The first stable germene: a compound with a germanium-carbon double bond

Abstract

There is now a great deal of interest in group 13, 14, and 15 elements in low coordination states.1 Since 1981, several new compounds of the type M=M/ (M and M': group 13, 14, and 15 elements) withbonds have been reported. In organogermanium chemistry, the first stable derivatives with a sp2-hybridized germanium have only been prepared very recently: they are the digermenes R2Ge=GeR22 (R = bis(trimethylsilvl) methyl,23 2,6-dimethylphenyl,2b 2,6-diethylphenyl2c), the germaphosphene R2Ge=PR,3a (R = mesityl, R' = 2,4,6-tri-rert-butylphenyl), and the germaimines R2Ge=NR,3b (R = (Me3Si)2N, R' = N=C-(R,,)(R,,/))• Germenes R2Ge=CR2' have long been speculated as reactive intermediates and could only be characterized by trapping reactions.lc,d'4'5

The reactions of germenes generated thermally from pivaloyl- and adamantoyltris(trimethylsilyl)germane with 1,3-butadienes

“…Again, no other isomers were detected in the reaction mixture. The structures of products 5 and 6 were confirmed by mass, and 1 H, 13 C, 29 Si NMR spectroscopic analysis (see Section 3).…”

“…The methods reported for the synthesis of the germenes mainly involve the following routes: (1) reaction of germylenes with carbenes [8], (2) Peterson-type reactions [9], (3) [2+2] cycloreversion of four-membered rings [10,11], and (4) defluorosilylation [12] or defluorolithiation [13][14][15][16][17]. The range of the synthetic methods for the germenes is rather limited.…”

Detached crystal growth from melt by the axial heat processing technique

“…6) has showed a very sharp transition from Ge to C at the mechanically bonded Ge-C interface, indicating non-existence of a chemical bonding, no inter-diffusion. In addition, although indirect Ge-C bonding in compounds has been reported [34][35][36][37][38], unlike Si-C, no direct chemical Ge-C bond has yet been shown. This is related to p-electron interactions and main quantum numbers (n Si ¼ 3 and n Ge ¼ 4) of melts.…”

“…However, for elements with the main quantum number of n ¼ 4 or greater (e.g., germanium), the metallic melt is practically inert to carbon. Because of this reason, while Si wets with C well and a stable SiC compound can form, no direct Ge x C y compound has been reported, except for some indirect compounds [34][35][36][37][38].…”

New compounds with Ge/Ge and Ge/C multiple bonds

“…Similar to the digermenes, compounds with a Ge@C double bond, the germenes, have been known for a number of years [5]. In contrast, the synthesis -by addition of diarylgermylenes to both triple bonds of 1,3-diynes -and structural characterisation of the acetylene-bridged bis(germaethenes) 1 and 2 were realised only recently [6][7][8].…”