Heavier analogs of 1,3-butadiene

Two recent remarkable experimental achievements in this field are the syntheses by Wei-denbruch and coworkers of the first stable tetrasila- and tetragermabutadienes, 52a327a and 52b327b, respectively. In the crystal, the l,2-Si=Si and l,2-Ge=Ge bond lengths are 217.5 pm and 235.7 pm, respectively, being longer than the Si=Si and the Ge=Ge 

Theoretical studies of butadiene analogs which contain one or more group 14 heavy atoms are limited to silabutadienes328,332-334 and germabutadienes335-337. A systematic theoretical study of the heavier analogs of butadiene is not yet available. 

2-Silabutadiene, H2C=SiH—CH=CH2 (54), is the most stable SiC 31 If, isomer, but 1-silabutadiene, H2Si=CH—CH=CH2 (55), and methylvinylsilylidene, H3CSiCH=CH2 (56), are by only ca 5 kcalmol-1 less stable332. 

Two possible isomers were studied for dimetallabutadienes 2,3-dimetallabutadiene, 57, M = Si328b and M = Ge337 and 1,4-dimetallabutadiene, 58, M = si3280,333,334 and M = Ge335. 

Miriam Kami, Yitzhak Apeloig, Jurgen Kapp and Paul von R. Schleyer 

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