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Low-Valent Silicon in Formally Antiaromatic Four-Membered Ring Systems


  • This work is supported by the DFG and the University of Bielefeld.


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The fundamental question of how silicon handles antiaromaticity in four-membered ring systems has been answered by the synthesis and characterization of the first tetrasilacyclobutadiene Si4Ar4 (1) and by the first dimeric silaisonitrile Si2(NAr′)2 (2). Compound 1 is best described by the charge-separated resonance structure 1′ and 2 by a structure with π-type lone pairs at the nitrogen atoms and vacant π orbitals at the silicon atoms.