Rare-earth metal complexes stabilized by amino-phosphineligand. Reaction with mesityl azide and catalysis of the cycloaddition of organic azides and aromatic alkynes

Abstract

Stoichiometric reactions between mesityl azide (MesN₃, Mes = 2,4,6-C₆H₂Me₃) and amino-phosphine ligated rare-earth metal alkyl, LLn(CH₂SiMe₃)₂(THF) (L = (2,6-C₆H₃Me₂)NCH₂C₆H₄P(C₆H₅)₂; Ln = Lu (1a), Sc (1b)), amide, LLu(NH(2,6-C₆H₃ⁱPr₂))₂(THF) (2) and acetylide at room temperature gave the amino-phosphazide ligated rare-earth metal bis(triazenyl) complexes, [L(MesN₃)]Ln[(MesN₃)(CH₂SiMe₃)]₂ (Ln = Lu (3a); Sc (3b)), bis(amido) complex [L(MesN₃)]Lu[NH(2,6-C₆H₃ⁱPr₂)]₂ (4), and bis(alkynyl) complex (5) (L(MesN₃)Lu (CCPh)₂)₂, respectively. The triazenyl group in 3 coordinates to the metal ion in a rare η²-mode viaN^β and N^γ atoms, generating a triangular metallocycle. The amino-phosphazide ligand, L(MesN₃), in 3, 4 and 5 chelates to the metal ion in a η³-mode viaN^α and N^γ atoms. In the presence of excess phenylacetylene, complex 3a isomerized to 3′, where the triazenyl group coordinates to the metal ion in a η³ mode viaN^α and N^γ atoms. Complexes 1, 2, 3 and 4 have shown an unprecedented catalytic activity towards the cycloaddition of organic azides and aromatic alkynes to afford 1,5-disubstituted 1,2,3-triazoles selectively.