Cadmium complexes porphyrins

Porphyrin, octaethyl-, cadmium complex cyclic voltammetry, 4, 399 <73JA5I40)... 

A number of studies concerning zinc complexes of porphyrins or related ligands have also been reported 1193-1196 cadmium complexes of a number of porphyrins have also been investigated,1197-1199 a number of NMR studies of zinc porphyrin complexes have been made1200,1201 and a number of donor-acceptor complexes of zinc tetrapyrrole species with 1,3,5-trinitrobenzene have been described.1202 Recent developments in metallo-phthalocyamine chemistry, including aspects of zinc complexes, have been reviewed.9-15,12026,1468 11... 

As alluded to above, metal complexes of a number of lanthanide and actinide texaphyrin complexes have also been prepared. In the case of Dy(III) texaphyrin 9.74, as in the case of the bis-pyridine cadmium complex 9.61b, the metal center sits directly within the mean plane of the macrocycle (Figure 9.1.12). This result stands in direct contrast to the highly labile, typically sandwich-type 2 1 or 3 2 complexes observed for porphyrin complexes with these larger metal cations. ... 

A review of expanded porphyrin ligands can be found. The texaphyrins (8) can be considered as 22- 7r-electron benzannulene systems with an IS-tt-electron delocalization path, based on crystal structure data as well as NMR. The cadmium complex of the macrocycle is found to be planar with pentadentate coordination of the macrocycle to cadmium, which becomes seven-coordinate as a result of axial coordination to two pyridine molecules. The cavity is neariy circular with a center-to-nitrogen distance of 2.39 A. Because of the larger size of this macrocycle, metal ion coordination is generally seen with the larger transition metals and lanthanides. 

A number of studies concerning zinc complexes of porphyrins or related ligands have also been reported cadmium complexes of a number of porphyrins have also been... 

Because of its ionic size, cadmium(II) does not fit well into the coordination site of the porphyrin nucleus (N-centre distance 200 pm), and the complexes are readily demetalated (stability group IV, Tables land 2). The complexes can be prepared, of course, but zinc(II) compounds have been overwhelmingly favored for PDT purposes. 

Unusual arene-cadmium 7r-complexes have been recently prepared and structurally characterized. For example, the /w /zz-bcn/i porphyrin complex 194, which can be obtained by reaction of the free base with CdCl2, possesses a cadmium atom that is bound to the Mfez-phcnylcnc unit of the ligand in an apparent /-fashion (Figure 32). The resulting Cd-C distance of 2.71 A is shorter than the sum of the van der Waals radii.252 Despite this relatively short contact, DFT calculations and AIM analysis point to the weakness of the interaction. Comparable weak arene-cadmium 7r-interactions are also observed in the /wra-benziporphyrin cadmium chloride complex 195.253... 

The cadmium(II) complex corresponding to 9 (M = Cd n = 2) was the first texaphyrin made [6], This aromatic expanded porphyrin was found to differ substantially from various porphyrin complexes and it was noted that its spectral and photophysical properties were such that it might prove useful as a PDT agent. However, it was also appreciated that the poor aqueous solubility and inherent toxicity of this particular metal complex would likely preclude its use in vivo [29-31], Nonetheless, the coordination chemistry of texaphyrins such as 9 was soon generalized to allow for the coordination of late first row transition metal (Mn(II), Co(II), Ni(II), Zn (II), Fe(III)) and trivalent lanthanide cations [26], This, in turn, opened up several possibilities for rational drag development. For instance, the Mn(II) texaphyrin complex was found to act as a peroxynitrite decomposition catalyst [32] and is being studied currently for possible use in treating amyotrophic lateral sclerosis. This work, which is outside the scope of this review, has recently been summarized by Crow [33],... 

Heterodinuclear metalloponhyrin, postulated in the metalloporphyrin fomiation catalyzed by mercury(II) or cadmium(Il)10 12 was detected kinetically in the reaction of zincfll) or copper(ll) with homodinuclear mercury(II) porphyrin complex of Hg2tpps2 - The following biphasic reaction was observed ... 

Metalloporphyrins also have more symmetrical macrocycles than free-base porphyrins, so that their Q band spectra generally consist of only two bands. The pictorial classification denotes these as a- and bands, the former at longer wavelength than the latter. The relative intensities of these two bands can be a qualitative yardstick of just how stable is the metal com-plexed to the four porphyrinic nitrogen atoms. Thus, when a > 3, the metal forms a stable square-planar complex with the porphyrin, e.g. Ni(II), Pd(II), and Sn(IV). Cadmium(II), on the other hand, which is easily displaced by protons, has 3 > a. 

Stromberg D, Sandstrom M, Wahlgren U (1990) Theoretical calculations on the stracture of the hexahydrated divalent zinc, cadmium and mercury ions. Chem Phys Lett 172 49-54 Svegensky DA, Shock EL, Helgeson HC (1997) Prediction of thermodynamic properties of aqueorrs metal complexes to 1000°C and 5 kb. Geochim Cosmochim Acta 61 1359-1412 Tabata M, Ozutsumi K (1992) Eqirilibrium and EXAFS studies of mercury(II) porphyrin in aqueous solution. Brrll Chem Soc Jap 65 1438-1444... 

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