Maximizing Property Tuning of Phosphorus Corrole Photocatalysts through a Trifluoromethylation Approach

Abstract

An eight-member series of CF3-substituted difluorophosphorus corroles was prepared for establishing a structure–activity profile of these high-potential photosensitizers. It consisted of preparing all four possible isomers of the monosubstituted corrole and complexes with 2-, 3-, 4-, and 5-CF3 groups on the macrocycle’s periphery. The synthetic pathway to these CF3-substituted derivatives, beginning with (tpfc)PF 2 , involves two different initial routes: (i) direct electrophilic CF3 incorporation using FSO2CF2CO2Me and copper iodide, or (ii) bromination to achieve the 2,3,8,17,18-pentabrominated compound using excess bromine in methanol. Crystallographic investigations revealed that distortion of the original planar macrocycle is evident even in the monosubstituted case and that it becomes truly severe for the penta-CF3-substituted derivative 5. There is a shift in redox potentials of about 193 mV per -CF3 group, which decreases to only 120 mV for the fifth one in 5. Differences in the electronic spectra suggest that the Gouterman four orbital model decreases in relevance upon gradual -CF3 substitution, a conclusion that was corroborated by DFT calculations. The very significant energy lowering of the frontier orbitals suggested that photoexcitation should lead to a highly oxidizing photocatalyst. This hypothesis was proven true by finding that the most synthetically accessible CF3-substituted derivative is an excellent catalyst for the photoinduced conversion of bromide to bromine (phenol, toluene, and benzene assay).

Phosphorus corrole complexes: from property tuning to applications in photocatalysis and triplet–triplet annihilation upconversion

“…The latter aspect is also tunable by the axial ligands and the number of F atoms in the meso -aryl substituents. The novelty regarding the synthetic part was to move away from hydroxo- and oxo-phosphorus corroles, which are substitution labile (converted into each other and react with solvents),47,48 to a well-defined series of substitution-inert trans -difluorophosphorus corroles, so as to allow for the systematic research described in this paper 49…”

Corroles and Hexaphyrins: Synthesis and Application in Cancer Photodynamic Therapy

“…Gross and coworkers explored the influence of the presence of trifluoromethyl groups in the structure of phosphorus corroles as photocatalysts [ 44 ]. The authors developed several strategies to functionalize the phosphorus(V) tri(pentafluorophenyl)corrole ( 26 ) in order to obtain a library of complexes with different numbers of CF 3 substitutions.…”

Corroles at work: a small macrocycle for great applications

“…CF 3 -Substituted TPFCorrPF 2 were investigated as photocatalysts for the bromination of phenol with HBr. 87 The presence of CF 3 substituents improves the oxidizing power of the related complex, with the hypothesis that the increase of this oxidizing power improves the efficiency of the photocatalyst. Following this hypothesis, the performances of the P corroles reported in Fig.…”