Synthesis, X-ray crystal structure, and reactivity of ternary complexes of crown ethers, organic π-acceptors, and salts

Abstract

Benzo- and dibenzo-18-crown-6 (1) and (2) form charge-transfer complexes with tetracyanoethylene (TCNE) in chloroform with association constants of 2.6 ± 0.2 and 4.5 ± 0.4 l mol^–1. In the presence of 1 equiv. of t-butylammonium perchlorate (Bu^tNH₃ClO₄) a solid ternary complex of (2), TCNE, and Bu^tNH₃ClO₄ is formed. Single-crystal X-ray analysis of a similar ternary complex of (2), Bu^tNH₃ClO₄ and 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) revealed the close proximity of the perchlorate anion and DDQ. Ternary complexes of TCNE, crown ethers (1)–(3), and salts with nucleophilic anions (Br^–, Cl^–, and F^–) react to give the TCNE^–· radical anion as proven by e.s.r. spectroscopy. In the presence of water and/or oxygen 18-crown-6 (3), TCNE, and Bu^tNH₃Br react to yield the 18-crown-6·Bu^tNH₃(NC)₂CC(CN)O complex.