Lutetium 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. 

Coordination compounds composed of tetrapyrrole macrocyclic ligands encompassing a large metal ion in a sandwich-like fashion have been known since 1936 when Linstead and co-workers (67) reported the first synthesis of Sn(IV) bis(phthalocyanine). Numerous homoleptic and heteroleptic sandwich-type or double-decker metal complexes with phthalocyanines (68-70) and porphyrins (71-75) have been studied and structurally characterized. The electrochromic properties of the lanthanide pc sandwich complexes (76) have been investigated and the stable radical bis(phthalocyaninato)lutetium has been found to be the first example of an intrinsic molecular semiconductor (77). In contrast to the wealth of literature describing porphyrin and pc sandwich complexes, re-... 

The composition may then be described as Ln (OEP) (OEP ). This is easily seen from the paramagnetism of Lu(0EP)2 which has the magnetic moment of a radical, i. e. 1,7 B. M, in the solid state (4) As lutetium ions other than diamagnetic fare not known, only a porphyrin radical state is left to explain the properties, A similar radical state has been found for another doubledecker molecule, lutetium bis(phthalocyaninate), Lu(Pc)2 which is hence to be described as Lu (Pc) (Pc ) (11,12). All the... 

As shown in Fig. 7.6, texaphyrins have a larger cavity than porphyrins so they can form complexes with lanthanide metals such as gadolinium (XCYTRIN ), that enhances the efficacy of treatment for certain brain tumours, and lutetium (LUTRIN ), used as a sensitizer for photodynamic therapy of recurrent breast cancer [17], Crucial to their success is the increased number of donor atoms available as the more lanthanide binding sites that a ligand can satisfy, the more stable the complex. 

HGURE 8.1. Formal potentials of redox species in W, NB and DCE versus NHE. Abbreviations ZnTMPyP = zinc tetra-7V-methyl-4-pyridium porphyrin, DcMFc = decamethylfetrocene, TCNQ = 7,7,8,8-tetracyanoquinodimethane, DiMFc = dimethylferrocene, Fc = ferrocene, RuTPP(py)2 = bisfpyridine) meso-tetraphenylporphyrinato ruthenium(II), SnPc2 = tin(IV) diphthalocyanine, LuPc2 = lutetium(in) di]dithalo-cyanine, DiFcET = diferrocenylethane, TAA = tris(4-methoxyphenyl)amine, TPB = tetraphenylborate, TBrPA = tris(4-bromophenyl)amine, TCIPB = tetrakis(4-chlorophenyl)borate. The data is from Ref. [26], except where otherwise noted Ref. [6], Ref. [29], Ref. [30], Ref. [31], Ref. [32]. Reprinted from Ref. [28], with permission from the Polarographic Society of Japan. 

The first monomeric porphyrinato rare earth complex was reported in 1974 [49]. However, only a few reports on these systems have appeared in the literature since then. In 1991, Schaverien and Orpent reported the synthesis of the monomeric porphyrinato lutetium complex Lu(OEP)[CH(Si(CH3)2] from the reaction between Lu CH[Si(CH3)3]2 3 and H2OEP in toluene [50]. Eigure 4.33 displays its molecular structure. The complex belongs to the monoclinic system and crystallizes in a space group P2 lc with a = 1.4879(6) nm, 7 = 2.0644(10) nm, c= 1.4161(5) nm, P= 96.38(3)°, V = 4.323(3) nm, andZ = 4. The coordination geometry can be described as square-pyramidal. In the crystal, the porphyrin... 

Lutetium texaphyrin (Lu-tex) is a water-soluble, porphyrin-related molecule which has been studied as a photosensitizer in experimental models of atherosclerosis and various tumors (29). In vitro work in our laboratory revealed preferential uptake of Lu-Tex by bovine capillary endothelial cells when compared with retinal pigment epithelial cells, suggesting the possibility of increased selectivity (R. Z. Renno and J. W. Miller, unpublished data). When Lu-Tex PDT was applied to the monkey model of experimental CNV, closure of the neovascular membranes was achieved at doses of l-2mg/kg with irradiation 10-40 minutes after injection using 732nm light at 50-100 J/cm2 (30). Limited toxicity to retinal and choroidal structures, similar to that seen with verteporfin was observed. 

Porphyrin complexes of yttrium, lanthanum, cerium, praesodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, lutetium, and thorium can be synthesized using this method. 

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... 

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. 

A recent addition to the PDT field has been the expanded porphyrin derivatives known as texaphyrins (that is, Texas-sized porphyrins). Sessler has developed a number of these molecules. Appropriate derivatives absorb as far out as 732 nm, and provide better penetration of the light to tissues. The lutetium derivative, termed motexafin lutetium (Lutrin), is under investigation for the treatmentof breast cancer. In addition,. some derivatives appear to accumulate in atherosclerotic plaques that can line blood vessels, making the notion of photoangioplasty a real possibility. 

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