Cerium porphyrin complexes

The geometry at cerium is distorted square antiprismatic with a mean stagger of -28°, a value noticeably less than that (42°) observed in the porphyrin complex. The Ce-N distances are in the range 2.411(9)-2.430(9) A, distances that are markedly shorter than those in the porphyrin structure that range between 2.467(3) and 2.483(3) A (Fig. 8). 

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. 

Yamashita, K., M. Ikeda, M. Takeuchi, and S. Shinkai (2003). Electropolymerization of bithienyl-appended cerium(III) triple decker porphyrin complex. Chem. Lett. 32(3), 264-265. 

Yamashita K, Ikeda M, Takeuchi M, Shinkai S (2003) Electropolymerization of bithienyl-appended Cerium(in) triple decker porphyrin complex. Chem Lett 32 264-265... 

For the cerium pz sandwich complex, only data for the analogous porphyrin sandwich is available. For the porphyrin, not only are one ring reduction and two ring oxidations observed, a metal-based Ce(IV)/Ce(III) reduction is observed, at a lower potential than the ring oxidation. The electron-transfer rate constant for the Ce(IV)/Ce(III) process was found to be very slow, 2.2 1.0 X 10 cm 1 because the/orbital of the cerium ion is buried between the two macrocycles making it difficult for the incoming electron to access it. For the Ce IVl pz, a similar Ce(IV/III) reduction is observed, at a lower potential than that observed for the porphyrin. 

To construct such a porphyrin-based positive allosteric system, we chose a cerium(iv) bis(porphyrinate) double decker compound 184-861 namely the tetrakis(4-pyridyl)porphyrin derivative 38.[871 This molecule satisfies the aforementioned requirements firstly, slow rotation of the two porphyrin planes with respect to one another should be possible at room temperature,1881 in analogy to similar cerium(iv) bis(diarylporphyrin) and bis(tetraarylporphyrin) complexes studied by Aida et al/861 Secondly, tilting of two porphyrin planes is more difficult than in 37, and thirdly, four pairs of 4-pyridyl groups are available as hydrogen bond acceptor sites for diols, hydroxycarboxylic acids, and dicarboxylic acids. Compound 39, which has only one pair of pyridyl groups, was used as a reference. 

Cerium also forms genuine bis(porphyrin) and bis(phthalocyanine) complexes with the metal in the (-b4) oxidation state. 

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... 

Selective complexation of di- and tetra-substituted porphyrins with cerium(III) ion led to novel double- and triple-decker sandwich complexes. In such complexes, the two or three porphyrin macrocyles were rotated by ca. 20-45. The various complexes were prepared by reaction of the parent porphyrins with cerium acetate. 

This chapter gives an overview on the chemistry of tetravalent lanthanide compounds, especially those of tetravalent cerium. Following a brief introduction, it covers the tetrahalides, dioxides, and other lanthanides(IV) salts. Coordination compounds of cerium in the oxidation state +4 include halogeno complexes and complexes of oxo acids, /3-diketonates and related Schiff-base complexes, as well as porphyrinates and related complexes. 

Even flien well-characterized coordination compoimds are limited to only a few classes of compounds. Notable are, e.g., halogeno complexes and complexes of oxo acids, p-diketonates and related SchifF-base complexes, as well as porphyrinates and related complexes. Two other important classes of cerium(lV) compounds, the alkoxides and amides of Ce" +, can be regarded as pjewfifo-organometallics and are discnssed together with the organocerium(IV) complexes in Tetravalent Chemistry OrganometalUc. 

Formally, tetravalent cerium is long known to form stable sandwich complexes with tetrapyrrole-type macrocyclic ligands such as porphyrines, phthalocyanines, and 2,3,-naphthalocyanines (Scheme 12). For the rare earth sandwich complex series, virtually all the neutral complexes can be formulated as Ln° (ring-1 ) (ring-2 ), in which a trivalent rare earth metal center is sandwiched between a... 

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