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

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•+(LiOTf2)-], 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.

Formation of Alkynylgermyl-Substituted Germylenes via a Catenation of Ge Atoms.

Reactions of amidinate-stabilized germylene chlorides R1Ge(:)Cl (R1 = PhC(NtBu)2) and R2Ge(:)Cl (R2 = PhC(NCy)2, Cy = cyclohexanyl) with trimethylsilylethynyl lithium salt (LLi, L = -C≡CTMS) afforded alkynylgermyl-substituted germylenes R1(:)Ge-GeL3 (1) and [R2GeL2]2Ge(:) (2), respectively. Both of them may undergo the formation of Ge-Ge single bonds with a concomitant 1,2-shift of ethynyl groups. DFT calculations determined the reaction pathways where two possible intermediates (:)GeL2 and RGe(:)L (R = R1, R2) are proposed, which were consistent with the trapping reactions of (:)GeL2 toward IAr-(:)GeL2 (3, IAr = :C{N(Ar)CH}2, Ar = 2,6-iPr2C6H3). The reaction of 1 with N3TMS gave a new aminogermylene R1(:)Ge-N(TMS)-GeL3 (4), indicating a reactive Ge-Ge bond.