Synthesis, characterization, and reactivity of dinuclear organo-rare-earth-metal alkyl complexes supported by 2-amidate-functionalized indolyl ligands: substituent effects on coordination and reactivity

Abstract

Two series of new dinuclear organo-rare-earth-metal alkyl complexes supported by 2-amidate-functionalized indolyl ligands with different haptic modes were synthesized and characterized. The treatment of [RE(CH₂SiMe₃)₃(THF)₂] with 1 equiv. of 2-(2,6-ⁱPr₂C₆H₃NHCO)C₈H₅NH (H₂L¹) and 2-(2-^tBuC₆H₄NHCO)C₈H₅NH (H₂L²) in toluene yielded the dinuclear organo-rare-earth-metal alkyl complexes {[η¹:(μ₂–η¹:η¹)-L¹]RE(CH₂SiMe₃)(THF)₂}₂ [RE = Gd (1a), Dy (1b), Y (1c), Er (1d), and Yb (1e)] and {[η¹:(μ₂–η¹:η¹):η¹-L²]RE(CH₂SiMe₃)(THF)₂}₂ [RE = Gd (2a), Dy (2b), Y (2c), Er (2d), and Yb (2e)] in good yields. When [RE(CH₂SiMe₃)₃(THF)₂] were treated with 2 equiv. of H₂L¹ or H₂L² in THF, the dinuclear organo-rare-earth-metal complexes {(η¹:η¹-HL)[η¹:(μ₂–η¹:η¹):η¹-L]RE(THF)}₂ (1ca: RE = Y, L = L¹; 2ea: RE = Yb, L = L²) were obtained. The complexes could react with small organic molecules such as N,N′-diisopropylcarbodiimide (DIC), phenyl isocyanate, N-methylallylamine, phenylacetylene, pyridine, N-phenylimidazole, or 4-dimethylaminopyridine (DMAP) to yield a series of new complexes with different reactivity patterns along with the reported rare-earth-metal alkyl complexes. In the presence of cocatalysts, these dinuclear organo-rare-earth-metal alkyl complexes could initiate isoprene polymerization with high activity (100% conversion of 2000 equiv. of isoprene in 12 h), yielding polymers with high regioselectivity (1,4 polymers up to 96.1%).