Antimony cyclopentadienyl complexes

Monomeric carbene complexes with 1 1 stoichiometry have now been isolated from the reaction of 4 (R = Bu, adamantyl or 2,4,6-trimethylphenyl R = H) with lithium l,2,4-tris(trimethylsilyl)cyclo-pentadienide (72). The crystal structure of one such complex (R = Bu) revealed that there is a single cr-interaction between the lithium and the carbene center (Li-C(carbene) 1.90 A) with the cyclopentadienyl ring coordinated in an if-fashion to the lithium center. A novel hyper-valent antimonide complex has also been reported (73). Thus, the nucleophilic addition of 4 (R = Mes R = Cl) to Sb(CF3)3 resulted in the isolation of the 1 1 complex with a pseudo-trigonal bipyramidal geometry at the antimony center. 

The first cyclopentadienyl n complexes of phosphorus, arsenic, and antimony have been characterized only recently. The salt-like species LXXXV-LXXXVII containing a cationic n complex are prepared via halide ion abstraction from pentamethylcyclopentadienyl element halides according to Eq. (47) (248-250). 

The cyclopentadienyl reactions have been illustrated for early as well as late transition metals and also the actinides. It is remarkable that the reactions are very similar across the entire group. This methodology results often in sandwich-type complexes of the Et units and has been found successful for both phosphorus and arsenic, but only one example has been reported for antimony. There are no reports of bismuth metal reacting with cyclopentadienyl metal fragments. Neither Sb nor Bi readily form the soluble E4 species as do P and As, and so their reactivities may be limited by solubility factors (Table XLI). 

Phosphorus, arsenic, antimony, and bismuth ligands have been discussed in CCC (1987).153 Complexes containing bonds between scandium, yttrium, and phosphorus or arsenic have been reviewed,154 as have complexes with neutral phosphorus ligands.155 Many of the complexes described in these reviews contain organic substituents such as cyclopentadienyl or alkyl groups. 

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