Ruthenium-Catalyzed Hydroarylations of Methylenecyclopropanes: Mild C−H Bond Functionalizations with Conservation of Cyclopropane Rings

Ring conservation was observed in the first catalytic intermolecular hydroarylation of methylenecyclopropanes via C−H bond functionalization, a remarkable reactivity mode for a transformation proceeding through (cyclopropylcarbinyl)metal intermediates

Modular Synthesis of a New Family of Tripodal Ligands, <i>all</i>-<i>cis</i>-1,2,3-Tris(diphenylphosphinomethyl)cyclopropane and Relatives^†

Bisbenzyl-protected all-cis-1,2,3-tris(hydroxymethyl)cyclopropane has been obtained in three steps from commercially available cis-2-butene-1,4-diol (75% overall yield) and used to prepare a number of all-cis-1,2,3-trisubstituted cyclopropane derivatives. Among them, the new tripodal ligand all-cis-tris(diphenylphosphinomethyl)cyclopropane (TriCyp-PPP) has been demonstrated to furnishwith π-allylpalladium chloride dimera highly active catalyst for the allylation of diethyl methylmalonate enolate with allyl acetate

Platinum(IV) Complexes with Tridentate, <i>NNC</i>-Coordinating Ligands: Synthesis, Structures, and Luminescence

Platinum­(II) complexes of NNC-cyclometalating ligands based on 6-phenyl-2,2′-bipyridine (HL1) have been widely investigated for their luminescence properties. We describe how PtL1Cl and five analogues with differently substituted aryl rings, PtL2–6Cl, can be oxidized with chlorine and/or iodobenzene dichloride to generate Pt­(IV) compounds of the form Pt­(NNC-Ln)­Cl3 (n = 1–6). The molecular structures of several of them have been determined by X-ray diffraction. These PtLnCl3 compounds react with 2-arylpyridines to give a new class of Pt­(IV) complex of the form [Pt­(NNC)­(NC)­Cl]+. Elevated temperatures are required, and the reaction is accompanied by competitive reduction processes and generation of side-products; however, four examples of such complexes have been isolated and their molecular structures determined. Reaction of PtL1Cl3 with HL1 similarly generates [Pt­(NNC-L1)2]2+, which we believe to be the first example of a bis-tridentate Pt­(IV) complex. The lowest-energy bands in the UV–vis absorption spectra of all the PtLnCl3 compounds are displaced to higher energy relative to the Pt­(II) precursors, but they red-shift with the electron richness of the aryl ring, consistent with predominantly 1[πAr → π*NN] character to the pertinent excited state. A similar trend is observed for the [Pt­(NNC)­(NC)­Cl]+ complexes. They display phosphorescence in solution at room temperature, centered around 500 nm for [PtL1(ppy)­Cl]+ and [Pt­(L1)2]2+, and 550 nm for methoxy-substituted derivatives. The lifetimes are in the microsecond range, rising to hundreds of microseconds at 77 K, consistent with triplet excited states of primarily 3[πAr → π*NN] character with relatively little participation of the metal

A Novel Strategy for the Synthesis of 3-(<i>N</i>-Heteryl)pyrrole Derivatives

A flexible approach to unknown 1-(1<i>H</i>-pyrrol-3-yl)pyridinium salts with selective control of the substitution patterns, by the reaction of pyridinium ylides with 2<i>H</i>-azirines, is disclosed. 3-(Pyridinium-1-yl)pyrrolides, a new type of stable ylide, were prepared from these salts in high yields by treatment with base. Atmospheric-pressure hydrogenation of the ylides with Adams' catalyst lead to 1-(pyrrol-3-yl)piperidines in good yields

Rare Case of Polymorphism in a Racemic Fluoxetine Nitrate Salt: Phase Behavior and Relative Stability

Polymorphism in racemic pharmaceutical compounds is relatively unexplored. However, this phenomenon may provide an additional tool to crystal engineering, opening the doors to rational design of chiral resolution, chiral enrichment, and chiral purification of pharmaceutical compounds. In this work we report two racemic polymorphs occurring for the nitrate salt of the antidepressant drug fluoxetine (FLX): a racemate (<i>P</i>2₁<i>/n</i>, <i>Z</i> = 4, <i>Z</i>′ = 1) and a kryptoracemate (<i>Pca</i>2₁, <i>Z</i> = 4, <i>Z</i>′ = 2). The relative stability of these polymorphs was established through a combination of techniques, namely, differential scanning calorimetric (DSC), thermogravimetric analysis (TGA), hot stage microscopy (HSM), and solubility measurements. Though the two polymorphs share some structural features, the N⁺–H···O^– hydrogen bonds have created dissimilar racemic motifs in their packing, resulting in different enantiomer orientations. The racemate is more stable over the temperature ranges we studied and is monotropically related to kryptoracemate. In our experiments, the obtaining of non-centrosymmetric lattice of racemic fluoxetine nitrate was shown to be dependent on kinetic factors. The thermodynamic relationships between both polymorphs were further confirmed by measuring their water solubility at 20 and 37 °C

