Title compounds of the type 2, 3, 5, 6-tetraphenyl-1, 4-di-X-1, 4-di-Y-1, 4-disilacyclohexa-2, 5- diene wherein X= Y= NMe2 (4); X= NMe2, Y= Cl (cis, trans-5); X= NMe2, Y= Me [(trans)-6] and X= t-Bu, Y= Cl (trans-8) were synthesized from Si2 (NMe2) 5Cl, sym-Si2 (NMe2) 4Cl2, sym-Si2 (NMe2) 4Me2, and sym-Si2Cl4 (t-Bu) 2, respectively, in the presence of diphenylacetylene at 200° C. Similarly the analogous title compound from the combination ...