Synthesis and characterization of 2-t-butylimino-functionalized indolyl rare-earth metal amido complexes for the catalytic addition of terminal alkynes to carbodiimides: the dimeric complexes with the alkynide species in the μ–η1:η2 bonding modes

Abstract

A series of new rare-earth metal amido complexes bearing a 2-t-butylimino-functionalized indolyl ligand were synthesized via dehydrogenation of a secondary amine, and their reactivities and catalytic performances were investigated. The reactions of 2-(^tBuNHCH₂)C₈H₅NH (1) with rare-earth metal amides [(Me₃Si)₂N]₃RE(μ-Cl)Li(THF)₃ afforded the complexes [2-(^tBuNCH)C₈H₅N]RE[N(SiMe₃)₂]₂ (RE = Er (2), Y (3), Dy (4), Sm (5), Nd (6)) containing the bidentate ligand via dehydrogenation of the amine to the imine group. Complexes 2–6 exhibited an excellent catalytic activity for the addition of terminal alkynes to carbodiimides affording a series of corresponding N,N′-dialkyl-propiolamidines. The catalysts can also be efficiently used for the preparation of the sterically bulky N,N′-diaryl-propiolamidine. Furthermore, the dimeric complexes {(μ–η¹:η²-RCC)RE[2-(^tBuNCH)C₈H₅N]₂}₂ (11: RE = Y, R = Ph; 12: RE = Yb, R = SiMe₃), with the alkynyl ligand in the μ–η¹:η² haptic modes, were isolated in attempts to study the catalytic mechanism.