5 years ago

Crown Ether Complexes of Alkali-Metal Chlorides from SO2

Crown Ether Complexes of Alkali-Metal Chlorides from SO2
Stefan S. Rudel, Magnus R. Buchner, Kirsten Reuter, Florian Kraus, Carsten von Hänisch
The structures of alkali-metal chloride SO2 solvates (Li–Cs) in conjunction with 12-crown-4 or 1,2-disila-12-crown-4 show strong discrepancies, despite the structural similarity of the ligands. Both types of crown ethers form 1:1 complexes with LiCl to give [Li(1,2-disila-12-crown-4)(SO2Cl)] (1) and [Li(12-crown-4)Cl]⋅4 SO2 (2). However, 1,2-disila-12-crown-4 proved unable to coordinate cations too large for the cavity diameter, for example, by the formation of sandwich-type complexes. As a result, 12-crown-4 reacts exclusively with the heavier alkali-metal chlorides NaCl, KCl and RbCl. Compounds [Na(12-crown-4)2]Cl⋅4 SO2 (3) and [M(12-crown-4)2(SO2)]Cl⋅4 SO2 (4: M=K; 5: M=Rb) all showed S-coordination to the chloride ions through four SO2 molecules. Compounds 4 and 5 additionally exhibit the first crystallographically confirmed non-bridging O,O′-coordination mode of SO2. Unexpectedly, the disila-crown ether supports the dissolution of RbCl and CsCl in the solvent and gives the homoleptic SO2-solvated alkali-metal chlorides [MCl⋅3 SO2] (6: M=Rb; 7: M=Cs), which incorporate bridging μ-O,O′-coordinating moieties and the unprecedented side-on O,O′-coordination mode. All compounds were characterised by single-crystal X-ray diffraction. The crown ether complexes were additionally studied by using NMR spectroscopy, and the presence of SO2 at ambient temperature was revealed by IR spectroscopy of the neat compounds. Different class: The syntheses of the alkali-metal chloride SO2 solvates (Li–Cs; see figure) in conjunction with 12-crown-4 or 1,2-disila-12-crown-4 are described. The structures of the obtained complexes show large differences, despite the structural similarity of the ligands used.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/chem.201701174

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