<i>E−Z</i> Isomerization and Aggregation Phenomena of Dithiafulvenes in CHCl₃

The physical−chemical properties of several 1,3-dithiafulvene (DTF) derivatives having a donor and acceptor group in the molecule were studied. The synthesis of these compounds produces selectively the E isomer, but when the compound is dissolved in CHCl3 isomerization to the Z isomer takes place with a rate that depends on the substituents. The interconversion rate is slow on the NMR time scale; therefore, two separated signals are observed, and they are used to measure the rate constant of isomerization. The equilibrium constant is, in all cases, very close to 1, and this is coincident with the fact that theoretical calculations of the energy of the two isomers in the gas phase differ by less than 0.1 kcal/mol. The isomerization reaction is completely reversible, and the E isomer can be obtained in pure form by selective crystallization. The derivatives with thioalkyl groups have a strong tendency to aggregate in CDCl3. The formation of the aggregates is evidenced from the changes in 1D 1H NMR and DOSY spectra as a function of concentration. The compounds are highly delocalized, and this is reflected by the low activation energy for the isomerization

Convergent Synthesis of a Metal–Organic Framework Supported Olefin Metathesis Catalyst

Synthesis of a metal–organic framework (MOF)-supported olefin metathesis catalyst has been accomplished for the first time following a new, convergent approach where an aldehyde-functionalized derivative of Hoveyda’s recently reported ruthenium catecholate olefin metathesis catalyst is condensed with an amine-functionalized IRMOF-74-III. The resulting material, denoted MOF-Ru, has well-defined, catalytically active ruthenium centers confined within channels having a ca. 20 Å diameter. MOF-Ru is a recyclable, single-site catalyst for self-cross-metathesis and ring-closing metathesis of terminal olefins. Comparison of this heterogeneous catalyst with a homogeneous analogue shows different responses to substrate size and shape suggestive of confinement effects. The MOF-Ru catalyst also displays greater resistance to double-bond migration that can be attributed to greater catalyst stability. For the preparation of well-defined, single-site heterogeneous catalysts where catalyst purity is essential, the convergent approach employed here, where the catalytic center is prepared ex situ and covalently linked to an intact MOF, offers an attractive alternative to in situ catalyst preparation as currently practiced in MOF chemistry

Convergent Synthesis of a Metal–Organic Framework Supported Olefin Metathesis Catalyst

Synthesis of a metal–organic framework (MOF)-supported olefin metathesis catalyst has been accomplished for the first time following a new, convergent approach where an aldehyde-functionalized derivative of Hoveyda’s recently reported ruthenium catecholate olefin metathesis catalyst is condensed with an amine-functionalized IRMOF-74-III. The resulting material, denoted MOF-Ru, has well-defined, catalytically active ruthenium centers confined within channels having a ca. 20 Å diameter. MOF-Ru is a recyclable, single-site catalyst for self-cross-metathesis and ring-closing metathesis of terminal olefins. Comparison of this heterogeneous catalyst with a homogeneous analogue shows different responses to substrate size and shape suggestive of confinement effects. The MOF-Ru catalyst also displays greater resistance to double-bond migration that can be attributed to greater catalyst stability. For the preparation of well-defined, single-site heterogeneous catalysts where catalyst purity is essential, the convergent approach employed here, where the catalytic center is prepared ex situ and covalently linked to an intact MOF, offers an attractive alternative to in situ catalyst preparation as currently practiced in MOF chemistry

Modular Synthesis of Metal–Organic Complex Arrays Containing Precisely Designed Metal Sequences

A modular synthetic approach is reported for the synthesis of heterometallic metal–organic complex arrays (MOCAs). Modules of four metal centers containing three different metals copper­(II), nickel­(II), platinum­(II), or ruthenium­(II) are prepared using a solid-phase polypeptide synthesis technique and then linked in solution to make MOCAs of eight metal centers as linear, T-branched, and H-branched compounds. The MOCA molecular topologies thus have specific unique linear and branched sequences of metals along the peptide backbone

Effect of Spatial Heterogeneity on the Unusual Uptake Behavior of Multivariate-Metal–Organic Frameworks

The uniqueness of multivariate metal–organic frameworks (MTV-MOFs) has been widely explored to discover their unknown opportunities. While mesoscopic apportionments have been studied, macroscopic heterogeneity and its spatial effects remain unexplored in MTV-MOFs. In this study, we investigated the effect of macroscopic heterogeneity on MTV-MOFs on their uptake behaviors by comparing three types of MTV-MOFs having the functional groups in inner, outer, or entire parts of crystals. Their adsorption behavior for carbon dioxide (CO2) and water (H2O) brought out that functional groups located in the outer part of the crystals dominantly influence the sorption behavior of MTV-MOFs. These results are also visualized by observing iodine adsorption in the three types of MTV-MOFs using scanning transmission electron microscopy–electron energy loss spectroscopy. We believe that this finding provides new ways to decipher and design MTV-MOFs for their unusual properties

1D Supramolecular Assemblies That Crystallize and Form Gels in Response to the Shape-Complementarity of Alcohols

