Reversible Interconversion of Permethylscandocene Tellurolates and Tellurides. X-ray Structure of [(C₅Me₅)₂Sc]₂(μ-Te)

Permethylscandocene tellurolates were synthesized by insertion of tellurium into the scandium–carbon bonds of the corresponding alkyl complexes. These tellurolates were found to be thermally unstable toward elimination of TeR₂, forming the dimeric scandium μ-telluride Cp*₂ScTeScCp*₂ (2). Photochemically induced reversion of the thermal reaction was observed when a mixture of 2 and TeR₂ was irradiated under a UV lamp through a Pyrex filter. X-ray analysis of 2 reveals an Sc-Te distance of 2.7528(12) Å and an ScTeSc angle of 172.07°. These data, coupled with allene-like orien-tation of the Cp* rings about the ScTeSc unit, suggest significant π-bonding between scandium and tellurium in this compound. Crystal data for 2: tetragonal space group P4̅2₁c, a = 15.0324(7) Å, c = 18.8884(14) Å, α, β, γ = 90°, V = 4268.3(4) ų, Z = 4, R = 0.040, R_w = 0.034 for 2092 reflections with I > 3σ(I).