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Preparation of Non-Substituted Metal Phthalocyanines at Low Temperature Using Activated Rieke Zinc and Magnesium a

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B. I. Kharisov ; L. A. Garza-Rodríguez ; H. M. Leija Gutiérrez ; U. Ortiz Méndez a a b ; R. García Caballero ; A. Yu. Tsivadze a Universidad Autónoma de Nuevo León. A.P., Ciudad Universitaria UANL. San Nicolás de los Garza, N.L.. México b Institute of Physical Chemistry. Moscow. Russia To link to this article: DOI: 10.1080/15533170500360248 URL: http://dx.doi.org/10.1080/15533170500360248 Full terms and conditions of use: http://www.informaworld.com/terms-and-conditions-of-access.pdf This article maybe used for research, teaching and private study purposes. Any substantial or systematic reproduction, re-distribution, re-selling, loan or sub-licensing, systematic supply or distribution in any form to anyone is expressly forbidden. The publisher does not give any warranty express or implied or make any representation that the contents will be complete or accurate or up to date. The accuracy of any instructions, formulae and drug doses should be independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims, proceedings, demand or costs or damages whatsoever or howsoever caused arising directly or indirectly in connection with or arising out of the use of this material. © Taylor and Francis 2007

Synthesis and Reactivity in Inorganic, Metal-Organic and Nano-Metal Chemistry, 35:755–760, 2005 Copyright # 2005 Taylor & Francis, Inc. ISSN: 1553-3174 print/1532-2440 online DOI: 10.1080/15533170500360248

Preparation of Non-Substituted Metal Phthalocyanines at Low Temperature Using Activated Rieke Zinc and Magnesium Downloaded By: [Garza Rdz, M.C. Luis Angel] At: 07:11 22 February 2007

B. I. Kharisov, L. A. Garza-Rodrı´guez, H. M. Leija Gutie´rrez, U. Ortiz Meńdez, and R. Garcıá Caballero Universidad Autońoma de Nuevo Leoń. A.P., Ciudad Universitaria UANL, San Nicola´s de los Garza, N.L., Me´xico

A. Yu. Tsivadze Institute of Physical Chemistry, Moscow, Russia

Synthesis of non-substituted metal phthalocyaninates starting from phthalonitrile in various alcohols in presence of chemically activated Rieke zinc and magnesium in three forms (ordinary magnesium turnings, activated Rieke magnesium and complex Mg(anthracene) . 3THF) at low temperatures (20 –5088 C) is described. It is shown that the presence of active elemental metal causes a rapid PcM formation in low-weight alcohols. Keywords

zinc and magnesium phthalocyaninate, Rieke metals, synthesis at low temperature

INTRODUCTION Well-known classic non-substituted phthalocyanine PcH2 and its metal complexes are usually obtained from different precursors in non-aqueous solvents in 80 –2508C temperature range (Leznoff and Lever, 1990; Thomas, 1990). Using phthalonitrile as a precursor and applying a series of techniques (UV-treatment of the reaction system (Tomoda et al., 1976; Kharisov et al., 2005a), use of elemental metals in the form of finely divided metal powders (Leznoff et al., 2000; Kharisov et al., 2004), solid strong bases (Nemykin et al., 2000) and zeolites (Kharisov et al., 2005b), direct electrochemical synthesis (Turek et al., 1987; Petit et al., 1991; Kharisov et al., 1999, 2000) using sacrificial anodes (and even cathodes), phthalocyanine preparations can be carried at Received 18 August 2005; accepted 9 September 2005. The authors are very grateful to CONACyT (project 39,558-Q) and UANL (PAICyT-2005) for financial support. Address correspondence to B. I. Kharisov, Facultad de Ciencias Quimicas, Universidad Autońoma de Nuevo Leoń, 66450 San Nicola´s de los Garza 18-F, Nuevo Leoń, A.P. 18-F, C.P. 66450, Me´xico. E-mail: [email protected]

