Pseudo-trigonal bipyramidal complexes

Turning finally to compounds with bonds from the heavier Group 14 elements to heavier Group 15 elements we may note compounds such as [Sn C(PMe2)3)2] which has the pseudo trigonal bipyramidal structure (6). This complex, which has Sn bonded exclusively to four P atoms, is formed as yellow crystals by the... 

There are only a few examples of complexes of tin(II) and lead(II)81,82. Figure 10 shows [B(Pz)4]2Sn where the tin atom is four-coordinated in the solid state, adopting a pseudo-trigonal bipyramidal structure with the lone pair of the tin(II) in the equatorial position. The analogous lead complex has also been described83. 

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. 

Our first study of these systems was the synthesis in 1998 of the polymeric complex [ 1( 6 5)2( )2] through the reaction between triphenylphosphine oxide, thallium nitrate and lithium bis(pentafluorophenyl)aurate(I) [71]. This complex consisted of an extended unsupported linear chain of alternate gold and thallium centers. These atoms displayed Au-Tl interactions of 3.0358(8) and 3.0862(8) A, and the thallium atoms showed a distorted pseudo-trigonal-bipyramidal environment, taking into account the stereochemically active inert pair of this atom. As described below, the environment around thallium is one of the main factors that affects the optical properties of these mixed systems. 

A combination of intra- and intermolecular coordination is present in the diphenylmagnesium derivative l-oxa-6-magnesadibenzo(4,5,7,8)cycIo-decadiene-(THF)2 (39). This complex has a pseudo-trigonal bipyramidal (TBP) geometry, which is rare in organomagnesium chemistry (cf. 15, 28, and 29). The two six-membered chelate rings in 39 must be responsible for... 

The stoichiometry of complexation is ordinarily 1 1 (acidrcarbonyl) for boron- and aluminum-centered Lewis acids, which give pseudo-tetrahedral complexes, and 1 2 for octahedral Ti complexes. Tin(TV)-derived Lewis acids can form either 1 2 octahedral or 1 1 trigonal bipyramidal complexes, depending on the nature of their ligands and on the carbonyl base. 

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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