Porphyrazines sandwich complexes

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. 

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). 

Keywords TDDFT Excitation energies Excited states Transition metal complexes Electronic spectra Metallotetrapyrroles Metallocarbonyls a-diimine complexes Porphyrins Porphyrazines Phthalocyanines Werner complexes Sandwich complexes... 

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. 

Besides porphyrins, cocrystallates of Ceo were also found with porphyrazines, as another representative of the diverse family of Mr-extended macrocyclic complexes. They reveal interesting supramolecular structures while, for copper (II) a Cy-symmetric sandwich... 

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