Aggregation, Reaggregation and Degradation of a Trifunctional Thallium(I) Amide Induced by Weak TlI ⃛ TlI Attraction

Metal exchange of the solvated tripodal lithium amide [H3CC{CH2N(Li-solv)SiMe3}3] (1, solv = ether solvent) with thallium(I) chloride leads to the previously reported pentametallated dimeric thallium amide [{H3CC(CH2NSiMe3)3}2(H)Tl5] (2) in high yield. That the redox-induced partial demetallation of the amide presumably occurs at an intermediate stage of the metal exchange is inferred from the isolation and structural characterization of the mixed Tl-Li amide [H3CC{CH3N(Tl) SiMe3}3][H3CC{CH2NSiMe3}3(H)(Tl)(Li-thf)]·(toluene) (3), which has a crystal structure closely related to that of 2. In both cases the central structural motif, defined by weakly attractive Tl Tl contacts, is a tetrahedral metal array in which a triangular thallium triamide unit is capped by an exposed Tl atom of a second building block. Compound 3 may be converted to 2 by metal exchange with TlCl. The two supramolecular components of 2 reaggregate upon recrystallization in a nonpolar solvent such as pentane to yield the dimeric aggregate of the fully metallated thallium amide [H3CC{CH2N(Tl)-SiMe3}3]2 (4). An X-ray crystallographic study of 4 established the existence of dimeric aggregation through Tl Tl interactions leading to a more open dimeric form than 2 and 3, which is interpreted as being due to a structural mismatch of the building blocks. Compound 4 may be thermally degraded by prolonged stirring in toluene at ambient temperature to yield the previously reported mixed-valence TlITlII amide [H3CC(CH2NSiMe3)3Tl2] (5).