Phosphorus Post‐Functionalization of Diphosphahexaarenes

Abstract

Diphosphahexaarenes are highly stable π‐extended frameworks containing two six‐membered phosphorus heterocycles that have emerged recently. Herein, we present a detailed investigation on the post‐functionalization reactions of their phosphorus centers with special emphasis on the selectivity of the processes and the impact of the phosphorus functionalizations into the physicochemical properties. These studies reveal that indeed the phosphorus atoms of the diphosphahexaarenes are readily available to be functionalized with quaternizing and oxidizing agents as well as borane groups without compromising the stability of the system. In addition, the optoelectronic properties of the diphosphahexaarenes are impacted by the phosphorus post‐modifications.

Cationic Organophosphorus Chromophores: A Diamond in the Rough among Ionic Dyes

“…The involvement of the quaternized cycle‐embedded phosphorus atom into the LUMO means that increasing the number of the cationic centers connected via π‐conjugated skeleton necessarily influences frontier orbitals, optical band gap and the electrochemical properties of the system. In line with dicationic nature, the diphosphahexaarene 49 (Figure 17) presents a set of reduction potentials with the lowest value of −1.1 V, while no oxidation was observed [49d] . This points to high stability of the cation, also confirmed by the absence of photodegradation under prolonged irradiation.…”

Planarizable Push‐Pull Probes with Sulfoximine‐Bridged Dithienothiophene Acceptors

“…Among possible alternatives of endocyclic acceptors, [3,26–29] sulfoximines were appealing considering their accessibility from sulfides and the possibility of late stage functionalization of the imine, which seemed attractive to tune the optoelectronic properties [30] . These modifications should have an effect in the interaction with membranes, and they should also provide information about general properties for further use of sulfoximines as the core in fluorescent molecules ( Figure 1), for which only a few examples can be found in literature [31–33] …”

Two-Fold Intramolecular Phosphacyclization: From Fluorescent Diphosphapyrene Salts to Pentavalent Derivatives

“…This is in sharp contrast with, for instance, oxidized, pentavalent λ 5 ; σ 2 -endo, σ 2 -exo phosphorus atoms, which can be easily interconverted into trivalent λ 3 ; σ 2 -endo, σ 1 -exo once inserted into π-systems. 30,36,37 The trivalent form may be then postfunctionalized with oxidizing agents, transition metals, Lewis acids, etc., to tailor the properties of the π-system. 19 Thus, the possibility of converting quaternized λ 4 ; σ 2 -endo, σ 2 -exo phosphorus atoms of π-extended 6MPHs into λ 5 ; σ 2 -endo, σ 2 -exo or trivalent λ 3 ; σ 2endo, σ 1 -exo centers would clearly revalue the π-extended phosphonium motifs for further purposes.…”

“…Currently, π-extended phosphonium salts based on 6MPHs, i.e., with a λ 4 ; σ 2 -endo , σ 2 -exo phosphorus center, are at the focus of organophosphorus chemistry; ,,− they provide a promising platform to conceive near-infrared fluorophores for bioimaging, electrofluorochromic systems, and viologen-like materials. , Quaternized phosphorus atoms strongly reduce the LUMO level of π-systems and thus decrease the optical band gap. A large variety of molecular motifs emerged to exploit this feature. ,,− However, the quaternized λ 4 ; σ 2 -endo , σ 2 -exo phosphorus centers from isolated 6MPHs have not been demonstrated to be reversible; i.e.…”

“…Common methodologies to prepare π-extended 6MPHs with a quaternized λ 4 ; σ 2 -endo, σ 2 -exo center involve the phospha-cyclization using halophenylphosphine derivatives and the subsequent alkylation of the resulting trivalent λ 3 ; σ 2 -endo , σ 1 -exo phosphorus atom, ,, the cyclization of diphenylphosphine derivatives with PhICl 2 and the Cu-catalyzed cyclization of diphenylphosphines with , and without , alkynes as coreactants. Methodologies to prepare π-extended 6MPHs with two quaternized λ 4 ; σ 2 -endo , σ 2 -exo centers are, on the other hand, only limited to Cu-catalyzed cyclization of diphenylphosphines with alkynes as coreactants and solely one example without coreactant (Figure ).…”