N-9-Fluorenylmethyloxycarbonyl (Fmoc)- and C-tertiary butyl (t-Bu)-protected glutamate (L-2), bearing a phenanthroline moiety at the side residue, forms 1D supramolecular assemblies via H-bonding as well as undergoing π-stacking interactions to afford crystals or gels that depend on the shape-complementarity of coexisting alcohols, as demonstrated by structural analyses on these assemblies by means of single-crystal X-ray diffractometry and supplemented with small- and wide-angle X-ray scattering data. Moreover, the rheological measurements on the gels help to define a model for when gels and crystals are expected and found. These observations and conclusions highlight an important, but not very appreciated, aspect of solute–solvent interactions within supramolecular assemblies that can allow the constituent-aggregating molecules in some systems to exhibit high selectivity toward the structures of their solvents. The consequences of this selectivity, as demonstrated here by single-crystal and powder X-ray diffraction data, can lead to self-assembled structures which alter completely the bulk phase properties and morphology of the materials. In that regard, rheological measurements have helped to develop a model to explain when gels and phase-separated mixtures of crystals and solvents are expected

1D Supramolecular Assemblies That Crystallize and Form Gels in Response to the Shape-Complementarity of Alcohols

N-9-Fluorenylmethyloxycarbonyl (Fmoc)- and C-tertiary butyl (t-Bu)-protected glutamate (L-2), bearing a phenanthroline moiety at the side residue, forms 1D supramolecular assemblies via H-bonding as well as undergoing π-stacking interactions to afford crystals or gels that depend on the shape-complementarity of coexisting alcohols, as demonstrated by structural analyses on these assemblies by means of single-crystal X-ray diffractometry and supplemented with small- and wide-angle X-ray scattering data. Moreover, the rheological measurements on the gels help to define a model for when gels and crystals are expected and found. These observations and conclusions highlight an important, but not very appreciated, aspect of solute–solvent interactions within supramolecular assemblies that can allow the constituent-aggregating molecules in some systems to exhibit high selectivity toward the structures of their solvents. The consequences of this selectivity, as demonstrated here by single-crystal and powder X-ray diffraction data, can lead to self-assembled structures which alter completely the bulk phase properties and morphology of the materials. In that regard, rheological measurements have helped to develop a model to explain when gels and phase-separated mixtures of crystals and solvents are expected

1D Supramolecular Assemblies That Crystallize and Form Gels in Response to the Shape-Complementarity of Alcohols

N-9-Fluorenylmethyloxycarbonyl (Fmoc)- and C-tertiary butyl (t-Bu)-protected glutamate (L-2), bearing a phenanthroline moiety at the side residue, forms 1D supramolecular assemblies via H-bonding as well as undergoing π-stacking interactions to afford crystals or gels that depend on the shape-complementarity of coexisting alcohols, as demonstrated by structural analyses on these assemblies by means of single-crystal X-ray diffractometry and supplemented with small- and wide-angle X-ray scattering data. Moreover, the rheological measurements on the gels help to define a model for when gels and crystals are expected and found. These observations and conclusions highlight an important, but not very appreciated, aspect of solute–solvent interactions within supramolecular assemblies that can allow the constituent-aggregating molecules in some systems to exhibit high selectivity toward the structures of their solvents. The consequences of this selectivity, as demonstrated here by single-crystal and powder X-ray diffraction data, can lead to self-assembled structures which alter completely the bulk phase properties and morphology of the materials. In that regard, rheological measurements have helped to develop a model to explain when gels and phase-separated mixtures of crystals and solvents are expected

1D Supramolecular Assemblies That Crystallize and Form Gels in Response to the Shape-Complementarity of Alcohols

N-9-Fluorenylmethyloxycarbonyl (Fmoc)- and C-tertiary butyl (t-Bu)-protected glutamate (L-2), bearing a phenanthroline moiety at the side residue, forms 1D supramolecular assemblies via H-bonding as well as undergoing π-stacking interactions to afford crystals or gels that depend on the shape-complementarity of coexisting alcohols, as demonstrated by structural analyses on these assemblies by means of single-crystal X-ray diffractometry and supplemented with small- and wide-angle X-ray scattering data. Moreover, the rheological measurements on the gels help to define a model for when gels and crystals are expected and found. These observations and conclusions highlight an important, but not very appreciated, aspect of solute–solvent interactions within supramolecular assemblies that can allow the constituent-aggregating molecules in some systems to exhibit high selectivity toward the structures of their solvents. The consequences of this selectivity, as demonstrated here by single-crystal and powder X-ray diffraction data, can lead to self-assembled structures which alter completely the bulk phase properties and morphology of the materials. In that regard, rheological measurements have helped to develop a model to explain when gels and phase-separated mixtures of crystals and solvents are expected

1D Supramolecular Assemblies That Crystallize and Form Gels in Response to the Shape-Complementarity of Alcohols

N-9-Fluorenylmethyloxycarbonyl (Fmoc)- and C-tertiary butyl (t-Bu)-protected glutamate (L-2), bearing a phenanthroline moiety at the side residue, forms 1D supramolecular assemblies via H-bonding as well as undergoing π-stacking interactions to afford crystals or gels that depend on the shape-complementarity of coexisting alcohols, as demonstrated by structural analyses on these assemblies by means of single-crystal X-ray diffractometry and supplemented with small- and wide-angle X-ray scattering data. Moreover, the rheological measurements on the gels help to define a model for when gels and crystals are expected and found. These observations and conclusions highlight an important, but not very appreciated, aspect of solute–solvent interactions within supramolecular assemblies that can allow the constituent-aggregating molecules in some systems to exhibit high selectivity toward the structures of their solvents. The consequences of this selectivity, as demonstrated here by single-crystal and powder X-ray diffraction data, can lead to self-assembled structures which alter completely the bulk phase properties and morphology of the materials. In that regard, rheological measurements have helped to develop a model to explain when gels and phase-separated mixtures of crystals and solvents are expected