Abstract:

Cyclic diynes with tetramethyldisilyl groups as bridging units were synthesized from a,w-bis(chloromethyl)diynes and 1,2-dichloro-1,1,2,2-tetramethyldisilane with Li in the presence of catalytic amts. of biphenyl. X-ray studies of single crystals of the title compds. reveal a twisted-chair conformation for 1,1,2,2-tetramethyl-1,2-disilacycloundeca-4,9-diyne, 1,1,2,2-tetramethyl-1,2-disilacyclododeca-4,10-diyne, 1,1,2,2-tetramethyl-1,2-disilacyclotrideca-4,11-diyne, and 1,1,2,2,6,6,9,9-octamethyl-1,2,6,9-tetrasilacyclododeca-4,10-diyne, and a twisted half-chair conformation for 1,1,2,2-tetramethyl-1,2-disilacyclodeca-4,8-diyne and 1,1,2,2,6,6,7,7-octamethyl-1,2,6,7-tetrasilacyclodeca-4,8-diyne, whereas 1,1,2,2,6,6,8,8-octamethyl-1,2,6,8-tetrasilacycloundeca-4,9-diyne adopts a twisted-boat conformation in the solid state. The He(I) photoelectron spectra of the title compds. reveal ionization energies between 8.5-10 eV for the ionization processes from the p-orbitals.