NHC-Stabilized Silicon–Carbon Mixed Cumulene

Abstract

The NHC-stabilized silicon-carbon mixed cumulene (Me3Si)2C═Si(IPr)═Si(IPr)═C(SiMe3)2 (3, IPr = 1,3-diisopropyl-4,5-dimethyl-imidazol-2-ylidene) has been prepared by reaction of Ar(SiMe3)NK with the NHC-stabilized silene (Me3Si)2C═Si(SiMe3)Cl(IPr) (2) in toluene at low temperature via the elimination of trimethylsilyl and chloride groups from 2. X-ray crystal analysis of 3 indicated the formal C═Si═Si═C cumulene skeleton with the short Si-Si double bond distance of 2.1896(10) Å. DFT calculations disclosed its zwitterionic character. Reaction of 3 with diphenylacetylene resulted in the formation of a silatriafulvene with an exocyclic NHC-stabilized silene moiety.

Donor‐Stabilized Silylene/Phosphine‐Supported Carbon(0) Center with High Electron Density

“…[27] The Si1ÀCl bond lengths [2.1276(2) ]a re slightly elongated relative to classical Si À Cl bonds (2.06 ), probably because of the negative hyperconjugation between the n s -lone-pair orbital on the central carbon atom and the s* Si-Cl orbital. Similar bond elongations were also observed for the recently reported NHC-stabilized chlorosilene, [34] and in the case of Pchlorinated phosphonium ylides. [35] To gain more insight into the electronic situation of 3, DFT calculations were performed on 3b at the M06-2X/6-31G(d) level of theory.N BO atomic charges calculations show that the central carbon atom carries ac onsiderable negative charge (À1.82;F igure 2).…”

Silole Silylene Route to NHC‐Stabilized Fused 1‐Silabicycles and 1,1′‐Spirobisiloles

“…As expected, the similar reactiono f1 with 2b afforded the similar compound 3b (Scheme 2) in good yield. It wasi solated as dark-green crystals and was much more stable than 3a in solution.C ompounds 3a-b have been fully characterized by 1 H, 13 Ca nd 29 Si NMR spectroscopy.T he 29 Si NMR spectra of 3a and 3b exhibited ar esonance at À17.2 and À7.6 ppm, respectively,w hich were close to those observed in Lewis-base-stabilizeds ilenes, [10] indicating that the structure might contain the NHC-stabilized silene fragment. Single crystalso f3b suitable for XRD studies were obtained from THF.I ts molecular structure was confirmed by X-ray single-crystal analysis.…”

“…Compounds 3 a – b have been fully characterized by 1 H, 13 C and 29 Si NMR spectroscopy. The 29 Si NMR spectra of 3 a and 3 b exhibited a resonance at −17.2 and −7.6 ppm, respectively, which were close to those observed in Lewis‐base‐stabilized silenes, indicating that the structure might contain the NHC‐stabilized silene fragment. Single crystals of 3 b suitable for XRD studies were obtained from THF.…”

“…The structure of 3b featured af used bicyclic structurew ith aC ÀSi bridgeheads ingle bond.T he fused SiC 4 five-and SiC 3 four-membered rings were both essentially planar with ad ihedral angle of 111.5(4)8 ( Figure 1). The NHC was coordinated to the silicon atom with aC ÀSi bond distance of 1.919(3) .T he endocyclic C1ÀSi1 bond length of 1.801(3) was noticeably shorter than aC ÀSi single bond, which wasc omparable to those observed in Lewis-base-stabilized silenes, [10,11] indicating the double bond character.T he shortened C1ÀC2 single bond (1.444(3) )a nd the lengthenedC 2 ÀC3 double bond (1.409(3) )s uggested the significant electron delocalization in the C1-C2-C3m oiety.…”

Funktionelle polymere Materialien auf der Basis von Hauptgruppen‐Elementen

“…Frühe Studien konzentrierten sich in erster Linie auf die Struktur und Bindung dieser ungewçhnlichen Spezies,a ber jüngste Arbeiten führten auch zur Erkundung der optoelektronischen Effekte von Disilen-Gruppen. [140] Ein Meilenstein in dieser Hinsicht ist der Bericht von Tamao et al von 2015 über die iterative Synthese von Oligomeren, die sich von Oligo(phenylenvinylenen) (OPVs) ableiten, mit Si=Si-Doppelbindungen anstelle der Vinylen-Gruppen (Abbildung 21). [138] Systematische Studien an diesen Oligo(p-phe-nylendisilenylen) (Si-OPVs, 71)z eigten eine geschätzte effektive Konjugationslänge (ECL) von neun Einheiten und ein vorhergesagtes Absorptionsmaximum von 635 nm füre ine unendliche Kette.Während die ECL etwas kleiner als die für All-Kohlenstoff-PPVs (n ECL = 11) ist, liegen die Absorptionsund Emissionsmaxima bei viel grçßeren Wellenlängen.…”