Si(II) Cation-Promoted Formation of an Abnormal NHC-Bound Silylene and a cAAC-Silanyl Radical Ion

Abstract

The reaction of amidinatosilylene LSi(:)Cl [L = PhC­(NtBu)2] with N-heterocyclic carbene IAr [:C­{N­(Ar)­CH}2, where Ar = 2,6-iPr2C6H3] and NaOTf in tetrahydrofuran (THF) facilely afforded a silicon­(II) cation [LSi(:)-aIAr]+OTf– (1 + OTf – ), where IAr isomerizes to abnormal N-heterocyclic carbene aIAr, coordinating to the silicon­(II) center. Its Ge homologue, [LGe(:)-aIAr]+OTf– (2 + OTf – ), was also accessed via the same protocol. For the formation of 1 + , we propose that an in situ-generated Si­(II) cation [LSi(:)]+ under the treatment of LSi(:)Cl with NaOTf may isomerize IAr in THF. In contrast, the replacement of IAr with cyclic alkyl­(amino) carbene (cAAC) furnished a cAAC-silanyl radical ion [LSi­(H)-cAAC]•+(LiOTf2)− [3 •+ (LiOTf 2 ) – ], which may undergo an abstraction of the H radical from THF. All of the products were characterized by nuclear magnetic resonance spectroscopy, electron paramagnetic resonance, and X-ray crystallography, and their bonding scenarios were investigated by density functional theory calculations. These studies provide new perspective on carbene–silicon chemistry.

Recent advances in stable main group element radicals: preparation and characterization

“…Another cAAC-silanyl radical cation Si-C2 was synthesized by reacting Si-PC2 with one equivalent of cAAC in THF (Scheme 42). 68 The hydrogen is abstracted from the solvent (THF). The IR spectrum of Si-C2 shows a vibration absorption at 2247 cm −1 , which is attributed to the vibration of Si–H.…”

Recent Advances in the Domain of Cyclic (Alkyl)(Amino) Carbenes

“…The compound 102 on treatment with LDA in toluene produces bis-silylene (103) and free cAAC ligand (Scheme 41). [166] We have recently isolated transient acyclic germanium(I) radicals stabilized by cAACs. [167] The dark purple color crystals of CyÀ cAAC : GeN(SiMe 3 )Dipp (104) and MeÀ cAAC : GeN(SiPh 3 )-Mes (105) were isolated with 55 and 63% yield at À 30 °C (Scheme 42).…”

“…The compound 102 on treatment with LDA in toluene produces bis‐silylene ( 103 ) and free cAAC ligand (Scheme 41 ). [166] …”