis at low temperatures of (trimethylphosphito-P){tris[2-(diphenylphosphino)ethyl]phosphine-P,P′,P″,P″′}platinum(II)-dichloride, [Pt(PP3)(P(OMe)3)]Cl2 (2), leads to the title compound (1) in nearly quantitative yield. The 31P NMR spectrum of 1 shows an AMX3 pattern consistent with the formulation as [Pt(P(O)(OMe)2)(PP3)]Cl. 1 has been further characterized by an X-ray structure analysis, which shows a trigonal-bipyramidal stereochemistry with the (dimethylphosphito)-ligand occupying an axial position. NMR and X-ray results of 1 and [PtH(PP3)](BPh4) (3) are compared.

Dimethylhalonium-Ionen in Aluminiumhalogenid/Methylhalogenid-Lösungen / Dimethylhalonium-Ions in Aluminium Halide/Methyl Halide Solutions

Evidence for the formation of (CH3)2Br+ and (CH3)2I+ in CH3Br and CH3I solutions saturated with AlBr3 comes from the appearance of a second singlet in the 1H NMR spectrum. The (CH3)2Br+ ion is formed at -40 °C to about 5 mol%, the (CH3)2I+ ion at -12 °C with 50 mol% yield. At higher temperatures the concentration of the halonium ions decreases rapidly. The (CH3)2Br+ ion is not detectable at room temperature, the concentration of (CH3)2I+ decreases to about 30 mol%. Dilution of the saturated solutions with methyl halide also reduces the halonium ion concentration. An AlBr3/CH3Br solution with a molar ratio of 1:3 at -40 °C shows no sign of (CH3)2Br+ formation in the XH NMR spectrum. Both effects are best explained by formation of dimethylhalonium ions from the adduct CH3X-AIX3 and by dependence of adduct concentration on temperature and dilution. Exchange of (CH3)2Br+ and (CH3)2I+ with methyl halide is slow on the NMR time scale at low temperatures similar to the results in SbF5/SO2. The 1H NMR singlets of (CH3)2Br+ and (CH3)2I+ are shifted to lower field by 1.32 and 1.68 ppm in comparison with the chemical shifts in SbF5/SO2 solution

Oxidative quenching within photosensitizer-acceptor dyads based on bis(bidentate) phosphine-connected osmium(II) bipyridyl light absorbers and reactive metal sites

For the first time oxidative quenching of OsP₂N₄ chromophores by reactive Pt^II or Pd^II sites containing cis, trans, cis-1,2,3,4-tetrakis(diphenylphosphino)cyclobutane (dppcb) is directly observed despite the presence of a saturated cyclobutane backbone “bridge”. This dramatic effect is measured as a sudden temperature-dependent onset of a reduction in phosphorescence lifetime in [Os(bpy)₂(dppcb)MCl₂](SbF₆)₂ (M = Pt, 1; Pd, 2). The appearance of this additional energy release is not detectable in [Os(bpy)₂(dppcbO₂)](PF₆)₂ (3), where dppcbO₂ is cis, trans, cis-1,2-bis(diphenylphosphinoyl)-3,4-bis(diphenylphosphino)cyclobutane. Obviously, the square-planar metal centers in 1 and 2 are responsible for this effect. In line with these observations, the emission quantum yields at room temperature for 1 and 2 are drastically reduced compared with 3. Since this luminescence quenching implies strong intramolecular interaction between the Os^II excited states and the acceptor sites and depends on the metal⋯metal distances, also the single crystal X-ray structures of 1–3 are given.

Surprising photochemical reactivity and visible light-driven energy transfer in heterodimetallic complexes

The bis(bidentate) phosphine cis,trans,cis-1,2,3,4-tetrakis(diphenylphosphino)cyclobutane (dppcb) has been used for the synthesis of a series of novel heterodimetallic complexes starting from [Ru(bpy)(2)(dppcb)]X(2) (1; X = PF(6), SbF(6)), so-called dyads, showing surprising photochemical reactivity. They consist of [Ru(bpy)(2)](2+)"antenna" sites absorbing light combined with reactive square-planar metal centres. Thus, irradiating [Ru(bpy)(2)(dppcb)MCl(2)]X(2) (M = Pt, 2; Pd, 3; X = PF(6), SbF(6)) dissolved in CH(3)CN with visible light, produces the unique heterodimetallic compounds [Ru(bpy)(CH(3)CN)(2)(dppcb)MCl(2)]X(2) (M = Pt, 7; Pd, 8; X = PF(6), SbF(6)). In an analogous reaction the separable diastereoisomers (ΔΛ/ΛΔ)- and (ΔΔ/ΛΛ)-[Ru(bpy)(2)(dppcb)Os(bpy)(2)](PF(6))(4) (5/6) lead to [Ru(bpy)(CH(3)CN)(2)(dppcb)Os(bpy)(2)](PF(6))(4) (9), where only the RuP(2)N(4) moiety of 5/6 is photochemically reactive. By contrast, in the case of [Ru(bpy)(2)(dppcb)NiCl(2)]X(2) (4; X = PF(6), SbF(6)) no clean photoreaction is observed. Interestingly, this difference in photochemical behaviour is completely in line with the related photophysical parameters, where 2, 3, and 5/6, but not 4, show long-lived excited states at ambient temperature necessary for this type of photoreaction. Furthermore, the photochemical as well as the photophysical properties of 2-4 are also in accordance with their single crystal X-ray structures presented in this work. It seems likely that differences in "steric pressure" play a major role for these properties. The unique complexes 7-9 are also fully characterized by single-crystal X-ray structure analyses, clearly showing that the stretching vibration modes of the ligand CH(3)CN, present only in 7-9, cannot be directly influenced by "steric pressure". This has dramatic consequences for their photophysical parameters. The trans-[Ru(bpy)(CH(3)CN)(2)](2+) chromophore of 9 acts as efficient "antenna" for visible light-driven energy transfer to the Os-centred "trap" site, resulting in k(en) ≥ 2 × 10(9) s(-1) for the energy transfer. Since electron transfer is made possible by the use of this intervening energy transfer, in dyads like 2-4 highly reactive M(0) species (M = Pt, Pd, Ni) could be generated. These species are not stable in water and M(II) hydride intermediates are usually formed, further reacting with H(+) to give H(2). Thus, derivatives of 3, namely [M(bpy)(2)(dppcb)Pd(bpy)](PF(6))(4) (M = Os, Ru) dissolved in 1:1 (v/v) H(2)O-CH(3)CN produce H(2) during photolysis with visible light.

