N‐Heterocyclic Carbene Coordinated Neutral and Cationic Heavier Cyclopropylidenes

Abstract

Cyclopropylidene is a transient intermediate of the allene-propyne-cyclopropene isomerization. The incorporation of heavier Group 14 elements into the cyclopropylidene scaffold has to date been restricted to the formal replacement of the carbenic carbon atom by a base-coordinated silicon(II) center. Herein we report the synthesis and characterization of NHC-coordinated heavier cyclopropylidenes (Si2GeR3X, and Si3R3Br; X=Cl, Mes; R=Tip=2,4,6-iPr3C6H2) in which the three-membered ring is exclusively formed by silicon and germanium. In case of the chloro-substituted Si2Ge-cyclopropylidene, a stable heavier cycloprop-1-yl-2-ylidene cation is obtained by NHC-induced chloride dissociation.

Synthesis of a α-Chlorosilyl Functionalized Donor-Stabilized Chlorogermylene

“…In contrast, there are again two signals for the adjacent diastereotopic methyl groups of the N-isopropyl moiety. In 13 C{ 1 H} NMR, the carbenic carbon shows a resonance at δ = 171.01 ppm, which is similar to the chemical shifts observed for other NHC-coordinated Ge(II) compounds [18,19]. In 29 Si{ 1 H} NMR, the singlet at δ = −3.39 ppm is strongly highfield shifted compared with that of the free N-heterocyclic silylene (δ = +78.3 ppm) [25].…”

“…The distance between carbenic carbon and germanium(II) center is 2.081(2) Å, which is slightly shorter than that of the corresponding NHC-coordinated germanium(II)dichloride (2.106(3) Å) [26]. compounds [18,19]. In 29 Si{ 1 H} NMR, the singlet at δ = −3.39 ppm is strongly highfield shifted compared with that of the free N-heterocyclic silylene (δ = +78.3 ppm) [25].…”

“…While the interconversion of functional groups is just beginning to emerge in the case of heavier multiple bonds [10], numerous examples have been reported for the heavier tetrylenes [11][12][13][14][15]. Recently, Scheschkewitz et al have taken a similar approach with the synthesis of the multiply functional NHC-coordinated silagermenylidenes, I and II (Scheme 1) [16,17], which serve as precursors for cyclic NHC-coordinated germylenes of type III, IV, and V under consumption of the Si=Ge bond, but retention of the low-valent germanium center (Scheme 1) [16,18,19]. The leaving group characteristics of the peripheral chloro functionality of II can be exploited for the incorporation of different organic substituents by treatment with organolithium reagents in order to fine-tune the steric requirements of the ligand scaffold of cyclic germylenes of type IV [20,21].…”

Correction

“…When viewed together with previous results on base-coordinated species [7][8][9] , it is clear that much more is to be expected from this unprecedented structural motif. 249 Bk, which has a half-life of only 320 days.…”

Mono‐ and Dicoordinate Germanium(0) as a Four‐Electron Donor

“…[5a] In compound 5a the angle between carbenic carbon-germanium-carbenicc arbon is 91.2(2)8 which is significantly highert han that of bis-NHC stabilized cyclic germylone (86.68). [32] Using an optimized fourfold excess of NHC Me 4 ,w ew ere thus able to isolate (NHC Me 4 ) 2 Ge(Fe(CO) 4 ) 2 , 5b along with NHC Me 4 :Fe(CO) 4 , 6b in about 50 %y ield by crystallization from hot THF or MeCN (Scheme 4). [32] Using an optimized fourfold excess of NHC Me 4 ,w ew ere thus able to isolate (NHC Me 4 ) 2 Ge(Fe(CO) 4 ) 2 , 5b along with NHC Me 4 :Fe(CO) 4 , 6b in about 50 %y ield by crystallization from hot THF or MeCN (Scheme 4).…”