Metal methyl complexes of the type [M(CH₃)_n] are the simplest metalorganic complexes. However, they are not known for all metals. For example, there had been no such methyl complex of the rare-earth element scandium. Other rare-earth metals can form trimethyl compounds starting from the corresponding tetramethylaluminate complexes [M(AlMe₄)₃]. [Sc(AlMe₄)₃], however, had not been synthesized so far.

Reiner Anwander and colleagues, University of Tübingen, Germany, have synthesized both the required tetramethylaluminate precursor complex and trimethylscandium [ScMe₃]_n. The team reacted the complex [Li₃ScMe₆(thf)_1.2] with AlMe₃. The tetramethylaluminate product co-crystallizes with AlMe₃ to give [Sc(AlMe₄)₃(Al₂Me₆)_0.5]. This precursor can be converted to trimethylscandium by donor-induced aluminate cleavage. For this, the researchers added diethyl ether to a solution of [Sc(AlMe₄)₃(Al₂Me₆)_0.5]. [ScMe₃]_n then precipitated as a white solid.

Trimethylscandium decomposes when exposed to air, water, or temperatures over –40 °C. It can be stabilized by the addition of trimethyltriazacyclononane (Me₃TACN), which gives the complex [(Me₃TACN)ScMe₃]. This complex is stable enough to be structurally characterized.

• Trimethylscandium,
  Damir Barisic, Dominic Diether, Cäcilia Maichle-Mössmer, Reiner Anwander,
  J. Am. Chem. Soc. 2019.
  https://doi.org/10.1021/jacs.9b06879