A Novel Strategy for the Synthesis of 3-(<i>N</i>-Heteryl)pyrrole Derivatives

A flexible approach to unknown 1-(1<i>H</i>-pyrrol-3-yl)pyridinium salts with selective control of the substitution patterns, by the reaction of pyridinium ylides with 2<i>H</i>-azirines, is disclosed. 3-(Pyridinium-1-yl)pyrrolides, a new type of stable ylide, were prepared from these salts in high yields by treatment with base. Atmospheric-pressure hydrogenation of the ylides with Adams' catalyst lead to 1-(pyrrol-3-yl)piperidines in good yields

Nonconcerted Cycloaddition of 2<i>H</i>-Azirines to Acylketenes: A Route to N-Bridgehead Heterocycles

Reactions of acylketenes, generated from diazo diketones, with 2-unsubstituted and 2-monosubstituted 3-aryl-2<i>H</i>-azirines lead to 1:1 or 2:1 adducts, which are derivatives of 5-oxa-1-azabicyclo[4.1.0]­hept-3-ene or 5,7-dioxa-1-azabicyclo[4.4.1]­undeca-3,8-diene. According to DFT B3LYP/6-31G­(d) computations, the formation of (4+2)-monoadducts proceeds via a stepwise non-pericyclic mechanism. Reaction with methanol transforms quantitatively both 1:1 and 2:1 adducts into 1,4-oxazepine derivatives

The “Magic Linker”: Highly Effective Gelation from Sterically Awkward Packing

Bis­(urea)­s based on the 4,4′-methylenebis­(2,6-diethylphenylene) (4,4′-MDEP) spacer are highly effective low molecular weight gelators, and the first single crystal structure of a bis­(urea) based on this spacer is reported. The structure is a conformational isomorph with eight crystallographically independent molecules (Z′ = 8) arranged in four tennis-ball type dimers with the 2,6-diethylphenylene units adopting five different conformations in the ratio 4:5:3:2:2. The awkward shape and conformational promiscuity arising from the orientations of the ethyl groups in this system is linked to its gelation behavior. A total of seven 4,4′-MDEP derivatives have been prepared, and six are versatile gelators, confirming the particularly effective nature of the MDEP spacer. Only the nitrophenyl derivative does not form gels, likely because of intramolecular CH···O hydrogen bonding arising from the electron-withdrawing nature of the nitro substituent and hence inhibition of the urea α-tape hydrogen-bonded motif

Extensive Polymorphism in the Molecular Ferroelectric 18-Crown‑6 Oxonium Tetrachloro-Gallium(III)

The materials property of ferroelectricity is intimately linked with symmetry-changing phase transitions. Characterizing such transitions is therefore essential for understanding molecular ferroelectrics. In this paper, we explore the temperature and thermal history dependence of polymorphic phase transitions in the multiaxial molecular ferroelectric 18-crown-6 oxonium tetrachloro-gallium­(III). We have solved the structures of two previously suggested polymorphs (D and Y) ab initio from high-temperature powder diffraction data. We also report the structure of a new polymorph (X) using low-temperature powder diffraction data and identify a fifth (W) that can form on cooling. These polymorphs can be related using two distinct group–subgroup trees. Structure types A–C observed in this and related compounds can be derived from high-temperature polymorph D by group–subgroup relationships. The X and Y polymorphs can be described as child structures of a hypothetical polymorph Z using a molecular rotational distortion mode description. The ferroelectric properties of the various polymorphs can be rationalized based on our structural findings

Extensive Polymorphism in the Molecular Ferroelectric 18-Crown‑6 Oxonium Tetrachloro-Gallium(III)

The materials property of ferroelectricity is intimately linked with symmetry-changing phase transitions. Characterizing such transitions is therefore essential for understanding molecular ferroelectrics. In this paper, we explore the temperature and thermal history dependence of polymorphic phase transitions in the multiaxial molecular ferroelectric 18-crown-6 oxonium tetrachloro-gallium­(III). We have solved the structures of two previously suggested polymorphs (D and Y) ab initio from high-temperature powder diffraction data. We also report the structure of a new polymorph (X) using low-temperature powder diffraction data and identify a fifth (W) that can form on cooling. These polymorphs can be related using two distinct group–subgroup trees. Structure types A–C observed in this and related compounds can be derived from high-temperature polymorph D by group–subgroup relationships. The X and Y polymorphs can be described as child structures of a hypothetical polymorph Z using a molecular rotational distortion mode description. The ferroelectric properties of the various polymorphs can be rationalized based on our structural findings