Cláudia A. Figueira

Exploring the influence of steric hindrance and electronic nature of substituents in the supramolecular arrangements of 5-(substituted phenyl)-2-formylpyrroles

A family of 5-(substituted phenyl)-2-formylpyrrole compounds, exhibiting different electronic and steric features at the phenyl ring, was synthesised through the formylation reaction of the corresponding 2-(substituted phenyl)pyrrole precursors, using Vilsmeier–Haack acylation conditions. The products were obtained in moderate to high yields, being systematically characterised by NMR spectroscopy, elemental analysis and single crystal X-ray diffraction. The corresponding crystalline packings were discussed on the basis of three types of arrangements, leading to the formation of dimers, polymers or the newly observed tetramers, all of them essentially governed by strong N–H⋯O hydrogen bonding interactions. Important C–H⋯O, C–H⋯π, π⋯π and, in the case of fluorinated compounds, C–H⋯F interactions also contributed to the growth of the three-dimensional crystalline network. DFT calculations helped to rationalise the relationship between the steric and electronic properties of the molecules and the basic units observed in the corresponding solid state structures.

Erratum to: Dehydrogenation of 2-Phenyl-1-pyrroline with Palladium-Supported Catalysts: An Effective Route to the Synthesis of 2-Phenylpyrrole

The catalytic dehydrogenation of 5-phenyl-3,4- dihydro-2H-pyrrole (2-phenyl-1-pyrroline) to 2-phenyl- 1H-pyrrole in the presence of palladium-supported on activated carbon (Pd/C) or on alumina (Pd/Al2O3 )i s reported. Highly pure 2-phenylpyrrole is obtained in good yields and selectivities, in a ca. 20 gram-scale, after a simple work-up. The Pd/Al2O3 catalyst exhibited substan- tially higher activities than the Pd/C ones. Graphical Abstract

Iminopyrrole derivatives containing electron-withdrawing substituents: the formation of dimers and supramolecular arrangements

The crystal structures of two p-substituted phenylformiminopyrrole derivatives, namely 2-[(4-fluorophenyl)iminomethyl]pyrrole, C(11)H(9)FN(2), (1), and 2-[(1H-pyrrol-2-ylmethylidene)amino]benzonitrile, C(12)H(9)N(3), (2), bear F and C[triple-bond]N electron-withdrawing groups, respectively. Both structures feature two independent molecules in the asymmetric unit forming dimers via N-H...N hydrogen bonds. In the case of (1), each dimer interacts with two other dimers via C-H...F contacts, thus forming one-dimensional chains in the b direction, whereas in the case of (2), a weak C-H...N interaction connects the dimers in one-dimensional chains in the (110) direction.

trans-Chlorido(phenyl)bis(triphenylphosphine)nickel(II) and its 1:1 cocrystal with chloridobis(triphenylphosphine)nickel(I)

Two conformational polymorphs of trans-chlorido(phenyl)bis(triphenylphosphine)nickel(II), [Ni(C(6)H(5))Cl(C(18)H(15)P)(2)], (1), viz. orange needle-shaped crystals (form I) and brown prism-shaped crystals (form II), were obtained under different crystallization conditions from a mixture of toluene and n-hexane, and characterized by single-crystal X-ray diffraction at low temperature. These two forms were compared with that published previously [Zeller, Herdtweck & Strassner (2003). Eur. J. Inorg. Chem. pp. 1802-1806], characterized at room temperature. Additionally, blue-green prisms of a 1:1 cocrystal of complex (1) with chloridobis(triphenylphosphine)nickel(I), (2), viz. trans-chlorido(phenyl)bis(triphenylphosphine)nickel(II)-chloridobis(triphenylphosphine)nickel(I) (1/1), [Ni(C(6)H(5))Cl(C(18)H(15)P)(2)].[NiCl(C(18)H(15)P)(2)], (3), were obtained concomitantly with form I. In forms I and II, as well as in the cocrystal, the overall crystal packings are determined by an energetic interplay between intramolecular torsions and weak intermolecular C-H...pi and C-H...Cl interactions.

5-phenyl-3,4-dihydro-2H-pyrrole: the first example of a planar monosubstituted 1-pyrroline.

In the title compound, C10H11N, the molecules assemble as pseudo-dimers through pi-pi interactions, each dimer being rotated by about 90 degrees with respect to its neighbours. The relative positioning of the dimers and C-H...pi interactions give, when seen along a, a supramolecular zigzag arrangement. The compound contains a planar pyrroline ring and, as a whole, its molecular conformation is also planar, which represents the first example of a totally planar 2-substituted 1-pyrroline and the simplest ever reported by X-ray diffraction.