Lanthanides porphyrins

To date, the only organometallic lanthanide porphyrin complexes to be reported contain yttrium and lutetium, and they will be considered in the section on scandium. Representative structural types of porphyrin complexes containing groups 3 and 4 metals are shown in Fig. 3 and selected data for all the structurally characterized complexes are given in Table 11. 

Stelmakh and Tsvirko have also proposed the mechanism [b] for the production of S2 state fluorescence in Mg, Zn, and lanthanide-porphyrins complexes (15), and showed the possibility of another mechanism of pumping by triplet-triplet annihilation (16)(mechanism [a]). The latter process was considered to predominate at relatively low values of the excitation densities. However, the contribution of the mecahnism [C] was not determined experimentally. The experimental results in the present work are summarized as follows ... 

Fig. 18. Lanthanide porphyrinates with substituted TPP2 and anionic capping ligand.

Scheme 11 shows the standard route to lanthanide porphyrin complexes [24,235,236], Depending on the lanthanide metal all intermediates and products can be isolated via column chromatography on alumina. 

In the process of lanthanide complex formation with the porphyrins, the ligand loses two protons and yields lanthanide hydroxy porphyrin or lanthanide porphyrin X, where X = C1, Br, NOJ, etc. Many lanthanide complexes with substituted porphyrins have been prepared by heating a mixture of porphyrin and the lanthanide salt in imidazole melt in the range 210-240°C. When the complex formation is complete the solvent (i.e.) imidazole is eliminated by either sublimation [81] or by dissolution of the mixture in benzene, followed by washing with water [82]. Further purification requires column chromatography. The starting material can be anhydrous lanthanide chloride or hydrated lanthanide acetylacetonate. After purification the final product tends to be a monohydroxy lanthanide porphyrin complex. 

Mixed complexes such as lanthanide porphyrin diketonates have been prepared and these are soluble in organic solvents [83,84]. These mixed complexes are prepared in organic solvents like 4-phenylpyridine, or 1,2,4-trichlorobenzene with refluxing. After the reaction is complete, the solvent is removed by distillation under reduced pressure and the product purified by column chromatography. 

II 000 cm-1). Nevertheless, the photophysics of lanthanide porphyrinates is attractive because it could be of great help in medicine. For instance, hematoporphyrin derivatives are known to accumulate in malignant tumours and are used in medical diagnosis and photodynamic therapy of cancer. It is noteworthy that the Yb(III) complex with meso-tetra(3-pyridyl)porphyrin displays a substantial quantum yield (1.4%) when inserted into micelles formed by the non-ionic surfactant Triton X-100, a medium that can be considered as a model for biological tissues. 

Wong, C.-R, Venteicher, R.F., and Horrocks, WD. Jr (1974) Lanthanide porphyrin complexes. Potential new class of nuclear magnetic resonance dipolar probe. Journal of the American Chemical Society, 96, 7149. 

Harrison, B.S., Foley, T.J., Bouguettaya, M., etal. (2001) Near-infrared electroluminescence from conjugated polymer/lanthanide porphyrin blends. Applied Physics Letter, 79, 3770-3772. 

The NIR emission intensity of the lanthanide porphyrinate complexes follows the trend Yb > Nd > Er. This agrees with observations on other luminescent lanthanide complexes and reflects the fact that the efficiency of nonradiative decay increases as the energy of the luminescent state decreases. The emission yields of the ternary lan-thanide(III) monoporphyrinate complexes with hydridotris(pyrazol-l-yl)borate or (cyclopen-tadienyl)tris(diethylphosphito)cobaltate as a co-ligand are generally higher than those of other Yb(III), Nd(III), and Er(III) complexes because the coordination environment provided by the porphyrinate in combination with the tripodal anion effectively shields the Ln + ion from interacting with solvent (C-H) vibrational modes that enhance the rate of nonradiative decay. 

He, H.,Zhu, X., Hou, A., eta/. (2004) Reactivity of aqua coordinated monoporphyrinate lanthanide complexes synthetic, structural and photoluminescent studies of lanthanide porphyrinate dimmers. Dalton Transactions, 4064. 

Some new lanthanide porphyrin complexes of general formula Ln(iii)TAP(/i-diketonate), where TAP = tetraarylporphine, have been prepared (468,469) and their shift reagent capabilities assessed. The complexes of the early lanthanides (Pr, Nd, Sm, Eu) induce very small shifts whereas the complexes of Tb, Dy, and Ho produce quite large low frequency shifts in y-picoline. Analogous shift reagents based on silicon, germanium, low-spin iron, (517, 518) and cobalt (519) have been reported. 

Most of the lanthanide porphyrin complexes are paramagnetic, except those of lanthanum and lutetium which are diamagnetic. They all show paramagnetic behaviors in the NMR spectra similar to those of the lanthanide 0-diketonate complexes, except that the shift capabilities are less.4 Some of these paramagnetic lanthanide complexes (i.e., that of ytterbium) show Curie behavior at low temperature. Diamagnetic lutetium shows some ring current phenomena.4... 

Buchler, Weiss and coworkers have recently described the structures of lanthanide porphyrins. The structures of cerium(IV) doubledecker and biscerium(III) tripledecker molecules have been described [Ce(OEP)2] and [Ce2(OEP)3] have cerium ions with approximate square-antiprismatic geometry in both complexes. In the double-decker complex, the Ce-Np bond length is 2.475(1) A. The two porphyrin rings are rotated by about 43° with respect to each other. A quite similar structure is seen for [Eu(OEP)2] . In this structure, Eu-Np is slightly longer at 2.510(2) A. The two rings... 

A new synthetic route to half-sandwich lanthanide porphyrinates has recently been developed by Wong et al. (1999) it involves lanthanide amides as the precursors ... 

The first molecular structure of half-sandwich lanthanide porphyrins was reported by Schaverien and Orpen (1991). The lutetium alkyl complex Lu(OEP)[CH(SiMc3)2] has a structure resembling that of the scandium analog (Arnold et al. 1993), exhibiting a square pyramidal geometry. The five-coordinated lutetiiun atom lies 0.918 A above the N4 plane, and the porphyrin ring also displays a saucer shape. 

Results of carried out researches demonstrate the possibility of receiving the lanthanide porphyrin complexes by use of microwave radiation technique. Thus, the time of process is considerably reduced, energy consumptions decreased, reactions are carried out at lower temperatures, there is no need for an inert atmosphere. 

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