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

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.