Stabilization of reactive rare earth alkyl complexes through mechanistic studies

Area of Science:

• Organometallic Chemistry
• Catalysis
• Materials Science

Background:

• Rare earth tris(alkyl) complexes, like M(CH2SiMe3)3(sol), are vital precursors and homogeneous catalysts for alkene polymerization and alkane functionalization.
• The thermal instability of these complexes, often synthesized from lithium neosilyl anion, limits their practical applications.

Purpose of the Study:

• To synthesize and kinetically characterize a new series of rare earth neosilyl solvates with enhanced kinetic stability.
• To investigate the decomposition mechanisms of rare earth neosilyl complexes and identify factors influencing their stability.

Main Methods:

• Synthesis of 12 new and characterization of 7 known rare earth neosilyl complexes, M(CH2SiMe3)3(sol), where M = Sc(iii), Y(iii), Lu(iii), Sm(iii) and sol = THF, TMEDA, DMPE, diglyme (G2), triglyme (G3).
• Comprehensive kinetic studies to determine decomposition pathways and half-lives (t1/2) of various complexes.
• Evaluation of the impact of LiCl on the reactivity and kinetics of Y(r)3(THF)2 and Lu(r)3(THF)2.

Main Results:

• Higher-denticity donors did not effectively prevent neosilyl gamma-H elimination as anticipated.
• Scandium complex Sc(r)3(G2) exhibited significantly increased kinetic stability (t1/2 = 258.1 h) compared to Sc(r)3(THF)2 (t1/2 = 43 h).
• Lutetium and Yttrium complexes showed unexpected decomposition pathways with certain donors, limiting stability.
• Small amounts of LiCl influenced the kinetics of Y(r)3(THF)2 and Lu(r)3(THF)2.

Conclusions:

• Steric hindrance alone is insufficient to guarantee kinetic stability in rare earth neosilyl complexes.
• The choice of solvent ligand and the presence of LiCl are critical factors affecting the stability and reactivity of these organometallic compounds.
• A novel synthetic route to Y(r)3(THF)2, avoiding the use of Li(r), was developed, offering a more practical precursor.