Synthesis of Stable Nonaromatic Fluorenonephyrin Macrocycle

Abstract

A new derivative of our recently reported nonaromatic fluorenophyrin 5 named fluorenonephyrin 6 was synthesized over a sequence of six steps starting with commercially available fluorene as precursor. Our attempts to direct oxidation of 5 to 6 were not successful. Hence, we synthesized 2,7-bis(phenyl(1H-pyrrol-2-yl)methyl)-9-fluorenone (fluorenone tripyrrane) in five simple steps from fluorene, and condensed it with pentafluorobenzaldehyde under mild acidic conditions in CH 2 Cl 2 followed by oxidation with DDQ and chromatographic purification to afford fluorenonephyrin (9%). 6 was characterized and studied by HR-MS, 1D and 2D NMR spectroscopy, absorption, electrochemical and DFT/TD-DFT techniques. The DFT studies revealed that 6 was more distorted than 5 and that introduction of C=O in the macrocyclic core remarkably distorts the pyrrole rings of the dipyrrin unit from the mean plane of macrocyclic framework. The macrocycle showed a band at around 390 nm and a broad band at around 650 nm. The redox properties indicated that the macrocycle was highly electron-deficient in nature. TD-DFT studies were in accordance with the experimental observations.

Phenanthrene cyclocarbonylation – core post-synthetic modification of phenanthriporphyrin

“…The spectroscopic pattern of 7-H + (Fig. 1, Trace B) closely resembles the spectrum of 7 with noticeable upfield relocation of H(2,9), H (13,19), and H (14,18) and downfield one of the NH signal suggesting the slight increase of paratropicity due to the monoprotonation.…”

“…It is consistent with the macrocyclic structure of 7 as being built of 4,5-phenanthrylene ketone moiety linked with the meso-phenyl-dipyrromethene unit through two phenylmethine bridges. Significantly, the 13 C chemical shift (Fig. S1 †) determined for the inner C( 28) atom (δ = 201.9 ppm) confirms the incorporation of the carbonyl group within the macrocyclic frame of 7.…”

“…1A). Accordingly, the chemical shifts of perimeter pyrrolic protons equal 6.62 ppm for H (13,19) and 6.27 ppm for H (14,18).…”

“…11 Fluorenophyrin 6 , and its keto derivative 6-CO were synthesized by Ravikanth et al starting from fluorene as a fundamental building block. 12,13…”

“…11 Fluorenophyrin 6, and its keto derivative 6-CO were synthesized by Ravikanth et al starting from fluorene as a fundamental building block. 12,13 Formally, 1 can be classified as a dicarbaporphyrinoid, 14,15 a porphyrinoid with two carbon atoms in the (CCNN) core. Phenanthriporphyrin 1 acts as a distinctively antiaromatic ligand, producing the hypervalent organophosphorus(V) derivative 1-P and the organocopper(III) complex 1-Cu.…”