NHC-Supported 2-Sila and 2-Germavinylidenes: Synthesis, Dynamics, First Reactivity and Theoretical Studies

• Published in: Angewandte Chemie International Edition 2024-07, Vol.63 (31), p.e202400227
• Main Authors: Kumar, Sandeep, Maurer, Leonard R, Schnakenburg, Gregor, Das, Ujjal, Filippou, Alexander C
• Format: Article
• Language: English
• Subjects: Chemical analysis; Chemical bonds; Chemical synthesis; Dynamic structural analysis; Germanium; Hyperspaces; Isomers; NMR; Nuclear magnetic resonance; Potential energy; Quantum chemistry; Reagents; Silicon; Vinylidene
• ISSN: 1433-7851; 1521-3773; 1521-3773
• DOI: 10.1002/anie.202400227

2-tetrelavinylidenes (C=EH ; E=Si, Ge) are according to quantum chemical studies the least stable isomers on the [E,C,2H] potential energy hypersurface isomerizing easily via the trans-bent tetrelaacetylenes HE≡CH to the thermodynamically most stable 1-tetrelavinylidenes (E=CH ). Consequently, experimental studies on 2-tetrelavinylidenes (C=ER ) and their derivatives are lacking. Herein we report experimental and theoretical studies of the first N-heterocyclic carbene (NHC) supported 2-silavinylidene (NHC)C=SiBr(Tbb) (1-Si: NHC=C[N(Dipp)CH] , Dipp=2,6-diisopropylphenyl, Tbb=2,6-bis[bis(trimethylsilyl)methyl]-4-tert-butylphenyl) and the isovalent 2-germavinylidenes (NHC)C=GeBr(R) (1-Ge, 1-GeMind: R=Tbb, Mind (1,1,3,3,5,5,7,7-octamethyl-s-hydrindacene-4-yl)). The NHC-supported 2-tetrelavinylidenes were obtained selectively from the 1,2-dibromoditetrelenes (E)-(R)BrE=EBr(R) using the diazoolefin (NHC)CN as vinylidene transfer reagent. 1-E (E=Si, Ge) have a planar vinylidene core, a bent-dicoordinated vinylidene carbon atom (C ), a very short E=C bond and an almost orthogonal orientation of the NHC five-membered ring to the vinylidene core. Quantum chemical analysis of the electronic structures of 1-E suggest a significantly bent 1-tetrelaallene and tetrelyne character. NMR studies shed light into the dynamics of 1-E involving NHC-rotation around the C -C bond with a low activation barrier. Furthermore, the synthetic potential of 1-E is demonstrated by the synthesis and full characterization of the unprecedented NHC-supported bromogermynes BrGe=C(EBr Tbb)(NHC) (2-SiGe: E=Si; 2-GeGe: E=Ge).