Porphyrazine complexes

Electronic Spectra of Thiadiazole and Selenodiazole Porphyrazine Complexes 2... 

Mg and Cd are easily dissociated from their porphyrazine complexes in acetic acid.188,190 Demetallation of Mg- and Cd-Ph8Tap in pyridine-acetic acid is first order in the metal complexes and second order in the solvated proton. Similar results are reported on the Zn- and Ni-Ph8Tap-DMS0-H2S04 H20 system. 

DFT/TDDFT interpretation of the ground and excited states of porphyrazine complexes 02CCR(230)5. 

In view of the potential appHcation of metal porphyrazine complexes as catalysts for various oxidation reactions (45), much attention has been focused on the mechanistic investigations involving the activation of small molecules such as O2, NO, CO, and CO2 by these macrocychc systems. Since the electronic and structural properties of the porphyrazine l%and differ significantly from that of porphyrin rings, the relevant question is if changes in the macrocycle Hgand wiU be reflected in the mechanism of nitric... 

By prolonged refluxing of 6,7,10,1 l-tetrakis(decyloxy)-l,4-diazatriphenylene-2,3-dinitrile (L595) with either CuC or NiCl2 as the template salt and 1,8-diazabicyclo [5.4.0]undec-7-ene as the catalyst in 2-methylbutan-2-ol, mesogenic porphyrazine complexes [M(L596)], where M = Cu or Ni, bearing decyloxy side-chains have been synthesised (Eq. 2.229) [434]. 

Meso substitution of porphyrines to give tetraazaporphyrines, so-called porphyrazines, modulates the electronic character of the macrocycle. While porphyrazines have received considerably less attention than porphyrines over many years, this has changed due to the development of efficient syntheses of soluble derivatives.1 6-1809 Also, various porphyrazines (and phtalocyanines) with peripheral groups for metal ion coordination have been prepared and used for the construction of multimetallic complexes.1806 Ni porphyrazines (695) typically show absorptions spectra with a strong Q band at around 615nm. 

The Ni complex of ra-dihydroxylated porphyrazine (696) gives (697) upon reaction with air.1810 The decaptation reaction is assumed to result from Ni-mediated air oxidation of the ds-diol unit and subsequent loss of C02. 

The effect of peripheral substituents on absorption spectrum and in vitro PDT activity has been studied for the zinc(II) porphyrazine (5,10,15,20-tetraazaporphyrin) system.276 277 Water-soluble zinc(II) polyazaphthalocyanines have been synthesized for PDT applications.278,279 A zinc(II) bis(dimethylamino)porphyrazine is photooxidised to give the zinc(II)-,seco-porphyrazine, the reaction being autocatalytic.280 The zinc(II)-complex of a hexaalkyltexaphyrin chloride has Amax (MeOH) 732 nm and A 0.61,281 but the system does not appear to have been developed for PDT. 

In this chapter, the porphyrazines are named in one of two ways. For simple substitution patterns, substituents will be denoted directly for example, Cu(II) oc-taethylporphyrazine can be written Cu[pz(Et)g], When the pattern is more complex, or general concepts are discussed, the porphyrazines are systematically named based on the nature of their substituents, using the general formula, M[pz (AmB4 ), where M represents the metal ion and its axial ligands (or two hydro-... 

Nitrogen substituted porphyrazines were the second type of heteroatom-deriva-tized pz macrocycle reported and were prepared from the readily derivatized diami-nomalconitrilc (DAMN) (7). Octakis(dimethylamino)porphyrazines are extremely electron-rich systems and have been used to prepare charge-transfer complexes with Cgo, as well as to peripherally chelate metals or convert to crown appended systems (38, 39). The unsymmetrical dimethylaminoporphyrazine analogues have also been reported (29), as well as the first example of the desymmetrized seco-pz from the dimethylaminoporphyrazine (8, 40). The nitrogen substituted porphyrazines are discussed in Section V. 

Octapropylporphyrazines, M[pz( -Pr)s], which can be prepared from 4-octyne by the same synthetic route used to prepare octaethylporphyrazines (Scheme 4), have been used to prepare pz sandwich complexes that are cofacial dimers of two porphyrazines linked by a lanthanide ion (34). 

