Synthesis, Characterization, Molecular Structure and Theoretical Studies of Axially Fluoro‐Substituted Subazaporphyrins

Abstract

A new and general synthetic method for the preparation of fluoro‐substituted subazaporphyrins is reported that involves the treatment of the corresponding chloro‐ or aryloxy‐substituted subazaporphyrins (SubAPs) with BF3⋅OEt2. The strategy has been applied to both subphthalocyanines (SubPcs) and subporphyrazines (SubPzs). The yields were high for the latter, although low yields were obtained for the benzo derivatives. In contrast to the corresponding chloro derivatives, fluorosubazaporphyrins are quite robust towards hydrolysis. All of the new compounds were characterized by several spectroscopic techniques, which included 1H, 13C, 19F, 15N, and 11B NMR spectroscopy, IR spectroscopy, UV/Vis spectrophotometry, and mass spectrometry (both high and low resolution). In addition, DFT calculations provided theoretical NMR spectroscopy values that are in good agreement with the experimental ones. The high dipole moments exhibited by the fluorosubazaporphyrins as a result of the presence of a fluorine atom in an axial position are responsible for the spontaneous and singular supramolecular aggregation of the macrocycles in the crystalline state. The molecular and crystal structures of two one‐dimensional fluorine SubAPs, namely, a SubPc and a SubPz, are discussed. Molecules of the same class stack in alternating configurations along the c axis, which gives rise to columns that contain large numbers of monomers. SubPz 3 c forms aggregates with the macrocycles arranged in a parallel fashion with the BF bonds perfectly aligned within a column, whereas with SubPc 3 b the neighboring columns cause a commensurate sinusoidal distortion along the columns in the c direction, which prevents the alignment of the BF bonds. However, the most remarkable feature, common to both crystalline architectures, is the extremely short and unusual intermolecular F⋅⋅⋅N distances of the contiguous molecules, which are shorter than the sum of the corresponding van der Waals radii. Theoretical calculations have shown that these short distances can be explained by the existence of a cooperativity effect as the number of monomers included in the cluster increases.

Heterocyclic Subphthalocyanine Analogue – Boron(III) Subporphyrazine with Fused 1,2,5-Thiadiazole Rings

“…It is interesting, that the LDI mass-spectrum of the reaction mixture containing this violet product contains in addition to peaks at 408 Da (100 %) and 454 Da (8 %) the cluster peak with maxima at 490 Da (21 %) The electronic absorption spectrum of [(SN 2 ) 3 SubPABCl] (Figure 3) contains two intense absorption bands due to p → p* transitions of the subporphyrazine p-chromophore positioned at 538 nm (Q-band) and 308 nm (B-band). These bands are typical for subphthalocyanines [26,27] and their origin can be similarly assigned to HOMO → LUMO and § Tris(1,2,5-thiadiazolo)subporphyrazinatoboron(III) chloride, [(SN 2 ) 3 HOMO-1 → LUMO transitions, respectively. The additional band of lower intensity which is observed at 390 nm very likely originates from the n → p* transition between the heteroatoms of the annulated 1,2,5-thiadiazole and the central subporphyrazine p-chromophore.…”

“…Therefore annulation of the p-electrondeficient 1,2,5-thiadiazole rings instead of benzene rings increases the HOMO-LUMO gap due to stronger stabilization of HOMO as compared to LUMO, just like it is observed in going from the phthalocyanine complexes [PcM] to corresponding 1,2,5-thiadiazole fused analogues [(SN 2 ) 4 PAM]. [28] It is interesting, that perfluorination of subphthalocyanine macrocycle, which endows it with n-type behavior [6] leads to stronger stabilization of LUMO than HOMO and associated bathochromic shift of both p → p* transitions (for [F 12 SubPcBCl] l Q =574 nm, l B =311 nm [27] ). In perfluorinated (sub) phthalocyanines, the strong negative inductive effect (-I) of electronegative fluorine atoms is partly compensated by their positive conjugation effect (+C).…”

Beryllium subphthalocyanines self-assembling properties

“…Moreover, directional strong non-covalent interactions may help to the formation of aggregates. In this sense, cooperative effects are related to the dipole moment, this property being essential for the construction of molecular wires in one dimension.Following a similar study to that developed for BSubPz, 31 we have investigated the aggregation process from one to three monomer units of beryllium subporphirazines (BeSubPzH 2 O, see Figure 6 and Table S3), a smaller and much affordable system from the computational point of view that has similar photochemical properties to those of BeSubPc. 22 The BeSubPz core is identical to that of BeSubPc, but lacks of peripheral benzene rings.…”

“…This is not only due to the different size and shape of the macrocycles or differences between Be and B atoms, but also to the R substituents which largely affect the packing along the three dimensions and determine the supramolecular oganization. 31 In the BSubPc crystal, parallel columns of aggregates are distorted along the c axis, avoiding the alignment of the B-F bonds. Additionally, F-N intermolecular distances are considerably shorter than the sum of the corresponding van der Waals radii.…”

“…31 Curved structures of BSubPc(F,R) complexes behave differently to BePc when crystallizing. This is not only due to the different size and shape of the macrocycles or differences between Be and B atoms, but also to the R substituents which largely affect the packing along the three dimensions and determine the supramolecular oganization.…”