NHC‐Supported 2‐Sila and 2‐Germavinylidenes: Synthesis, Dynamics, First Reactivity and Theoretical Studies
Sandeep Kumar, Leonard R. Maurer, Gregor Schnakenburg, Ujjal Das, Alexander C. Filippou
Abstract
Abstract 2‐tetrelavinylidenes (C=EH 2 ; 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 2 ). Consequently, experimental studies on 2‐tetrelavinylidenes (C=ER 2 ) 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] 2 , 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 2 as vinylidene transfer reagent. 1‐E (E=Si, Ge) have a planar vinylidene core, a bent‐dicoordinated vinylidene carbon atom (C VNL ), a very short E=C VNL 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 VNL −C NHC 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 2 Tbb)(NHC) ( 2‐SiGe : E=Si; 2‐GeGe : E=Ge).