A Striking Mode of Activation of Carbon Disulfide with a Cooperative Bis(silylene).

The reactivity of the 1,4-substituted bis(silylenyl)terphenylene 1, 1,4-[ortho-(LSi)C6 H4 ]2 C6 H4 , (L=RC(NtBu)2 , R=Ph, Mes) towards CS2 is reported. It results in a dearomatization of the phenylene ring, affording the 1,3-substituted cyclohexadiene derivative 2. According to DFT calculations, a transient silene containing a Si=C bond capable of π(C=C) addition at the aromatic phenylene ring is a key intermediate. In contrast, addition of CS2 to the biphenyl-substituted mono-silylene ortho-(LSi)C6 H4 -C6 H5 3 leaves the aromatic π-system intact and forms, in a [1+2] cycloaddition reaction, the corresponding thiasilirane 4 with a three-membered SiSC ring. Further experimental studies led to the isolation of the novel mesoionic five-membered Si2 S2 C heterocycle 6, which reacts with CS2 under C-C bond formation. All isolated new compounds were fully characterized and their molecular structures determined by single-crystal X-ray diffraction analyses.