Porphyrins lanthanide complexes

Phthalocyanines are tetraaza tetrabenzo analogues of porphyrins. Lanthanide complexes with phthalocyanines are prepared by the condensation of phthalonitrile (4 moles) with a lanthanide salt. The monocomplexes were prepared by heating a 1 4 mixture of lanthanide saltiphthalonitrile at 275°C. The molten solution solidified after an hour and purification of the complex is done by removal of excess phthalonitrile and impurities with organic solvents. Final purification is done by chromatography [85]. The bis complexes are prepared in a similar fashion but with a large excess of phthalonitrile [86]. Mixed ligand... 

OrganometaUic complexes ofpyridyl Schiff bases 12AHC(107)133. Porphyrin lanthanide complexes for NIR emission 12CCR1468. 

First works on synthesis of porphyrin lanthanide complexes, both hydrophobic tetraaiylporphyrins [2, 3] and water-soluble [4], appeared at the end of the XX century. Classical techniques are based on boihng of porphyrin with lanthanide metal acetylacetonate in 1,2,4-trichlorobenzene in the inert atmosphere throughout 2.5 3 h. In case of hydrophilic derivatives a short alloying in an imidazole was applied, then the imidazole subhmation was carried out and metallocomplexes were isolated by various chromatography methods. 

As demonstrated above, lanthanide complexes containing phthalocyanines and various porphyrins as ligands have been studied in great detail. In contrast, the number of studies on analogous complexes containing phthalocyaninato and tetrapyrrole ligands like tetrabenzoporphyrinato-, tetraazaporphyrinato- or N-confused porphyrinato-, is rather limited [151-155], though such compounds also attract considerable interest. 

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). 

Paramagnetic shifts may be induced in cations which associate with suitable lanthanide complexes. Thus in aqueous solution, [M(hpda)3]6, where M = Dy or Tm and H3hpda = 4-hydroxypyridine-2,6-dicarboxylic add, associates with Mg2-1, 39K+, 23Na+, 87Rb+ or 14NH4 and produces shifts of up to 25 p.p.m. which are most marked above pH 7.582 A similar effect is shown for cations (and anions and uncharged molecules) by lanthanide tetra-p-sulfonatophenyl-porphyrins in aqueous solutions.583 This is discussed in Section 39.2.6.3, as are the large shifts produced in aqueous solution by Na[Eu(dota)(H20)] (H4 dota = 23).584... 

Fig. 5. Sublimation behavior of various lanthanide complexes at 10 3 mbar (OEP = 2, 3, 7, 8,12, 13, 17, 18-octa(ethyl) porphyrin acac = acetylacetonate)...

The last category was concerned with miscellaneous subjects, while citing some chirogenic porphyrin-based systems. Representative reviews include chiral lanthanide complexes by Aspinall [41], coordination chemistry of tin porphyrins by Arnold and Blok [42], photoprocesses of copper complexes that bind to DNA by McMillin and McNett [43], nonplanar porphyrins and their significance in proteins by Shelnutt et al. [44], cytochrome P450 biomimetic systems by Feiters, Rowan, and Nolte [45] and phthalocyanines by Kobayashi [46,47]. 

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. 

The most practical use for these expanded porphyrin macrocycles is in complexa-tion of larger cations. Preliminary investigations into lanthanide complexes of indicate that most of the lanthanides form complexes with L via template reactions... 

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. 

A, N -dimethyl-palladium complex, 21 133 N4C20H14, Porphyrin actinide and lanthanide complexes,... 

Lanthanide complexes of porphyrins and phthalocyanins as liquid crystals and surfactants 02CRV2303. 

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... 

Interestingly, in the case of lanthanide ions as metal centers, triple decker porphyrin sandwich complexes were also synthesized and studied (Wittmer. Holten, 19%). 

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