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

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-(Pr2C6H3NHC)-Pr-i?O)C8H5NH (H2L1) and 2-(2-(BuC6H4NHC)-Bu-t?O)C8H5NH (H2L2) in toluene yielded the dinuclear organo-rare-earth-metal alkyl complexes {[(1):((2)-(1):(1))-L-1]RE(CH2SiMe3)(THF)(2)}(2) [RE = Gd (1a), Dy (1b), Y (1c), Er (1d), and Yb (1e)] and {[(1):((2)-(1):(1)):(1)-L-2]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 {((1):(1)-HL)[(1):((2)-(1):(1)):(1)-L]RE(THF)}(2) (1ca: RE = Y, L = L-1; 2ea: RE = Yb, L = L-2) 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%).