199731-66-3Relevant academic research and scientific papers
Oxaferrocene cryptands as efficient molecular switches for alkali and alkaline earth metal ions
Plenio, Herbert,Aberle, Clemens
, p. 5950 - 5957 (1997)
The reactions of 3,4-diphenylcyclopent-2-en-1-one, cyclopent-2-en-1-one, 3,4-dimethylcyclopent-2-en-1-one, and 2,3,4,5-tetramethylcyclopent-2-en-1-one with various trialkylsilyl triflates (SiR3 = SiMe3, SiEt3, SiMe2tBu, SiiPr3) result in the formation of the respective cyclopentadienyl silyl ethers in virtually quantitative yields. The reactions of these cyclopentadienes with n-BuLi and FeCl2 give the respective 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 SiMe2tBu protection (NBu4F·3H2O in CH3CN). Carrying out the deprotection in the presence of carbon electrophiles leads to the respective ferrocenyl alkyl ethers in excellent yields. Using 1-chloro-2-tosylethane results in 1,1′-bis(2-chloroethoxy)-3,3′,4,4′-tetraphenylferrocene which was converted into 1,1′-bis-(2-iodoethoxy)-3,3′,4,4′-tetraphenylferrocene 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 ferrocene cryptands 23, 24, and 25 were generated as the 1 + 1 products in yields of 67-80%. The coordination of alkali and alkaline earth metal ions within the cavities of these ferrocene cryptands results in large 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 stability 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 × 106.
