Star porphyrazines and related multimetallic macrocycles

Synthesis, characterization and computational investigation of novel metalloporphyrazines containing 15-membered O2S2-donor macrocyclic moieties

New metalloporphyrazines (MgPz, ZnPz) containing peripheral tetrasubstitutions derived from 7,8-dihydro-6[Formula: see text],14[Formula: see text],19[Formula: see text]-dibenzo[bj][1,12,5,8]-dioxadithiacyclopentadecine-16,17-dicarbonitrile (6) have been synthesized by a multistep reaction sequence and characterized. Compound 6 has been prepared by the reaction of 1,3-di(2-bromomethyl phenoxy) propane (3) or 1,3-di(2-iodomethylphenoxy) propane (4) which were prepared via bromination or iodination of {2-[3-(2-hydroxymethylphenoxy)propoxy]-phenyl}methanol (2) and cis-1,2-dicyano-1,2-ethylenedithiolate (5). The novel magnesium porphyrazine was prepared by the cyclotetramerization reaction of 6 with magnesium butoxide. The one-step synthesis of porphyrazinato zinc complex has been achieved without a reaction sequence by using dicyano compound (6) and zinc butoxide. The prediction of the geometry optimization, normal mode frequencies, [Formula: see text]H, [Formula: see text]C NMR, UV absorption spectra, chemical shifts, electronic properties and NBO analysis of the compound were examined by using B3LYP method with a 6-31G([Formula: see text], [Formula: see text] basis set. These novel compounds were characterized by a combination of elemental analysis, [Formula: see text]H, [Formula: see text]C NMR, FT-IR, UV-vis and MS spectral data. An X-ray crystal structure of dicarbodinitrile compound (6) was also investigated.

Profiling energetics and spectroscopic signatures in prototropic tautomers of asymmetric phthalocyanine analogues

Density functional theory (DFT) and time-dependent density functional theory (TDDFT) were used to explain discrepancies in UV-vis and MCD spectra of the metal-free tribenzo[b,g,l]thiopheno[3,4-q]porphyrazine (1), substituted tribenzo[b,g,l]porphyrazine (2), and 2,3-bis(methylcarboxyl)phthalocyanine (3). On the basis of gas-phase and polarized continuum solvation model (PCM) DFT and TDDFT calculations, it was suggested that both NH tautomers contribute to the spectroscopic signature of 1, whereas the Q-band region of 2 and 3 is dominated by a single NH tautomer. For all tested compounds, it was found that the combination of the BP86 exchange-correlation functional, 6-31G(d) basis set, and TDDFT-PCM approach provides the best accuracy in energies of the Q(x)- and Q(y)-bands of the individual NH tautomers as well as correctly describes their relative energy differences, which are important in understanding of experimental spectroscopy of the target systems.

The chemistry of porphyrazines: an overview

The main synthetic approaches for the preparation of porphyrazines are outlined. In addition, some structural and spectroscopic properties, especially the UV-vis absorption profiles emanating from their peripheral functionalization, the modification of the tetraazaporphyrin skeleton or the arrangement of macrocycles in a supramolecular manner, are discussed. Cyclotetramerization of appropriate dinitrile derivatives or modification of peripheral substituents on porphyrazines constitute the main synthetic routes. Moreover, the use of special templates, as well as different intermediates or nonpyrrolic precursors, are tools for the attainment of azaporphyrin analogues of distinct nature and unusual characteristics.

Synthesis, spectroscopic and electrochemical investigations of supramolecular nickel(II)tetraazaporphyrin complexes

The ( bpy )2 Ru II and ( phen )2 Ru II moieties were linked to [ Ni ( OBTTAP )]1, periphery through coordinate bonds in order to synthesize cationic di- and pentanuclear complexes 2-5 that were obtained as PF 6− salts. They were characterized by IR, 1 H NMR, UV-vis, and mass spectral data. The electronic absorption, emission and redox data of these bichromophoric systems indicate the presence of a high degree of intercomponent electronic interaction. The position and relative intensities of the Soret and Q bands in these complexes is altered due to peripheral binding of the metal units. The compounds were non-emissive for the Q band excitation but, Soret excitation led to a strong S 2 emission, observed between 400-450 nm. In cyclic voltammetry, the compounds exhibited one Ru centered oxidation together with one or two OBTTAP centered oxidations. The Ru II/ Ru III oxidations were observed at significantly lower potentials as compared to the corresponding simple maleonitrile-benzylthioether complexes and has been interpretted in terms of weaker d π( S )– d π( Ru ) interactions.

