Reactivity of an N‐Heterocyclic Carbene Stabilized Hydrosilylene towards a Ketone and CO2: Experimental and Theoretical Study

Abstract

The reaction of N‐heterocyclic carbene (NHC)‐stabilized hydrosilylene 1, tBu3SiSi(H)←NHC, with one and two equivalents of benzophenone gave rise to bicyclic compounds 2 and 3, tBu3Si(R)[Si‐CH2‐N(CMeCMeNMe)‐CPh2‐O] (R = H, OCHPh2). The NHC plays a crucial role in this reactivity, as it is directly involved in C–C bond formation and supplies the C–H‐activated methyl group. In the formation of 3, the terminal Si–H bond of the hydrosilylene is involved in transition‐metal‐free hydrosilylation. All steps in these mechanisms are based on NHC‐stabilized zwitterionic transition states and intermediates and were investigated by utilizing DFT calculations. In addition, the CO2 activation of 1 to yield cis/trans‐cyclotrisiloxane 4, [(tBu3Si)(H)Si‐O]3, stereoselectively and its mechanistic study are reported.

The Quest for Stable Silaaldehydes: Synthesis and Reactivity of a Masked Silacarbonyl

“…[12] These compounds react with carbon dioxide, affording NHC-stabilized silaacylium salt [(IMe 4 ) 2 ( Mes Ter)Si(O)][Cl] (3)w ith comparably high double-bondc haractero ft he Si=Ob ond, [5c] and NHC-free cyclotrisiloxane[ ( tBu 3 Si)(H)SiO] 3 regarded as a trimer of silaaldehyde intermediate. [13] Exploration of the reactivity of silyliumylidene (1)t owards chalcogens and H 2 Se nabled an access to NHC-stabilized heavierc halcogen silaacylium derivatives [14] and thiosilaaldehyde. [15] Herein, we report our study devotedt ot he synthesis of as ilaaldehyde, isolated as a Si,O-donor-acceptor complex, and its unique reactivity showing strong relationship to the chemistry of carbonyl congeners ( Figure 1b).…”

Facile Access to Stable Silylium Ions Stabilized by N-Heterocyclic Imines

“…The difference in the steric bulk of the precursors 1 and 3 leads to different products based on the reaction kinetics. Figure 3 shows the energy profile along the reaction path calculated at the B97-D/6-31G(d) level of theory which has been successfully applied in low-valent silicon compounds [38][39][40][41][42][43][44][45][46][47]. The first step in the reaction is the abstraction of a Me group of a Me 3 Si moiety by the B(C 6 F 5 ) 3 (TS1 Dip ) with the associated energy of +18.9 kcal/mol for 2[MeB(C 6 F 5 ) 3 ] 2 .…”

Synthesis and Reactivity of Functionalized Silicon(II) Compounds: Iminosilylene, Phosphinosilylene, Hydrosilylene, and Related Compounds

“…54 The reaction of hydrosilylene 46 with benzophenone under different reaction conditions and stoichiometry leads to two different bicyclic compounds 50 and 51 (Scheme 14) as a couple of diastereomeric mixtures (R/R, S/S, or R/S, S/R). With one equivalent of benzophenone at ¹78°C, bicycle 50 was obtained as major product.…”

“…Indeed, hydrosilylene 46 in the presence of excess carbon dioxide led to cis/transcyclotrisiloxane 52, the formal trimer of silaaldehyde in 82% yield as a colorless compound (Scheme 15). 54 Compound 52 crystallizes from diethylether at 4°C and the solid state structure shows the six-membered Si 3 O 3 ring skeleton. The presence of strong steric repulsion of two bulky supersilyl groups at equatorial position is presumably responsible for boat conformation of 52 in the solid state.…”