Trimethylscandium

The hitherto unknown homoleptic tetramethyl­aluminate complex [Sc­(AlMe₄)₃] could be obtained by reacting the ate complex [Li₃ScMe₆(thf)_1.2] with AlMe₃ in the cold. It cocrystallizes with AlMe₃ as [Sc­(AlMe₄)₃(Al₂Me₆)_0.5] and decomposes at ambient temperature in n-pentane via multiple C–H bond activations to the mixed methyl/methylidene complex [Sc₃(μ₃-CH₂)₂(μ₂-CH₃)₃­(AlMe₄)₂(AlMe₃)₂]. Donor-induced methylaluminate cleavage of [Sc­(AlMe₄)₃(Al₂Me₆)_0.5] produced [ScMe₃]_n in good yield, which could be derivatized with trimethyltriazacyclononane (Me₃TACN) to form the structurally characterizable [(Me₃TACN)­ScMe₃]. Additionally, half-sandwich complex [Cp*Sc­(AlMe₄)₂] and sandwich complex [Cp*₂Sc­(AlMe₄)] were accessible by salt metathesis reactions from [Sc­(AlMe₄)₃(Al₂Me₆)_0.5] and KCp* (Cp* = C₅Me₅). ⁴⁵Sc NMR spectroscopy was applied as a significant probe to evidence the existence of [ScMe₃]_n. Compounds [(Me₃TACN)­ScMe₃] (+624.6 ppm) and [ScMe₃(thf)_x] (+601.7 ppm) gave large ⁴⁵Sc NMR shifts, revealing the strong deshielding effect of the σ-bonded alkyl ligands on the scandium nuclei. Ultimately, cationized [Sc­(AlMe₄)₃­(Al₂Me₆)_0.5] was employed in isoprene polymerization, leading to polymers in high yields (>95%) and with high (>90%) cis-1,4-polyisoprene content.