Porphyrazines: Designer Macrocycles by Peripheral Substituent Change

It is rare that such a diverse array of applications can be realized from a single basic molecular unit, however, such is the power of the tetrapyrrolic macrocycle motif. Indeed, their potential in areas such as chemical dyes, optical sensors, optoelectronics, and biomedical agents is a function of their rich electronic and optical properties. While the naturally occurring porphyrins and the synthetic phthalocyanines have been extensively studied, the related tetraazaporphyrins or porphyrazines remain comparatively underdeveloped. Since porphyrazines maintain a unique position in this family: analogous derivatives are virtually inaccessible for the porphyrins, and direct fusion of heteroatomic substituents onto the porphyrazine β-positions results in a more pronounced effect compared with the substitution of an equivalent group onto the benzenoid rings of the phthalocyanine; a driving force exists to further explore the synthesis and applications of these novel macrocycles. This review will provide a historical overview of the synthetic strategies towards functionalized porphyrazines and describe new strategies towards the preparation and applications of heteroatom-appended porphyrazines, particularly in the context of their multimetallic complexes, catalysis, surface chemistry, and as biomedical agents.

Selective detection of minor prototropic tautomers in low-symmetry tetraazaporphyrin derivatives by the combined use of electronic absorption, MCD, and CI calculations

A series of low-symmetry metal-free tetraazaporphyrin (TAP) derivatives, i.e. monobenzo-substituted (1H2), adjacently dibenzo-substituted (2AdH2), oppositely dibenzo-substituted (2OpH2), and tribenzo-substituted (3H2) TAP derivatives, has been investigated by the combined use of electronic absorption, MCD, and CI calculations, proving the existence of two prototropic tautomers in 1H2 and 3H2.

Synthesis, Characterization, and Properties of Subporphyrazines: A New Class of Nonplanar, Aromatic Macrocycles with Absorption in the Green Region

Novel subphthalocyanine analogues that display strong absorption in the green region have been synthesized by using a boron template cyclotrimerization of maleonitrile derivatives. The spectroscopic properties of these macrocycles indicate that, like subphthalocyanines, they have 14 pi electrons and are aromatic compounds with a conical shape. The removal of the three fused benzene rings from the subphthalocyanine skeleton produces a 75-80 nm blue shift of the Q-band and a slight lowering of the absorption coefficients for this band. In addition, the reduction of the pi system from 18 to 14 electrons that accompanies progression from porphyrazines to subporphyrazines causes a hypsochromic shift of the Q-band of around 100 nm. Subporphyrazines that are peripherally functionalized with six thioether chains, and in which the sulfur atoms are attached directly to the pyrrole moieties, exhibit optical features that may be explained in terms of the extension of pi conjugation over the six thiolene groups, as well as strong pi donation from the sulfur lone pairs to the macrocycle. These two effects are quantitatively and qualitatively very similar to those observed for porphyrazines that possess the same type of substitution. In addition, the mesomorphic behavior at low temperatures of a macrocycle that is substituted with six thiododecyl chains was demonstrated by using differential scanning calorimetry and optical polarising microscopy.

Two-electron reduction of alkyl(sulfanyl)porphyrazines: a route to free-base and peripherally metallated asymmetric porphyrazines

