Insights into the Coordination Ability of Siloxanes Employing Partially Silicon Based Crown Ethers: A Comparative Analysis of s-Block Metal Complexes.

Herein we present the synthesis and coordination chemistry of the partially silicon based crown ether analogues 1,2,4,5-tetrasila-benzo[15]crown-5 (1) and 1,2,4,5-tetrasila[18]crown-6 (7). Stable complexes of alkali and alkaline earth metal iodides could be obtained showing the good coordination ability of these ligands. The complexes [M (1,2,4,5-tetrasila-benzo[15]crown-5)I] (M = Li (2), Na (4)) and [M (1,2,4,5-tetrasila-benzo[15]crown-5)I] (M = Mg (3), Ca (5), Sr (6)) were obtained by equimolar reaction of 1 with the respective alkali or alkaline earth metal iodide. Depending on the ionic radii of the respective cations, the coordination modes of the siloxane backbone are significantly different and could be well-represented by means of Si NMR spectroscopy. In addition, we were able to generate the unusual dinuclear complex [Ba(1,2,4,5-tetrasila[18]crown-6)I] (8) by reaction of 7 with BaI. All compounds were characterized via single crystal X-ray diffraction (XRD) analysis.