Stannylenes molecular structure

FIGURE 4. Molecular structure of stannylene 29, showing weak Lewis acid/Lewis base interactions of lone-pairs on N with empty p-orbital of Sn... 

FIGURE 13. Molecular structure of the chloro(alkyl)stannylene 61a (left) and of chloro(alkyl)plum-bylene 62b (right) in the crystal, both forming asymmetric halogen-bridged dimers due to competitive intramolecular Lewis acid/Lewis base interactions. These are depicted as dashed lines (----) and the longer E—Cl bonds as thin solid lines... 

Besides the triatomic CAs, the molecular structures have been determined experimentally for only labile silylidene and germylidene, as shown in Table 10. At the same time most of the stable CAs have been characterized by X-ray analysis or by electron diffraction. The available structural data for some stable germylenes, stannylenes and plumbylenes have partly been presented in Section IV. The comprehensive consideration of the geometries of stable CAs is beyond the scope of the present review. 

FIGURE 9. Molecular structure of adduct 49 in the crystal, showing its four constituting stannylene sub-units... 

Fig. 7. Molecular structure of the stannylene 61. Reprinted with permission from Kira...

In stannocenes, the tin atoms formally possess the coordination number 10, and the " Sn magnetic shielding is high (Scheme 2.1.5), in contrast to the stannylenes. Numerous stannocenes are instructive examples, for which the molecular structures have been determined in the solid state, and the Sn NMR spectra have been measured both in the solid state and in solution. 

Figure 2.8.1 Molecular structures of benzannulated N-heterocyclic stannylenes with sterically nondemanding or Lewis base functionalized N,N -substituents...

Figure 2.8.2 Molecular structure of the donor-functionalized bis-stannylene 7 (top) and arrangement of the molecules in the crystal lattice (bottom)...

The platinum(O) complexes 17 and 18 also contain a tetrahedrally coordinated transition metal center. The molecular structures of 17 and 18 (Figure 2.8.7) are similar to those found for the analogous complexes 15 and 16. The sterically unprotected stannylene tin atoms in 17 are coordinated by THF molecules in the solid state (these THF molecules are not shown in Figure 2.8.7). 

Figure 2.8.7 Molecular structures of the homoleptic platinum (0) complexes of bis-stannylenes 17 (left, coordinated THF molecules are not shown for clarity) and 18 (right)...

Figure 2.8.8 Molecular structures of the molybdenum complexes with the N-alkyl-substituted bis-stannylene 20 (right) and the N-donor-substituted bis-stannylene 22 (right)...

As previously pointed out in Chapter 2, monomeric stannylene can be in equilibrium with oligomeric species which are formed by tin-tin or tin-substituent inter-molecular interactions. The tendency for the formation of the oligomers increases the more the molecules approach one another. Thus, when passing from the vapor to the liquid phase and finally to the solid state, the molecules usually exhibit quite different structures. In Table 13 examples of the corresponding structural changes are given. 

In the case of tin(II) compounds, the lowest " Sn nuclear shielding is observed for monomeric dialkyl-stannylenes (Scheme 2.1.2). However, it has been suggested that agostic B—H..Sn interactions significantly increase " Sn nuclear shielding. For diarylstannylenes, one observes a wide range of 5" Sn data, " and this may be caused by intra- or inter-molecular association. The latter is also evident from crystal structures. " ... 

---