meso‐Aryl [28]Hexaphyrin Silicon Complexes Bearing Various Si‐Substituents and 1,16‐Dihydrohexaphyrin bis‐Chlorosilicon Complex

Abstract

Herein, the synthesis of Möbius aromatic [28]hexaphyrin silicon complexes bearing various Si-substituents from reactions of [28]hexaphyrin 1 with suitable silicon sources in the presence of a base is reported. Si-substituents newly introduced are vinyl (4), phenyl (6), hydroxy (7), and hydride groups (8). X-ray crystallographic analysis of complexes 6 and 7 has shown trigonal bipyramidal penta-coordinated silicon atoms, which are favorable for the hexaphyrin ligands to take on smoothly twisted Möbius conformations. N-fused Si-vinyl complex 5 was also isolated and structurally well characterized. Through these studies, the Si-substituent effect has been shown to be relatively small. Reaction of 1 with HSiCl3 in CH2Cl2 gave 1,16-dihydrohexaphyrin bis-chlorosilicon complex 9, probably through intramolecular hydride transfer from the silane to the pyrrolic α-carbon.

Möbius Aromatic [28]Hexaphyrin Germanium(IV) and Tin(IV) Complexes: Efficient Formation of Triplet Excited States

“…Recently,w er eported that the incorporation of an Si IV atom into [28]hexaphyrin 1 led to the rigidification of atwisted structure to give the [28]hexaphyrin Si IV complex 2.T his complex displays at rigonal-bipyramidal coordination geometry at the Si IV atom and distinct 28p Mçbius aromaticity,but the quantum yield of the T 1 state is almost zero. [6] In this study,w ee xamined the incorporation of heavier Ge IV and Sn IV atoms into 1 with the hope of similarly rigidifying twisted Mçbius structures and accelerating the intersystem crossing to the triplet excited state (T 1 ). This approach will be useful for experimental verification of the Baird rule for twisted Mçbius systems.…”

Doubly N‐Fused [24]Pentaphyrin Silicon Complex and Its Fluorosilicate: Enhanced Möbius Aromaticity in the Fluorosilicate

“…By following the previously reported procedures on the synthesis of [28]hexaphyrin Si IV complexes, [11] N-fused [ 24]pentaphyrin 4 was heatedi nt he presence of an excessa mount of MeSiCl 3 and N,N-diisopropylethylamine (DIPEA) at 40 8Cf or 24 hi na cetonitrile. However,t his primarily led to the recovery of 4.T hus, the reaction conditions were made harsher.N amely, the reactionw as carried out in DMF at 80 8Cf or 14 h, which providedd oubly N-fused [24]pentaphyrin 6 (7 %) and Si IV complex of doubly N-fused [24]pentaphyrin 7 (38 %; Scheme2).…”

“…The Dd value (chemical shift difference between the inner and outer pyrrolic b-protons)o f6 is 6.13 ppm at 25 8Ci nC D 2 Cl 2 .T he Dd value increasedt o1 0.22 ppm at À90 8Ci nC D 2 Cl 2 and decreased to 3.91 ppm at 140 8Ci n 1,1,2,2-[D 2 ]tetrachloroethane ( Figure S4 in the Supporting Information).T hese data suggest certain conformationalf lexibility of 6 in solution. [6,11] The 1 HNMR spectrum of 7 showeds ignals due to the outer pyrrolic b-H in the range of 8.51 to 6.34 ppm and as inglet due to the Si-CH 3 at À2.20 ppm, exhibiting as lightly stronger diatropic ring current as comparedw ith 6. The 1 HNMR spectra of 7 were rather temperature independent in the range of 25-140 8C, indicating its rigid structure.…”

“…[10] Despite this progress,t he realization of Mçbius aromatic molecules in as mall expanded porphyrin stillr emains challenging because of their severe steric distortion and difficulty in achieving pconjugation.R ecently, we reporteda ne ffective incorporation of silicon atom into [28]hexaphyrin 1 to provide Si IV complex 2 (Scheme 1), which was aM çbiusa romatic molecule with as moothly twisted p-conjugated circuit owing to at rigonal bipyramidal coordination of the Si-atomt hat wasb ound to the three pyrrolic nitrogena toms and one pyrrolic b-carbon. [11] With this as ab ackground, we envisioned silicon incorporation into N-fused [24]pentaphyrin 4 with the aim to explore as mallM çbiusa romatic molecule. Pentaphyrin substrate 4 is smaller than hexaphyrin 1 and it might be more difficult to achieve am olecular twist with smooth macrocyclic p-conjugation.…”

Möbius Aromatic [28]Hexaphyrin Germanium(IV) and Tin(IV) Complexes: Efficient Formation of Triplet Excited States

“…Whereas the synthesis of 2 required an excess amount of SiCl 4 (ca. 50 equiv), a long reaction time (9 h), and heating (40 °C), Ge IV and Sn IV atoms were smoothly incorporated into 1 . Notably, the yields of 3 and 4 were much higher than that of 2 (53 %) in spite of the mild reaction conditions…”