Synthesis of Donor–Acceptor-Type Benzo[b]phosphole and Naphtho[2,3-b]phosphole Oxides and Their Solvatochromic Properties

Benzophosphol-3-yl Triflates as Precursors of 1,3-Diarylbenzophosphole Oxides

A simple method for the synthesis of 3-arylbenzophosphole oxides under Suzuki-Miyaura coupling conditions has been presented. It employs benzophosphol-3-yl triflate starting materials which, prior to our work, had not been used for the synthesis of 3-arylbenzophosphole oxides. The reactions proceed over 24 h and provide a library of 3-arylbenzophosphole oxides. The synthetic access to the benzophosphol-3-yl triflates has been improved. The preliminary photophysical properties of some 3-arylbenzophosphole oxides have been investigated by absorption and emission measurements. The theoretical calculations were performed to establish structure-property relationships.

One Stone Three Birds: Regiodivergent Access to Amino-Substituted Benzophospholes and Their Structure-Property Relationships

Three series new NH₂-benzophosphole oxides were synthesized from cycloaddition of o-aminophenyl phosphine oxide with alkynes. The relationship between the location of the amino group and the photophysical properties were studied by absorption and emission spectroscopies and theoretical calculation. 4-NH₂-benzophosphole oxides show strong fluorescence emission and high fluorescence quantum efficiency. This "One stone three birds" process provides rapid access to multiple organophosphorus-based luminogens for the structure-property relationship study.

Palladium-catalysed C–H arylation of benzophospholes with aryl halides

A palladium-catalysed C–H arylation of benzophospholes with aryl halides has been developed. The reaction with aryl iodides and bromides proceeds well even under phosphine ligand-free Pd(OAc)₂ catalysis whereas the Pd(PCy₃)₂ is effective for the coupling with less reactive aryl chlorides. The optimal conditions are also applicable to the double arylations with organic dihalides and annulation reaction with ortho-dihalogenated benzenes, making the corresponding benzophosphole-based acceptor–donor–acceptor-type molecules and highly condensed heteroacene-type molecules of potent interest in materials chemistry. Although there are many reports of catalytic C–H functionalisations of related benzoheteroles such as indoles, benzothiophenes, and benzofurans, this is the first successful example of the catalytic direct C–H transformation of benzophospholes, to the best of our knowledge. The preliminary optoelectronic properties of some newly synthesized benzophosphole derivatives are also investigated.

A palladium-catalysed C–H arylation of benzophospholes with aryl halides has been developed to form the corresponding acceptor–donor–acceptor-type molecules and highly condensed heteroacene-type molecules of potent interest in material chemistry.

Periphery Modification of Tetrathiafulvalenes: Recent Development and Applications

Tetrathiafulvalene (TTF) and its analogs are fascinating molecules in materials science based on their excellent electron-donating abilities. This personal account describes recent advances in the synthesis of TTF analogs for functional materials via the palladium-catalyzed modification of peripheries of TTF analogs. We first consider three types of molecules: fluorophore-TTF hybrid molecules, multi-redox systems, and an organic ligand for metal-organic frameworks. These molecules were successfully synthesized via Stille coupling or palladium-catalyzed direct C-H arylation and their structural, electrochemical, and optical properties were clarified. Subsequently, phosphorus-substituted TTF analogs were successfully synthesized for future applications of redox-active phosphine ligands for metal catalysts. The development of these molecules can significantly affect the advancement of chemical science.

Synthesis of triphenylene-fused phosphole oxides via C-H functionalizations

The synthesis of triphenylene-fused phosphole oxides has been achieved through two distinct C–H functionalization reactions as key steps. The phosphole ring was constructed by a three-component coupling of 3-(methoxymethoxy)phenylzinc chloride, an alkyne, and dichlorophenylphosphine, involving the regioselective C–H activation of the C2 position of the arylzinc intermediate via 1,4-cobalt migration. The resulting 7-hydroxybenzo[b]phosphole derivative was used for further π-extension through Suzuki–Miyaura couplings and a Scholl reaction, the latter closing the triphenylene ring. The absorption and emission spectra of the thus-synthesized compounds illustrated their nature as hybrids of triphenylene and benzo[b]phosphole.

Synthesis and Properties of Phospha[5]helicenes Bearing an Inner-Rim Phosphorus Center

New phospha[5]helicene derivatives featuring angular fusion of phosphole and carbohelicene moieties have been synthesized using 7-hydroxybenzo[ b]phosphole oxide as a key intermediate, which can be regioselectively prepared through one-pot multicomponent coupling. The structural behavior of the present phospha[5]helicene oxide, sulfide, and gold complex in the solid and solution states, along with DFT calculations, demonstrated close correlation between the P-centered chirality and the helical chirality as well as facile helicity inversion and equilibrium between the diastereomers in solution.

Regioselective functionalization at the 7-position of 1,2,3-triphenylbenzo[b]phosphole oxide via P[double bond, length as m-dash]O-directed lithiation

Various 7-substituted benzo[b]phosphole derivatives were prepared by P[double bond, length as m-dash]O-directed lithiation of 1,2,3-triphenylbenzo[b]phosphole P-oxide and subsequent iodination and cross-coupling reactions. The electron-donating groups introduced at the 7-position produced dramatic solvatofluorochromism owing to the strong charge-transfer character of the excited state of the entire π-system.