Facile Formation of Stable Neutral Radicals and Cations from [22]Smaragdyrin BF2 Complexes

Stabilization of the Neutral [25]Hexaphyrin(1.0.1.0.1.0) Radical by Hetero-Bimetal-Coordination

Stabilization of hexaphyrin(1.0.1.0.1.0) (named "rosarin") in its 25π radical state is achieved using a hetero-bimetal-coordination strategy. The antiaromatic BF2 complex B-1 was first synthesized, and then rhodium ion was inserted into B-1 to produce the BF2/Rh(CO)2 mixed complex Rh-B-1 as a highly air-stable radical. The structures of B-1 and Rh-B-1 were determined by single-crystal X-ray diffractions, and the antiaromatic or radical character was identified by various spectroscopy evidence and theoretical calculations. Rh-B-1 exhibits excellent redox properties, enabling amphoteric aromatic-antiaromatic conversion to their 24/26π states. Compared to the 24/26π conjugation systems on the same skeleton, Rh-B-1 has the narrowest electrochemical and optical band gaps, with the longest absorption band at 1010 nm. The ring-current analysis reveals intense paratropic currents for B-1 and co-existing diatropic-paratropic currents for Rh-B-1. This hetero-bimetal-coordination system provides a novel platform for organic radical stabilization on porphyrinoids, showing the prospect of modulating ligand oxidation states through rational coordination design.

Carbazole Based Smaragdyrins: Synthesis, Aromaticity Switching, and Formation of a Spiro-Dimer

Carbazole-incorporated smaragdyrin BF2-complex 3 was synthesized by SNAr reaction of 3,5-dibromo-8-mesityl-BODIPY 1 with 3,6-di(tert-butyl)-1,8-di(pyrrol-2-yl)carbazole 2 as a nucleophile. Demetalation of 3 with ZrCl4 gave the corresponding smaragdyrin free base 4 in a good yield. Oxidations of 3 and 4 with MnO2 gave smaragdyrins 5 and 6, respectively, both followed by aromaticity switching, since the oxidized products showed a moderate paratropic ring current owing to their 20π-electronic circuits. Further, treatment of 4 with [RhCl(CO)2]2 in the presence of NaOAc gave RhI complex 7, and oxidation of 3 with RuCl3 in the presence of triethylamine led to the formation of a spiro dimer product, 8.

Synthesis of Pyrrole-Sharing Fused Porphyrinoid Hybrids by Post-fabrication of Ni(II) Porphyrins

Pyrrole-sharing fused hybrids of NiII porphyrin with PdII N-confused(NC)-corrole and PdII NC-oxaporphyrin were synthesized by post-fabrication of NiII porphyrins. Specifically this consists of Friedel-Crafts type aromatic substitution reaction of meso-free NiII porphyrin with α,α'-dibromotripyrrin and Pd(OAc)2 assisted cyclization, and final heating to induce a Pd-C bond formation. NiII porphyrins fused with PdII NC-corrole and with PdII NC-oxaporphyrins show coplanar structures with a shared pyrrole unit. In these hybrids, the PdII NC-oxaporphyrin is aromatic and the PdII NC-corrole is moderately antiaromatic and these local electronic properties interact to influence the whole network.