Cyclic diynes with tetramethyldisilyl groups in the bridges. Syntheses andproperties

A series of cyclic diynes (8-15) with tetramethyldisilyl groups as bridging units have been synthesized from alpha,omega-bis(chloromethyl)diynes and 1 ,2-dichloro-1,1,2,2-tetramethyldisilane with lithium in the presence of cat alytic amounts of biphenyl. X-Ray investigations of single crystals of 8-14 reveal a twisted-chair conformation for 9-11 and 14, and a twisted half-ch air conformation for 8 and 12, whereas 13 adopts a twisted-boat conformatio n in the solid state. The He(I) photoelectron spectra of 8-14 reveal ioniza tion energies between 8.5-10 eV for the ionization processes from the pi-or bitals.