Catalytic properties of tetraimidophthalocyanines

J. inorg,nucl.Chem., 1973.Vol. 35, pp. 153-156. PergamonPress. Printedin Great Britain

CATALYTIC PROPERTIES OF TETRAIMIDOPHTHALOCYANINES D. J. BAKER, D. R. BOSTON and J. C. BAILAR, Jr. School of Chemical Sciences, Department of Chemistry University of Illinois, Urbana, Illinois 61801 (Received 15 March 1971) A b s t r a c t - T h e catalytic properties of the tetra.functional phthalocyanine complexes derived from l, 2, 4, 5-tetracyanobenzene and ferric chloride and/or cupric chloride were investigated and compared to those previously obtained by Inoue, et al. It was found that, although the iron tetraimido derivative strongly catalyzes the oxidation of the ethylene acetal of acetaldehyde, its activity differs little from that of unsubstituted iron(II) phthalocyanine. M6ssbauer and magnetic data were obtained on the iron complexes. INTRODUCTION

TIaE CATALYTIC properties of metal phthalocyanines have been under investigation for several decades [1,2]. A major topic of interest has been the catalytic oxidation of organic substrates (e.g. alkenes and aldehydes) with molecular oxygen. It has been claimed that, in certain cases, polymeric phthalocyanines possess catalytic ability far superior to their monomeric counterparts [3]. In our reinvestigation[4] of the work reported by Inoue, e t al.[5], we discovered that the phthalocyanine derivatives they prepared by heating 1,2,4,5-tetracyanobenzene with ferric chloride and/or cupric chloride in ethylene glycol are not polymeric, as they believed. Instead, the products obtained are generally the corresponding monomeric metal(II) tetraimidophthalocyanines. The details of the structural aspects of this work are described elsewhere [4]. This new structural information along with improved preparative procedures/4] prompted us to carry out a reinvestigation of the catalytic properties of these substances. EXPERIMENTAL The metal phthalocyanines were prepared and purified as previously described/4]. Both the crude products, which correspond to the catalysts used by Inoue et al.. and the purified compounds were tested for catalytic activity. Oxidation reactions were carried out at room temperature (about 23°C) and atmospheric pressure in the apparatus shown in Fig. 1. The reaction flask A was charged with 50 mg of catalyst and the system was then filled with oxygen, The substrate (5 ml) was added via syringe through the small stopcock in the reaction flask. Oxygen uptake was followed by recording the volume of paraffin oil needed to maintain atmospheric pressure within the apparatus, 1. F. H. Moser and A. L. Thomas, Phthalocyanine Compounds, Reinhold, New York (1963). 2. A. B. P. Lever, Advances in Inorganic Chemistry and Radio-Chemistry (Edited by H. J. Emeleus and A. G. Sharpe), Vol. 7, p. 27. Academic Press, New York (1965). 3. A. A. Berlin and A. I. Sherle, Inorg. macromol. Rev. 1,235 (1971). 4. D. R. Boston and J. C. Bailar, Jr., lnorg. Chem. 11, 1578 (1972). 5(a). H. lnoue, Y. Kida and E. Imoto, Bull. chem. Soc,, Japan. 38, 2214 (1965). 5(b). H. Inoue, Y. Kida and E. lmoto, ibid. 40, 184 (1967). 5(c). H. lnoue, Y. Kida and E. lmoto, ibid. 41, 684 (1968); 41,692 (1968). 153

154

D . J . BAKER, D. R. BOSTON and J. C. BAILAR, Jr.

Fig. I. Oxidation apparatus (not drawn to scale). (A) Reaction flask- 25 ml; (B) Warburg manometer; (C) B a l l a s t - 1000 ml; (C') B a l l a s t - 250 ml; (D) Graduated addition funnel. RESULTS

As reported by Inoue et al., the phthalocyanines derived fi'om 1,2,4,5-tetracyanobenzene and iron(III) chloride, or mixture of iron(III) chloride and copper(II) chloride, strongly catalyze the oxidation of acetaldehyde ethyleneacetal [5c]. Contrary to these reports [5], however, we found no enhancement of catalytic activity in mixed copper-iron phthalocyanine derivatives over that of the compounds containing only iron. Our results also differ from those of Inoue in regard to the catalytic activity of unsubstituted iron(II) phthalocyanine [5a, b]. Whereas he reported no significant activity with this compound, we found that iron(II) phthalocyanine is an active catalyst. In fact, when sublimed iron(II) phthalocyanine was used as a catalyst, more oxygen (235 ml) was absorbed after six hours than when the catalysts prepared by Inoue's method were used. Table 1 compares Table 1. Analytical and oxygen absorption data* for catalysts prepared from tetracyanobenzene and iron(III) chloride Cat. No.

