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.
Damir Barisic, Dominic Diether, Cäcilia Maichle-Mössmer, Reiner Anwander,
J. Am. Chem. Soc. 2019.