Rare-Earth Dialkyls Supported by Silaimine-Cp Ligand: Synthesis, Reactivity, and Catalytic Addition of Alkynes and Amines to Carbodiimides

Rare-earth metal dialkyls have attracted considerable attention in a variety of chemical transformations, such as hydroelementation of unsaturated substrates and olefin polymerization. However, stable rare-earth dialkyls are still very limited in number because of their poor thermal stability. In this paper, silaimine-functionalized cyclopentadienyl ligands C₅Me₄H–Si(L)═NR (L = PhC(NtBu)₂ and R = 2,6-iPr₂C₆H₃ for 1 and SiMe₃ for 2) were applied for the synthesis of yttrium and scandium dialkyls (3–5). σ-Bond metathesis reactions of silaimine-Cp yttrium dialkyl 3 with aniline and 2,6-dimethylpyridine yielded the yttrium diamide complex (6) and the C(sp³)–H bond-activated yttrium dibenzyl complex (7), respectively. The yttrium diamidinate complex (8) was generated from the reaction of 3 with N,N′-diisopropylcarbodiimide. The yttrium and scandium dialkyls 3 and 5 and the reaction products 6-thf, 7, and 8 have been structurally characterized by X-ray diffraction analysis. Notably, silaimine-Cp yttrium dialkyl 4 displayed high activity and excellent functional group tolerance in the catalytic addition of terminal alkynes and amines to carbodiimides.