Ligand‐Enabled Disproportionation of 1,2‐Diphenylhydrazine at a P V ‐Center**

We present herein the synthesis of a nearly square‐pyramidal chlorophosphorane supported by the tetradentate bis(amidophenolate) ligand, N,N′‐bis(3,5‐di‐tert‐butyl‐2‐phenoxy)‐1,2‐phenylenediamide. After chloride abstraction the resulting phosphonium cation efficiently promotes the disproportionation of 1,2‐diphenylhydrazine to aniline and azobenzene. Mechanistic studies, spectroscopic analyses and theoretical calculations suggest that this unprecedented reactivity mode for P^V‐centres is induced by the high electrophilicity at the cationic P^V‐center, which originates from the geometry constraints imposed by the rigid pincer ligand, combined with the ability of the o‐amidophenolate moieties to act as electron reservoir. This study illustrates the promising role of cooperativity between redox‐active ligands and phosphorus for the design of organocatalysts able to promote redox processes.

Phosphorus(V) tetrapyrazinocorrolazines bearing axial aryloxy groups as pH-sensitive fluorophores and photosensitizers

Phosphorus(V) complexes of octaphenyltetrapyrazinocorrolazine bearing two aryloxy groups in the axial position, [TPyzCAP(OAr)₂] (2a-c, Ar = phenyl (2a), 4-dimethylaminophenyl (2b), and 4-hydroxyphenyl (2c)), were prepared using a one-pot procedure by consecutive treatment of the dihydroxidophosphorus(V) derivative, [TPyzCAP(OH)₂] (1), with SOCl₂ and then with the corresponding phenol ArOH. Complex 2a containing axial PhO groups is fluorescent in all studied solvents (toluene, CH₂Cl₂, THF, and DMSO, Φ_F ∼ 0.16-0.31) and is efficient to generate singlet oxygen (Φ_Δ = 0.55 (THF), 0.68 (toluene)). The introduction of NMe₂ and OH groups in the para-position of the axial ArO ligands strongly affects the fluorescence parameters and photosensitizing properties due to the appearance of the solvent-sensitive and pH-switchable effects of photoinduced electron transfer (PET). The PET effect of NMe₂ groups completely quenches the excited state of 2b in all solvents, but it is switched-OFF upon their protonation, and in the presence of acid traces, the fluorescence of 2b becomes bright and singlet oxygen generation is strongly enhanced. The PET effect of the OH group is increased upon its deprotonation and in the presence of base 2c as well as 1 becomes non-fluorescent. Specific solvation in THF and DMSO increases the ionic character of the OH bonds, and the fluorescence and photosensitizing properties of 1 and 2c are strongly decreased in these solvents. According to the results of DFT calculations performed using the B3LYP functional with the cc-pVDZ basis set and cyclic voltammetric studies, the molecular orbitals localized on aryloxy ligands are destabilized upon the introduction of OH and especially NMe₂ groups and their close position to the HOMO of corrolazine macrocycle (above HOMO in 2b and between HOMO and HOMO-1 in 2c) leads to the appearance of the PET effect.

Synthesis, Structure, Spectral, and Anion Sensing Studies of an Aromatic meso-Fused Boron(III) Benzitriphyrin(2.1.1) Complex

An aromatic tricoordinated organo B(III) complex of benzitriphyrin(2.1.1) was synthesized by treating the nonaromatic phlorin analogue of meso-fused benzitriphyrin(2.1.1) with BCl₃ in triethylamine/toluene and refluxing for 2 h. The X-ray structure revealed that B(III) was in a trigonal-planar geometry and was coordinated to two nitrogen atoms and one carbon. Insertion of the small B(III) ion into the meso-fused phlorin analogue resulted in transforming the nonaromatic phlorin analogue to an aromatic B(III) benzitriphyrin(2.1.1) complex. Spectral and electrochemical studies supported the aromatic nature of the B(III) complex of benzitriphyrin(2.1.1). Theoretical studies supported the major contribution of the 18π delocalization pathway toward the aromatic nature of the B(III) meso-fused benzitriphyrin(2.1.1) in comparison to the 22π delocalization pathway. The B(III) benzitriphyrin(2.1.1) complex acts as a specific colorimetric and fluorogenic F^-/CN^- ion sensor.

