Pincer-porphyrin hybrids

[reaction: see text] Starting from tetrakis(3,5-bis(bromomethyl)phenyl)porphyrin, pincer-porphyrin hybrid molecules (tetrakis(ECE-pincer)porphyrin; E = N, P, S) based on a tetraphenylporphyrin skeleton have been prepared in high yields. These multi-ligand site compounds could be selectively metalated at their peripheries, which was shown by X-ray crystallography.     

Beitr?ge zur Chemie des Schwefels. 84

Zusammenfassung Durch Zonenschmelzen konnte hochreiner Schwefel dargestellt werden, dessen Verunreinigungsgehalt (Kohlenstoff: weniger als 2,4 · 10^–4%, Silicium 1,3 · 10^–6%, Magnesium: 4,0 · 10^–6%) wesentlich kleiner war als bei allen nach anderen Verfahren gereinigten Schwefelproben. Ein Verfahren zur Bestimmung von Silicium, Eisen und Magnesium in kleinen Schwefeleinwaagen durch Spektralanalyse ohne vorherige Anreicherung wurde ausgearbeitet.

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Summary High-purity sulphur was prepared by zone melting. The percentage of impurities (carbon < 2.4×10^–4%, silicon 1.3×10^–6%, magnesium 4.0×10^–6%) was considerably smaller than in sulphur purified by other procedures. A method is described for the determination of silicon, iron and magnesium in sulphur samples by direct spectroscopic analysis without enrichment of the elements to be analysed.

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83. Mitteilung: Lutz, H. D., u. Lj. Kosti: Z. Naturforsch. 21b, 892 (1966).

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Der Deutschen Forschungsgemeinschaft danken wir für die Förderung dieser Arbeit.     

Nanocrystal induced organization of a langmuir phospholipid monolayer

The influence of crystal surface charge on the thermodynamic and structural behavior of phospholipid monolayers has been investigated. We present how charged nanocrystals in the vicinity of an inherently nonordered lipid membrane provoke strong effects on the molecular arrangement within the monolayer. Apart from the induction of phase shifts and nucleation processes, the molecules were forced to adopt an ordered phase. A very recently developed X-ray scattering method is used for the first time to replace time-consuming specular reflectivity measurements. We conclude on the potential effects of crystal surface charge on cellular membranes.     

Bifunctional pincer-type organometallics as substrates for organic transformations and as novel building blocks for polymetallic materials

The reactivity of the bifunctionalized ligand NC(Br)N-I 1 [IC(6)H(2)(CH(2)NMe(2))(2)-3,5-Br-4] has been studied as a versatile synthon for organic and/or organometallic synthesis. Chemoselective metalation (M = Pd, Pt, Li) at the C(aryl)-I or C(aryl)-Br bonds was achieved by choosing the appropriate metal precursors. In this way a series of Pt(II) and Pd(II) complexes were prepared that have a second functional group available for further reactions. These Pt(II) and Pd(II) complexes were subjected to a wide range of organic and organometallic reactions, revealing the remarkable stability of their M-C sigma-bond and opening an easy route for the synthesis of mono- and (hetero)bimetallic building blocks. The scope of the chemistry of such building blocks shows that they are good candidates for use in the synthesis of dendrimers, bioorganometallic systems, or polymetallic materials. The X-ray crystal structures of the most representative complexes (2, 3a, 19, 20, and 24) are also reported.     

Electrocatalytic Proton Reduction by a Cobalt Complex Containing a Proton-Responsive Bis(alkylimdazole)methane Ligand: Involvement of a C−H Bond in H2 Formation

Homogeneous electrocatalytic proton reduction is reported using cobalt complex [ 1 ](BF₄)₂. This complex comprises two bis(1-methyl-4,5-diphenyl-1H-imidazol-2-yl)methane (HBMIM ) ligands that contain an acidic methylene moiety in their backbone. Upon reduction of [ 1 ](BF₄)₂ by either electrochemical or chemical means, one of its HBMIM ligands undergoes deprotonation under the formation of dihydrogen. Addition of a mild proton source (acetic acid) to deprotonated complex [ 2 ](BF₄) regenerates protonated complex [ 1 ](BF₄)₂. In presence of acetic acid in acetonitrile solvent [ 1 ](BF₄)₂ shows electrocatalytic proton reduction with a k_obs of ≈200 s⁻¹ at an overpotential of 590 mV. Mechanistic investigations supported by DFT (BP86) suggest that dihydrogen formation takes place in an intramolecular fashion through the participation of a methylene C−H bond of the HBMIM ligand and a Co^II−H bond through formal heterolytic splitting of the latter. These findings are of interest to the development of responsive ligands for molecular (base)metal (electro)catalysis.     

