2.5 2.0 1.5 1.0 0.5 0.0 300 400 500 600 700 800 l / nm Absorbance t = 0 min t = 3 min t = 20 min t = 60 min Substituted a,b,g-triazatetrabenzcorrole: an unusual reduction product of a phthalocyanine Junzhong Li, Lakshminarayanapuram R. Subramanian and Michael Hanack* Institut f�ur Organische Chemie, Lehrstuhl f�ur Organische Chemie II, Universit�at T�ubingen, Auf der Morgenstelle 18, D-72076 T�ubingen, Germany 4,5-Dipentyldiiminoisoindoline 1 reacts with hexachlorodisilane (Si2Cl6) to give the ring-contracted hydroxysilicona, b,g-triazatetrabenzcorrole 4 which in solution photolyses giving the ring cleavage compounds 5 and 6; the stability of triazatetrabenzcorroles 4 and 7 with silicon and germanium as central elements is studied by UVndash;VIS spectroscopy.Many of the properties of metallophthalocyanines (PcM) such as semiconductivity, photoconductivity and catalytic properties rely upon the redox properties of the PcM species.1,2 As a result, the redox chemistry of PcM has been investigated in detail, both by chemical and electrochemical methods with phthalocyanines containing redox inactive as well as redox active metals centres.3ndash;5 Accordingly, negative ions of Pc or PcM with low valent state metals such as PcCoI and PcSnII have been found,6ndash;8 however, the basic structure of the resulting reduced macrocycle remained the same.In 1986, Fujiki et al.9 ascertained for the first time that the earlier reported PcGeII,10 produced by reducing PcGeCl2 with NaBH4, did not retain the phthalocyanine moiety but was a phthalocyanine-like tetrapyrrole macrocycle, namely hydroxygermanium( iv)-a,b,g-triazatetrabenzcorrole (TBCGeOH) 2.However, probably due to the report9 that the stability of TBC complexes with different central elements follows the sequence TBCGeOH 2 TBCSiOH 3 TBCAl TBCGa, and also that the authors9 succeeded in obtaining only the pure TBCGeOH 2, no further reports on TBC macrocycles could be found to date.As part of our ongoing studies to synthesize precursors for polymers containing Pc units,1,2,11,12 4,5-dipentyldiiminoisoindoline 1 was treated with Si2Cl6 to examine the potential of producing phthalocyanine dimers with an Sindash;Si bond. Unexpectedly, during purification of the reaction mixture by flash chromatography (silica gel, CHCl3), besides obtaining (C5H11)8PcSi(OH)2, a deep green solid was also isolated which displayed a very sharp absorption at 448 nm (Soret band) with an intensity nearly twice that of the Q band in its electronic spectrum (Fig. 1), which was later found to be the typical UVndash; VIS spectrum of TBC macrocycles.9 The mass spectral, 1H NMR, IR and elemental analysis further proved that the compound obtained in this reaction is hydroxysilicon 4,5,11,12,18,19,25,26-octapentyl-a,b,g-triazatetrabenzcorrole (PTBCSiOH) 4.dagger; Further studies carried out by treating Si2Cl6 with 1 in different ratios indicated that if the ratio reached ca. 1 : 1, only PTBCSiOH 4 was obtained in 35 yield (Scheme 1). It seems that the excess of Si2Cl6 reacted with an intermediate phthalocyanine to form the TBC derivative 4 (vide infra). The mechanism for the formation of the TBC macrocycles by reaction of a reducing agent such as NaBH4 with, for example, PcGeCl2 has not been proven experimentally, although in the original work9 a mechanism for the Pc ring contraction