A Phosphorus-Based Pacman Dication Generated by Cooperative Self-Activation of a Pacman Phosphane

Formal coordination of phosphorus(III) by a calix[4]pyrrole Schiff base ligand was achieved through the reaction of this ligand with PCl₃ under basic conditions. The reaction product adopts a Pacman conformation with two P-Cl moieties, one in exo and one in endo position. It represents the first non-metal compound of calix[4]pyrrole Schiff base ligands and of Pacman ligands in general. The spatial neighborhood of the two phosphorus atoms enables cooperative reactions. As a first example, the chloride abstraction with AgOTf is presented, yielding a macrocyclic dication with two embedded phosphorus(III) monocations, which both undergo a cooperative, internal activation reaction with an adjacent C=N double bond. This intramolecular redox process affords two pentacoordinated phosphorus(V) centers within the Pacman dication. All reaction products were fully characterized and all results are supported by computations.

Photosensitized Protein Damage by DiethyleneglycoxyP(V)tetrakis(p-n-butoxyphenyl)porphyrin Through Electron Transfer: Activity Control Through Self-aggregation and Dissociation

DiethyleneglycoxyP(V)tetrakis(p-n-butoxyphenyl)porphyrin (EGP(V)TBPP) forms a self-aggregation in an aqueous solution, and the photoexcited state of this molecule was effectively deactivated. Association with human serum albumin (HSA), a water-soluble protein, causes dissociation of the self-aggregation, resulting in recovery of the photosensitizer activity of EGP(V)TBPP. Under visible light irradiation, EGP(V)TBPP photosensitized HSA oxidation. The photosensitized singlet oxygen-generating activity of EGP(V)TBPP was confirmed by near-infrared emission measurement. A singlet oxygen quencher, sodium azide, partially inhibited the HSA photodamage; however, the quenching effect was estimated to be 57%. Another 43% of the HSA photodamage could be explained by the electron transfer mechanism. The redox potential of EGP(V)TBPP and the calculated Gibbs energy of electron transfer from tryptophan to photoexcited EGP(V)TBPP demonstrated the possibility of HSA oxidation through electron extraction. Fluorescence lifetime measurements of EGP(V)TBPP verified the electron transfer from HSA. The photosensitizer activity of EGP(V)TBPP can be controlled through an association with biomolecules, such as protein, and the electron transfer-mediated biomolecule photooxidation plays an important role in photodynamic therapy under hypoxia.

Minding our P-block and Q-bands: paving inroads into main group corrole research to help instil broader potential

Main group chemistry is often considered less "dynamic" than transition metal (TM) chemistry because of predictable VSEPR-based central atom geometries, relatively slower redox switching and lack of electronic d-d transitions. However, we delineate what has been made possible with main group chemistry to give it its proper due and up-to-date treatment. The huge untapped potential regarding photophysical properties and functioning hereby spurred us to review a range of corrole reports addressing primarily photophysical trends, synthetic aspects, and important guidelines regarding substitution and inorganic principles. We also look at Ag and Au systems and also consider substitutions such as CF3, halogens, additives and also counterions. Throughout, as well as at the end of this review, we suggest various future directions; further future industrial catalytic and health science research is encouraged.

Non-aggregated lipophilic water-soluble tin porphyrins as photosensitizers for photodynamic therapy and photodynamic antimicrobial chemotherapy

Readily-synthesized water-soluble Sn(iv) tetrapyridylporphyrin dyes have been prepared which exhibit enhanced properties for use as photosensitizer dyes in biomedical applications.

Tuning Chemical and Physical Properties of Phosphorus Corroles for Advanced Applications

Although the affinity of metallocorroles to axial ligands is quite low, this is not the case when the chelated element is phosphorus. This work is hence focused on the mechanism of ligand exchange of six-coordinate phosphorus corroles as a tool for affecting their chemical and physical properties. These fundamental investigations allowed for the development of facile methodologies for the synthesis of a large series of complexes and the establishment of several new structure/activity profiles that may be used to understand and predict spectroscopic features and for tailor-made modification of photophysical and electrochemical properties. This is exemplified by the facile access to complexes with terminal groups that are of large potential for practical applications based on click chemistry, optical imaging, and surface science.

First entry into nonmetal-centred porphycenes: synthesis of a phosphorus(v) complex of octaethylporphycene

The first synthesis and structural characterization of a phosphorus(v) complex of porphycene, a constitutional isomer of porphyrin, are reported.