Preparation of Phthalocyanines with Eight Benzylchalcogeno Substituents from 5,6-Dibromo-4,7-diethylbenzo[1,2,3]trichalcogenoles

Abstract

Benzo[1,2,3]trichalcogenoles with two bromine atoms on the benzene ring, 5,6-dibromo-4,7-diethylbenzo[1,2,3]trichalcogenoles (1a) and (1b) (chalcogen: 1a = S; 1b = Se), were first prepared by treating 2,3,5,6-tetrabromo-1,4-diethylbenzene (TBDEB) with elemental sulfur or amorphous selenium in DBU at 140 degrees C (for 1a) and 100 degrees C (for 1b) for 24 h. The structures of 1a and 1b were verified by NMR spectroscopy, mass spectrometry, and elemental analysis. X-ray crystallographic analysis ultimately showed that the substitution reactions of TBDEB proceeded at the two adjacent bromine atoms. To apply 1a and 1b to construction of phthalocyanine derivatives with sulfur or selenium functional groups, 4,5-bis(benzylchalcogeno)-3,6-diethylphthalonitriles (5a) and (5b) as key intermediates were prepared by way of introduction of alkyl groups (2-cyanoethyl or 4-nitrophenethyl groups) on two chalcogen atoms, substitution of two bromine atoms with nitrile groups, and subsequent exchange of alkyl groups with benzyl groups. Compound 5a was treated with lithium in n-pentanol at 100 degrees C for 1 h to produce 2,3,9,10,16,17,23,24-octakis(benzylthio)-1,4,8,11,15,18,22,25-octaethylphthalocyanine (6a). A similar treatment of 5b in n-hexanol at 100 degrees C for 2 h gave phthalocyanine 6b. The structures of 6a and 6b were determined by (1)H NMR spectroscopy and MALDI-TOFMS. X-ray crystallographic analysis of 6a was also performed. The Q-band absorptions (lambda(max)) for 6a and 6b in UV-vis spectra were observed at 755 nm (log epsilon = 5.1) and 757 nm (log epsilon = 5.1), respectively, and their electrochemical properties were verified by cyclic voltammetry in dichloromethane with Ag/AgNO(3) as a reference electrode. Compounds 6a and 6b were further treated with lithium in THF/NH(3) at -78 degrees C and then with dibutyltin dichloride to produce phthalocyanine derivatives 8a and 8b with four dichalcogenastannole rings by way of octachalcogenate phthalocyanines 7a and 7b.

Preparation and Characterization of Nonclassical Tetraazaporphyrin, Bis(4‐methylpyridine)[1,3,5,7,9,11,13,15‐octaphenyltetra(3,4‐thieno)tetraazaporphyrinato]ruthenium(II)

“…X-ray crystallographic analysis showed that 3 has a monoclinic form and the space group is P2 1 /n (#14) with parameters a = 11.5476 (8), b = 18.4177 (16), c = 16.9028 (15) Å, and β = 92.878 (3)°. It appears that the unit cell consists of two molecules of 3.…”

“…[6,7] In a related study, we recently reported the preparation, structural determination, and optical and electrochemical properties of octaethyloctakis-(benzylthio)phthalocyanine and octaoctyltetrakis(trithiolo)-phthalocyanine and their derivatives. [8] On the other hand, it is known that tetraazaporphyrins fused to four five-membered heterocycles such as furans, pyrroles, and thiophenes are extremely unstable, although these compounds can be considered as isosteric structures of phthalocyanine. [9] Despite many early attempts to prepare tetraazaporphyrins with four five-membered heterocycles, up to now only tetra(2,3-thieno)tetraazaporphyrin (2,3-TTTAP) bearing four thiophene units linked at their 2,3-positions and several related compounds have been reported as stable derivatives.…”

Preparation and Electrochemical Properties of 1,4,8,11,15,18,22,25‐Octalkylphthalocyanines Containing Four Trithiole Rings

“…[15] To improve the synthetic procedure for phthalonitrile, we tried to introduce the o-xylylene group on the sulfur atoms as a protecting group. Compound 1a was treated with sodium borohydride and potassium carbonate in THF/methanol, and then with α,αЈ-dibromo-o-xylene to give 4,5-dibromo-3,6-diethyl-1,2-(o-xylylenedithio)benzene (2a) in 77 % yield.…”

“…[21] In contrast, peripheral modification of phthalocyanines through the S-C bond cleavage of thioethers is rare. [15] Deprotection and subsequent functionalization of 4b, 4c, and 4b-Ni was thus tried. Typically, the four o-xylylene groups of 4c were removed under argon by treatment with lithium metal in THF/liquid ammonia at -78°C for 1 h (Scheme 4).…”

“…[7a,10] In contrast, from our ongoing studies of several cyclic oligosulfides, [12][13][14] we recently reported on the preparation of 5,6-dibromo-4,7-diethylbenzo [1,2,3]trichalcogenoles 1a and 1aЈ and their conversion into phthalocyanines [PcXBn] bearing eight benzylthio or benzylseleno substituents by four-step reactions (Scheme 1). [15] In addition, phthalocyanines [PcXSnBu] with four dichalcogenastannole rings were obtained in low yields through the removal of the benzyl groups by Birch reduction with lithium/THF/ammonia and subsequent functionalization of the octachalcogenate anions with dibutyltin dichloride. This suggested that the procedure could be useful for the preparation of new phthalocyanines with eight peripheral chalcogenated functional groups.…”