Homoleptic tris(methoxydimethylsilyl)silanides of the alkaline earth metals: first zwitterionic silanides with two naked silyl anions

Abstract

The first zwitterionic alkaline earth metal silanides featuring two naked silyl anions were synthesized and a combined structural and computational study on these zwitterions revealed a correlation between the energy of the HOMO and the degree of negative charge of the naked silyl anions.

Modern concepts and methods in the chemistry of polyhedral metallasiloxanes

“…It is notable that despite the simplicity of splitting polysiloxane using organometallic derivatives, this method is not used widely to prepare PHMSs because the results are often difficult to predict. Branched silane oligomers with rather rigid disilane Si-Si units instead of flexible disiloxane SiOSi fragments have been used to synthesize PHMSs containing Al [126], Ca [127], Ti (86), and Zr (87) [128] (Scheme 30). These types of compounds are considered to be active catalytic systems [129].…”

Synthesis, Structure, and Reactivity of Zwitterionic Divalent Rare-Earth Metal Silanides

“…These discrete homoleptic complexes represent the first examples of metalcontaining zwitterions that are composed of two "naked" silyl anions. 7 On the other hand, zwitterionic silanides of the rare-earth metals regardless of their oxidation state have not been prepared so far. Herein, we report on the synthesis and structures of the first zwitterionic divalent europium, ytterbium and samarium silanides and the reaction behavior of the divalent ytterbium silanide toward BPh 3 and W(CO) 6 2 (M = Ca, Sr, Ba) in tetrahydrofuran (THF) as the solvent (Scheme 2).…”

“…Herein, we report on the synthesis and structures of the first zwitterionic divalent europium, ytterbium and samarium silanides and the reaction behavior of the divalent ytterbium silanide toward BPh 3 and W(CO) 6 2 (M = Ca, Sr, Ba) in tetrahydrofuran (THF) as the solvent (Scheme 2). 7 Owing to their zwitterionic nature, M-3 compounds proved to be poorly soluble, even in THF, and precipitated from the reaction mixture as crystalline materials, which greatly facilitated their isolation and purification. For the synthesis of the zwitterionic divalent rare earth silanides M-3 (M = Eu, Yb, Sm), assumed to be of low solubility similar to that of their alkaline earth counterparts, salt metathesis as an alternative route was envisioned because of the lack of commercially available divalent rare-earth alkoxides.…”

“…Figure 1 along with selected average bond lengths and angles of all structurally characterized metal silanides (Table 1) and the alkaline earth metals silanides Mg-3, Ca-3, Sr-3 and Ba-3, previously reported. 7 Compounds Eu-3, Yb-3 and Sm-3 are isostructural featuring spirocyclic bicyclooctane structures in which the central metal ions are octahedrally coordinated by six methoxy groups via dative bond interactions. To our knowledge, M-3 are the first examples of truly zwitterionic silanides that contain rare-earth metal cations regardless of their formal oxidation state.…”

“…[3][4][5][6][7][8][9][10] Interest in these types of highly reactive zwitterions primarily arises from the "naked" silyl anion that is rigidly locked and insulated from the metal cation by internal donor bridges. Unlike tetracoordinate borate-based zwitterions 11 , zwitterionic silanides are tri-coordinated and consequently contain a stereochemically active electron pair localized at the silyl anion, which behaves as a Lewis base that can bind to electrophilic transition and main group metal centers (Scheme 1).…”