CYCLIC DIYNES WITH SILICON IN THE BRIDGES - STRUCTURAL AND PHOTOELECTRON SPECTROSCOPIC INVESTIGATIONS

The structures of 6-isopropylidene-1, 1-dimethyl-1-silacyclodeca-3,8-d iyne (2), yl-1,6-disilabicyclo[4.4.4]tetradeca-3,8,12-triyne (4), and ,2,3,3-hexamethyl-1,2,3-trisilacyclodeca-4,9-diyne (6) have been inves tigated by means of X-ray crystallography. In 2 and 6 a chair conforma tion is adopted in the solid state. In 4 the three butyne groups are t wisted around the Si-Si axis against one another. The torsion along th e triple bond axis (Si-CH2...CH2Si) amounts to 29.0(1)degrees. The He( I) photoelectron (PE) spectra of 2 and 6 together with those of 1,1-di methyl-1-silacyclodeca-3,8-diyne (1), 1,1,6,6-tetramethyl-1,6-disilacy clodeca-3,8-diyne (3), 1,2,2-tetramethyl-1,2-disilacycloundeca-3,10-di yne (5), and ,2,2,3,3-hexamethyl-1,2,3-trisilacycloundeca-4,10- diyne (7) have also been recorded. The PE spectra were interpreted on the ba sis of results from SCF MO calculations (3-21G). They reveal a smalle r splitting of the pi-bands in 1-3 as compared to cyclodeca-1,6-diyne. In the PE spectra of 5-7 we encountered a strong interaction between the silicon chain and the in-plane pi-orbitals.