Electronic properties, polymerization, and cycloaddition of 3,4,7,8-tetragermacycloocta-1,5-diyne and related compounds

Permethylated 3,4,7,8-tetragermacycloocta-1,5-diyne (1) and 3,4-disila-7,8-digermacycloocta-1,5-diyne (2) were prepared. The photoelectron spectra of 1 and 2 were compared with that of their tetrasila analogue 3. The first ionization energy decreases in the order 3 > 2 > 1. Charge-transfer spectra of 1-tetracyanoethylene (TCNE), 2-TCNE and 3-TCNE complexes were observed. In CH₂Cl₂ containing TCNE 1 underwent oligomerization to give its higher homologues, and in CH₃CN containing a catalytic amount of TCNE both 1 and 2 were polymerized to give the corresponding polymers almost quantitatively, whereas the sila analogue 3 was stable under these conditions. All compounds 1, 2 and 3 cycloadded to 2,3-dichloro-5,6-dicyano-1,4-benzoquinone to give the corresponding 1 : 1 adducts in a [2 + 6] manner.