Anions germole

Cyclic Anions (Silole and Germole Anions and Dianions) 91... 

The silole and germole anions have been a topic of interest for quite some time, with initial theoretical studies of the silole anion dating back to 1983.198 The following narrative provides a brief glimpse into this area. 

Siloles, germoles, stannoles, and plumboles have been extensively reviewed.180 The aromaticity of these systems is still under scrutiny. In the study, the cyclopentadienyl anion had the highest aromatic character, with a NICS value of —14 and a Bird index of 100. Structures 138 and 139 also showed high and similar aromaticity indices (Scheme 59). For the planar silacyclopentadienyl anion 138, the NICS value is —10.2 and the Bird index 80, while the values for anion 139 are —10.9 and 77, respectively. 

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. 

The substitution of halogen by metal was also used to prepare metalloyl anions and, more specifically, the dianions of germoles (equation 21)34-37. 

In the particular case of germoles (C4Ge rings), the corresponding anions (MLi, MK) had either a localized non-aromatic structure with a negative charge localized on ger-manium or delocalized aromatic strucmre " , depending on the nature of the metal and the substituents. 

X-ray structural studies of the anions of germoles have recently stimulated a great deal of interest . Crown ethers (12-crown-4 for Li and 16-crown-6 for K) were used in monometallation reactions, giving free germacyclopentanienide ions . They have a non-aromatic ring with a pyramidal germanium center (Figure 5). 

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. 

The calculations support unequivocally the notion that dianions of germoles and siloles are highly delocalized and that the degree of aromaticity in these molecules is nearly as large as in the classic aromatic cyclopentadienyl anion.[10]... 

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