With a co-reduction procedure using 2 equivalents Mes SiCl and 1 equivalent NHC →SiCl an NHC-adduct of a trisilacyclopropylidene (SiMes ) SiNHC 1 was synthesized. Addition of NHC to 1 results in quantitative carbene exchange under release of NHC to yield (SiMes ) SiNHC 2. Both NHC-coordinated trisilacyclopropylidenes coordinate to BH . In reaction of 1 with SiMe N a NHC-coordinated trisilane with an exocyclic Si=N double bond is formed. With diphenylacetylene 1 undergoes a ring expansion at room temperature to afford a five-membered ring compound with an NHC-coordinated silylene functionality.

The reaction of the NHC-coordinated trisilacyclopropylidene F with freshly prepared W(CO) 6−n (thf) n (n = 1, 2) yielded in addition to the targeted tungsten pentacarbonyl complex 1 the unexpected NHC-coordinated Si 3 W-heterocycle 2 via oxidative insertion of a W(CO) 4 unit into the peripheral Si−Si single bond of F. The structurally analogous insertion product 3 is selectively accessible by reacting F with Mo(CO) 4 (nbd) in 71% yield. Moreover, F reacts selectively with Fe 2 (CO) 9 giving rise to the iron tetracarbonyl complex 4 that can either thermally or photolytically be converted under release of one equivalent of carbon monoxide into the NHCcoordinated Si 3 Fe-heterocycle 5 featuring a butterfly-type structural motif. FT-IR spectroscopy and DFT calculations of 1 and 4 reveal strong σ-donor and negligible π-acceptor properties of F. Natural bond orbital analysis (NBO) and quantum theory of atoms in molecules (QTAIM) of 2, 3, and 5 give evidence for weak transannular interactions in 2 and 3 and the presence of a transannular bond in 5.

The bicyclic amido-substituted silicon(I) ring compound Si 4 {N(SiMe 3 )Mes} 4 2 (Mes = Mesityl = 2,4,6-Me 3 C 6 H 2 ) features enhanced zwitterionic character and different reactivity from the analogous compound Si 4 {N(SiMe 3 )Dipp} 4 1 (Dipp = 2,6-i Pr 2 C 6 H 3 ) due to the smaller mesityl substituents. In a reaction with the N-heterocyclic carbene NHC Me 4 (1,3,4,5tetramethyl-imidazol-2-ylidene), we observe adduct formation to give Si 4 {N(SiMe 3 )Mes} 4 • NHC Me 4 (3). This adduct reacts further with the Lewis acid BH 3 to yield the Lewis acid-base complex Si 4 {N(SiMe 3 )Mes} 4 • NHC Me 4 • BH 3 (4). Coordination of AlBr 3 to 2 leads to the adduct 5. Calculated proton affinities and fluoride ion affinities reveal highly Lewis basic and very weak Lewis acidic character of the low-valent silicon atoms in 1 and 2. This is confirmed by protonation of 1 and 2 with Brookharts acid yielding 6 and 7. Reaction with diphenylacetylene only occurs at 111 °C with 2 in toluene and is accompanied by fragmentation of 2 to afford the silacyclopropene 8 and the trisilanorbornadiene species 9.

The NHC-coordinated trisilacyclopropylidene (A) is shown to behave as the basic component of an FLP used in combination with the Lewis acid B(2,3,5,6-C6F4H)3. This FLP cleaves dihydrogen highly selectively at...

:PC–tBu reacts with Si3Mes4NHCiPr2Me2E to afford a so-called “housane” 1, that rearranges upon irradiation with a high-pressure mercury lamp or at 60 °C to an NHC-stabilized cyclopentenyl anion analogue 2 with a three-center four-electron π-bond.