Multidecker metal sandwich complexe

Treatment of 3-borolenes or 2-boraindans with bulky lithium amides yields the dihthiated aromatic borolide dianions, which are applicable as hgand precursors for transition-metal complexes. Many borole complexes including a number of unusual multidecker sandwich complexes and mixed-metal clusters have been described. 4 3,2i2 An unexpected new entry into the synthesis of borole complexes has been recently discovered. Bochmann found that attack of B(C6Fs)3 at a zirconium bound diene leads to a pentafluorophenylborole complex throngh snccessive C-H activation steps. ... 

Figure 10. Multidecker metall-acarborane sandwich complexes. [9] The rotational orientations of the C2B3 rings vary in different complexes, and are arhitrarily depicted here.

Treatment of 3-borolenes or 2-boraindans with bulky lithium amides yields the dilithiated aromatic borolide dianions, which are applicable as ligand precursors for transition-metal complexes. Many borole complexes including a number of unusual multidecker sandwich complexes and mixed-metal clusters have been described. 

Interesting electrical properties are to be expected with the stepwise extension of this TT-system. The preparation of multilayered cyclophanes proved to be laborious [6] nevertheless new synthetic methods in transition metal chemistry of arenes have opened up a promising alternative approach via preparation of multidecker sandwich complexes (structure type D in Fig. 3). First row transition metals like chromium, iron and cobalt [51] form strong coordinative bonds with arenes when their oxidation state is low [48a] whereas second and third row elements like ruthenium, rhodium and iridium are strongly bonded towards arenes in higher oxidation states [48a, 51]. Sandwich complexes of cyclophanes can be divided into two groups ... 

Exclusively ir-aromatic metal clusterslike X X=Bq, Mg, Ca, NaX, Na2 3, Y Y= Zn, Cd, Hg, Be, Mg, Ca have also been studied. The NICS(O) value for Ca3 is positive whereas its NICS(l) value is negative. Some of them exhibit bond stretch isomerism . Trigonal dianion aromatic metal clusters " " " like Y F=Be, Mg, Ca containing two TT-electrons can replace the cyclopentadienyl rings to form various metallocene analogues (Fig. 17 and 18) and multidecker sandwich complexes They can stabilize a direct Zn-Zn bond and can trap hydrogen molecules. ... 

The di- and triborolyl ligands tend to i -coordination in sandwichforming reactions. There is a clear-cut tendency for stacking processes followed by the formation of multidecker species and often stabilization of the unusual oxidation states of the transition metals. The route to the linked sandwich and multidecker complexes is attractive for materials chemistry. Thia- and azaborolyl organome-tallic chemistry follows the same trends, although in the azaborolyl complexes the i -rather than i -coordination is sometimes realized. Moreover, coordination via the boron atom is known. In the B, N, Si-heterocycles, the heteroring is j " -coordinated. 

The borole ring and various 1,3-diborolyl anions have been extensively employed as ligands to prepare a huge array of transition metal complexes and multidecker sandwich compounds.96 97 Inevitably, the electronic character of the borole is profoundly changed upon complexation, so a study of such complexes can reveal nothing certain about B—C multiple bonding in the isolated ligand. 

Boratabenzene-bridged multidecker sandwiches are few in number, all prepared in the Herberich group. Stacking reactions of Cp Ru(HsCsBMe) with electrophilic metal reagents gave complexes 106 and 107. 2 interestingly,... 

In a kind of inversion of this concept, hydrocarbons can also serve as platforms for polycluster systems the tri- and tetrametallic complexes shown in Chart 8 (A and B) were recently prepared in our laboratory and characterized via X-ray crystallography at the University of Heidelberg (59). Compounds of this type are prototypes for extended oligomeric and polymeric networks such as that proposed in Chart 8(C), that are expected to exhibit extensive electron-delocalization between the metal centers (60). Systems of this kind, together with alkynyl-and phenyl-linked polyhedra, and multidecker sandwich-based arrays, are current targets of our research (61). 

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