Methylene-azaphosphirane as a reactive intermediate

Reaction of the transient phosphinidene complexes R-P=W(CO)5 with N-substituted-diphenylketenimines leads unexpectedly to the novel 2-aminophosphindoles, as confirmed by an X-ray crystal structure determined for one of the derivatives. Experimental evidence for a methylene-azaphosphirane intermediate was found by using the iron-complexed phosphinidene iPr2N-P=Fe(CO)4, which affords the 2-aminophosphindole together with the novel methylene-2,3-dihydro-1H-benzo[1,3]azaphosphole. Analysis of the reaction pathways with DFT indicates that the initially formed methylene-azaphosphirane yields both phosphorus heterocycles by way of a [1,5]- or [1,3]-sigmatropic shift, respectively, followed by a H-shift. Strain underlies both rearrangements, which causes these remarkably selective conversions that can be tuned by changing the substituents.     

Perfluoralkyljod-verbindungen: Darstellungen und eigenschaften von CF3JO,CF3JOF2 und CF3JO2

Perfluoroalkyl iodine compounds: preparations and properties of CF₃IO, CF₃IOF₂, and CF₃IO₂. The trifluoromethyl iodine compounds CF₃IO, CF₃IOF₂, and CF₃IO₂ are formed from the reactions of CF₃I, CF₃IF₂ or CF₃IF₄ with ozone or silicon dioxide respectively. Their preparartions, properties, ¹⁹F-nmr spectra, and ir spectra are described.     

Zur Kenntnis des Calciumbromats und - iodats,Kristallstruktur, röntgenographische,IR- und Raman-spektroskopische und thermoanalytische Untersuchungen

On Calcium Bromated and Iodates – Crystal Structure, X-Ray, IR and Raman Spectroscopical and Thermoanalytical Investigations The phase relationships (and both decomposition and disproportionation)of bromates and iodates of alkaline earth metals are studied by means of thermal analyses (DTA, DSC, TG) and (high-temperature) X-Ray, IR-, and (high-temperature) Raman spectroscopic measurements. The following compounds have been established: Ca(IO₃)₂ · 6 H₂O oF 216, the isotypic Ca(BrO₃)₂ · H₂O and Ca(IO₃)₂ · H₂O mP 48, Ca(IO₃)₂ I (Lautarit) mP 36, Ca(IO₃)₂ II and Ca(BrO₃)₂. The Crystal structure of Ca(IO₃)₂ · H₂O (brüggenite) (space group P2₁/c, Z = 4) has been determined by single crystal X-ray diffraction (MoKα). The final R value for 3888 reflections with I_o > 3σ₁ is 0.0487. The structures of bromates and iodates of alkaline earth metals known so far are discussed with respect to the energetic (mode frequencies) and geometric (bond lengths) distortion of the XO₃–ions as well as the strengths of H-bonds present in the respective hydrates.     

Die chemie der schweren carben-analogen R2M,M = Si,Ge, Sn: IX. Eigenschaften und thermolyse von neuen 7-silabicyclo[2.2.1]heptadienen

Factors governing the ease and mechanism of 7-silabicyclo[2.2.1]heptadienes thermolysis in order to generate free silylenes and the corresponding benzene derivatives are investigated. For this purpose, 29 new compounds of the types VII–X have been prepared. No indications for a polar mechanism or an intermediate biradical could be found. The degradation is exactly of first order in all cases investigated sofar, and is enhanced by phenyl groups at the bridgehead C atoms, if a conformation coplanar with the basic ring is allowed by the neighbouring substituents, but is not enhanced by phenyl groups at the Si. The X-ray structure of two typical derivatives is discussed with this respect. A special mechanism is operating in the easy thermolysis of carbomethoxy-substituted compounds leading to cyclic sila enolether intermediates.