Intramolecular Alkylation of α-Diimine Ligands Giving Amido—Imino and Diamido Scandium and Yttrium Complexes as Catalysts for Intramolecular Hydroamination/Cyclization

Abstract

Treatment of alkyl complexes M(CH2SiMe3)3(THF)2 (1a: M = Sc; 1b: M = Y) with α-diimine ligands, N,N′-bis(2,6-dimethylphenyl)-1,4-diaza-1,3-butadiene (2a) and N,N′-bis(2,6-diisopropylphenyl)-1,4-diaza-1,3-butadiene (2b), afforded the corresponding amido−imino complexes M(CH2SiMe3)2(2,6-R2Ph-DAB-CH2SiMe3)(THF) (3a: M = Sc, R = Me; 3b: M = Sc, R = iPr; 4a: M = Y, R = Me; 4b: M = Y, R = iPr) by selective monoalkylation of one of two C═N bonds of the ligands followed by intramolecular H migration, while in the reactions with a less bulky α-diimine ligand, N,N′-bis(4-methylphenyl)-1,4-diaza-1,3-butadiene (2c), complex 1a gave an diamido complex ScCH2SiMe3(4-MePh-DAB-(CH2SiMe3)2)(THF)2 (5c) as a product of the double alkylation. Upon heating a hexane solution of 3b, intramolecular activation of a C—H bond of an isopropyl group of the ligand proceeded to give a scandium monoalkyl complex ScCH2SiMe3(CH2C2H4-6-iPrPh-2,6-iPr2Ph-DAB-CH2SiMe3)(THF) (6b). Among them, amido—imino complexes of yttrium became catalysts for intramolecular hydroamination/cyclization of 2,2-dimethyl-4-pentenylamine at room temperature.