Reactivity of an NHC‐Stabilized Silylene towards Lewis Acids and Lewis Bases

Abstract

The reactivity of N‐heterocyclic carbene stabilized (NHC‐stabilized) aminochlorosilylene ArN(SiMe3)Si(IiPr)Cl (1, Ar = 2,6‐iPr2C6H3, IiPr = 1,3‐diisopropyl‐4,5‐dimethylimidazol‐2‐ylidene) with selected Lewis acids and Lewis bases is described. Treatment of 1 with BH3·THF yielded 1·BH3 (2) quantitatively. Compound 2 is a rare example of an air‐insensitive silylene–borane adduct showing both acidic and basic properties of chlorosilylene in a single molecule. Crystals of 1–(CH2)3CH2OB(C6F5)3 (3) were obtained from the reaction of 1 with B(C6F5)3 in THF. For the first time, a frustrated Lewis pair (FLP) composed of a silylene and a substituted borane was observed to activate small molecules. Reaction of 1 with IMe4 (IMe4 = 1,3,4,5‐tetramethylimidazol‐2‐ylidene) at room temperature afforded silylene ArN(SiMe3)Si(IMe4)Cl (4), which represents a rare example of an NHC‐stabilized silylene synthesized through ligand exchange.

An Isolable Bis(Silanone–Borane) Adduct

“…Starting from an in situ generated silylene–borane adduct, Teng et al. reported in 2016 on the activation of THF leading to the isolation of a corresponding ring‐opening product . Recently, Braun and co‐workers used a silylene–borane Lewis adduct as a tool for trapping a single water molecule, affording a zwitterionic silanol stabilized by intramolecular hydrogen bonds .…”

“…[18] Starting from an in situ generated silylene-borane adduct, Te ng et al reportedi n2 016 on the activation of THF leading to the isolation of ac orresponding ring-opening product. [20] Recently,B raun and co-workers used as ilylene-borane Lewis adduct as atool for trapping asingle water molecule, affording az witterionic silanol stabilized by intramolecular hydrogen bonds. [23] In 2017, our group reported the first intramolecular silylene-borane FLP which activatesH 2 ,O 2 ,CO 2 and even dehydrogenates water yielding ab orane-stabilized silanone E with ad ative Si=O!Bb ond.…”

NHCs in Main Group Chemistry

“…XRD analysis revealed the presence of a stereochemically active lone pair of electrons, due to the distorted trigonal pyramidal-coordinated Si(II) nucleus. Suprisingly, the Si−C CAAC distance ( Me2 CAAC)SiI 2 (661) (2.013(5) Å) is significantly elongated in comparison to those of the mono-and biradical derivatives and even to those of the NHC-stabilized SiX 2 complexes 602, 604−608 (1.984(7)− 2.007(5) Å). Thus, the bonding situation is best described as a coordinative bond with a negligible π-backbonding.…”

“…Finally, So and colleagues synthesized the first CAACstabilized dihalosilylene ( Me2 CAAC)SiI 2 (661) by adopting the same method as Filippou et al used for the preparation of the corresponding NHC derivative (IDipp)SiI 2 (606) (Scheme 109). 547,576 Conversion of the CAAC-coordinated SiI 4 524 with 2 equiv of potassium graphite in toluene furnishes the divalent diiodosilylene 661 in 58% yield.…”

“…In addition, reactivity studies of the NHC-stabilized aminochlorosilylene 670 with respect to Lewis acids and Lewis bases were conducted (Scheme 114). 661 Treatment of (I i Pr 2 Me 2 )[Dipp(TMS)N]SiCl (670) with an equimolar amount of the sterically less encumbered IMe 4 results in the formation of the NHC-coordinated silylene 671 via a selective NHC substitution in high yield. Complex 671 displays almost the identical 29 Si NMR resonance at δ = 2.7 ppm than its precursor 670 (δ = 3.1 ppm).…”