Bimolecular extrusion of TeR2 from beta-diketiminato supported scandium bis-tellurolates

Reaction of the well-defined, base-free dialkyl scandium compounds LnSc(CH2SiMe3)2 supported by the beta-diketiminato ligands ArNC(R)CHC(R)NAr (Ar = 2,6-diisopropyl; R = Me, L1: R = tBu, L2) with two equivalents of nBuP = Te gives the bis-tellurolate complexes LnSc(TeCH2SiMe3)2, 1b (L1) and 2b (L2). Tellurolate 2b was isolated and fully characterized, including an X-ray structure analysis, and exhibits two chemically distinct tellurolate ligands in solution on the NMR time scale. Tellurolate 1b is only moderately stable and decomposes with elimination of two equivalents of Te(CH2SiMe3)2 to form the dimeric bis-telluride 1d. This compound was characterized by X-ray crystallography and elemental analysis. In contast, tellurolate 2b decomposes with loss of only one equivalent of Te(CH2SiMe3)2, leading to the formation of a dinuclear complex with one bridging telluride unit joining two L2Sc(TeCH2SiMe3) fragments. This compound was also structurally characterized. The solution behavior of this material is complex, as it exists as three conformational isomers that undergo slow exchange on the NMR time scale. The production of dimer 2c, along with the results of crossover experiments, suggest strongly that TeR2 elimination from these bis-tellurolates is bimolecular.