Generation and reactions of overcrowded diaryldilithiostannane and diaryldipotassiostannane

Exhaustive reduction of an overcrowded dibromostannane bearing two bulky aromatic substituents, Tbt(Dip)SnBr₂ {Tbt = 2,4,6- tris[bis(trimethylsilyl)methyl]phenyl; Dip = 2,6-diisopropylphenyl}, with an excess amount of lithium naphthalenide in THF at -78°C gave the corresponding dilithiostannane, Tbt(Dip)SnLi₂, the generation of which was confirmed by trapping experiments with some electrophiles together with ¹¹⁹Sn and ⁷Li NMR spectroscopy. The diaryldilithiostannane was found to be stable in solution under an inert gas below -25°C. The potassium analogue, Tbt(Dip)-SnK₂, was also generated by the reduction of the dibromostannane in THF at -78°C by the use of KC₈ as a reductant. The reactions of dilithiostannane and dipotassiostannane obtained with o-dibromobenzene did not give a stannacyclopropabenzene derivative but an unexpected cyclization product, a stannacyclobutabenzene derivative, in contrast to the reactions of the corresponding dilithiosilane and dilithiogermane, Tbt(Dip)ELi₂ (E = Si, Ge), with o-dibromobenzene leading to the formation of the corresponding metallacyclopropabenzenes as stable crystalline compounds. A preliminary result of the synthesis of a tin-tellurium double-bond compound from the dilithiostannane is also presented.