Thermal reactions of 1,2-dimetallacyclohexa-3,5-dienes (1-3) with tetracyanoethylene (TCNE) were investigated. The reaction of 1,2-disilacyclohexa-3,5-diene (1) with TCNE mainly gave 4-amino-5,6-dicyano-2,2,11,11-tetramethyl-1,8,9,10-tetraphenyl-3-aza-2, 11-disilatricyclo[6.2.1.03,7]undeca-4,6,9-triene through a charge-transfer complex. The reaction of 1,2-digermacyclohexa-3,5-diene (2) with TCNE afforded 4-amino-5,6-dicyano-2,2,11,11-tetramethyl-1,8,9, 10-tetraphenyl-3-aza-2,11-digermatricyclo[6.2.1.03,7] undeca-4,6,9-triene. 2,2,3,3-Tetracyano-7,7-dimethyl-1,4,5,6- tetraphenyl-7-germabicyclo[2.2.1]hept-5-ene was also detected. On the other hand, 1-germa-2-silacyclohexa-3,5-diene (3) reacted with TCNE to give 4-amino-5,6-dicyano-2,2,11,11-tetramethyl-1,8,9,10- tetraphenyl-3- aza-11-germa-2-silatricyclo[6.2.1.03,7] undeca-4,6,9-triene, 4-amino-5,6-dicyano-2,2,11,11-tetramethyl-1,8,9,10- tetraphenyl-3-aza-11- germa-2-silatricyclo[6.3.01,8 .03,7]undeca-4,6,9- triene, and 2,2,3,3-tetracyano-7,7-dimethyl-1,4,5, 6-tetraphenyl-7- germabicyclo[2.2.1]hept-5-ene as main products. The mechanism of the formation of new heterocyclic compounds through electron-transfer reactions of 1,2-dimetallacyclohexa-3,5-dienes with TCNE is discussed. © 2003 Elsevier Science B.V. All rights reserved.