Thermal decomposition of [Me3SiNCH2CH2NSiMe3]•Li2(THF)2 to [LiN(SiMe3)2•THF]2 via a 1,4-trimethylsilyl shift

The dilithium salt [Me3SiNCH2CH2NSiMe3].Li-2(THF)(2) decomposes slowly upon heating forming a metastable structure of the crystalline [LiN(SiMe3).THF](2). The crystal structure of the new form was established by single crystal X-ray diffraction showing a decrease in the a and b parameter values of the unit cell, and an expansion of the c value as compared with the structure obtained at room temperature. The major discrepancies among the known and the metastable crystalline framework are the Li-O bond length and the dihedral angle disposition of the trimethylsilyl groups as regarded to the middle Li-N-Li-N heterocyclobutane ring. Attempts to trap the expected additional lithium imine product were unsuccessful although quenching experiments produced polyethyleneimine. (C) 1997 Elsevier Science S.A.