Evidence of the Lewis‐Amphoteric Character of Tris(pentafluoroethyl)silanide, [Si(C₂F₅)₃]⁻

Abstract

According to af irst view on the geometrical and electronic structure of the tris(pentafluoroethyl)silanide,t his anion appears as aLewis base.Quantum chemical calculations on perfluoroalkylated silanides show significantly lower HO-MO and LUMO energy levels in comparison to their nonfluorinated counterparts,whichimplies reduced Lewis basicity and increased Lewis acidity of the [Si(C 2 F 5 ) 3 ] À ion. With these findings and aH OMO-LUMO gap of 4.80 eV similar to Nheterocyclic silylenes (NHSis), perfluoroalkyl silanides are predestined to exhibit Lewis-amphoteric character similar to silylenes.Deprotonation of Si(C 2 F 5 ) 3 Hwith sterically demanding phosphazene bases afforded thermally stable phosphazenium salts of the [Si(C 2 F 5 ) 3 ] À anion, which add to benzaldehyde,b enzophenone,C S 2 ,a nd CO 2 in various manners.T his behavior also mirrors the reactivity of silylenes towards ketones as well as heterocumulenes and is rationalized by Lewis amphotericity being inherent in these silanides.

Nachweis des Lewis‐amphoteren Charakters von Tris(pentafluorethyl)silanid, [Si(C2F5)3]−

“…Abbildung 2. Molekülstruktur vom nicht fehlgeordnetenA nion in [EtP 4 H][Si(C 2 F 5 ) 3 ]i mF estkçrper [45]. Schwingungsellipsoidesind mit 50 %A ufenthaltswahrscheinlichkeit dargestellt.…”

“…Abbildung 3. Molekülstruktur des nicht fehlgeordnetenAnions [Si-(C 2 F 5 ) 3 (h 2 -CPh 2 O)] À (1b)i mKristall mit [tmgP 1 H] + als Gegenion [45]. Schwingungsellipsoides ind mit 50 %Aufenthaltswahrscheinlichkeit dargestellt.D as Kation und die Wasserstoffatome wurden nicht abgebildet.Ausgewählte Bindungslängen[pm] und -winkel [8 8]: Si1-O1 165.5-(2), C26-O1 152.0(4), Si1-C26 192.6(3);O 1-Si1-C26 49.5(1), C26-O1-Si1 74.6(2), O1-C26-Si1 55.9(1).…”

Tris(pentafluoroethyl)silanol Derivatives and the Lewis Amphoteric Tris(pentafluoroethyl)silanolate Anion, [Si(C2F5)3O]−

“…The tris(pentafluoroethyl)silanide ion, [Si(C 2 F 5 ) 3 ] − , as we recently presented, resembles silylenes with respect to its Lewis amphoteric character: it reacts as a Lewis base as well as a Lewis acid. [10] This unique behavior is due to the electron‐withdrawing character of the perfluoroalkyl substituents, which results in energetically low‐lying HOMO and LUMO compared to those in its non‐fluorinated counterpart. [10] Calculations of the Kohn‐Sham and natural bond orbitals (NBOs) of trimethylsilanolate, [Si(CH 3 ) 3 O] − , and tris(trifluoromethyl)silanolate, [Si(CF 3 ) 3 O] − , anions provide ambiguous results (cf.…”

“… [10] This unique behavior is due to the electron‐withdrawing character of the perfluoroalkyl substituents, which results in energetically low‐lying HOMO and LUMO compared to those in its non‐fluorinated counterpart. [10] Calculations of the Kohn‐Sham and natural bond orbitals (NBOs) of trimethylsilanolate, [Si(CH 3 ) 3 O] − , and tris(trifluoromethyl)silanolate, [Si(CF 3 ) 3 O] − , anions provide ambiguous results (cf. Supporting Information).…”

“…The required silane Si(C 2 F 5 ) 3 H is easily accessible through reaction of SiCl 3 H with three equivalents of pentafluoroethyllithium, LiC 2 F 5 , in n ‐dibutyl ether and subsequent isothermic distillation (Scheme 2 ). [10] …”