Stable 5,5′-Substituted 2,2′-Bipyrroles: Building Blocks for Macrocyclic and Materials Chemistry

Abstract

The preparation and characterization of a family of stable 2,2'-bipyrroles substituted at positions 5 and 5' with thienyl, phenyl, TMS-ethynyl, and vinyl groups is reported herein. The synthesis of these new bipyrroles comprises three steps: formation of the corresponding 5,5'-unsubstituted bipyrrole, bromination, and Stille or Suzuki coupling. The best results in the coupling are obtained using the Stille reaction under microwave irradiation. The new compounds have been fully characterized by UV-vis absorption, fluorescence, and IR spectroscopies and cyclic voltammetry. X-ray single-crystal analysis of four of the synthesized bipyrroles indicates a trans coplanar geometry of the pyrrole rings. Furthermore, the substituents at positions 5,5' remain coplanar to the central rings. This particular geometry extends the π-conjugation of the systems, which is in agreement with a red-shifting observed for the λ of the substituted molecules compared to the unsubstituted bipyrrole. All of these new compounds display a moderate fluorescence. In contrast with unsubstituted bipyrroles, these bipyrroles are endowed with a high chemical and thermal stability and solubility in organic solvents.

Extended 2,2′-Bipyrroles: New Monomers for Conjugated Polymers with Tailored Processability

“…The syntheses of monomers 1a – c is predicated on the Suzuki and Stille couplings of dibrominated bipyrrole 2 and the corresponding boronic acid or stannilated derivative (Figure 2). In turn, the starting bromopyrrole is accessible from our previously reported methodology in two steps from ethyl cinnamate in an overall yield of 41% [30].…”

“…Once the brominated bipyrroles were in hand, preparation of substituted bipyrroles 1 was carried out by either Stille or Suzuki cross-coupling reactions. In particular, compounds 1a and 1c were synthesized following procedures previously reported by our group in 72% and 87% yield, respectively [29,30]. Extended bipyrrole 1b was prepared by Stille coupling adapting the methodology used to prepare 1c .…”

“…Elemental analyses were performed on a Carlo-Erba CHNS-O/EA 1108 instrument (Val de Reuil, France). Compounds 1a and 1b were prepared according to reported methodologies [29,30]. Experiments were performed in an Initiator (Biotage, Uppsala, Sweden) microwave apparatus, operating at a frequency of 2.45 GHz with continuous irradiation power from 0 to 400 W. Reactions were carried out in 5 and 20 mL glass tubes (Biotage, Uppsala, Sweden), sealed with aluminium/Teflon crimp tops, which can be exposed to up to 250 °C and 20 bar internal pressure.…”

Vinylpyrroles: solid-state structures and aggregation-induced emission properties

“…The hydrogen bonding interactions are oen found in the bipyrrole systems. 33,34,42 Although the molecular structures were similar, the intermolecular interactions present in 1 and 2 were different. The shortest inter-layer distance in 1, which is dened as the distance between the mean plane of the pyrrole ring (i.e., N1, C1, C2, C3, and C4), was determined to be 3.50Å.…”

Synthesis, Crystal Structure, and Photoluminescent Properties of 3,3′,4,4′-Tetraethyl-5,5′-divinyl-2,2′-bipyrrole Derivatives

“…The interlayer distance between the mean planes defined by N1, C1, C2, C3, and C4 was determined to be 3.211 Å, but direct interaction between the pyrrole rings was not observed ( Figure 3 B). Instead, there is another intermolecular interaction between a carbonyl group of barbituric unit (O1) and an electron deficient vinyl group (C9) of the neighboring molecule ( Figure 3 C) [ 21 , 39 , 40 , 41 ]. Compound 4 also showed strong intramolecular hydrogen bonding between the carbonyl oxygen atom and the NH groups.…”