Double-decker sandwich compound

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-... 

Synthesis. The first double-decker complex derived from a pz ligand was reported by Ricciardi et al. (35) in 1993 (Scheme 6). The octa-octylthioporphyrazine (20) was refluxed for 1 week in the presence of Lu(OAc)3 forming the sandwich compound 21 in (an unusually high) 90% yield. 

Optical Properties. The double-decker complexes of porphyrazines have characteristic electronic absorption spectra (Table V). The intense Soret bands of the double-decker complexes are blue shifted with respect to the single pz ligand as a consequence of the strong n-n interactions. Another characteristic of sandwich compounds is the additional appearance of absorption bands shifted to the red (termed Q ) and to the blue (termed Q") of the normal g-band region. These new transitions are thought to result from orbitals delocalized over the two macrocyclic ligands (33, 82). 

During the last few years, adlayers of sandwich compounds such as bisPc double-decker complexes of Y, Ce, Pr, La, and Er have also been investigated at... 

Several examples illustrate how organometallic molecules are strikingly different from those encountered in classical inorganic and organic chemistry. Ligands1 of cyclic delocalized n systems (e.g., benzene or cyclopentadienyl) can team up with metal atoms to form sandwich compounds with a metal sandwiched between them. Sometimes atoms of other elements, such as phosphorus or sulfur, can be included as well. Examples of these double- and multiple-decker sandwich... 

Due to their large size, the inclusion of rare-earth metals into phthalocyanines leads to neutral, double-decker, bis(phthalocyaninato)lanthanide(III) complexes.In these compounds, the triva-lent lanthanide(III) ion is sandwiched between the two macrocyclic ligands, with the rings being rotated with respect to each other by 45°. The coordination polyhedron corresponds to a distorted square antiprism due to the non-equivalent bending deformations of both macrocyles... 

Although the redox behavior of double- and triple-decker porphyrinato complexes has been well documented, the electrochemical properties of half-sandwich analogs remain little studied. The first systematic study of the electrochemistry of this class of tetrapyrrole derivatives was reported by Kadish et al. (1991). The complex Eu(TPP)(facam) was examined, and was found to have higher stability in the oxidized and reduced forms than the corresponding acac and tmhd analogs. The compound can be prepared by treating Eu(TPP)(acac) with 3-(trifluoroacetyl)camphor (Hfacam) and sodium hydroxide in an EtOH/water mixture. As shown in fig. 12, Ae cyclic voltammograms of Eu(TPP)(facam)... 

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