Germanium-carbon double bonds

The existence of a germanium-carbon pjr-pjr double bond in the intermediate complex is likely. The intermediate was not isolated as such, but as its dimer. Compounds containing a carbon-germanium double bond were prepared by Satg6 and coworkers59, like the fluorenylidenedimethylgermanium, where stabilization arises from change transfer in the aromatic system. 

Although no 73Ge NMR spectra of stable doubly bonded germanium compounds have been recorded, NMR chemical shift data for the heteroatom of the double bond are available these are listed in Table II. The chemical shift of the, sp2-hybridized carbon atom of dimesitylneopentylger-mene (entry 1, Table II), without any polar substituents, falls at 8 124.2.26 The chemical shifts of the boron-substituted sp2-hybridized carbon atoms of two stable germenes (entry 2, Table II) fall in the upfield region of the... 

Recently, Schleyer and co-workers reported a theoretical study on the stabilities and geometries of a series of carbonyl type compounds, R2M=0 (M = C, Si, Ge, Sn, Pb R = H, CH3), and those of carbene type isomers [R(RO)M ] as shown in Table II.15 These results show that in (CH3)2 M=0 series the carbene type structure is more stable than the double bond type structure in the case of germanium, tin, and lead, unlike the case of carbon in which the double bond structure is preferred. 

The germabenzene species 15 reacts in two different fashions with a variety of substrates to give cylcoaddition products (Scheme 7).30 With MesCNO and 2,3-dimethylbutadiene, 15 behaves similarly to a compound with a single Ge-C double bond, whereas in reactions with styrene and phenylacetylene, 15 behaves as a 1-germabuta-l,3-diene to give Diels-Alder-type adducts. The germanium-carbon doubly bonded species 23 reacts with nitriles in several different ways, including as a 1,2-dipolar species with Bu CN, as a 1,4-dipolar species with PhCN, and as a base with various /3-functionalized nitriles (Scheme 8). 

The germanium-carbon double bond in germene 53 was found to undergo an interesting thermal dissociation (Scheme 22). When the benzene-rf6 solution of germene 53 was... 

Raasch has reported that the thermolysis of a ketenedithioacetal resulted in the dissociation into the corresponding thioketene and thioketone56. It should be noted that it is not the retro[2+2]cycloaddition similar to the carbon analogue, but the cleavage of the germanium-carbon double bond that has taken place in the thermolysis of germene 53. 

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