Ein gemischtes, schwereres Si=Ge Analogon eines Vinylanions

Metathesis Reactions of a NHC‐Stabilized Phosphaborene

The BP unsaturated unit is a very attractive functional group as it provides novel reactivity and unique physical properties. Nonetheless, applications remain limited so far due to the bulky nature of B/P‐protecting groups, required to prevent oligomerization. Herein, we report the synthesis and isolation of a N‐heterocyclic carbene (NHC)‐stabilized phosphaborene, bearing a trimethylsilyl (TMS) functionality at the P‐terminal, as a room‐temperature‐stable crystalline solid accessible via facile NHC‐induced trimethylsilyl chloride (TMSCl) elimination from its phosphinoborane precursor. This phosphaborene compound, bearing a genuine B=P bond, exhibits a remarkable ability for undergoing P‐centre metathesis reactions, which allows the isolation of a series of unprecedented phosphaborenes. X‐ray crystallographic analysis, UV/Vis spectroscopy, and DFT calculations provide insights into the B=P bonding situation.

Synthesis of Genuine Germenyl Lithiums and the First Persistent Germenyl Radicals

The first isolated genuine germenyl lithiums (R₃Si)(1‐Ad)C=Ge(SiMetBu₂)(Li⋅2 L) (R₃Si=tBu₂MeSi, L=THF (1  a), or L=12‐crown‐4 (1  b) and R₃Si=tBuMe₂Si, L=THF (2  a), or L=12‐crown‐4 (2  b)), were synthesized by reaction of the corresponding acyl germanes 3 and 4, respectively, with tBu₂MeSiLi in THF at 70 °C. The novel 1  a and 2  b were characterized by NMR and UV/Vis spectroscopy, and also by X‐ray crystallography (r(C=Ge)=1.865 Å for 1  a and 1.877 Å for 2  b). Nucleophilic addition reaction of 1  a with MeI and a C−H insertion reactions to the C=Ge bond of 1  a, 2  a and 2  b, are reported. Oxidation of 1  a and 2  b (toluene, 230 K) produces the first persistent germenyl radicals (R₃Si)(1‐Ad)C=Ge⋅‐(SiMetBu₂) (R₃Si=tBu₂MeSi (13  a), R₃Si=tBuMe₂Si (13  b)), which were characterized by EPR spectroscopy (t_1/2≈30 min at 230 K, g=2.029, a_av(⁷³Ge) is 55.0G for 13  a and 60.2G for 13  b). The experimental EPR parameters and DFT calculations indicate that 13  a and 13  b have a strongly bent structure at Ge (calc. ∡(C=Ge−Si)=136.7° (13  a), 135.9° (13  b)), and that the unpaired electron has a substantial s‐character.