Octaethylporphyrin complexes

The olive-green osmium(VI) octaethylporphyrin complex 0s02(0EP) (IR v(0s—0) 825 cm-1) is representative of a number of osmyP porphyrins [185] they can readily be transformed into a number of osmium porphyrins in lower oxidation states (Figure 1.73). 

Figure 2.42 Synthesis of a dimeric rhodium(II) octaethylporphyrin complex.

Reaction of [Rh(CO)2Cl]2 with porphyrins (e.g. H2TPP) leads to Rh(por-phyrin)(CO)Cl, which readily lose CO. Some of the chemistry of the octaethylporphyrin complexes [102] is shown in Figures 2.51 and 2.52. 

The crystal structure of the cerium sandwich complex (31) (34) shows it to be similar to that of the related Cclv bis(octaethylporphyrinate) complex (Fig. 7) (83, 84). 

Platinum porphyrin complexes can be prepared by reaction with PtCl2(PhCN)2. Purification of the final complex is by medium pressure liquid chromatography on alumina. The strongly phosphorescent platinum(II) porphyrin complexes are efficient sensitizers for stilbene isomerization. The quantum yields for the cis to trans process are greater than unity because of a quantum chain process in which the metalloporphyrin serves both as an energy donor and an acceptor.1110 Picosecond laser spectroscopy has been used to obtain time-resolved excited-state spectra of platinum octaethylporphyrin complexes, and to probe the excited-state energy levels.1111 Tetrabenzoporphyrin complexes have been prepared for platinum in both the divalent and tetravalent oxidation states. The divalent complex shows strong phosphorescence at 745 nm.1112... 

The comparative photophysics of Pt(II) and Pt(IV) porphyrins [297] have been investigated. A correlation of X-ray crystallographic data and spectroscopic properties was done for a variety of octaethylporphyrin complexes of divalent metals, incorporating those of Ni, Pd, Pt, Cu, and Ag, giving useful UV/Vis and IR data for the synthetic chemist as well [298]. 

Fig. 10. Thallium(III) octaethylporphyrin complex. From Smith (240) with permission.

Porphyrins, hydroporphyrins, azaporphyrins, phthalocyanines, corroles, corrins, and related macrocycles were discussed in CCC (1987).144 The octaethylporphyrin complexes of scandium were also previously mentioned in CCC (1987).1 The octaethylporphyrin (oep) scandium chloride complex (oep)ScCl, prepared by the reaction of the dilithium porphyrin with ScCl3(thf)3, has proved... 

The alkylzirconium(m) octaethylporphyrin complex, (OEP)ZrCH2SiMe3 1, was prepared from the dialkylzirconium(rv) complex by reduction with H2 (1 atm) in toluene at 20 °C (Scheme 1). This reaction therefore appears to be a rather rare example of the chemical reduction of Zr(rv) to Zr(m) by H2. The structure of 1 was elucidated by single crystal X-ray diffraction and has a Zr-C bond length of 2.216(8) A. Although this complex formally contains zirconium in oxidation state hi, careful consideration of the structural and spectroscopic data led the authors to conclude that this was an overly simplistic view. At 77 K, an EPR signal typical of a metal-centered radical was observed, while no signal was detected at 293 K. The UV/Vis spectrum of 1 contains bands typical of a porphyrin anion. The electronic structure of 1 is therefore better described as a combination of two resonance forms a Zr(m) metal-based radical, and a zwitterionic form with a positively charged Zr(iv) center and a porphyrin radical anion. 

Another promising example of a metal-based sensor can be seen in the work of Lee and Okura (239) who used entrapped platinum octaethylporphyrin complexes to form photostable devices. In their study, they found by adding the surfactant Triton X-100 to the sol-gel mixture, they could improve homogeneity and phosphorescence of the dye-containing glass. Encapsulated porphyrin molecules have also been used successfully in the sensing of nitrogen dioxide (240) and, as will be discussed below, can be used to sense metal ions. 

It is well known that chemical shifts for meso protons of the octaethylporphyrin complexes depend upon the oxidation state of the central metal. Divalent metals have a resonance in the region of 9.75-10.08 ppm while for tri- and tetravalent metals this resonance is in the range of 10.13-10.39 and 10.30-10.58 ppm respectively. For the In(OEP)(R) series the indium oxidation state is III and the observed methine proton shifts of 10.17-10.37 ppm correspond to those of a typical trivalent metal (Table 3). The exact position of the In(OEP)(R) methinic protons resonance varies systematically with the electron-donating ability of the axial ligand i.e. the more basic the axial ligand, the higher the field. Similar results are observed for o-bonded complexes of the rhodium series . ... 

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