Germyl migration

Entry 3 constitutes the first reported example of a metal vinylidene-mediated reaction involving a 1,2-germyl migration. The formation of germylated product is extremely rapid, in agreement with the high reactivity of alkynylgermanes. Both Au(III)- and Au(I)-salts catalyze the observed reaction therefore, a Au(I)-vinylidene mediated reaction mechanism is favored (Scheme 9.24). 

The reaction illustrated in equation 24 involves a series of 1,3-alkyl, silyl and germyl migrations between the metal-silylene and germylene transients formed subsequent to an a-elimination reaction initiated by the elimination of CO109. 

Base-free alkyl-substituted germyl(germylene)tungsten carbonyl complexes 37 and 38 were synthesized by the photolysis of digermyl complexes of tungsten 39 and 40 in benzene (equation 38). These complexes are formed by the 1,2-germyl migrations after the initial photodissociation of CO from 39 and 40146. 

In some of the carbene formation chemistry noted above, a secondary reaction has been observed. Thus, treatment of (>/5-C5II5)M(( ()) GeR3 (M = Mo, W, n = 3 M = Fe, n = 2) with bases such as LDA, MeLi etc., followed by alkylation with RX, resulted in the formation of a series of products derived from germyl migration to the cyclopentadienyl ring, [( 5-C5H4GeR3)M(CO) R] (equation 52)153-155. 

Mochida, K., Ginyama, H., Takahashi, M., and Kira, M., Photochemical reactions of digermanyl-substituted naphthalenes the germyl migration to the aromatic ring, /. Organomet. Chem., 553, 163, 1998. 

The authors proposed a mechanism for the demethanative coupling where Ge-C bond cleavage and Ge-Ge bond formation are attained by sequential a-CH3 and germyl to germylene migration steps via an intermediacy of metal-germylene species. 62b... 

FIGURE 70. Calculated transition states at MP2 of the 1,2-migration of silyl, germyl and stannyl substituents of radicals H3E-CH2X to H3EX-CH2 (X = CH2, NH, O E = Si, Ge, Sn). Bond distances are in A, angles in deg. The calculated activation energies (kcal mol 1) at QCISD//MP2 refer to the forward reaction ( A E1 i ) and the reverse reaction (A E ), respectively. Reproduced by permission of The Royal Society of Chemistry from Reference 190... 

Treatment of hydrogermanium cyclopentadiene transition metal complexes with LDA can lead initially to a competition between the deprotonation of the hydrogen linked to germanium or to the cyclopentadienyl ring, but a migration of the germyl group to cyclopentadiene was actually observed (equation 192)9. 

Intramolecular migration of the germyl group from the metal... 

In contrast to the alkyl, silyl, and germyl complexes, when E is Sn, not SnR3 but only one alkyl group on the Sn migrates to the phosphenium P to give a stannylene complex (39).23,34 Since the transition metal-phosphorus bond has considerable double-bond character (see below), the conversion from 36 to 39 corresponds to a double-bond migration from Fe=P to Fe=Sn. 

Antoniotti, P., Canepa, C., Tonachini, G. Theoretical studies on Wittig-type anionic migrations of alkyl, silyl and germyl groups. Trends in Organic Chemistry i095, 5, 189-201. 

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