Sandwiches and Triple-deckers

The reactions of the Group VIII di- and triborolyl or carboranes sandwiches are directed basically to their extension to multidecker derivatives. 

Similar triple-decker complexes are known, e.g., [(17-p-MeC6H4CHMe2) Ru(i7 -Et2C2B3H3)Ru(i7 VMeC6H4CHMe2)] and [(i7 -Cp)Co(i7 -Et2C2 B3H3) 

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JOM(215)255). Similar nickel sandwiches and triple-deckers are known (77AGE468, 78ZN(B)1410, 81 JOM(207)343). The latter can be reduced to the anionic species using metallic potassium (81JOM(208)137). 

Sandwich and triple-decker complexes are routinely observed for Por and Pc ligands and have attracted most attention (Fig. 21 Buchler, WeiB). The sandwich systems are thermally stable and sublimable and show only limited moisture sensitivity. The lanthanide cations are located between two saucershaped macrocycles usually forming a square antiprismatic coordination polyhedron. The separation of the two macrocyclic rings is very close, starting at... 

Lanthanides form phthalocyanines PcMX, sandwich-like complexes of the type Pc2M, and triple-decker complexes of the type Pc3M2. 

Mononuclear and Dinuclear Complexes of C4B Rings (Double-Decker and Triple-Decker Sandwiches)... 

Phosphoratabenzene complexes of the type LM[H2Me2C4PB-N(CFIMe2)2] (L = (CO)3Mn or Cp Ru) have been prepared by Ashe et at.152 Double- and triple-decker sandwiches 133-135 were obtained by Siebert and co-workers from the reaction of the diborole complex 33 (Section 3.01.3.2) with elemental phosphorus.36 The structures of these complexes have not yet been confirmed crystallographically, and the proposed triple-decker 135 has been seen only in the mass spectrum of 134. 

Fig. 4.31. Structures of two complexes of cerium with octaethylporphyrin double-decker (or sandwich) CeIV(EtgPor)2 (left) and triple-decker Ce ,11 (EtgPor)3 (right). Redrawn from J.W. Buchler et al., J. Am. Chem.

Four possible general structural types are illustrated in Fig. 3. Structure types A and B are represented by the mono- and bis(tricarbonyl-chromium) complexes (ML = Cr(CO)3) and double decker and triple decker sandwich complexes (e.g. MLx = FeCp RufCgHg) CoCp ). The benzene rings of the cyclophane ligands can be replaced by cyclopentadienyl- or cyclobutadienyl-ligands. 

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)... 

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. 

Wang, X., Sabat, M., and Grimes, R. (1995). Organotransition-metal metallocarboranes. 44. construction of pentadecker and hexadecker sandwiches from triple-decker building blocks, J. Am. Chem. Soc. 117, 12227. 

Simple derivatives such as (p-cymene)OsCl2(DMSO) have been reported and the substitution chemistry of [(arene)RuL3l2+ complexes explored. The synthesis of cyclophane ruthenium sandwich complexes has been achieved to give mononuclear and triple-decker-sandwich complexes(52). 

Figure 27.13 The triple-decker sandwich cation, [Ni2(>j -C5H5)3]+. Note that the C5H5 rings are neither staggered nor eclipsed , and the nickel atoms are closer to the outer than to the central ring.

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