Synthesis and characterization of new metallophthalocyanines bearing macrocyclic N₃O₂ groups on peripheral positions

Introduction

Phthalocyanines have been used as dyes and pigments for decades. They have also found practical applications as semiconductors, catalysts, chemical sensors, liquid crystals and materials for nonlinear optics (Moser and Thomas, 1983; Lkahl et al., 1986; Leznoff and Lever, 1996). A great number of remarkable applications of phthalocyanines arise from their unique 18π electron aromatic system, which instills high thermal and chemical stability and unique photoelectric properties (Du et al., 2003). A disadvantage of phthalocyanines is their limited solubility in common organic solvents. To increase solubility, phthalocyanines with long chains or macrocyclic moieties (Young and Onyebuagu, 1990; Bekaroğlu, 1996) have been synthesized. Although the term ‘macrocyclic’ was not included in the literature until the end of the third quarter of the 20th century, the natural macrocyclic structure bearing phthalocyanine rings as well as their metal complexes have been well known since the beginning of the 20th century. The chemistry of macrocyclic compounds and their complexes have shown rapid development after 1964. Synthetic macrocyclic compounds can be used as models for natural products (Gokel and Garcia, 1977).

We have previously described the synthesis of new metal-free phthalocyanines and metallophthalocyanines bearing macrocyclic N₂S₂O₂ groups on peripheral positions (Kantekin et al., 2008). In this paper, we discuss metallophthalocyanines carrying symmetrically four macrocyclic N₃O₂ groups on peripheral positions.

Results and discussion

A convenient method for synthesis of phthalocyanines containing macrocyclic moieties uses the dibromo or dicyano derivatives of the corresponding macrocyclic units. In this work, the dibromo compound 1 (Keleşoğlu et al., 2010) was allowed to react with CuCN under the conditions of the Rosenmund von Braun reaction (Koçak et al., 1994) to furnish the desired compound 2 in 66% yield after purification by chromatography (Scheme 1). The structure of 2 is fully supported by IR, ¹H NMR and ¹³C NMR spectro­scopy, mass spectrometry and elemental analysis.

Scheme 1

The synthesis of the Zn complex 3 was accomplished by reacting 2 with anhydrous Zn(CH₃COO)₂ in dry n-pentanol in the presence of a catalytic amount of DBU as a strong base at 160°C under nitrogen. The desired compound 3 was obtained in 18% yield after purification by chromatography. The IR spectrum of 3 clearly lacks the C≡N stretching vibration at 2228 cm^-1 that is seen in the IR spectrum of 2. The NMR spectrum of this compound is similar to the spectrum of the precursor dicyano compound 2. The mass spectrum of 3 shows a peak at m/z = 2729 for [M+1]⁺. The elemental analysis confirms the given composition of compound 3.

The synthesis of NiPc 4 was accomplished by reacting 2 with anhydrous NiCl₂ under similar conditions. The product 4 was obtained in 17% yield after purification by chromatography. The synthesis of CoPc 5 was accomplished in a similar way by reacting 2 with anhydrous CoCl₂. After chromatography, the desired compound 5 was obtained in 15% yield. The given structures of 4 and 5 are fully consistent with their spectra and elemental analysis results.

The electronic spectra of phthalocyanines 3–5 (Figures 1–3) show the typical B and Q bands of symmetrically substituted phthalocyanine (Stillman et al., 2002). The UV-Vis absorption spectra of the metallophthalocyanines 4 and 5 show intense Q band absorptions at λ_max 685 nm (ε 5.28), 682 nm (ε 5.12), with weaker absorptions at λ_max 618 nm (ε 4.55) and 618 nm (ε 4.45), respectively. The UV-Vis absorption spectrum of the metallophthalocyanine 3 shows less intense and broader Q band at λ_max 680 nm (ε 5.12) nm, with weaker absorption at λ_max 616 nm (ε 4.59). These observations suggest that the Zn complex 3 is aggregated (Schutte et al., 1993; Arslan and Yilmaz, 2007). The B bands of compounds 3, 4 and 5 are observed at λ_max 307 nm (ε 5.29), 324 nm (ε 5.24) and 256 nm (ε 5.23), respectively, as expected.

Figure 1

Figure 2

Figure 3

Conclusion

New dicarbonitrile derivative 2 and metallophthalocyanines 3–5 carrying N₃O₂ groups on peripheral positions were synthesized and characterized. The compounds were characterized by IR, UV-Vis, ¹H NMR, ¹³C NMR, mass spectra and elemental analysis.

Experimental

All reactions were carried out under dry nitrogen. The IR spectra were recorded on a Perkin Elmer 1600 FTIR spectrophotometer using potassium bromide pellets. ¹H (200 MHz) and ¹³C (75 MHz) NMR spectra were recorded on a Varian Mercury 200 spectrometer in CDCl₃. Electrospray mass spectra were measured on Varian 711 and VG Zapspec spectrometers. Elemental analysis was done on a LECO Elemental Analyzer (CHNS O932). UV-visible absorption spectra were measured by a Unicam 929 AA UV-visible spectrophotometer. Melting points were measured on an Electrothermal apparatus.