Influence of Substituents, Reaction Conditions and Central Metals on the Isomer Distributions of 1(4)-Tetrasubstituted Phthalocyanines

Abstract

The 1(4)-and 2(3)-tetraalkoxy-substituted nickel (5), copper (6), and metal-free phthalocyanines 7 and 8 were synthesized from the corresponding substituted phthalonitriles 2 and 4, respectively, and the four structural isomers formed for each phthalocyanine were separated by HPLC. In the case of 1(4)-tetraalkoxy-substituted phthalocyanines, the ratio of the four isomers was found to be different from the expected statistical distribution of D 2h :C s :C 2v :C 4h 12.5:50:25:12.5. For the 1(4)-substituted metal-free phthalocyanine 7 a very high proportion of the C 4h isomer (87 %) is formed. In the case of the 1(4)-substituted metal phthalocyanines 5 and 6 the strikingly low proportion of the D 2h isomer (found: 2 ± 4 % compared to statistical distribution: 12.5 %) is interpreted by a template mechanism (given in Scheme 2) in which strong steric hindrance of the respective neighboring groups prevent the formation of the D 2h isomer. To investigate further the mechanism of formation of phthalocyanines the synthesis of 1(4)-and 2(3)-tetraalkoxy-substituted metal phthalocyanines containing chiral alkoxy groups (13 ± 17) was studied under different reaction conditions starting from the corresponding alkoxy-substituted phthalonitriles 10 and 11. In all investigated cases the chiral alkoxy groups in the starting phthalonitrile again affect the distribution of the structural isomers of the formed phthalocyanines, leading to a higher proportion of the C 4h isomer in comparison with the 1(4)-tetraalkoxysubstituted phthalocyanines with racemic alkoxy groups.

Synthesis and Isolation of 2,9,17,23-Tetrakis[(3,5-dimethyl-1H-pyrazol-1-yl)phenoxy]phthalocyanine and Its Magnesium(II) and Zinc(II) Complexes

“…The symmetry of regioisomer can be determined by the number of signals in 1 H NMR spectrum. [43][44][45] In the case C 4h and D 2h regioisomers all isoindole fragments with substituents R (A, B, C, D) are magnetically equivalent and the 1 H NMR spectra of these regioisomers must be similar to spectrum of corresponding substituted phthalonitrile. The C 2v regioisomer contains magnetically equivalent (A, D) and (B, C) pairs of isoindole fragments but these pairs are magnetically nonequivalent among themselves and 1 H NMR spectrum of this regioisomer must contain two signals with equal intensity of each proton of isoindole fragments with substituent R. In the case of C S regioisomer all isoindole fragments with substituent R (A, B, C, D) are magnetically nonequivalent and 1 H NMR spectrum of this regioisomer …”

“…The separation of the mixture of the four regioisomers by column chromatography is highly challenging [40] and was achieved by preparative thin layer chromatography or HPLC with chiral column. [41][42][43][44][45][46] It is known that due to the presence of bulky substitutients, a pure regioisomer of 3-substituted ZnPc can be isolated by column chromatograpy. So, the one C 4h isomer of non-peripheral 3-(alkylaryloxy)-tetrasubstituted phthalocyanine was isolated by column chromatography in high yield.…”

Phthalocyanines: The Need for Selective Synthetic Approaches

“…Chiral analogues of many phthalocyanine derivatives [15] [62] can be expected to be synthetic targets in the near future. On the other hand, the greater chemical flexibility of related porphyrazines facilitates the selective synthesis of low-symmetry single compounds.…”

“…In order to clarify the aforementioned results, Hanack and co-workers [15] carried out a systematic study of the selectivity of phthalocyanine formation by varying the reaction conditions, the central metal atoms, and the positions of the substituents on the diiminoisoindole units. It now seems clear from this survey that two mechanisms of Pc formation are involved.…”

“…Surprisingly, when a chiral substituent was introduced in the 3-position of a dicyano derivative, the resulting phthalocyanine isomer mixture was found to contain a high proportion of the C 4h isomer with respect to the statistical distribution (up to 29% instead of 12.5%) or with respect to the same reaction with the corresponding racemate (29% instead of 10% in one case). [15] The Directed Approach…”