A Zwitterionic Silylene as Reactive Intermediate and Its Unusual Dimerization to an N‐Heterobicyclic Disilane

A way to synthesize the transient zwitterionic silylene L′Si : 8 {L’=CH[(C=CH 2 )CMe(N( t Bu)) 2 ]} and achieve its facile dimerization to the remarkable N‐heterobicyclic disilane 8 2 is described. At first, employing the β‐diketiminate ligand L [L=CH(CMeN( t Bu)) 2 ], both starting materials LH ( 2 ) and its N ‐lithium salt LLi ( 3 ) can react with SiBr 4 to yield the silylene precursor L′SiBr 2 ( 4 ) by silicon‐induced CH activation at an exocyclic methyl group on the backbone of the ligand. Compound 4 reacts with SiBr 4 above room temperature to afford the unexpected terminal CH(SiBr 3 )‐substituted dibromosilane 6 along with the unique tricyclic trisilane 7 . Reduction of 4 with KC 8 at 0 °C furnishes the novel N‐heterobicyclic disilane 8 2 , which is a formal dimer of the desired zwitterionic silylene L′Si : ( 8 ). It has been reasoned that compound 8 2 may results from [4+1] cycloaddition of two molecules of 8 to give the transient dimer 8 2 ′ , which subsequently undergoes hydrogen transfer from a terminal methyl group on the backbone of the C 3 N 2 Si ligand to the low‐coordinate Si atom. The latter dimerization can be rationalized by the intrinsic zwitterionic character of 8 and insufficient steric protection through the t Bu groups at the nitrogen atoms. The novel compounds 3 , 4 , 6 , 7 , and 8 2 have been characterized by 1 H, 13 C, and 29 Si NMR spectroscopy, mass spectrometry, and elemental analysis. Additionally, the structures of 3 , 6 , 7 , and 8 2 were also established by single‐crystal X‐ray diffraction analyses.