Lewis base coordination versus cation-π interaction in monomeric and hexameric potassium thiolates

The synthesis and structural identification of a family of crown-ether-coordinated and crown-ether-free potassium thiolates are described. [Li(15-crown-5)(SCPh3)] (1), [K(18-crown-6)(SCPh3)(C6H6)(0.5)] (2), [K(18-crown-6)(SCPh3)(thf)(0.5)] (3), [K(dibenzo-18-crown-6)(SCPh3)(hmpa)0.5] (hmpa = hexamethylphosphoramide; 4), and [K(dibenzo-18-crown-6)(SCPh3)(tol)] (tol = toluene; 5) are available via metathesis of nBuLi or KH with triphenylmethanethiol in toluene, added crown ether, and respective Lewis donors. In the absence of crown ether, however, metathesis with NaH or KH and triphenylsilanethiol or triphenylmethanethiol in toluene leads to the hexameric aggregates [(NaSSiPh3)(6)(tol)(2)] (6), [(KSCPh3)6(hmpa)(2)].2 tol (7), and [(KSCPh3)6(tol)(2)] (8). It is shown that the strongly coordinating hmpa can ligate the hexameric framework in 7; employment of stoichiometric amounts of pyridine, 1,4-dioxane, or chelating pmdta (N,N,N',N',N "-pentamethyldiethylenetriamine) results in the isolation of toluene-coordinated 8. Compounds 1-8 were unequivocally identified by X-ray crystallography, H-1 NMR, C-13 NMR (depending on solubility), IR spectroscopy, and melting point. The monomeric formulations of 1-5 are clearly related to the ability of the appropriate crown ether to sequester the alkali-metal cation, thereby satiating much of its coordination environment. In contrast, aggregation is observed in the absence of crown ether (compounds 6-8), where the M6S6 hexameric core is stabilized through numerous cation-pi interactions with several of the 18 phenyl groups comprising the organic periphery and two donor molecules.