Ab initio study on the thermolysis of β-hydroxyolefins in gas phase

Thermolysis studies of β-hydroxyolefins in gas phase were realized using ab initio MP2 and DFT methods at the 6-31G^* levels to explore the possibility of determining a possible concerted process with a six-membered cyclic transition state (TS). Vibrational frequency calculations were carried out in order to confirm the stationary states, including TS structures. IRC calculations have been performed in all cases in order to verify that localized TS structures connect with the corresponding minimum stationary points associated with the reactant and products. With the aim of corroborating the postulated mechanism in the experimental study, we present a theoretical study in order to calculate the rate constants and the activation parameters. The results obtained are in accordance with the experimental conclusions.     

Designing Molecular Printboards: A Photolithographic Platform for Recodable Surfaces

A light induced strategy for the design of β‐cyclodextrin (CD) based supramolecular devices is introduced, presenting a novel tool to fabricate multifunctional biointerfaces. Precision photolithography of a modified β‐CD was established on a light sensitive tetrazole surface immobilized on a bioinspired polydopamine (PDA) anchor layer via various shadow masks, as well as via direct laser writing (DLW), in order to craft any desired printboard design. Interfacial molecular recognition provided by light generated cavitate domains was demonstrated via spatially resolved encoding, erasing, and recoding of distinct supramolecular guest patterns. Thus, the light directed shaping of receptor monolayers introduces a powerful path to control supramolecular assemblies on various surfaces.     

Why flow means green – Evaluating the merits of continuous processing in the context of sustainability

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Cyclisation of α,ω-dienes promoted by bis(indenyl)zirconium sandwich and ansa-titanocene dinitrogen complexes

Metallation of a variety of α,ω-dienes has been explored with an η(9),η(5)-bis(indenyl)zirconium sandwich compound and an ansa-titanocene dinitrogen complex. The η(9),η(5)-bis(indenyl)zirconium sandwich compound, (η(9)-C(9)H(5)-1,3-Pr(2))(η(5)-C(9)H(5)-1,3-(i)Pr(2))Zr, served as an isolable source of Negishi's reagent and readily formed a kinetic mixture of cis and trans diastereomers of the corresponding zirconacyclopentanes upon diene metallation. For pure hydrocarbon substrates such as 1,6-heptadiene and 1,7-octadiene, an equimolar amount of cis and trans diastereomers were the kinetic products; isomerization to the thermodynamically favoured trans isomers was observed over time at ambient temperature or upon heating to 105 °C, respectively. By contrast, substitution of the methylene or ethylene spacer in the α, ω-diene with a fluorenyl group (e.g. 9,9-diallylfluorene) resulted in exclusive kinetic formation of the trans diastereomer. Amino-substituted dienes were also readily cyclised and one example was characterised by single-crystal X-ray diffraction. Similar studies were also conducted with the ansa-titanocene dinitrogen complex, [Me(2)Si(η(5)-C(5)Me(4))(η(5)-C(5)H(3)-3-(t)Bu)Ti](2)(μ(2),η(1),η(1)-N(2)), and both kinetic and thermodynamic selectivities evaluated. The use of a C(1) symmetric ansa-metallocene increases the number of isomeric possibilities. For diallyl tert-butyl amine, diene metallation was more selective than for the bis(indenyl)zirconium sandwich compound and isomerization was also more rapid. Preliminary functionalisation reactivity for both the zircona- and titanocycles was also explored.     

On the elucidation of the mechanism of Vinca alkaloid fluorination in superacidic medium

Detailed investigations on one of the key steps of the superacidic fluorination of Vinca alkaloids that is the origin of C20' activation are reported. While two different pathways can be envisioned for the emergence of the transient secondary carbocationic intermediate, isotopic labeling experiments unambiguously revealed the involvement of a 1,2-hydride shift mechanism.     

Halide and nitrite recognizing hexanuclear metallacycle copper(II) pyrazolates

Halide-centered hexanuclear, anionic copper(II) pyrazolate complexes [trans-Cu(6)((3,5-CF(3))(2)pz)(6)(OH)(6)X](-), X = Cl, Br, I are isolated in a good yield from the redox reaction of the trinuclear copper(I) pyrazolate complex [μ-Cu(3)((3,5-CF(3))(2)pz)(3)] with a halide source such as PPh(3)AuCl or [Bu(4)N]X, X = Cl, Br, or I, in air. X-ray structures of the anion-centered hexanuclear complexes show that the six copper atoms are bridged by bis(3,5-trifluoromethyl)pyrazolate and hydroxyl ligands above and below the six copper atom plane. The anions are located at the center of the cavity and weakly bound to the six copper atoms in a μ(6)-arrangement, Cu-X = ~3.1 ?. A nitrite-centered hexanuclear copper(II) pyrazolate complex [trans-Cu(6)((3,5-CF(3))(2)pz)(6)(OH)(6)(NO(2))](-) was obtained when a solution of [PPN]NO(2) in CH(3)CN was added dropwise to the trinuclear copper(I) pyrazolate complex [μ-Cu(3)((3,5-CF(3))(2)pz)(3)] dissolved in CH(3)CN, in air. Blue crystals are produced by slow evaporation of the acetonitrile solvent. The X-ray structure of [PPN][trans-Cu(6)((3,5-CF(3))(2)pz)(6)(OH)(6)(NO(2))] complex shows the nitrite anion sits in the hexanuclear cavity and is perpendicular to the copper plane with a O-N-O angle of 118.3(7)°. The (19)F and (1)H NMR of the pyrazolate ring atoms are sensitive to the anion present in the ring. Anion exchange of the NO(2)(-) by Cl(-) can be observed easily by (1)H NMR.     

Which, if any, hydrates will crystallise? Predicting hydrate formation of two dihydroxybenzoic acids

A study of two dihydroxybenzoic acid isomers shows that computational methods can be used to predict hydrate formation, the compound:water ratio and hydrate crystal structures. The calculations also help identify a novel hydrate found in the solid form screening that validates this study.     

Poly(ether ketone)–polyisobutylene block copolymers: Synthesis and phase behavior

Telechelic poly(ether ketone)s (PEKs) and polyisobutylenes (PIBs) were combined to form PIB? PEK? PIB triblock copolymers and (PIB? PEK)_n multiblock copolymers via the formation of urea linkages. Monovalent and bivalent amino telechelic PIBs were prepared quantitatively from allyl telechelic PIBs by a newly developed reaction sequence featuring nucleophilic reaction steps. Telechelic PEK? NCO polymers were prepared from the corresponding amino telechelic PEKs via a reaction with diphosgene. The highly reactive PEK? NCO and PIB? NH₂ telechelics formed PEK? PIB block copolymers only quantitatively when appropriately reactive primary amino groups were present on the amino telechelic PIBs. The obtained block copolymers were microphase‐separated and featured mostly lamellar structures, as determined by small‐angle X‐ray scattering (SAXS). Temperature‐dependent SAXS measurements revealed ordered polymers in the melt up to 210 °C. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 188–202, 2005