Germoles—

Organometallic chemistry of silole and germole, recently dominated by the -q species, tends to enhancement of the range of the representatives. Cases of the TiVSi, Ge) coordination in the pure and mixed situations are known as well. 

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. 

Metallocyclopentenes are frequently formed in photochemical reactions of the Group 14 metal alkyls or catenates in the presence of dimethylbutadiene. This class of compound also has an extensive photochemistry82. For example, photolysis of 51 (R = H or Me) produced the allylic alcohols 52 and 53 and, for R = H, 54. These alcohols could be dehydrated over AI2O3 to give the germole 55 along with other diene compounds. 

The synthesis and reactivities of germoles have been well documented and new aspects of their chemistry have been developed.17-25 Several spirocyclic species have been prepared including the l,l -spirogermole 7, as shown in Equation (14),21 and the compounds 8-10, as shown in Scheme l.20... 

The direct reduction of organogermanium halides using LiAlH4 is well known.95,98-112 Several species of interest have been prepared by this method including the germole 35 (Equation (79)),100 the mesityl derivative 36 (Equation (80)),101 the supermesityl derivative 37 (Equation (81)),102 and the optically active species 38 (Scheme ll),103 39 (Equation (82)),104 40 (Equation (83)),105 and 41 (Scheme 12).106... 

The synthesis of alkali salts of the sterically encumbered germole 98 (Equations (159) and (160)),18 as well as the dilithio salt of tetraphenylgermole 99 (Equation (161)),19 have been reported. The latter species crystallized in two isomorphic forms (99a and 99b, Figure 6) and the dianion was shown to be aromatic. 

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... 

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. 

Photolysis of diazidogermacyclopentane 29 gave the germylene 30 and the germole 33 as main products,36 but also the two germadienes 31 and... 

Photochemical rearrangements of transient germadienes 3136 and 3236 have been evidenced from the corresponding germole or germylene (see Section II,A,6). 

Dimesityl- and dibutylgermylenes react with acetylene in the presence of a catalytic amount of palladium complexes to yield the corresponding C-unsubstituted germoles (85) and compound (86). When acetylene was bubbled into a toluene solution of hexamesitylcyclotrigermane in the presence of Pd(PPh3)4 at 80 °C, 1,1-dimesitylgermole was obtained in 85% yield (Eq. 10). ° ... 

Space precludes an extensive survey of silicon, germanium, tin and lead substituted derivatives of cyclopentadiene (the siloles and analogues). Until 1979, few plumboles were known (79RTC437), but now, with the siloles, germoles and stannoles, they represent one of the most extensively studied areas of Group IV substituted heterocyclic chemistry. The references prefacing Section 1.20.9 cover reviews for this section. 

Flash vacuum pyrolysis of the silacyclopentene (121) affords 1,1-dimethylsilole. Though it dimerizes below room temperature, it can be trapped as an adduct with maleic anhydride and can be regenerated by a retro Diels-Alder reaction of the dimer (Scheme 1951 (81JOM(209)C25). It is also formed from the peroxidation of l,l-dimethylsilacyclopent-3-ene, followed by reduction to the cyclopent-4-ene-3-ol and catalyzed vacuum flow dehydration (Scheme 196) (81JOM(216)32l). The germole can be prepared similarly <81JOM(2lo)C33>. 

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