Metal organic frameworks showing hydrocarbon adsorption properties commensurate with their pore structure

Commensurate adsorption occurs when the number of molecules adsorbed per unit cell relates to the symmetry of the framework and its topology. While rare in zeolite materials, commensurate adsorption has been observed in several MOF materials. In some MOF materials, several molecules having dimensions within a limited size range show this effect. This paper describes the commensurate adsorption properties of three MOF materials and also two MOFs showing unusual combined structure-composition adsorption features.     

Structure elucidation of β-carotene isomers by HPLC-NMR coupling using a C30 bonded phase

The separation of cis/trans isomers of β-carotene has been performed with a C₃₀ stationary phase employing ¹H NMR spectroscopy as an on-line detection technique. 1D as well as 2D NMR spectra have been recorded in the stopped-flow mode for the predominant chromatographic peaks. Structural assignment of the five identified isomers was performed via comparison of simulated 1D ¹H NMR spectra on the basis of the structures of β-carotene cis/trans isomers with the experimental data, and also by the analysis of the proton-proton connectivities in the 2D NMR spectra of three isomers with the highest concentration. The chromatographic retention behaviour of the isomers agreed well with previously reported data. The advantage of the applied hyphenated coupling technique compared to conventional off-line techniques lies in the fact that chromatographic separation and NMR detection are performed in a closed system, so that reisomerization of the separated compounds is inhibited. Received: 29 May 1996 / Revised: 1 July 1996 / Accepted: 4 July 1996     

Optimized synthesis, structural investigations, ligand tuning and synthetic evaluation of silyloxy-based alkyne metathesis catalysts

Nitride- and alkylidyne complexes of molybdenum endowed with triarylsilanolate ligands are excellent (pre)catalysts for alkyne-metathesis reactions of all sorts, since they combine high activity with an outstanding tolerance toward polar and/or sensitive functional groups. Structural and reactivity data suggest that this promising application profile results from a favorable match between the characteristics of the high-valent molybdenum center and the electronic and steric features of the chosen Ar(3) SiO groups. This interplay ensures a well-balanced level of Lewis acidity at the central atom, which is critical for high activity. Moreover, the bulky silanolates, while disfavoring bimolecular decomposition of the operative alkylidyne unit, do not obstruct substrate binding. In addition, Ar(3) SiO groups have the advantage that they are more stable within the coordination sphere of a high-valent molybdenum center than tert-alkoxides, which commonly served as ancillary ligands in previous generations of alkyne metathesis catalysts. From a practical point of view it is important to note that complexes of the general type [(Ar(3) SiO)(3) Mo?X] (X = N, CR; R = aryl, alkyl, Ar = aryl) can be rendered air-stable with the aid of 1,10-phenanthroline, 2,2'-bipyridine or derivatives thereof. Although the resulting adducts are themselves catalytically inert, treatment with Lewis acidic additives such as ZnCl(2) or MnCl(2) removes the stabilizing N-donor ligand and gently releases the catalytically active template into the solution. This procedure gives excellent results in alkyne metathesis starting from air-stable and hence user-friendly precursor complexes. The thermal and hydrolytic stability of representative molybdenum alkylidyne and -nitride complexes of this series was investigated and the structure of several decomposition products elucidated.     

Preparation and Properties of Novel Cationically Active Oligo-p-Methoxystyryl-Silica Composites

Abstract

The preparation of cationically active oligo-p-methoxystyrene-silica composites by cationic interfacial polymerization is described. In addition to the effective preparation of the interfacial initiator, p-methoxybenzylium-hydrogen sulfate-silica, and p-methoxybenzylium-trifluoroacetate-silica, a procedure to yield new kinds of composites is reported. The outstanding properties of the “living” oligo-p-methoxy-styryl-hydrogen sulfate-silica is demonstrated by means of zeta potential measurements, solid-state ¹³C-NMR spectroscopy, UV/Vis spectroscopy, and electron scanning microscopy.     

Palladium-Catalyzed Arylation of Endocyclic 1-Azaallyl Anions: Concise Synthesis of Unprotected Enantioenriched cis-2,3-Diarylpiperidines

Unprotected cis-2,3-diarylpiperidines are synthesized through an unprecedented palladium-catalyzed cross-coupling reaction between aryl halides and elusive endocyclic 1-azaallyl anions. These intermediates are generated in situ by the deprotonation of 2-aryl-1-piperideines, precursors that are readily prepared in two operations from simple piperidines. An asymmetric version of this reaction with (2R, 3R)-iPr-BI-DIME as the ligand provides products in moderate to good yields and enantioselectivities. This study significantly expands the synthetic utility of endocyclic 1-azaallyl anions.     

