Synthesis and structure of the silylated benzene radical anion salts [K([18]crown-6){C6H4(SiMe3)2-1,4}] and [K([18]crown-6)(THF)2][C6H2(SiMe3)4-1,2,4,5]

The crystalline compound K(18]crown-6){C₆H₄(SiMe₃)₂-1,4}] (1) was prepared by the low-temperature reduction of the para-disilylated benzene with K/18]crown-6 in toluene followed by recrystallisation from the same solvent. Reduction of 1,2,4,5-tetrasilylated benzene with 2(K/18]crown-6) in toluene produced a hydrocarbon-insoluble powder identified as the dianionic derivative K(18]crown-6)]₂C₆H₂(SiMe₃)₄-1,2,4,5)] (2), which upon crystallisation from THF/Et₂O yielded K(18]crown-6)(THF)₂]C₆H₂(SiMe₃)₄-1,2,4,5] (3). An X-ray diffraction study revealed that 1 comprised a contact ion pair with the crown-encapsulated K cation η⁵-connected to the planar ring of the substituted benzene radical anion, while 3 contained a well separated cation and anion.