Triple-decker sandwich complex

Figure 80 The structure of the triple-decker sandwich complex (CsPryBatCOTJBafCsPr s) 153.

The cyclo-P3 unit can also behave as a three electron bridging ligand (45) to give a variety of homo and heterometallic triple-decker sandwich complexes which are treated in a recent review (100). 

A typical structure of these so called triple-decker sandwich complexes is that of the complex [(p3)Ni -(j)3-P3) Ni(p3)](BPh4)2-2.5Me2CO (73). In each complex the trihapto P3 (or trihapto As3) groups form a bridge between the two Ni(p3) residues.292 Each nickel atom is thus six-coordinated by three phosphorus atoms from the ligand p3 and by three phosphorus atoms from the cyclo-P3 (or arsenic atoms from the cyclo-As ), which acts as a three-electron-donor ligand. 

In the case of "simple sandwich complexes the X-ray diffraction studies have shown that the M-PCtriphos), M-P(cyclo) and P-(cyclo)-P[cyclo) distances reveal effects of both the increase in the principal quantum number and the "lantanide contraction". For "triple decker sandwich complexes the li-li distances increase whereas the P[cyclo)-P(cyclo) distances decrease with increasing number of valence electrons. 

Additional d electrons on the metals increase the number to be counted in the aromaticity formalism. As this can be applied by two metals (d6 - d8), the family of triple-decker sandwich complexes should consist of members having 30, 31, 32, 33, and 34 valence electrons. Analogous to the 17-valence-electron ferricenium cation, obtained by oxidation of ferrocene, 29-valence-electron species ( n,8/d5/7r8/d8/7r6) would be expected to be stable, and this has been confirmed by chemical and electrochemical studies (see Section III). 

Fig. 6. Triple-decker sandwich complexes having 30-34 valence electrons. (Compound 27 has 34 28 and 30, 30 and 29, 33 valence electrons.)...

Fig. 20. Bis( 7)5-cyclopentadienylmetal)(fi-1,3-diborolene) triple-decker sandwich complexes (78—81).

Flo. 21. Borole and thiadiborolene triple-decker sandwich complexes. 

H. Sitzmann, M. D. Walter and G. Wolmershauser, A triple-decker sandwich complex of barium. Angew. Chem. Int. Ed. 41, 2315-16 (2002). 

Scheme 6.5 Preparation of homo- and hetero-metallic triple-decker sandwich complexes 7-12 containing a bridging pentamethylcyclopentadienyl ligand...

Scheme 6.8 Arene-bridged triple-decker sandwich complexes 17-19 with 26 (V2), 30 (Cr2) and 34 (Ni2) valence electrons...

Scheme 6.10 Triple-decker sandwich complexes 25-30 with bridging five- and six-membered heterocyclic ligands (the substituents at the ring atoms are alkyl or aryl groups)...

E. Dubler, M. Textor, H. R. Oswald, and A. Salzer, X-Ray Structure Analysis of the Triple-Decker Sandwich Complex Tris(j -cyclopentadienyl)dinickel Tetrafluoroborate,... 

T. L. Court, and H. Werner, Concerning the Mechanism of Formation of the Cationic Triple Decker Sandwich Complex [Ni2(C5H5)3]+, and the Isolation of [NiC5H5]BF4, J. Organomet. Chem. 65, 245-251 (1974). 

W. M. Lamanna, Metal Vapor Synthesis of a Novel Triple-Decker Sandwich Complex (p6-Mesitylene)2( J,-p6 6-mesitylene)Cr2, J. Am. Chem. Soc. 108, 2096-2097 (1986). 

G. E. Herberich, B. Hessner, G. Huttner, and L. Zsolnai, A Triple-Decker Sandwich Complex of Rhodium with Dibora benzene as the Bridging Ligand, Angew. Chem. Int. Ed. Engl. 20, 472-473 (1981). 

Thermolysis of LNb(CO)4 (L if-1,3-Bu -C5II3) and P4 in decalin afforded the triple-decker sandwich complexes [LNb]2(//2-//r //r -PrJ (262).637,638 Although the P6 ligand is essentially planar, it exhibits pronounced in-planeo distortions with three pairs of P—P interatomic distances of 2.105(2), 2.116(3), and 2.347(3) A. Extended Huckel calculations suggested that the distortion is due to the presence of two electrons in nearly degenerate 2t antibonding orbitals. 

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