Phosphorus Centers of Different Hybridization in Phosphaalkene‐Substituted Phospholes

Abstract

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.

Palladium-Catalyzed Arylation of a Sterically Demandinggem-Dibromophosphaethene

“…The 1 H NMR spectrum of 7 indicated that the phenyl group was cis with respect to the Mes* group. Inversion of the stereochemistry would occur during the cross‐coupling process, including the predominant side‐on coordination of palladium to the P=C skeleton . The steric inversion process was also characterized in the KTC‐type coupling of 3 b and phenylmagnesium bromide, and 8 was isolated as the stereoisomer of 7 (Eq.…”

Stereoselective Catalytic Synthesis of Alkynylated Phosphaethenes Leading to Activation‐Free Gold Catalysis

“…In this paper, we disclose the Sonogashira process, for the regioselective catalytic alkynylation of 1 and its application in activation‐free gold catalysis. In comparable previous works, Ott and co‐workers intensively studied various alkynyl‐substituted phosphaethenes for the development of π‐extended phosphaethene derivatives .…”

Organophosphorus Compounds in Organic Electronics

“…The group of Matano and Réau have developed a similar approach, reacting in situ generated [Ti(η 2 ‐propene)(O‐ i Pr) 2 ] with suitable diynes forming a titanadiene intermediate that undergoes an analogous metal/phosphorous exchanges with suitable chloro‐ or bromo‐phosphanes. Both approaches use substituted diyne fragments in the syntheses of symmetrically diferrocenyl‐, pyridine‐, thiophene‐, benzene‐, and pyrrole‐substituted phospholes or asymmetric arylphosphaalkene phospholes . Great improvement in both approaches was achieved by the linkage of the two acetylene moieties by an alkyl bridge (‐CH 2 ‐) n (for n =3, 4), which results in high (regio‐)selectivity and increased overall yields, making these approach now one of the most powerful synthetic strategies.…”