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A Second Modification of Potassium Fluorenide and the Structure of Potassium 9‐ tert ‐Butylfluorenide: Effect of Crystallization Conditions and Substituents on Solid‐State Contact Ion Pair Interactions
Author(s) -
Janiak Christoph
Publication year - 1993
Publication title -
chemische berichte
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 0009-2940
DOI - 10.1002/cber.19931260716
Subject(s) - chemistry , monoclinic crystal system , potassium , tetrahydrofuran , steric effects , crystallization , crystal structure , crystallography , tetramethylethylenediamine , stereochemistry , medicinal chemistry , diethyl ether , organic chemistry , solvent
Crystallization 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 ][C 13 H 9 ] ( 1 ) or {[K(THF) 2 ][μ‐C 13 H 8 ( t Bu)][K(tmeda)][μ‐C 13 H 8 ( t Bu)]}∞ ( 2 ). Compound 1 is a monomeric solvated ion pair with one η 5 ‐coordinated fluorenyl and two chelating tmeda ligands and crystallizes in the monoclinic space group C 2/ 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 P 2 1 / c . A comparative AM1 study on the fluorenyl and 9‐ tert ‐butylfluorenyl anion suggests a steric origin for the haptotropic potassium shift in 2 . 1 H‐ and 13 C‐NMR data for 1 and 2 as well as for 9‐ tert ‐butylfluorene are reported.