Stable Alkali-Metal Complexes of Hybrid Disila-Crown Ethers

The complexation ability of hybrid disilane and ethylene containing crown ether ring systems was analyzed using 1,2-disila[12]­crown-4 (1), 1,2-disila­[15]­crown-5 (2), 1,2-disila[18]­crown-6 (3), and 1,2,7,8-tetrasila[12]­crown-4 (7). Alkali-metal complexes (Li+, Na+, K+) were obtained and analyzed via X-ray diffraction. The complex stability of [Li­(1,2-disila[12]­crown-4)]+ and [Li­(1,2,7,8-tetrasila[12]­crown-4)]+ was determined, in relation to the lithium complex of [12]­crown-4, by density functional theory (DFT) calculations employing the BP86/def2-TZVP level of theory. In solution, the exchange of lithium cations between pure [12]­crown-4 and hybrid [12]­crown-4 is on even terms, as has been shown from the relative binding affinity of compounds 1 and 7 by means of dynamic proton nuclear magnetic resonance (NMR) spectroscopy.