Construction of Inorganic Crown Ethers by s‐Block‐Metal‐Templated Si−O Bond Activation

Abstract

We herein report the synthesis,structures,coordination ability,and mechanism of formation of silicon analogs of crowne thers.A no ligomerization of 2 D 2 (I)( 2 D n , = (Me 4 Si 2 O) n )w as achieved by the reaction with GaI 3 and MI x (M = Li, Na, Mg, Ca, Sr). In these reactions the metal cations serve as template and the anions (I À /[GaI 4 ] À )a re required as nucleophiles.I nc ase of MI x = LiI, [Li( 2 D 3 )GaI 4 ]( 1)i s formed. In case of MI x = NaI, MgI 2 ,C aI 2 ,a nd SrI 2 the compounds [M( 2 D 4 )(GaI 4 ) x ]( M = Mg 2+ (3), Ca 2+ (4), Sr 2+(5)a re obtained. Furthermore the proton complex [H( 2 D 3 )]-[Ga 2 I 7 ]( 6)w as isolated and structurally characterized. All complexes were characterized by means of multinuclear NMR spectroscopy, DOSY experiments and, except for compound 3, also by single crystal X-ray diffraction. Quantum chemical calculations were carried out to compare the affinity of M + to 2 D n and other ligands and to shed light on the formation of larger rings from smaller ones.

Siloxane Coordination Revisited: Si−O Bond Character, Reactivity and Magnificent Molecular Shapes

“…H + and Li + are coordinated by Si 6 [9]crown‐3 ( 2 D 3 ) instead of [12]crown‐4 (see 50 and 51 ) and Na + , Mg 2+ , Ca 2+ , Sr 2+ are coordinated by Si 8 [12]crown‐4 ( 2 D 4 ) (see 52 – 55 ) instead of [3n]crown‐n (n=5, 6) according to the solid state structures (Figure 24). DOSY (=diffusion ordered spectroscopy) experiments confirm these structures in solution, 29 Si NMR shifts are given in Table 4 [174] . Using MeCN as a donor solvent readily removes the respective metal centre from the ligand.…”

“…Especially 2 D 4 is found to coordinate much stronger. Hence, these crown ethers also exhibit a macrocyclic effect, though to a less extent than observed for organic crown ethers [174] …”

“…2 D 2 /s‐block metal iodide/gallium(III)iodide Lewis acid systems have been established which made the synthesis of such systems possible (Scheme 8). [174] Combining both, sufficient Lewis acidity of an early s‐block metal ion and the in‐situ generated, small WCA [GaI 4 ] − were the key to find access to these new all‐silicon versions of crown ethers. The cation recognition of these systems is substantially different to that of organic crown ethers, though.…”

Offsets between hyperconjugations, p→d donations and Pauli repulsions impact the bonding of E–O–E systems. Case study on elements of Group 14

“…Special attention has been paid to siloxanes, [16][17][18][19][20][21][22] owing to their ubiquity in nature as constituent parts of silicates, 23 but also for their widespread applications in day-to-day life in fields such as material science, 24,25 catalysis, [25][26][27] cosmetics 28 and so forth. Various theoretical 6,7,[29][30][31][32][33][34][35][36][37][38] and experimental 22,[39][40][41][42][43] studies regarding the nature of the Si-O bond were mainly influenced by the conceptual thoughts of two different bonding schools, those supporting the ionic character of the Si-O-Si linkage 36,37 versus the advocates of the covalent nature of Si-O bonding, 44,45 that often culminated in contrasting opinions. 37 Yet a recent paper of Grabowsky and co-workers 38 stressed on the basis of a comprehensive bond-index study that these apparently antipodal concepts are rather complementary as both the ionicity and the covalency of Si-O-Si units increase simultaneously with angle widening.…”

Aufbau anorganischer Kronenether durch s‐Block‐Metall‐templatgesteuerte Si‐O‐Bindungsaktivierung

“…Diese wird bei 16.6 ppm beobachtet und Abbildung 3. Strukturvergleich von einem Erdalkalimetall-sowie einem Protonenkomplex eines anorganischen Kronenethers [86]. Die Molekülstrukturen von 4 (links) und 6 (rechts) sind auf das anorganische Gerüst reduziert.…”