lower temperatures, although frequently with relatively low yields in comparison with classic syntheses. In these conditions, at low temperatures, an additional “impulse” is needed for the phthalonitrile cyclization process; precisely, surface energy of strong base (solid CH3ONa) (Nemykin et al., 2000) or extra energy of defects in the surface of elemental metals (Kharisov et al., 2004) could serve as an impulse to reach the energetic barrier. Therefore, any source of additional energy could be useful for the successful synthesis at low temperatures. Metals in activated form (Fu¨rstner, 1996), in particular those obtained from anhydrous metal salts and alkali metals (so-called Rieke metals (Fu¨rstner, 1996; Rieke, 2000; Rieke et al., 1996, 1997; Rieke and Kim, 1998a, 1998b, 2000; Talukdar et al., 1998; Lee et al., 2000; Sugimoto, 2003) could be extremely useful to carry out PcM synthesis at low temperature. The peculiarity of such pyrophoric forms of metals is a high number of defects and imperfections in metal surface, which make them much more active in comparison with the same metals in their “standard” form (sheet, wire or non-active powder). In the present work, we have studied the interaction of activated metallic zinc and magnesium in the form of Rieke metals with phthalonitrile in a series of non-aqueous solvents in the temperature range 20– 508C. Elemental magnesium in non-activated form or in active forms f(Mg ) and its complexes (sources of “soluble” zerovalent magnesium Mg(anthracene) . 3THF and MgH2 g are widely used in synthetic organic and organometallic chemistry (Fu¨rstner, 1996;). Sometimes its use requires a preactivation by different methods (sonication or formation of intermediate active magnesium complexes) (Baker et al., 1991). With respect to its application in phthalocyanine chemistry, the reaction of elemental magnesium with phthalonitrile was first studied by Linstead et al., (1934). In these pioneering experiments, the reaction mixture needed to be heated up to 2958C

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(boiling point of phthalonitrile) to start the reaction; the reported yield was only 9.5%. Then, Rieke Burnst (1987) used activated magnesium Mg in refluxing glyme forming magnesium phthalocyanine (according to IR-spectral data) for 5 min with 38% yield at room temperature conditions. Among non-synthetic reports on magnesium phthalocyaninate, recent works of Mizuguchi (2001a, 2001b) should be noted, where its crystal structure and p-p interactions are discussed. In our current work, we have used different forms of magnesium and zinc for phthalocyanine preparation in lowweight alcohols at low temperatures (208– 508C). EXPERIMENTAL PART Materials and Equipment Phthalonitrile, metallic magnesium and zinc, 30% solution of CH3ONa in CH3OH, anthracene, and PcH2 (Aldrich) as a standard were used as supplied. Solvents (methanol, ethanol, propanol, 1-butanol, from Aldrich and Fisher) were distilled by standard methods before use. Metals were treated by techniques below before use. Organic microanalyser (PerkinElmer) was used for C, H and N contents determination. Infrared spectra were recorded on Bruker (Tensor 27) and Perkin-Elmer, respectively. Ultrasonic treatment of reaction systems was carried out in the ultrasonic cleaners of different capacity (3 and 11 L), as well as using stronger ultrasonic source (sonic dismembrator, Fisher, model 500, in some selected experiments). Use of Activated Elemental Metals in Synthetic Procedures Magnesium was used in the following three forms: 1) usual metallic magnesium in the form of turnings, chemically treated before use; 2) Rieke magnesium; 3) classic complex Mg(anthracene) . 3THF. Zinc was used in the form of Rieke metal only, since preliminary experiments with use of nonactivated zinc gave only traces of zinc phthalocyaninate. Non-activated magnesium turnings were used for phthalonitrile cyclization after careful purification of its surface from oxide layer as follows. Mg turnings (20 g) were cut to decrease their size and collocated to a 500 mL flask, to which 4 M solution of NH4Cl (100 mL) was added. The mixture was heated for 30 min at room temperature at controlled pH 4 – 8 with use of 6 M HCl to avoid formation of magnesium hydroxide. Then solution was decanted, magnesium was washed two times with 100 mL of distilled water (50 mL), three times with absolute ethanol (50 mL) and two times with THF (50 mL), and stored under THF. Preparation of Rieke Magnesium and Zinc The Rieke magnesium was prepared as follows (Rieke et al., 1988). All manipulations with precursors and formed activated metal were carried out in a box filled with nitrogen and dried with P4O10. Commercial anhydrous magnesium chloride, dried in oven at 1308C before use (38.50 g, 0.4044 mol),

