Abstract
AbstractCrystallization of potassium fluorenide or 9‐tert‐butylfluorenide [formed from potassium metal and fluorene or 9‐tert‐butylfluorene in tetramethylethylenediamine (tmeda)] from a mixture of tmeda, tetrahydrofuran (THF) and diethyl ether yields [K(tmeda)2][C13H9] (1) or {[K(THF)2][μ‐C13H8(tBu)][K(tmeda)][μ‐C13H8(tBu)]}∞ (2). Compound 1 is a monomeric solvated ion pair with one η5‐coordinated fluorenyl and two chelating tmeda ligands and crystallizes in the monoclinic space group C2/c. Compound 1 is an example of polymorphism in organo‐potassium compounds, as a polymeric structure of 1 obtained under slightly different crystallization conditions has been reported earlier. Compound 2 forms a polymeric chain with potassium coordinated to two anellated six‐membered rings from two bridging 9‐tert‐butylfluorenyl systems and alternatingly solvated by one chelating tmeda or two THF. The crystal system for 2 is monoclinic, space group P21/c. A comparative AM1 study on the fluorenyl and 9‐tert‐butylfluorenyl anion suggests a steric origin for the haptotropic potassium shift in 2. 1H‐ and 13C‐NMR data for 1 and 2 as well as for 9‐tert‐butylfluorene are reported.
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