Pseudo-trigonal bipyramidal geometry

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. 

Fig. 3. Structure of 4 in the crystal [15]. The molecule has a distorted pseudo trigonal bipyramidal geometry with a (stereochemically active) lone pair in the equatorial plane. Of the disordered methyl groups at Si3 only one orientation is shown.

More recently, the tripodal pyridyl-amino-bis(amido) ligand complex Ti(NR)(NC5H4CH2N-(CH2CH2NSiMe3)2) was prepared, structurally characterized, and its chemistry examined. Crystallographic data showed a pseudo-trigonal bipyramidal geometry at Ti.251... 

The crystal structure has been determined by X-ray diffraction methods. This compound is obtained as a mixture of two isomers with the alkyl group located in equatorial or axial positions in a pseudo-trigonal-bipyramidal geometry. In the crude reaction product the equatorial complex is present with a slight preference over the axial in a ratio of 1.8 1. Slow conversion between both isomers is observed at room temperature.81... 

The air and thermally stable (to >350 °G) polyferrocenylphenylphosphine 64 was shown to react with low concentrations of Go2(GO)g to lead to products containing chelated cobalt centers. " According to IR and P NMR data, three Go-P bonds are present per metal atom and the cobalt environments possess a pseudo-trigonal-bipyramidal geometry. The catalytic potential of the materials in the hydroformylation of 1-hexene was studied and was shown to be similar to that of the complex HGo(GO)3PPh3. 

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