metallic potassium (30.78 g, 0.7874 mol) in the form of small pieces and THF (350 mL), freshly distilled over metallic sodium were collocated in a 500-mL flask with refrigerator (all inside the nitrogen-containing glove box) and stirred vigorously with simultaneous gradual heating to boiling point of THF (668C). Reaching melting point of potassium, the heating and stirring were immediately suspended, since the reaction became very exothermic and needed cooling. After this active reaction step, the mixture was stirred vigorously for 3 h to guarantee a total consumption of potassium, then the flask was kept without stirring and heating for 3 –5 h in order to precipitate the formed metal. Then THF was decanted, new portion of fresh THF (250 – 300 mL) was added, the mixture was stirred for 5 min and kept for 1 h. This last operation was repeated once again. Rieke zinc was prepared similarly using anhydrous zinc chloride (21.550 g, 0.1581 mol), metallic potassium (11.448 g, 0.0256 mol), and THF (300 mL). Alternatively, the equipment shown in Fig. 1 was used for Rieke metal preparation. The obtained powders (Rieke magnesium and zinc) were kept for further use in phthalonitrile cyclization processes. Since the activity of freshly obtained Rieke metals generally decreases (Fu¨rstner, 1996) in hours or days due to further agglomeration of formed small metal particles, the Rieke metals were used for phthalocyanine preparation immediately or up to 2 days after its preparation. Preparation of the Complex Mg(anthracene) . 3THF This procedure was carried out according to published literature (Fu¨rstner, 1996) with small changes. All manipulations were carried out under nitrogen. A mixture of 24.3 g (1.0 mol) of purified magnesium pulverized turnings and 200 g of anthracene was introduced into a three-necked 2 L flask and heated for 10 min at 1108C in an oven. Thereafter, the flask was equipped with a glass reflux condenser and a magnetic stirring bar and flushed with nitrogen; 1 L of anhydrous THF and a few drops (0.05 mL) of ethyl bromide were added. The suspension was stirred for 36 h at 608C and 12 h more in an ultrasonic field to achieve the conversion of Mg to the bulky orange precipitate of Mg(anthracene) . 3THF. Then the product was separated mechanically from magnesium pieces, washed with 2 150 mL of THF and dried for 20 h in vacuo. Yield 64%. According to Fu¨rstner (1996), the final product contains trace amounts of anthracene and elemental magnesium due to the equilibrium existing between Mg(anthracene) 3THF and its precursors. Use of Activated Metals for Phthalocyanine Preparation Generally, a Rieke metal (0.2 – 0.5 g) or Mg(anthracene) . 3THF complex (0.5 g) was added to the solution (20 mL of a solvent), containing 3 –5 g of phthalonitrile and 5 drops of 30% solution of CH3ONa in methanol. The flask was put into an ultrasonic cleaner and maintained under treatment a T ¼ 0 – 508C for 24 –72 h. Then the formed blue product was

NON-SUBSTITUTED METAL PHTHALOCYANINES

Downloaded By: [Garza Rdz, M.C. Luis Angel] At: 07:11 22 February 2007 FIG. 1. Equipment for synthesis of Rieke metals.

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separated from unreacted metal by shaking and decanting of more light metal phthalocyaninate phase with the solvent, washed with ethanol in Soxhlet equipment and dried in air. Some experiments were carried out without ultrasonic treatment.


Purification and Identification of the Products Phthalocyanines formed were purified by washing with hot ethanol in a Soxhlet equipment and dried in air. The products were characterized by metal content by atomic absorption spectroscopy. According to elemental analysis data, compositions of the obtained products correspond to typical metal phthalocyanines PcM. The samples of formed products, showed the best correspondence between found and calculated data, are as follows. Zinc phthalocyaninate: found/calcd.: Zn (10.55/11.32), C (65.87/66.44), N (18.51/19.38), H (2.46/2.77). Magnesium phthalocyaninate: found/calcd.: Mg (3.88/4.63), C (70.88/71.53), N (19.97/20.86), H (2.48/2.98). Some variations of composition (0.05 – 0.30%) were observed in different experiments. The IR spectra (KBr pellet) of metal phthalocyanines contain the following main bands (cm21), among others: 3500– 3380 (v.s.,w), 2929 (m), 2851 (m) fn(C –H)g; 2300– 2280 (s), 1730 (v.s.), 1622 (s), 1514 (m) fn(C –C) of benzene ringsg; 1472 (m) fn(C – C) of pyrrol ringsg; 1365 (s) (pyrrol nuclei-mesoatoms of N); 1320 (m), 1150 (s) fg(C– H)g. IR spectra of the same PcM, obtained in different solvents, are almost identical (the difference is in the peak intensity). RESULTS AND DISCUSSION According to the chemical analysis of the formed products, corresponding metal phthalocyaninates of 90 –96% purity (for phthalocyanine chemistry, such grade of purity is absolutely normal) are formed in all cases. Using non-activated magnesium after careful elimination of oxidation products from its surface, it is possible to obtain magnesium phthalocyaninate in various non-aqueous solvents with relatively good yields in the temperature interval 20 –508C (Table 1). In the case of more active Rieke magnesium, metal phthalocyanine yields in various solvents are considerably higher. However, in the case of zero-valent magnesium in the form of a Mg-anthracene complex, it is still difficult to evaluate its influence on the phthalocyanine cyclization due to low yields of the final product. As it is seen, when Rieke metals are used, the best results are observed in 1-propanol and 1-butanol. This is distinct from our unpublished results with the use of copper and nickel, where methanol and ethanol were the highest-yielding solvents. Magnesium is evidently more active in comparison with zinc; this fact is in accordance with classic organometallic monographs and textbooks. Comparing non-active and Rieke metals, the