Synthesis and characterization of palladium(ii) complexes with new diphosphonium-diphosphine and diphosphine ligands. Production of low molecular weight alternating polyketones via catalytic CO/ethene copolymerisation

The bis-cationic diphosphonium-diphosphine 6,7-di(di-2-methoxyphenyl)phosphinyl-2,2,4,4-tetra(di-2-methoxyphenyl)-2 lambda 4,4 lambda 4-diphosphoniumbicyclo[3.1.1]heptane-bis(PF6) ((o-MeO-PCP)(PF6)2) and the diphosphine rac-2,4-bis((di-2-methoxyphenyl)phosphino)pentane (rac-o-MeO-bdpp) have been synthesized. Both ligands have been employed to coordinate PdCl2 and Pd(OAc)2 to give [PdCl2(o-MeO-PCP)](PF6)2 (1a), PdCl2(rac-o-MeO-bdpp) (1b), [Pd(OAc)2(o-MeO-PCP)](PF6)2 (2a) and Pd(OAc)2(rac-o-MeO-bdpp) (2b). The ligands and complexes have been fully characterized in solution by multinuclear NMR spectroscopy. In addition, 1a and 1b have been authenticated by single crystal X-ray structure analyses. The Pd(II) complexes 1a and 1b have been employed as catalyst precursors for the CO/ethene copolymerisation in water-acetic acid mixtures, while 2a and 2b have been tested in methanol in the presence of p-toluenesulfonic acid. Irrespective of the reaction media, perfectly alternating polyketones were obtained in excellent yields and with number-average molecular weights ranging from 7.1-13.9 kg mol(-1) with the diphosphonium-diphosphine catalysts and from 37.2-48.2 kg mol(-1) with the diphosphine catalysts.

Synthesis, catalytic properties and biological activity of new water soluble ruthenium cyclopentadienyl PTA complexes [(C5R5)RuCl(PTA)2] (R = H, Me; PTA = 1,3,5-triaza-7-phosphaadamantane)

The new water soluble ruthenium complexes [(C5R5)RuCl(PTA)2] (R = H, Me; PTA = 1,3,5-triaza-7-phosphaadamantane) were synthesised and characterised. Their evaluation as regioselective catalysts for hydrogenation of unsaturated ketones in aqueous biphasic conditions and as cytotoxic agents towards the TS/A adenocarcinoma cell line is briefly presented.

Binary system of (R)- and (S)-nitrendipine--polymorphism and structure

Three monotropically related modifications of (RS)-nitrendipine (RS-NTD) were investigated. With the aid of the optical antipodes of NTD, it was possible to construct a binary phase diagram, from which it is obvious that the thermodynamically stable mod. I of RS-NTD (mp 156-158.5 degrees C, heat of fusion 41.1 +/- 0.2 kJ mol-1) is a racemic compound, while mod. II (mp 130-134 degrees C, heat of fusion 29.4 kJ mol-1) and mod. III (mp 124-126 degrees C, heat of fusion 27.2 kJ mol-1) occur as conglomerates of different modifications of R- and S-NTD. The eutectic points (calculated) are at 150 degrees C and at 19% and 81% molar fraction of an enantiomer, respectively. Two modifications of the enantiomers are characterized (En-mod. I, thermodynamically stable form, mp 156-158 degrees C, heat of fusion 34.5 +/- 1.3 kJ mol-1 and En-mod. III, mp 121 degrees C), whereas a third modification (En-mod. II) must be hypothesized pursuant to the phase diagram (mp ca. 152 degrees C). IR spectra, DSC curves, and X-ray powder diffractograms of the different phases are described. The crystal structure of the enantiomer En-mod. I is reported (monoclinic, P2(1), density 1.346 g cm-3) and compared with the X-ray structure of the racemic compound (monoclinic, P2(1)/c, density 1.356 g cm-3). A comparison with similar studies on nimodipine has been made to emphasize the parallels to a substance of this chemical group.