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-(tBuN[double bond, length as m-dash]CH)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-RC[triple bond, length as m-dash]C)RE[2-(tBuN[double bond, length as m-dash]CH)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.