Cyclic Diynes with Silicon in the Bridges: Structural and Photoelectron Spectroscopic Investigations

The structures of 6‐isopropylidene‐1,1‐dimethyl‐1‐silacyclodeca‐3,8‐diyne ( 2 ), 1,6‐dimethyl‐1,6‐disilabicyclo[4.4.4]tetradeca‐3,8,12‐tryine ( 4 ), and 1,1,2,2,3,3‐hexamethyl‐1,2,3‐trisilacyclodeca‐4,9‐diyne ( 6 ) have been investigated by means of X‐ray crystallography. In 2 and 6 a chair conformation is adopted in the solid solid state. In 4 the three butyne groups are twisted around the SiSi axis against one another. The torsion along the triple bond axis (Si‐CH 2 ‐CH 2,/ Si) amounts to 29.0(1). The He(I) photoelectron (PE) spectra of 2 and 6 together with those of 1,1‐dimethyl‐1‐silacyclodeca‐3,8‐diyne ( 1 ), 1,1,6,6‐tetramethyl‐1,6‐disilacyclodeca‐3,8‐diyne ( 3 ),1,12,2,3,3‐hexamethyl‐1,2,3‐trisilacycloundeca‐4,10‐diyne ( 7 ) have also been recorded. The PE spectra were interpreted on the basis of results from SCF MO calculations (3–21G*). They reveal a smaller splitting of the π‐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 π‐orbitals.