Compounds of Germanium and Tin, 2l. A Tetraaryldigermene with a Short Germanium‐Germanium Double Bond and a Nearly Planar Environment of Both Germanium Atoms

Abstract

Treatment of GeC1, . dioxane with the Grignard reagent RMgBr (R = 2-tBu-4,5,6-Me3C6H) furnishes the tetraaryldigermene R2Ge=GeR2 (8). X-ray structure-analysis of 8 reveals a short Ge=Ge double bond, a nearly planar environment of both germanium atoms and extremely widened C-Ge-C angles of 128". In solution, 8 dissociates into two germylene molecules R2Ge: which can be trapped with oxygen or by [4 + 11 cycloaddition reactions with l,4-dihetero-1,3-dienes. A similar cycloadduct of a stannylene was obtained by thermolysis of (R;SII)~ (R' = 2,4,6-iPr3C6H2), in the presence of a 1,4-diazabutadiene and characterized by an Xrdy structure-analysis.The double-bond system of alkenes is usually characterized by a planar arrangement of the substituents. Twisting of the C=C double bond can only occur in the presence of very bulky groups. However, homonuclear double bonds between the heavier homologues of carbon exhibit a different behaviour and, in particular, digermenes and distannenes show marked trans folding of the substituentsc21. Thus, for example, trans bent angles y~ of 35 to 47" have been calculated for H2Ge=GeH2, the parent compound of the digermene~ ['-~]. Such calculations are corroborated by experiment: X-ray-crystallographic studies of the tetraalkyland tetraarpldigermenes 1-3 have in each case revealed some degree of trans pyramidalization where, in addition, a slight twisting of the double bond by the angle z may also occur in order to reduce the steric overcrowding (Scheme 1y3.8-101. We have now found that a similar planar arrangement of the substituents about the Ge=Ge double bond is not only realized with electropositive groups, but can also be achieved in a tetraaryldigermene by judicious choice of the orrho-alkyl groups. Thus, the reaction of the germanium(T1) chloride . dioxane adduct with the Grignard reagent 7 resulted in the formation of the digermene 8, which was isolated in good yield in the form of orange-yellow, air-sensitive crystals. An X-ray crystal-structure analysis of 8 revealed some interesting features (Figure 1).The steric influence of the bulky ortho-ter/-butyl groups does not lead to a stretching of the Ge=Ge double bond as is the case in compounds 2 and 3. Instead, the system responds to possible interactions between these groups by a twisting of z = 20.4". The short germanium-germanium separation of 225.2 pm is also surprising when one considers that the analogously substituted distannene R2SnSnR2 exhibits a very large tin-tin separation, which IS appreciably larger than even a normal tin-tin single-bond Even more unusual are the completely planar environments of both germanium atoms, the two @so-carbon atoms and the respective other gerinanium atom being exactly coplanar (angular sums in each case 360").On the other hand, the largest displacement parameters UAGe) = 84 pm2 > 1/2( U, I + U33) = 38 pm' can lead toChevn. Beu./Recueil1997,130, [735][736][737][738]

Molecular structures of new compounds with Ge=C and Sn=C double bonds [1]

“…Compound 5 is indeed stable for unlimited SCHEME 2 SCHEME 1 times in the solid state but dissociates into the germylene molecules 6 in solution [12]. Reaction of 6 with the cryptodiborylcarbene 7 [13a-f] in toluene at room temperature furnishes the germene 8 within a few minutes; this product can then be isolated in 62% yield.…”

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

“…This result is surprising since a similar digermene with 2-tert-butyl-4,5,6-trimethylphenyl groups possessing an additional methyl group in the ortho-positions exhibits a very short Ge@Ge bond of 225.1 pm and almost planar environments around the two germanium atoms in spite of the increased steric demands [9]. The bonding parameters determined for 4 again clearly show that a correlation with the steric requirements of the substituents is hardly possible [3].…”

Multiply Bonded Germanium, Tin and Lead Compounds

“…Tetraalkyldigermene 1 is synthesized by the reaction of a dichlorogermylene-dioxane complex with a Grignard reagent or by the reaction of a stable diaminogermylene with an organolithium reagent (Scheme 2) 14 . Tetraaryldigermenes are also prepared by the treatment of the corresponding dihalogermylenes with an appropriate organometallic reagent (Scheme 2) 13,20 .…”

“…Therefore, it should be important to make a systematic comparison of the structural features of (E)-10 with other digermenes, the results of which are summarized in Table 2 15,17,19,20,32 . Although the twist angle (γ ) along the Ge-Ge axis and the bent angles (the angle δ formed by the C-Ge-C plane and Ge-Ge axis) of (E)-10 are 12, 16 and 18°, respectively, being in the range of those for the previously reported digermenes, the Ge(1)-Ge(2) bond length [2.416(4)Å] of digermene (E)-10 is remarkably longer than those for the previously formed digermenes [2.…”

“…On the other hand, (2-t-Bu-4,5,6-Me 3 C 6 H) 2 Ge=Ge(2-t-Bu-4,5,6-Me 3 C 6 H) 2 41 was also synthesized as a stable digermene and was characterized by X-ray crystallography 20 SCHEME 15 Furthermore, as described in the previous section, the spectroscopic observation of an equilibrium between a digermene and germylenes was first achieved in the case of highly crowded digermene (E)-10 by UV-vis spectroscopy (see Scheme 7) 23 .…”