Synthesis, Electronic Properties, and Reactivity of Phospholes and 1,1′‐Biphospholes Bearing 2‐ or 3‐Thienyl C‐Substituents

Abstract

Two series of phospholes and 1,1'-biphospholes bearing either 2- or 3-thienyl substituents at the C atoms are prepared by using the Fagan-Nugent route. Their optical (UV/Vis absorption, fluorescence spectra) and electrochemical properties are systematically evaluated. Of particular interest, the first ever reported 3-thienyl-substituted phospholes exhibit higher LUMO levels than their 2-thienyl analogues, and show accordingly different physical properties. This study also reveals that the 1,1'-biphospholes exhibit sigma-pi conjugation. The phosphole and 1,1'-biphosphole derivatives bearing 3-thienyl substituents are characterized by X-ray diffraction study. The structure-property relationship established following the experimental data are fully supported by theoretical studies including time-dependent(TD)-DFT spectra. A photocyclization reaction performed on the thioxo- and oxophospholes having 3-thienyl substituents affords a novel ring-fused phosphole-thiophene derivative, which was characterized by an X-ray diffraction study. The structure and electronic properties of this novel dithienophosphole are discussed based on experimental and theoretical data.

3,4‐Dithiaphosphole and 3,3′,4,4′‐Tetrathia‐1,1′‐Biphosphole π‐Conjugated Systems: S Makes the Impact

“…Phosphole 4 b bearing phenyl substituents was characterized by an X‐ray diffraction study (Figure 4, Table 2). The angles and bond lengths of the P ring are classical and compare well with those observed for other phosphole derivatives 8a,k,l. For example, the P atom has a strong pyramidal character (∑P ang =294.7°) and the endocyclic PC bond lengths (1.808(2)–1.816(2) Å, Table 3) approach that of a P–C single bond (1.84 Å).…”

“…The fact that 1) these low‐energy bands are considerably redshifted relative to the absorption of the corresponding 1‐phenylphospholes 4 a , b (Figure 6), and that 2) the shape of the spectra of 5 a , b are very similar to those of the corresponding reference derivatives S , T 8j (Figure 7), clearly show that σ–π conjugation is effective in the newly prepared derivatives 5 a , b . These data confirm that the P–P skeleton is a powerful σ scaffold to establish through‐bond electronic interaction between π chromophores 8a,j…”

“…Their 31 P{ 1 H} NMR spectra display a singlet at classical chemical shifts for 1‐phenylphosphole derivatives ( 4 a , δ =+9.9 ppm; 4 b , δ = +10.2 ppm) and 1,1′‐biphospholes ( 5 a , δ =+5.0 ppm; 5 b , δ =+7.2 ppm) 5. 8a,j,l Their 13 C NMR spectra recorded at room temperature are very simple, thereby indicating symmetric structures and/or a rapid rotation around the PP bond for 1,1′‐biphospholes. The 13 C{ 1 H} data of the carbon skeleton of 5 a , b and those of the corresponding phospholes 4 a , b are very similar, except the PC α signals that are shielded by approximately δ =3–5 ppm in 4 a , b relative to 5 a,b .…”

“…The second main strategy to diversify the properties of linear π‐conjugated systems (i.e., the attachment of lateral substituents R 1 and R 2 with specific electronic or steric demands, Scheme ) has not been fully investigated with phosphole building blocks. In fact, all the phosphole moieties B that have been used to date for the tailoring of π systems A (Scheme ) feature alkyl groups at their 3‐ and 4‐positions, except one example concerning per‐aryl derivatives 8a. This is mainly due to synthetic reasons since these 3,4‐dialkylphosphole synthons are easily accessible using the two well‐established methods depicted in Scheme 5a–c.…”

Anorganische Chemie 2009

“…Funktionalisiert man alle C‐Atome in Phosphol mit Thiopheneinheiten entsteht ein zweidimensional erweitertes p‐System. Dessen elektronische Struktur lässt sich effizient über chemische Modifikation des Phosphorzentrums steuern 1_72. Ethinyl‐Funktionalisierung der 2,5‐Position in Phospholen modifiziert die photophysikalischen Eigenschaften der Materialien und eröffnet ebenfalls den Zugang zu Oligophospholen.73,74)…”