Reversibility is fundamental for transition metal catalysis, but equally for main group chemistry and especially low-valent silicon compounds, the interplay between oxidative addition and reductive elimination is key for a potential catalytic cycle. Herein, we report a highly reactive acyclic iminosilylsilylene 1, which readily performs an intramolecular insertion into a C═C bond of its aromatic ligand framework to give silacycloheptatriene (silepin) 2. UV-vis studies of this Si(IV) compound indicated a facile transformation back to Si(II) at elevated temperatures, further supported by density functional theory calculations and experimentally demonstrated by isolation of a silylene-borane adduct 3 following addition of B(CF). This tendency to undergo reductive elimination was exploited in the investigation of silepin 2 as a synthetic equivalent of silylene in the activation of small molecules. In fact, the first monomeric, four-coordinate silicon carbonate complex 4 was isolated and fully characterized in the reaction with carbon dioxide under mild conditions. Additionally, the exposure of 2 to ethylene or molecular hydrogen gave silirane 5 and Si(IV) dihydride 6, respectively.
The first acceptor-free heavier germanium analogue of an acylium ion, [RGe(O)(NHC) 2 ]X (R = Mes Ter= 2,6-(2,4,6-Me 3 C 6 H 2 ) 2 C 6 H 3 ; NHC = IMe 4 = 1,3,4,5-tetramethylimidazol-2-ylidene; X = (Cl or BArF= {(3,5-(CF 3 ) 2 C 6 H 5 ) 4 B}), was isolated by reacting [RGe(NHC) 2 ]X with N 2 O. Conversion of the germa-acylium ion to the first solely donor-stabilized germanium ester [(NHC)RGe(O)(OSiPh 3 )] and corresponding heavier analogues ([RGe(S)(NHC) 2 ]X and [RGe(Se)(NHC) 2 ]X) demonstrated its classical acylium-like behavior. The polarized terminal GeO bond in the germa-acylium ion was utilized to activate CO 2 and silane, with the former found to be an example of reversible activation of CO 2 , thus mimicking the behavior of transition metal oxides. Furthermore, its transition metal like nature is demonstrated as it was found to be an active catalyst in both CO 2 hydrosilylation and reductive N-functionalization of amines using CO 2 as C 1 source. Mechanistic studies were undertaken both experimentally and computationally, which revealed the reaction proceeds via a NHC-siloxygermylene [(NHC)RGe(OSiHPh 2 )].
Bis-NHC stabilized germyliumylidenes [RGe(NHC) 2 ] + are typically Lewis basic (LB) in nature, owing to their lone pair and coordination of two NHCs to the vacant p-orbitals of the germanium center. However, they can also show Lewis acidity (LA) via GeÀ C NHC σ* orbital. Utilizing this unique electronic feature, we report the first example of bis-NHCstabilized germyliumylidene [ Mes TerGe(NHC) 2 ]Cl (1), ( Mes Ter = 2,6-(2,4,6-Me 3 C 6 H 2 ) 2 C 6 H 3 ; NHC = IMe 4 = 1,3,4,5-tetramethylimidazol-2-ylidene) catalyzed reduction of CO 2 with amines and arylsilane, which proceeds via its Lewis basic nature. In contrast, the Lewis acid nature of 1 is utilized in the catalyzed hydroboration and cyanosilylation of carbonyls, thus highlighting the versatile ambiphilic nature of bis-NHC stabilized germyliumylidenes.
Use of a silyl supported stannylene (MesTerSn(SitBu3) [MesTer=2,6‐(2,4,6‐Me3C6H2)2C6H3] enables activation of white phosphorus under mild conditions, which is reversible under UV light. The reaction of a silylene chloride with the activated P4 complex results in facile P‐atom transfer. The computational analysis rationalizes the electronic features and high reactivity of the heteroleptic silyl‐substituted stannylene in contrast to the previously reported bis(aryl)stannylene.
The first donor-acceptor complex of as ilaaldehyde, with the general formula (NHC)(Ar)Si(H)OGaCl 3 (NHC = N-heterocyclic carbene), was synthesized using the reactiono fs ilyliumylidene-NHC complex [(NHC) 2 (Ar)Si]Cl with water in the presence of GaCl 3 .C onversion of this complex to the corresponding silacarboxylate dimer [(NHC)(Ar)SiO 2 GaCl 2 ] 2 ,f ree silaacetal ArSi(H)(OR) 2 ,s ilaacyl chloride( NHC)(Ar)Si(Cl)OGaCl 3 ,a nd phosphasilene-NHC adduct( NHC)(Ar)Si(H)PTMS unveili ts true potentiala sa synthoni nsilacarbonylchemistry.Supporting information and the ORCID identification number(s) for the author(s) of this articlecan be found under: https://doi.
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