Crystal structure of 2-ethenyl-4,4,7,7-tetrakis(2-tert-butyl-4,5,6-trimethylphenyl)- 5,8-diphenyl-3-aza-4,7-digermabicyclo[4.2.0]octa-2,5,8-triene— hexane (1:2), C71H91Ge2N · 2C6H14
Zeitschrift für Kristallographie - New Crystal Structures
Source of material The title compound results from the reaction of a acrylonitrile with the acetylene-linked bis(germaethene) R 2Ge(C6H5)C-C-C-GeR 2 (C 6 H 5 ), R = 2-t-Bu-4,5,6-Me 3 C 6 H, prepared from tetrakis (2-tert-butyl-4,5,6-trimethylphenyl)digermene and 1,4diphenylbuta-1,3-diyne, as yellow crystals, mp 459 K -464 K. Discussion The reaction of the acetylene-linked bis(germaethene) with 1,2-dicyanoethylene proceeds by [2+4] cycloaddition of one of the C-N bonds to the Ge=C and C-C bonds,
... followed by a [2+2] cycloaddition of the remaining Ge=C bond to the newly formed C=C bond to give a bicyclic compound. An unprecedented C-H activation of a tert-butyl and an aryl C-H bond leads finally to a hexacyclic compound via a tetracyclic product  . Acrylonitrile reacts similarly by [2+4] and [2+2] cycloadditions to furnish the bicyclic title compound. In this case, no C-H addition to the endocyclic C=N bond is observed. The title compound crystallizes with two molecules of n-hexane that serve merely to stabilize the lattice. The two n-hexane molecules (C72-C83) are disordered and were refined on two positions with occupancy factors of 0.5 each. With a sum of endocyclic angles of 357.5°for the four-membered ring and 714.4°for the six-membered ring both cycles are nearly planar. The smallest endocyclic angles occur at the two germanium atoms. Because of the steric bulk of the aryl groups all Ge-C-aryl bonds are slightly longer than the normal single bond length of 1.97 Å .