was proposed. Si2Cl6 is a known deoxygenating reagent, for example, it has been used to produce phosphine from phosphine oxide13 and phosphine sulfides.14 On the other hand, Si2Cl6 is very sensitive to water, affording products in which the Sindash;Si bond is broken or an oxygen is inserted into the Sindash;Si bond.As a result, during the reaction of 1 with Si2Cl6 the dihydroxysilicon phthalocyanine (C5H11)8PcSi(OH)2 and/or m-oxo dimers (C5H11)8PcSi(OH)2O will be produced first, and then reduced by an excess of Si2Cl6 to form PTBCSiOH 4.Indeed, in the reaction of Si2Cl6 with the isoindoline 1 in a ratio of 1 : 2, (C5H11)8PcSi(OH)2 was isolated by flash chromatography. The assumption that (C5H11)8PcSi(OH)2 was formed first and then reduced by Si2Cl6 was confirmed by reacting (C5H11)8PcSi(OH)2 with Si2Cl6 in quinoline and isolating PTBCSiOH 4 from the reaction mixture. PTBCSiOH 4 is stable in the solid state under ambient conditions. However, air saturated solutions of 4 are found to be light sensitive.Of particular interest is that the green solution of 4 in, for example, CHCl3 changed from green to red under light after some time. The resulting lsquo;photolysisrsquo; products were separated on silica gel with a mixture of CHCl3 and CH2Cl2 (v:v, 3:2) as eluent to give a purple and a red compound. Based on mass spectroscopy, IR, UVndash;VIS and 1H NMR data, the purple 5Dagger; and the red 6dagger; compounds were characterized as cleavage products of the 1,2-double bond of compound 4. As a result, the central coordinated element is lost.The overall reaction is shown in Scheme 1. The UVndash;VIS spectra of PTBCSiOH 4 (Fig. 1) and PTBCGeOH 7 produced by reducing (C5H11)8PcGeCl2 with NaBH4 according to a literature method9 (Fig. 2) in CHCl3 under air with irradiation at different times were determined in order to investigate the influence of the central element on the stability of TBC complexes under these conditions. In contrast to the earlier report,9 it is evident both from the decrease in intensity of the Soret and the Q bands that PTBCSiOH 4 is more stable than the germanium complex 7 under the same conditions.As a ring contracted entity of Pc, the TBC ring will prefer the central element with a smaller radius than that of Pc. Obviously Si, with a smaller radius than Ge, forms a more stable complex with the TBC macrocycle than Ge, though the accurate radius of the internal hole of the TBC ring is not known. Fujiki et al.9 did not succeed in producing pure unsubstituted Fig. 1 Changes in the electronic absorption spectra of PTBCSiOH 4 in CHCl3 under air upon irradiation with light (l = 650ndash;730 nm) at room temperature Chem. Commun., 1997 679R R C NH C NH NH NH N N N O R R NH N HN R R R R R R N N R R N N R R N N R R N M R R OH NH N N N O R R NH N HN R R R R R R O 1 2 Si2Cl6 quinoline hn 5 6 1 2 M = Ge, R = H 3 M = Si, R = H 4 M = Si, R = C5H11 7 M = Ge, R = C5H11 + 2.5 2.0 1.5 1.0 0.5 0.0 300 400 500 600 700 800 l / nm Absorbance t = 0 min t = 3 min t = 1 min t = 10 min t = 5 min t = 20 min TBCSiOH 3 by reducing PcSiCl2 with NaBH4, however, pure substituted PTBCSiOH 4 was obtained by using Si2Cl6, which shows that reducing agents have an influence on the formation of TBC derivatives from the corresponding Pc complexes.The reason for the conflicting results of Fujiki et al.9 and