Germole dianion

The coupling of aryl aldehydes and ketones to give chiral diols can be achieved by reaction with the tetraphenyl-germole dianion 99 (Equation (212), Table 29).17 Hexamethyldigermane can be employed to generate synthetically important allylgermanes with high stereoselectivity (Equation (213), Table 30), and the reaction pathway for this process has been proposed.267... 

The germacyclopentadienide anions present structures consistent with substantial localization of the negative charge on germanium unlike silicon (vide supra)-, germole dianions would be reasonable candidates for stable aromatic germanium derivatives. 

In summary, the anions of group 14 metalloles (C4E rings) have either localized nonaromatic or delocalized aromatic structures, depending of the metal E, Si vs Ge and Sn, and on the substituents, methyl vs phenyl group. As pointed out by West and coworkers198, structural studies of metallole anions and dianions of this kind with different substituents will be of value. Additionally, it should be noted that experimentally observed structures in the solid state for silole and germole dianions are greatly influenced by the nature of the alkali metal counterion. 

Alkali metal reduction of dihalide precursors is shown to be a valuable route to various silole and germole dianions in solution. Crystal structure determinations for [K(18-crown-6)+h(C4Me4Si2 ] and the dimer [K4(18-crown-6)3][C4Me4Ge]2 are consistent with the presence of delocalized jr-systems and with -bonding modes for all of the potassium cations. 

Heterobinuclear complexes featuring the bridging germole dianion ligand have been described (equation 45)59,60. 

An example of rj5 bonding type is evident in the case of the bis(germole dianion) complex [K4(18-crown-6)]3[C4Me4Ge]2 (Figure 7)21. 

The X-ray structure determination of the germole dianion tp5-Li.TMEI)A tp5-I.i11 21ij1 -Li11 /2IEI4C4GCI36 showed three lithium cations around one germole ring in the i]1, rj5 and rj5 sites (Figure 9). 

Silole and Germole Dianions and their Dilithium Derivatives Are they Aromatic ... 

Keywords Ab initio calculations / Aromaticity / Germole Dianion / Silaaromatics / Germaromatics... 

Summary According to structural, thermodynamic, electronic, and magnetic criteria silole and germole dianions show indications of cyclic delocalization. The degree of aromaticity in the silole- l(Si) and germole dianions l(Ge) is of the same magnitude as that in the cyclopentadienyl anion. 

In this paper we report on our studies of the bonding in the free silole and germole dianions and their lithium derivatives using ab initio quantum mechanical methods [5], Several criteria for aromaticity, suggested recently by Schleyer et al. [6], were evaluated to test the degree of delocalization in Group IVa metallole dianions. 

The silole- l(Si) and the germole dianions l(Ge) are calculated to be planar (inner-cyclic dihedral angle S = 0°, see Table 1), The structural data, summarized in Table 1, clearly indicate the occurence of cyclic delocalization in the dianions. Thus, the C-C bond distances in the butadiene part of the... 

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