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.