ourselves on the stability of TBC complexes of Si and Ge might be due to the use of an unsubstituted 3 and a substituted 4 respectively in illumination experiments.Footnotes * E-mail: hanack@uni-tuebingen.de dagger; Selected data for 4: IR n/cm21 (KBr) 2955, 2928, 1626, 1462, 1416, 1377, 1261, 1111, 1020, 887, 804, 733. UVndash;VIS (CHCl3) lmax/nm (relative absorbance) 295(0.27), 342(0.24), 416(0.39), 434(0.35), 448(1.00), 620(0.12), 675(0.56). dH (250 MHz, 2H8THF) 9.35 (s, 2 H, Harom.), 9.25 (s, 2 H, Harom.), 8.69 (s, 2 H, Harom.), 7.98 (s, 2 H, Harom.), 3.38 (m, 8 H, CH2), 2.85 (m, 8 H, CH2), 2.16ndash;1.64 (m, 48 H, CH2), 1.15 (m, 24 H, CH3), 21.54 (s, 1 H, OH).MS(FD) m/z: 1104.1 (M+). Anal. calc. for C72H97N7SiO(1103.8): C, 78.28; H, 8.85; N, 8.88. Found: C, 77.38; H, 8.60; N, 8.48. For 5: IR n/cm21 (KBr) 2959, 2928, 2856, 1744, 1730, 1609(s), 1468, 1261, 1221, 1096, 1028, 804, 730. UVndash;VIS (CHCl3) lmax/nm (relative absorbance) 366(0.86), 519(0.81), 553(1.00), 597(0.70). dH (250 MHz, CDCl3) 11.68 (s, 3 H, NH), 8.30 (s, 2 H, Harom.), 7.95 (s, 2 H, Harom.), 7.80 (s, 2 H, Harom.), 7.73 (s, 2 H, Harom.), 2.79 (m, 16 H, CH2), 1.69 (m, 16 H, CH2), 1.23 (m, 32 H, CH2), 0.93 (m, 24 H, CH3).MS(FD and FAB) m/z: 1078.5 (M+). For 6: IR n/cm21 (KBr) 2955, 2928, 1744, 1674, 1614, 1564, 1477, 1468, 1209, 1138. UVndash;VIS (CHCl3) lmax/nm (relative absorbance) 337(0.59), 515(1.00), 554(0.88). dH (250 MHz, CDCl3) 11.41 (s, 1 H, NHs, 1 H, NH), 9.35 (s, 1 H, NH), 8.45 (s, 1 H, Harom.), 8.33 (s, 1 H, Harom.), 8.16 (s, 1 H, Harom.), 7.90 (s, 1 H, Harom.), 7.87 (s, 1 H, Harom.), 7.79 (s, 1 H, Harom.), 7.66 (s, 1 H, Harom.), 7.57 (s, 1 H, Harom.), 2.74 (m, 16 H, CH2), 1.67 (m, 16 H, CH2), 1.24 (m, 32 H, CH2), 0.88 (m, 24 H, CH3).MS(FD) m/z: 1093.3 (M+). References 1 M. Hanack, S. Deger and A. Lange, Coord. Chem. Rev., 1988, 83, 115. 2 M. Hanack and M. Lang, Adv. Mater., 1994, 6, 819. 3 A. B. P. Lever, E. R. Milaeva and G. Speier, in Phthalocyanine: Properties and Applications, ed. C. C. Leznoff and A. B. P. Lever, VCH, Weinheim, 1989, p. 1. 4 D. W. Clack and Y. R. Yandle, Inorg. Chem., 1972, 11, 1738. 5 R. Behnisch and M. Hanack, Synth. Met., 1990, 36, 387. 6 D. W. Clack, N. S. Hush and I. S. Woolsey, Inorg. Chim. Acta, 1976, 19, 129. 7 M. J. Stillman and A. J. Thompson, J. Chem. Soc., Faraday Trans. 2, 1974, 805. 8 W. J. Kroenke and M. E. Kenney, Inorg. Chem., 1964, 3, 251. 9 M. Fujiki, H. Tabei and K. Isa, J. Am. Chem. Soc., 1986, 108, 1532. 10 R. L. Stover, C. L. Thrall and R. D. Joyner, Inorg. Chem., 1975, 10, 2335. 11 H. Schultz, H. Lehmann, M. Rein and M. Hanack, Struct. Bonding (Berlin), 1990, 74, 41. 12 M. Hanack, A. Datz, R. Fay, K. Fischer, U. Keppeler, J. Koch, J. Metz, M. Mezger, O. Schneider and H. J. Schulze, in Handbook of Conducting Polymers, ed. T. A. Skotheim, Marcel Dekker, New York, 1986, p. 133. 13 K. Naumann, G. Zon and K. Mislow, J. Am. Chem. Soc., 1969, 91, 7012. 14 G. Zon, K. E. Debruin, K. Nauman and K. Mislow, J. Am. Chem. Soc., 1969, 91, 7023. Received, 23rd January 1997; Com. 7/00532F Scheme 1 Synthetic scheme for PTBCSiOH and its photolysis products Fig. 2 Changes in the electronic absorption spectra PTBCGeOH 7 in CHCl3 under air upon irradiation with light (l = 650ndash;730 nm) at room temperature 680 Chem. Commun., 1997
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