Silicon bridged cyclophanes

SCHEME 16.37 2-Pyrone cycloaddition to silicon-bridged cyclophane. 

The cyclophane 12 bridged by two silicon atoms exhibits two absorption bands with maxima at 223 nm (e = 18,400) and 263 nm (e = 22,400). Similar to 12, two absorption bands with maxima at 223 nm (e = 25,000) and 254 nm (e = 23,500) were observed for the cyclophane 17 bridged by two germanium atoms. On the other band, the cyclophane 22 bridged by two tin atoms shows an absorption band... 

A decrease in interarene distances a and b is also observed, when a chromium atom is bound inside the cavity of the cyclophane (Fig. 34) [56, 58]. Replacement of a bridging carbon in 8 with silicon increases the interarene distances substantially therefore inclusion of a chromium atom gives almost the same geometric parameters as were observed for 52 (Fig. 34) [56, 58]. No X-ray structure is known for 10, but from its radical cation 56, which shows decreased interarene distances compared to 55 the benzene rings are still considerably distorted into boat forms (Fig. 34) [54, 125]. 

The first [2.2]paracyclophane bridged by silicon, tetrasila[2.2]paracyclophane (7) was prepared and characterized by Sakurai and coworkers with the aid of UV, IR, H, and Si NMR spectra (S = 6.45) together with X-ray crystallographic data. Cyclophane 7 displays a strong ct-tt mixing between Si—Si bonds and aromatic rings as evidenced... 

---