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Abstract
Alkaline earth metal iodides were used as templates for the synthesis of novel silicon‐based ligands. Siloxane moieties were (cross‐)coupled and ion‐specific, silicon‐rich crown ether analogues were obtained. The reaction of 1,2,7,8‐tetrasila[12]crown‐4 (I) and 1,2‐disila[9]crown‐3 (II) with MgI2 yielded exclusively [Mg(1,2,7,8‐tetrasila[12]crown‐4)I2] (1). The larger Ca2+ ion was then employed for cross‐coupling of I and II and yielded the complex [Ca(1,2,7,8‐tetrasila[15]crown‐5)I2] (2). Cross‐coupling of I and 1,2,4,5‐tetrasila[9]crown‐3 (III) with SrI2 enables the synthesis of the silicon‐dominant 1,2,4,5,10,11‐hexasila[15]crown‐5 ether complex of SrI2 (3). Further, the compounds [Sr(1,2,10,11‐tetrasila[18]crown‐6)I2] (4), [Sr(1,2,13,14‐tetrasila[24]crown‐8)I2] (5), and [Sr(1,2,13,14‐tetrasila‐dibenzo[24]crown‐8)I2] (6) were obtained by coupling I, 1,2‐disila[12]crown‐4 (IV) or 1,2‐disila‐benzo[12]crown‐4 (V), respectively. Using various anions, the (cross‐)coupled ligands were also observed in an X‐ray structure within the mentioned complexes. These template‐assisted (cross‐)couplings of various ligands are the first of their kind and a novel method to obtain macrocycles and/or their metal complexes to be established. Further, the Si−O bond activations presented herein might be of importance for silane or even organic functionalization.
Highlights
It is well known for crown ethers to form coordination compounds with metal centers across a wide range of the periodic table
We report the synthesis of novel hybrid disila-crown ether moieties, which are accessible by alkaline earth metal-template synthesis
Instead, [Mg(1,2,7,8-tetrasila[12]crown-4)I2] (1) was obtained and, as can be seen from the molecular structure determined by single-crystal X-ray diffraction analysis (SC-XRD), the moiety of crown ether I is large enough to bind Mg2+ (Figure 1)
Summary
It is well known for crown ethers to form coordination compounds with metal centers across a wide range of the periodic table. 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 Dn type (D = Me2SiO, n = 6, 7).[22,23,24,25,26] The nature of a cation, which shall be complexed within siloxane moieties, is preferably hard.[13,27,28,29,30,31] In the case of the early alkaline earth-metal ions, even the commercially available cyclosiloxanes are able to dissolve salts characterized by a high lattice energy and stable complexes were obtained.[32] Soft cations like Rb+ and Cs+ so far relucted silyl ether coordination.[33,34] Overall, sila-ligands are suitable ligands for early s-block-metal coordination chemistry and opened a new chapter in host– guest chemistry over the years In this contribution, we report the synthesis of novel hybrid disila-crown ether moieties, which are accessible by alkaline earth metal-template synthesis. Please see the cited literature.[6,7,11,12,13]
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