Complexes of group 14 Ge, Sn, Pb

It is apparent from most of the examples previously described that the most common formal oxidation state found for the Group 14 element is E(IV) (E = Ge, Sn, Pb). Relatively few examples of divalent germanium, tin, or lead complexes have been described, and of these, many are not well characterized. Cobalt-containing compounds are no exception in this regard and there appears to be only one report in the literature that describes a species of this type, viz. [Ge Co(CO)4 2], 67, although the precise structure of this complex is unknown (77). Two main synthetic routes are described, Eqs. (4) and (S), the starting complex in the latter reaction being... 

Divalent compounds of group-14 elements Si to Pb where the elements E are stabilized via intramolecular mono- and bidentate chelation, shown schematically in Figure 33, have been the subject of an extensive theoretical study by Scholler et al.146. The complexes are experimentally known for E = Si, Ge, Sn and L = P, but not yet for the other elements which were calculated. Table 32 gives relevant calculated bond lengths and angles. The analysis of the bonding situation shows that the central element E is weakly coordinated by the axial E—L bonds which become somewhat stronger when... 

In this section are covered complexes that contain v-block-(Si, Ge, Sn, Pb) bonds as their primary point of interest. Cluster compounds that contain Group 14-Group 14 bonds, or in which an... 

Unfortunately, 207Pb NMR spectra of transition metal-lead complexes have not always been recorded, although U9Sn NMR spectra of analogous tin compounds have been measured. No reason has been given why 207Pb NMR data could not be obtained (e.g. in (Schiff-base) divalent group 14 element species [(Salen)M] M (CO)6 (n - 1, 2 M - Ge, Sn, Pb M = Cr, W).100 The same situation is found for [Salen]Sn(II) and [Salen]Pb(II) derivatives.101... 

Several main group derivatives of boratabenzene have been synthesized through reaction of boratabenzene salts with the appropriate metal halides. For example, treatment of [CsFlsBMelLi with group 14 electrophiles MesEX (E = Si, Ge, Sn, Pb) led to -bonded compounds (139) that are fluxional in solution. In contrast, reaction with divalent group 14 halides ECI2 led to bent-sandwich structures such as the -bonded complex (140). ... 

Group 14 elements (C, Si, Ge, Sn, Pb) have diverse speciation characteristics. C is partitioned dominantly between C032- and HC03-, while for both Si and Ge, uncharged forms are dominant (Si(OH)40 and Ge(OH)40) with lesser concentrations (< 15%) of SiO(OH)3- and GeO(OH)3-. The sparse data available for assessment of SnIV speciation indicate that Sn(OH)40 is dominant over a wide range of pH. The speciation of Pb is apparently unique among seawater constituents in that Pbll is partitioned between chloride complexes and carbonate complexes. [17] The latter are dominant above pH 7.85. 

Of the group 14 elements (Si, Ge, Sn and Pb), only tin is known to form a variety of poly(pyrazoIyl)borato alkyl derivatives. For example, the reactions between K[pzTp] and the silicon derivatives Me SiCl4 (n = 1-3) have not given tractable products (115). Similarly, the reaction between K[pzTp] and Me2GeCl2 gives a complex that has been spectroscopically characterized as [pzTp]2GeMe2, but which readily decomposes. 

Herrmann and coworkers183 reported a series of Cp-manganese carbonyl complexes which bind Ge, Sn and Pb as central atoms linearly coordinated in clusters, to two Mn atoms in one series and trigonal-planar coordinated to three Mn atoms in another series 8 and 9. The group 14 atoms are double-bonded to two Mn atoms in these compounds, or carry one double bond and two single bonds to three Mn atoms. Potentiometric measurements of these compounds show irreversible reductions and oxidation by CV. No products could be isolated from either reduction or oxidation. The exceptionally high oxidation potential of (/i-Pb) r/ -CsHs )Mn(CO)2]2 as compared to the apparently similar Sn compound is noteworthy (Table 15). 

Some complexes which satisfy this definition are dealt with elsewhere, however. Those with X or Y as the Group V donors P, As or Sb are dealt with in Chapter 14 of this volume. Those with X or Y = Hg are described in Chapter 11 and the Group IV donors Si, Ge, Sn and Pb are included in Chapter 12.2, With very few exceptions this means that the relevant X,Y combinations are pairs derived from nitrogen, oxygen, sulfur or selenium donor groups. However, some specific examples of these combinations also occur elsewhere in this work. Amino acids (generally N—O bidentates) are covered in Chapter 20.2, Schiff base ligands (N—O or N—S) in Chapter 20.1, and several S—O... 

Subvalent halides of heavier group 14 elements MX2 (M = Ge, Sn, and Pb X = F, Cl, Br, and I) and their complexes exhibit the following structural features and properties. 

---