Polyhedral clathrate hydrates of a strong base: Phase relations and crystal structures in the system tetramethylammonium hydroxide-water

The tetramethylammonium hydroxide-water system has been studied by low-temperature differential thermal analysis and X-ray powder diffraction. The melting diagram was constructed for concentrations between 66.7 and 100 mol% H₂O. It shows the existence and stability ranges of as many as eight crystalline hydrate phases:- and-Me₄NOH·2H₂O (phase transition at –85°C, decomposition atca. 105°C), Me₄NOH·4 H₂O (melting point 44°C, incongruent), and-Me₄NOH·5 H₂O (phase transition at 42°C, melting point 68°C, congruent),- and-Me₄NOH·7.5 H₂O (phase transition at 6°C, melting point 16°C, incongruent), and Me₄NOH·10 H₂O (melting point –20°C, incongruent). The structures of all these phases, except the already known one of-Me₄NOH·5 H₂O, were determined from single-crystal MoK diffractometer data. The decahydrate and the high-temperature forms of the 7.5-hydrate and the pentahydrate are genuinepolyhedral clathrate hydrates, the first ones reported of a strong base. Their mostly novel three-dimensional anionic host structures, formed by the hydrogen-bonded OH^– ions and H₂O molecules, arefour-connected throughout, in spite of their proton deficiency which is apparently leveled by disorder. Disorder also affects the enclosed cationic Me₄N⁺ guest species. Like the low-temperature form of the pentahydrate, that of the 7.5-hydrate has a clathrate-related, but not fully polyhedral structure, some of the oxygen atoms being three-connected only. The tetrahydrate presents the rare case of both a hydrogen bond of the type OH^–...OH₂ and a (deprotonated) water-channel structure. This is fully ordered and apart from that can be derived from the polyhedral one of the-pentahydrate just by removing the appropriate number of water molecules from certain positions. The structures of- and-Me₄NOH·2 H₂O contain identical one-dimensionalspiro chains [HO^–(HOH)_/42] with the hydroxide protonnot participating in the hydrogen bonding. The Me₄N⁺ ion is ordered in the and disordered in the phase.Supplementary Data relating to this article are deposited with the British Library as Supplementary Publication No. SUP 82076 (66 pages).Dedicated to Dr D. W. Davidson in honor of his great contributions to the sciences of inclusion phenomena.     

Monomere und dimere Oxovanadium(IV)-phenolate: Synthese,Struktur und Reaktionen mit reduzierenden und arylierenden Reagenzien

Monomeric and Dimeric Oxovanadium(IV)-phenolate Complexes: Synthesis, Structure, and Reaction with a Reducing and Arylation Agent Reaction of [OVCl₂(THF)₂] with LiOMes yields dimeric [Li(Et₂O)₂OVCl₂(μ-OMes)]₂ ( 1 ) which can be converted with excess LiOMes to the substitution product [Li(THF)₂OV(OMes)₃(THF)] ( 2 ). Treatment of ( 1 ) with LiMes results in the formation of complexes [Li(THF)₃OVMes₃] ( 3 ) and [Li(THF)₃OVMes₂(OMes)] ( 4 ). Complex [{Li(THF)₂OV(OMes)₂(μ-OH)}₂ · 2 THF] ( 6 ) has been isolated as a by-product of an unknown reaction of [OV(OMes)₃] and Li. The structures of 1 , 2 , 3 , and 6 have been determined by X-ray analysis. In 1 (monoclinic, P2₁/c, a = 9.522(1) Å, b = 19.777(2) Å, c = 12.311(1) Å, β = 104.45(1)°, Z = 2) the vanadium atoms which are bridged by the phenolate ligands show a square-pyramidal coordination sphere. The central atom in 2 (monoclinic, P2₁/c, a = 17.755(2) Å, b = 11.629(1) Å, c = 20.956(3) Å, β = 113.98(1)°, Z = 4) has a bipyramidal environment which is realized by coordination of a THF donor molecule. The (THF)₂Li fragment is bound via bridging phenolate ligands. The structure of 3 (orthorhombic, P2₁2₁2₁, a = 15.465(2) Å, b = 15.456(2) Å, c = 15.469(2) Å, Z = 4) is built up by two tetrahedrons linked by the oxo atom. Dimeric 6 (triclinic, P1, a = 10.780(4) Å, b = 11.428(2) Å, c = 13.734(3) Å, α = 77.24(2)°, β = 84.79(2)°, γ = 74.35(2)°, Z = 1) has a structure similar to 1 . The vanadium atoms are bridged by two OH groups while phenolate ligands link the lithium cations with the vanadium atoms.