Sandwich complexes of porphyrazines are prepared by direct intercalation of lanthanides between two pz ligands, the route commonly utilized for the preparation of porphyrin sandwich complexes. Interestingly, the synthetic method used for the preparation of bis(phthalocyanines), starting from the dinitrile or the dilithium substituted monophthalocyanine, has never been successfully implemented for the synthesis of porphyrazines (77). 

EPR-IR. The neutral sandwich complexes of Lu and the one-electron oxidized sandwich complexes of Zr have a jr-radical anion that can be observed by EPR spectroscopy. The EPR spectra for compounds 21, 23, 25, 27 and Collman s mixed porphyrin-pz system (30) give a signal for an S = j system with a g value of 2.0037, which is typical for an organic n radical (35). Further evidence for the Jt-radical character in sandwich compounds of phthalocyanines, porphyrins, and porphyrazines may be obtained from infrared (IR) spectroscopy by the presence of diagnostic marker bands (81). These intense bands are found in the IR spectra of Lu(III) compounds (21) (1150 cm-1) (35), 23 (1140 cm-1) (78), and 25 (1261 cm4) (34) and are absent in the Zr(IV) and Ce(IV) compounds 27,29, and 31. 

Optical Properties. The double-decker complexes of porphyrazines have characteristic electronic absorption spectra (Table V). The intense Soret bands of the double-decker complexes are blue shifted with respect to the single pz ligand as a consequence of the strong n-n interactions. Another characteristic of sandwich compounds is the additional appearance of absorption bands shifted to the red (termed Q ) and to the blue (termed Q") of the normal g-band region. These new transitions are thought to result from orbitals delocalized over the two macrocyclic ligands (33, 82). 

Electrochemistry. The redox processes for porphyrazines 21, 25, 28, 29, the heteroleptic Zr (pz/porphyrin) 30 and 31 have been measured by cyclic voltammetry and the formal potentials are given in Table VII. The potentials are compared to the available data for the analogous porphyrin and pc complexes. In general, the electrochemical behavior of the pz sandwiches more closely mirror that observed for the phthalocyanines than the porphyrins. In particular, all of the porphyrazines have at least one ring-based oxidation, attributable to the formation of the bis Jt-radical cation for Lu(III) sandwiches and the formation of the 7T-radical cation for the Zr(IV) and Ce(IV) sandwiches. Additionally, all of the porphyrazines exhibit at least one ring-based reduction. 

All of the zirconium pz and porphyrin sandwich complexes have up to two reversible ring oxidations and three reversible ring reductions. The zirconium porphyrazines are harder to oxidize by -400 mV and easier to reduce by at least 400 mV than the analogous porphyrins, making them better oxidants and worse reductants. The heteroleptic pz-porphyrin sandwich complex has oxidation and reduction potentials between those measured for the porphyrin and the pz sandwiches, as expected (Table VII). 

The diphosphinonickel appended porphyrazines 63a-63d show a five peak absorption spectrum that is similar to the parent, 60a. An additional peak observed at 300 nm is due to a Ni —> P charge-transfer band seen in other Ni(II) diphosphine complexes (123). The peak is more intense than those reported in the literature for small molecule analogues because there are four Ni-P units per porphyrazine. 

Synthesis. The trimetalic nickel binary pz (75) was prepared from 69a (Scheme 14) (22). Porphyrazine 69b was reductively deprotected with sodium in ammonia then reprotected forming 74, which allowed for purification of the molecule. The pivolyl protecting group was cleaved by saponification with sodium methoxide and the dithiolate, in situ, was reacted with NiCl2-6H20 to yield the binary pz complex 75. 

Titrations of Ag+ with porphyrazines 81c and 81h resulted in a decrease and broadening of the Q band up to 2 equiv of metal coupled with the appearance of at least five isobestic points. Further addition of Ag+ resulted in a visible change from purple to blue and a decrease of the 675-nm band and appearance of a sharp peak at 650 nm, which reached a maximum at 6 equiv of Ag+. The n-n transition disappeared between 0 and 6 equiv. The Hg+ ion gave similar results. Compound pz 81f displayed more complex interactions in titrations with AgC104. 

---