Phosphaalkenes in π-Conjugation with Acetylenic Arenes

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Phosphole-substituted phosphaalkenes (PPAs) of the general formula Mes*P=C(CH3)–(C4H2P(Ph))–R 5 a–c (Mes*=2,4,6-tBu3Ph; R=2-pyridyl (a), 2-thienyl (b), phenyl (c)) have been prepared from octa-1,7-diyne-substituted phosphaalkenes by utilizing the Fagan–Nugent route. The presence of two differently hybridized phosphorus centers (σ2,λ3 and σ3,λ3) in 5 offers the possibility to selectively tune the HOMO–LUMO gap of the compounds by utilizing the different reactivity of the two phosphorus heteroatoms. Oxidation of 5 a–c by sulfur proceeds exclusively at the σ3,λ3-phosphorus atom, thus giving rise to the corresponding thioxophospholes 6 a–c. Similarly, 5 a is selectively coordinated by AuCl at the σ3,λ3-phosphorus atom. Subsequent second AuCl coordination at the σ2,λ3-phosphorus heteroatom results in a dimetallic species that is characterized by a gold–gold interaction that provokes a change in π conjugation. Spectroscopic, electrochemical, and theoretical investigations show that the phosphaalkene and the phosphole both have a sizable impact on the electronic properties of the compounds. The presence of the phosphaalkene unit induces a decrease of the HOMO–LUMO gap relative to reference phosphole-containing π systems that lack a P=C substituent.

Section: Introductionmentioning

confidence: 62%

Phosphorus Centers of Different Hybridization in Phosphaalkene‐Substituted Phospholes

Öberg

Orthaber

Lescop

et al. 2014

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“…In the case of 7 a , b , it is possible to protodesilylate the acetylene termini, which can then be further elaborated by desirable substituents to fine‐tune the photophysical and electrochemical properties of the F9Ps . The feasibility of such a strategy was exemplified by the deprotection of phosphaalkene 7 a with K 2 CO 3 and isolation of the terminal bis‐acetylene 8 a .…”

Section: Resultsmentioning

confidence: 99%

Tuning the Electronic Properties of Acetylenic Fluorenes by Phosphaalkene Incorporation

Svyaschenko

Orthaber

Ott

2016

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Versatile synthetic protocols for 2,7- and 3,6-diacetylenic fluorene-9-ylidene phosphanes (F9Ps) were developed. Protodesilylation of trimethylsilyl-protected acetylenic F9Ps affords terminal acetylenes that can be employed in Sonogashira and Glaser-type C-C coupling reactions to give thienyl-decorated and butadiyne-bridged fluorene-9-ylidene phosphanes, respectively. As evidenced by UV/Vis spectroscopy and cyclic voltammetry and corroborated by ab initio calculations, the presence of the P center in the F9Ps induces a significantly reduced HOMO-LUMO splitting that originates from stabilization of the LUMO levels. Variation of the acetylene substitution pattern is an additional tool to influence the optical and electronic properties. Whereas 3,6-disubstituted F9Ps have strong absorptions around 400 nm, mainly due to π-π* transitions, 2,7-diacetylenic F9Ps exhibit longest-wavelength absorptions that have significant charge-transfer character with an onset around 520 nm.

“…These results show that these multifunctional P,S building blocks are valuable synthons for the molecular engineering of p-conjugated molecular or polymeric conjugated systems, and extend the family of organophosphorus-based materials. [26] Experimental Section X-ray crystallography studies: Single crystals suitable for X-ray crystal analysis were obtained by slow diffusion of vapors of pentane into a solution of 4 b, 6 a, or 8 b in dichloromethane. Single-crystal data collection was performed at 100 K with an APEX II Bruker-AXS (Centre de DiffractomØtrie, UniversitØ de Rennes 1, France) with Mo Ka radiation (l = 0.71073 ).…”

Section: Resultsmentioning

confidence: 99%

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

Fadhel

Benkő

Gras

et al. 2010

Conjugated systems based on phospholes and 1,1'-biphospholes bearing 3,4-ethylenedithia bridges have been prepared using the Fagan-Nugent route. The mechanism of this organometallic route leading to intermediate zirconacyclopentadienes has been investigated by using theoretical calculations. This study revealed that the oxidative coupling leading to zirconacyclopentadienes is favored over oxidative addition within the S-C≡C bond both thermodynamically and kinetically. The impact of the presence of the S atoms on the optical and electrochemical behavior of the phospholes and 1,1'-biphospholes has been systematically evaluated both experimentally and theoretically. A comparison with their "all-carbon" analogues is provided. Of particular interest, this comparative study revealed that the introduction of S atoms has an impact on the electronic properties of phosphole-based conjugated systems. A decrease of the HOMO-LUMO separation and a stabilization of the LUMO level were observed. These general trends are also observed with 1,1'-biphospholes exhibiting σ-π conjugation. The P atom of the 3,4-ethylenedithiaphospholes can be selectively oxidized by S(8) or O(2). These P modifications result in a lowering of the HOMO-LUMO separation as well as an increase of the reduction and oxidation potentials. The S atoms of the 3,4-ethylenedithia bridge of the 2,5-phosphole have been oxidized using m-chloroperoxybenzoic acid. The resulting 3,4-ethylenesulfoxide oxophosphole was characterized by an X-ray diffraction study. Experimental and theoretical studies show that this novel chemical manipulation results in an increase of the HOMO-LUMO separation and an important decrease of the LUMO level. The electropolymerization of 2-thienyl-capped 3,4-ethylenedithiathioxophosphole and 1,1'-biphosphole is reported. The impact of the S substituents on the polymer properties is discussed.