OXAFERROCENE CRYPTANDS AS EFFICIENT MOLECULAR SWITCHES FOR ALKALI ANDALKALINE-EARTH METAL-IONS

The reactions of 3,4-diphenylcyclopent-2-en-1-one, cyclopent-2-en-1-on e, 3,4-dimethylcyclopent-2-en-1-one, and 2,3,4,5-tetramethylcyclopent- 2-en-1-one with various trialkylsilyl triflates (SiR3 = SiMe3, SiEt3, (SiMe2Bu)-Bu-t, (SiPr3)-Pr-i) result in the formation of the respectiv e cyclopentadienyl silyl ethers in virtually quantitative yields. The reactions of these cyclopentadienes with n-BuLi and FeCl2 give the res pective substituted ferrocenyl trialkylsilyl ethers in 48-57% yields, which are synthetic equivalents of hydroxyferrocenes as generated by a suitable cleavage protocol: SiMe3-protected ferrocene alcohols (CH3CN + 10% H2O + Na2CO3); SiEt3 (CH3CN + 10% H2O + Na2CO3 + NaF); and (SiM e2Bu)-Bu-t protection (NBu4F . 3H(2)O in CH3CN). Carrying out the depr otection in the presence of carbon electrophiles leads to the respecti ve ferrocenyl alkyl ethers in excellent yields. Using 1-chloro-2-tosyl ethane results in bis(2-chloroethoxy)-3,3',4,4'-tetraphenylferrocene w hich was converted into '-bis(2-iodoethoxy)-3,3',4,4'-tetraphenylferro cene in 89% yield, to be finally reacted with diazacrown ethers (diaza -12-C-4, diaza-15-C-5, diaza-18-C-6). In this manner the respective fe rrocene cryptands 23, 24, and 25 were generated as the 1 + 1 products in yields of 67-80%. The coordination of alkali and alkaline earth met al ions within the cavities of these ferrocene cryptands results in la rge anodic shifts of the redox potentials of the ferrocene units (23, E = +0.290 V; 23 + Ca2+, E = +0.670 V; 23 + Na+, E = +0.505 V; 24, E = +0.285 V; 24 + K+, E = +0.455 V) as determined by cyclic voltammetry. These anodic shifts are correlated with a decrease in the complex sta bility constant K of the respective metal ion complex (redox-switching effect) and in the case of 23 and Ca2+ amounts to a reduction of K by 3.4 x 10(6).