Treatment of octakis(octylthio)porphyrazine (H(2)OOSPz) with cis-bis(benzonitrile)dichloroplatinum(II) in a 1,2,4-trichlorobenzene (TCB)-n-BuOH mixture at 190 degree C affords the asymmetric porphyrazine 2H-heptakis(octylthio)porphyrazine, H(2)HOSPz, in ca. 40% yield. In the key synthetic step the two-electron reduced diprotonated porphyrazine, [H(2)OOPz(4-)(H(+))(2)](hemiporphyrazinogen), forms in nearly quantitative yield. This species undergoes nucleophilic substitution of an octylsulfide group by H(-), affording the asymmetric porphyrazine, this process being favoured by the high-temperature induced charge and structural intramolecular rearrangements. The resulting molecule shows mesomorphic behaviour. Interestingly, in the presence of sodium acetate, or in neat TCB, the asymmetric porphyrazine does not form at all. Under these conditions, a PtCl(2) molecular fragment coordinates both to a porphyrazine aza bridge and to a thioether moiety leading to the formation of the [H(2)OOSPz]PtCl(2) complex. The S,N-coordination of the PtCl(2) unit was proved by (1)H, (195)Pt[(1)H], and (13)C NMR spectroscopy, and supported by DFT (B3LYP) calculations. The complex conjugates high asymmetry with strong solvatochromism and, therefore, it is potentially interesting for nonlinear optics.

Synthesis and reactions of aminoporphyrazines with annulated five- and seven-membered rings

The novel five- and seven-membered ring appended aminoporphyrazines 3 and 12 have been prepared via mixed Linstead macrocyclization. The structures of both have been unequivocally established by X-ray crystallographic studies. Reductive deselenation of selenadiazole 3 in the presence of 9,10-phenanthrenequinone or 2,3-butanedione results in the formation of pyrazines 6a,b, whereas oxidation of porphyrazine 12 gave the corresponding seco derivative 14. seco-Porphyrazine 14 mediates the generation of singlet oxygen with a quantum yield of 0.74.

Mono-aromatic ring-fused versus adjacently di-aromatic ring-fused tetraazaporphyrins: regioselective synthesis and their spectroscopic and electrochemical properties

A method which preferentially produces adjacently di-aromatic ring-substituted tetraazaporphyrins (TAPs) has been developed, and their electrochemical and spectroscopic properties have been studied and compared with those of the corresponding series of mono-aromatic ring-fused TAPs. Mono-aromatic ring-fused TAPs show a split Q-band, and the splitting energy increases with increasing size of the aromatic ring. In addition, for the split Q-bands, the relative intensity of the band at longer wavelength decreases with increasing molecular size of the fused aromatics, compared with the shorter wavelength band. In the di-aromatic ring-fused TAPs, this kind of splitting is not seen, and only a shift of the band is observed. The intensity and band position of the split or unsplit Q-bands are quantitatively evaluated by simultaneous band deconvolution analysis, using both electronic absorption and magnetic circular dichroism spectra. The preparation of these TAP compounds has made it possible to adjust the Q-band position in a stepwise manner between ca. 600 and 750 nm. The first reduction and oxidation potentials of the TAP ring shift negatively with increasing number and size of the fused aromatics. The extent of the shift is found to be very small for the LUMOs but significant for the HOMOs. These spectroscopic and electrochemical properties are almost perfectly reproduced by molecular orbital calculations within the framework of the Pariser-Parr-Pople approximation. In particular, a small variation of the LUMO level and large destabilization of the HOMO level on ring expansion are rationalized from the extent of stretch of molecular orbitals: i.e., since the LUMOs are localized in the central TAP moiety irrespective of the molecular size, while the HOMOs have appreciable coefficients even over the fused aromatics, the HOMO level destabilizes while the LUMO level remains constant with increasing molecular size. In one CoTAP derivative, Co(III/II) and the first ligand oxidation couples occur experimentally at the same potential.

Peripherally metalated secoporphyrazines: a new generation of photoactive pigments

Base-catalyzed cross condensation of dipropylmaleonitrile 1 with bis(dimethylamino)maleonitrile 2 in an equimolar ratio afforded the porphyrazines 3a, 4a, 5a, 6a and 7a. Subsequent demetalation of 5a with TFA followed by remetalation with Zn(OAc)(2) gave ligand 5c in good yield. Compound 5c was, in turn, selectively oxidized and further peripherally functionalized using Pt(PhCN)(2)Cl(2) and PdCl(2) to yield the novel seco solitaire porphyrazines 10a and 10b. The photophysical profiles of the seco solitaire porphyrazines 10a and 10b were evaluated by means of absorption, emission, and transient absorption spectroscopy. The new pigments 10a and 10b were found to be photochemically more stable than the solitaire complexes 3d and 3e and mediated the generation of singlet oxygen with quantum yields of 0.59 and 0.45, respectively.