Expanding the Chemistry of Pentafluorophenyl-N-Confused Porphyrin: Diketonate Substitution and Derivatizations at the External 3-C Position of the Inverted Pyrrole Ring

Abstract

In this study, we synthesized two new 3-C-substituted pentafluorophenyl-N-confused porphyrins (PFNCPs), one with acetylacetonate (PFNCP-acac, 2a) and the other with ylidene-2-propanone (PFNCP-ac, 3a), through a one-pot reaction in the absence of a catalyst. Under mild acidic and heating conditions, the acac-substituted compound underwent acyl cleavage degradation, yielding ac-substituted product 3a. Subsequent chelation of the acac-substituted PFNCP with BF₂ resulted in a boron diketonate derivative, PFNCP-acacBF₂ (4). Additionally, an electrocyclic reaction of the ac-substituted PFNCP 3a, without a catalyst, produced a tricyclic fused [6,6,5]-TF-PFNCP (5). This tricyclic product could also be obtained directly from PFNCP-acac 2a under heating conditions. The absorption spectra revealed that acac- and ac-substituted macrocycles exhibit either a single or split Soret band, respectively, in the 400–550 nm range, along with multiple Q bands spanning the 580–690 nm region. While BF₂ derivatization caused a slight red shift in the absorption spectra, the [6,6,5]-tricyclic fused NCP demonstrated a significant red shift. All newly synthesized compounds were characterized by using single-crystal X-ray structures, ¹H NMR spectroscopy, and mass spectrometry. Density functional theory (DFT) studies were conducted to elucidate the photophysical properties of these macrocycles.