Fe/40Ct

C/N:~

Volume (ml) (3 hr)

8 8.4 22 29 30 30.4

3.7 0.92 6.2 l .l 1.5 2.1

3.1 3.2 3-4 3-3 3.2 3'5

9O 85

oxygen

150

160 158 170

*Substrate = ethylene acetal of acetaldehyde. tCalculated for [C4oHt2N~2Os]Fe: Fe/40C = 1.0. ~:Calculated for [C4oH~N~2Os]Fe: C/N : 3-33.

absorbed (6 hr) 175 I08 180 187 210 234

Catalytic properties of tetraimidophthalocyanines

155

several of the Inoue catalysts prepared in our laboratory. For an iron tetraimidophthalocyanine (C40H~2N 12OaFe), one would expect a C/N ratio of 3.33 and one iron atom per forty carbon atoms. Since the C/N ratios of the compounds described in Table 1 are close to the calculated values, it is believed that the high values for iron in cases No. 8, 22 and 30A are due to the presence of iron oxides. These could be removed by washing with dilute acid. In order to determine the effect of this nonstoichiometric iron on the catalytic activity of the imidophthalocyanine complexes, a comparison was made before and after removal of the "excess" iron from the catalyst (samples 8 and 8A). It was found that the acid-washed complex (8A) was also an active catalyst-although not quite as active as prior to the acid treatment. When a catalyst was reused (after filtering and washing with acetone and methanol), no loss of activity was detected. A second recycling, however, resulted in an almost total loss of activity. It was evident that major decomposition of the catalyst had occurred since, after the run, the catalyst was much lighter in color than before (from practically black to rust brown). Catalyst numbers 30 and 30,4 show the result of subsequent catalytic runs on the same sample. Analysis of the sample after only one oxidation run (No. 30A) indicates loss of nitrogen (probably via solvolysis of the imide functions). The increase in the Fe/C ratio implies the loss of organic material from the system. The results of our investigations using cyclohexene as the substrate indicate that unsubstituted iron(II) phthalocyanine catalyzes the oxidation of cyclohexene [6], but that the tetraimido derivative shows little or no activity (Table 2). Unsubstituted copper(II) phthalocyanine (when precipitated from sulfuric acid) did not catalyze the oxidation of cyclohexene, but the copper-imido derivative did. These results are in direct contrast to the work with the acetal in which the catalytic activities of the unsubstituted iron phthalocyanine and the tetraimido derivative were found to differ little, and the copper compounds showed no catalytic activity. Table 2 compares these various catalyst-substrate combinations. In an attempt to relate structural features of the iron complexes to the differences in catalytic activity, Mtissbauer and magnetic data were obtained on two tetraimidophthalocyanine iron(II) compounds and compared with similar data for unsubstituted iron(II) phthalocyanine (Table 3). Mrssbauer analysis at 4"2°K of sample 30 displayed a doublet centered at 0-51 mm/sec with a AEq of 1.96mm/sec. This pattern is superimposed on two less intense six-line sets centered at 0.48 mm/sec. The internal field is estimated to be 460 kOe in the Table 2, Typical oxygen absorption values for various metal phthalocyaninesubstrate combinations

Acetal Cyclohexene * PC

=

FePC*

Imido-FePC

170 ml/3 hr 200 roll3 hr

160 ml/3 hr 25 ml/3 hr

phthalocyanine.

6. A. H. Cook, J. chem. Soc. 1774 (1938).

lmido-CuPC No reaction 146 ml/29 hr

CuPC No reaction No reaction

156

D. J. BAKER, D. R. BOSTON and J. C. BAILAR, Jr Table 3. Mrssbauer and magnetic data for FePC and imido-FePC /~o. (290°K) Tetraimido-FePC

FePC

AEq

~* (4.2°K)

No. 29

3.14

No. 30

3.14

1-96

0.51 mm/sec

3.89[9]

2.70 [8]

0.49 mm/sec [8]

H~ (4.2°K)

458 kOe 0

*Isomer shift relative to that of iron metal.

more intense pattern. This splitting is similar to that found in such materials as /3-FeO(OH)(466 kOe [7]). It is difficult to draw any definite conclusions from the magnetic data because of the presence of iron oxide-type impurities. A temperature study down to 4.2°K on the imido phthalocyanine compounds (Nos. 29 and 30) showed, qualitatively, the same type of behavior as that reported for the unsubstituted iron(II) phthalocyanine [9]. Our studies indicate that the basic catalytic properties of the iron(II) phthalocyanine derivatives prepared by Inoue, et al. differ little from the catalytic properties of unsubstituted iron(II) phthalocyanine in the oxidation of acetaldehyde ethylene acetal. Variations in activity (towards cyclohexene) may be due to some electronic modification of the complex as indicated by the change in A E q in going from the unsubstituted phthalocyanine to the tetralmido form. Acknowledgments-The work reported here was supported by the Advanced Research Projects Agency (Contract HC 15-67-C-0221). The help of Prof. P. G. Debrunner and Prof. D. N. Hendrickson with Mrssbauer and magnetic measurements is gratefully acknowledged. 7. M.J. Rossiter and A. E. M. Hodgson, J. inorg, nucl. Chem. 27, 63 (1965). 8. B.W. Dale and R. J. P. Williams, P. R. Edwards and C. E. Johnson, J. chem. Phys. 49, 3445 (1968). 9. C. G. Barraclough, R. L. Martin, S. Mitra and R. C. Sherwood, J. chem. Phys. 53, 1643 (1970).