Electronic nature of zwitterionic alkali metal methanides, silanides and germanides – a combined experimental and computational approach

Abstract

Zwitterionic group 14 complexes of the alkali metals of formula [E(SiMe2OCH2CH2OMe)3M], where E = C, Si or Ge and M = Li, Na or K, have been prepared, structurally characterized and their electronic nature was investigated by computational methods.

Strain‐Modulated Reactivity: An Acidic Silane

“…CH‐acidic fluorenes 4 and 5 as well as 2,6‐lutidinium‐BAr F 4 salt 6 were used as reference acids (Figure 3). Fluorenes have previously been used to measure the acidity of silanes, [12, 24] and their conjugate bases are strongly delocalized anions which are not expected to coordinate to the protonated silicon centre. 2,6‐Lutidine is also unlikely to coordinate due to steric bulk.…”

“…Because of the generally hydridic character of Si−H bonds, Brønsted SiH‐acids are rare in general. Recent examples by Krempner and co‐workers [12] and Beckmann and co‐workers, [13] shown in Figure 1 B, mostly rely on electronic effects. In this paper, we show that ring strain can significantly contribute to the acidic character of a Si−H bond.…”

“… A) An example of strain‐release Lewis acidity for siletanes [1l] . B) Selected acidic silanes [12, 13] and the silane discussed in this work (acidic protons are shown in bold). Experimental p K a values are given as projected onto the DMSO scale.…”

Synthesis and Complexation of a Free Germanide Bearing a Tridentate N-Heterocyclic Substituent

“…For example, Aquino et al investigated the electronic properties, e.g., Brønsted acidity, of zwitterionic silyl-substituted methanides, silanides, and germanides (R 3 E(II) anions), showing that basicity decreases down group 14 (Scheme 1, A). 13 They also note that the methanides are markedly different from the silanides and germanides, both structurally and electronically, mainly due to significant hyperconjugation of the lone pair into the adjacent silyl groups. The decreased basicity also translates in increased stability of E(II) compounds going down group 14.…”

Tris[(1-isopropylbenzimidazol-2-yl)dimethylsilyl]methyl metal complexes, [TismPriBenz]M: a new class of metallacarbatranes, isomerization to a tris(N-heterocyclic carbene) derivative, and evidence for an inverted ligand field

“…Furthermore, tripodal molecules of the type HC(SiMe 2 X) 3 are known, e.g. X = NR, 14 PR 2 , 15 CH 2 PR 2 , 16 S, 17 Se, 17 and OC 2 H 4 OMe, 18 and thus provide a precedent for the synthesis of variants that include heterocyclic nitrogen donors.…”