TABLE 1 Metal phthalocyaninate yields at different temperature (treatment 12 h, with CH3ONa) Temperature, 8C

Solvent

Metal phthalocyaninate yield, wt.%

Non-activated magnesium (purified turnings) 50 Methanol 18 – 22 35 Methanol 15 – 20 20 Methanol 11 – 17 20– 50 Ethanol, 1-Propanol, 0 – 15 1-Buthanol (badly reproducible) Rieke magnesium 50 Methanol 50 Ethanol 50 1-Propanol 50 1-Butanol 35 Methanol 35 Ethanol 35 1-Propanol 35 1-Butanol 20 Methanol 20 Ethanol 20 1-Propanol 20 1-Butanol

33 27 57 85 21 36 21 66 5 7 43 36

Non-activated zinc 20– 50 All 4 alcohols

Traces

Rieke zinc 50 50 50 50 35 35 35 35 20

10 8 Traces 39 12 Traces Traces 9 Traces

Methanol Ethanol 1-Propanol 1-Butanol Methanol Ethanol 1-Propanol 1-Butanol All 4 alcohols

Mg(anthracene) . 3THF complex 20– 50 All 4 alcohols

Traces

latter possess more activity; such effect is due to high specific surface areas (Fu¨rstner, 1996) for activated magnesium and zinc, used in the present work. Additionally, particle sizes of Rieke magnesium are much smaller in comparison with the particles of standard magnesium, prepared by grinding of metal turnings, so higher surface energy of the Rieke form contributes to easier cyclization of phthalonitrile and, as a consequence, lower initial temperature of this process. Evidently, high number of defects and imperfections in the activated metal surface and small size of metal aggregates make them very active not only with respect to phthalonitrile cyclization, but

NON-SUBSTITUTED METAL PHTHALOCYANINES


also in other reported organic reactions (Fu¨rstner, 1996; Rieke, 2000; Rieke et al., 1996, 1997; Rieke and Kim, 1998a, 1998b, 2000; Talukdar et al., 1998; Lee et al., 2000; Sugimoto, 2003). A mechanism involving participation of small metal aggregates Mn (M ¼ Mg, Zn) in presence of CH3ONa can be proposed. Mn is an aggregate with high number of defects, which, under strong ultrasonic treatment, used in the present work, forms preferential sites of reaction and further allows elimination of metal atom(s) reacting with organic substrate. Alternatively, in the case of application of strong ultrasonic treatment, these aggregates can be eliminated completely from the main metal surface and serve as a center for phthalonitrile cyclization. In general, the reported mechanism with participation of a metal surface and an organic substrate in Ultrasonic-field [Fu¨rstner, 1996, p.138] includes creation of defects and preferential sites of reaction on the metal surface and further “extraction” of a metal atom, “associated” with an organic partner. To achieve lower temperature for the phthalocyanine preprations, realized in our laboratory, it is noted that the use of activated metals is much more effective in comparison with the use of ultraviolet treatment (Tomoda et al., 1976; Kharisov et al., 2005a), zeolites (Kharisov et al., 2005b) and direct electrochemical synthesis starting from sacrificial metal anodes (Kharisov et al., 1991, 2000). Temperature of synthesis depends on the activity of metal particles and theoretically may be decreased below 08C. Also, nature of non-aqueous solvents used has an important role in order to carry out such an interaction at low temperatures. CONCLUSIONS Non-substituted metal phthalocyaninates (M ¼ Mg, Zn) were obtained from phthalonitrile as a precursor and metals in different forms: non-activated metal and Rieke metal at low temperatures (20 – 508C). The last form seems to be stronger with respect to the cyclization of phthalonitrile in a series of alcohols. The mechanism, including small metal aggregates in the surface of the activated metal, is proposed. It is suggested that high quantity of defects and imperfections in the surface of activated forms of metals contributes to cyclization of phthalonitrile at low temperatures. REFERENCES Baker, K. V.; Brown, J. M.; Hughes, N.; Skarnulis, A. J.; Sexton, A. Mechanical activation of magnesium turnings for the preparation of reactive Grignard reagents. J. Org. Chem. 1991, 56, 698– 703. Burns, T. P.; Rieke, R. D. Highly reactive magnesium and its application to organic syntheses. J. Org. Chem. 1987, 52 (16), 3674– 3680. Fu¨rstner, A. Active Metals. Preparation, Characterization, Applications; VCH: Weinheim., 1996, p. 465. Fu¨rstner, A. Chemistry of and with highly reactive metals. In Angew. Chem. Int. Ed. Engl., 1993, (published on-line in 2003), 32(2), pp. 164– 189.

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