Stannabenzene has not been isolated so far because of its high reactivity. In order to synthesize and isolate a stable stannabenzene, we have introduced two steric protection groups, the Tbt (2,4,6-tris[bis(trimethylsilyl)methyl]phenyl) or the Bbt (2,6-bis[bis(trimethylsilyl)methyl]-4-[tris(trimethylsilyl)methyl]phenyl) group on the tin atom and the t-butyl group on the 2-position, to the stannabenzene skeleton. Such a combination of steric protection groups was found to suppress the dimerization of stannabenzene to some extent, giving an equilibrated mixture of the corresponding stannabenzene and its dimer.

Stannabenzenes 3, neutral stannaaromatic compounds having the simplest aromatic unit, were successfully generated by the reaction of the corresponding bromostannanes 5-Br with lithium diisopropylamide in hexane at -40 °C. The generation of 3 was indicated by the formation of the [4 þ 2] dimer 6 at room temperature. The thermal stability of 3 was completely different from that of the sila-and germabenzenes bearing the same substituent. The structural and electronic properties of stannabenzene were estimated by theoretical calculations.Benzene is representative of aromatic compounds, which are important from the viewpoints of not only fundamental chemistry but also application toward organic synthesis and material science. 1 Its chemical behavior, structure, and energetic and magnetic features have been widely studied from both experimental and theoretical standpoints, and such findings have contributed to understand the concept "aromaticity". 1,2 Although a variety of heterabenzene, in which one carbon atom of benzene is replaced with a heteroatom, have been synthesized and focused for a long time to discuss "aromaticity", the benzene analogues of heavier group 14 elements (Si, Ge, Sn, and Pb) have been recognized as highly reactive species. 3 For example, the parent silabenzene (SiC 5 H 6 ) has been generated by flash thermolysis and studied in the gas phase and in low-temperature matrices, but it was found to oligomerize above 80 K. 4 This result is in sharp contrast with the high thermal stability of phosphabenzene, containing a phosphorus atom, which is an element in the same row as silicon. 5 Recently, the chemistry of heteraaromatic compounds of heavier group 14 elements has experienced remarkable