Structural Study of Mismatched Disila-Crown Ether Complexes

Abstract

Mismatched complexes of the alkali metals cations Li + and Na + were synthesized from 1,2-disila[18]crown-6 (1 and 2) and of K + from 1,2,4,5-tetrasila[18]crown-6 (4). In these alkali metal complexes, not all crown ether O atoms participate in the coordination, which depicts the coordination ability of the C-, Si/C-, and Si-bonded O atoms. Furthermore, the inverse case-the coordination of the large Ba 2+ ion by the relatively small ligand 1,2-disila[15]crown-5-was investigated, yielding the dinuclear complex 5. This structure represents a first outlook on sandwich complexes based on hybrid crown ethers.

Alkaline Earth Metal Template (Cross‐)Coupling Reactions with Hybrid Disila‐Crown Ether Analogues

“…In addition, 29 Si{ 1 H} NMR spectroscopy revealed highfield chemical shift and a single resonance at 11.5 ppm is found. This value compares well to the free ligand V and also to related metal‐free disila‐ligand systems . The problem so far is that a significant amount of the cryptand remains in the oily residue after conversion, so no further coordination chemistry could be performed yet.…”

“…This enables the formation of [Sr(1,2,10,11‐tetrasila[18]crown‐6)I] + fragments to build infinite chains along [001] which is most likely the driving force for crystallization. The O Si ⋅⋅⋅Sr 2+ distances in 4 a compare well to those in compound 3 a and [Sr(1,2‐disila[18]crown6)I 2 ] …”

“…Given that the understanding of the Si−O bond was established in this case, research in the field of coordination chemistry with cyclosiloxanes and related ligand systems showed clearly that these effects have to be taken into account. Nonetheless, the coordination chemistry turned out to be very suitable for early Group 1 and 2 metal ions, especially within disila‐ligands, which provide more suitable bite angles than cyclosiloxanes of D n type (D=Me 2 SiO, n =6, 7) . The nature of a cation, which shall be complexed within siloxane moieties, is preferably hard .…”

Hybrid Disila-Crown Ethers as Hosts for Ammonium Cations: The O–Si–Si–O Linkage as an Acceptor for Hydrogen Bonding

“…Even in VT NMR experiments, subsequently cooling the solution to 190 K did not result in an inequivalence of the SiMe 2 groups. The respective NMR shifts are in the range of sodium and potassium metal ion complexes of disila-crown ethers [11,14].…”

“…Simple substitution of -SiMe 2 -units with -Si 2 Me 4 -units in a residuary -C 2 H 4 O-framework yields framework yields disilane-bearing ligands with a respectable coordination ability very close to their organic analogs. Alkali and alkaline earth metal salts could easily be coordinated by ligands of this class, so the coordination ability of siloxane compounds should be reconsidered [11][12][13][14][15]. However, the discussion around siloxane bonding is not restricted to the coordination of Lewis acids and includes the ability to form hydrogen bonds.…”