Dong Zhaowen

There is growing interest in compounds containing functionalized E=E multiple bonds (E=Si, Ge, Sn, Pb) because of their potential to exhibit novel physical and chemical properties. However, compounds containing multiple functionalizations are rare, with scarcity increasing with increasing degree of substitution. The first ditetrelene R₂E=ER₂ in which the E=E bond is substituted by four heteroatoms (other than Si) is described. The tetraphosphadisilene {(Mes)₂P}₂Si=Si{P(Mes)₂}₂ (7) is readily isolated from the reaction between SiBr₄ and [(Mes)₂P]Li, the latter of which acts as a sacrificial reducing agent. The structure of 7 is presented, while the bonding in, and stability of 7 were probed using DFT calculations.

Tetraphosphadisilene compound {(Mes)₂P}₂Si=Si{P(Mes)₂}₂ is a readily accessible complex that is stable in the solid state, and is unlike tetraaminodisilenes (R₂N)₂Si=Si(NR₂)₂, which are typically unstable with respect to their silylene monomers (R₂N)₂Si. Tetraphosphadisilene is the first structurally characterized example of a ditetrelene substituted by more than two heteroatoms other than silicon.

Metallocenes The half-sandwich cation [SnCp]⁺, a toluene adduct thereof, and the quadruple-decker [Sn₃Cp₄]²⁺ were synthesized and characterized as salts of weakly coordinating anions as described by I. Krossing et al. in their Communication on page 2880 ff.

Reduction of the stable germabenzene, 1-Tbt-2-tert-butyl-germabenzene (Tbt=2,4,6-tris[bis(trimethylsilyl)methyl]phenyl), with KC₈ resulted in the formation of 2-tert-butylgermabenzenylpotassium, that is, the germanium analogue of phenylpotassium, under concomitant elimination of the aryl group from the Ge atom. Under an inert atmosphere, this germabenzenylpotassium could be isolated in the form of stable yellow crystals. In the crystalline state, as well as in solution, the germabenzenyl moiety adopts a monomeric form, even though the X-ray diffraction analysis suggests the presence of highly reactive Ge=C double bonds. The spectroscopic and X-ray crystallographic analyses, in combination with theoretical calculations indicate an ambident character for this germabenzenyl anion, with contributions from aromatic and germylene resonance structures.

Ge is not C: Reduction of a stable germabenzene with KC₈ resulted in the formation of the germanium analogue of phenylpotassium, under concomitant elimination of the aryl group from the Ge atom. Its ambident character with contributions from aromatic and germylene resonance structures was supported experimentally and theoretically.

The synthesis of a bicyclic germylene from the reaction of a germole dianion with hafnocene dichloride is reported. This germylene is stabilized by a homoconjugative interaction of the dicoordinated germanium atom with a remote C=C double bond. First reactivity studies revealed its nucleophilic character and resulted in the synthesis of bimetallic hafnium/iron and hafnium/tungsten complexes with a germylene group linker.

A germane approach to stabilization: A germylene stabilized by homoconjugation is described. The structural parameters and a theoretical analysis of the bonding situation revealed a homoconjugative interaction between the C=C bond and the empty Ge 4p orbital. Reactivity studies confirmed its nucleophilic character, and bimetallic hafnium/iron and hafnium/tungsten complexes were synthesized.

Isolable dialkylsilylene 5 reacts with dihydrogen in the presence of a small amount of a conventional Lewis acid (BPh₃, BEt₃) or a base (PPh₃, PEt₃, NPh₃, NEt₃) at low temperatures in a hydrocarbon solvent, giving the corresponding dihydrosilane 10 in high yields. Both 5/Lewis acid and Lewis base/5 pairs work as a frustrated Lewis pair (FLP) to split dihydrogen, being in accord with the amphoteric nature of silylene 5.

Splitting up based on frustration: Amphoteric dialkylsilylene 5 that forms frustrated Lewis pairs (FLPs) with either a Lewis acid or base splits dihydrogen at low temperatures in hexane giving the corresponding dihydrosilane 10 in high yields.