New Yttrium Complexes Bearing Diamidoamine Ligands as Efficient and Diastereoselective Catalysts for the Intramolecular Hydroamination of Alkenes and Alkynes

New diamidoamine yttrium complexes [Y(Mes 2 N 2 NMe){N(SiHMe 2 ) 2 }(THF)] (Mes 2 N 2 NMe 2 - = (2,4,6-Me 3 C 6 H 2 NCH 2 CH 2 ) 2 NMe 2 - ), [Y(Ar 2 N 2 NMe){N(SiMe 3 ) 2 }], and [Y(Ar 2 N 2 NMe)( o -C 6 H 4 CH 2 NMe 2 )] (Ar 2 N 2 NMe 2 - = (ArNCH 2 CH 2 ) 2 NMe 2 - with Ar = 2,4,6-Me 3 C 6 H 2, 2,6-Et 2 C 6 H 3, 2,6-Cl 2 C 6 H 3 ) were prepared by transamination or arene elimination reactions starting from the corresponding trisamido or trisaryl yttrium complexes. The structures of [Y(Mes 2 N 2 NMe){N(SiHMe 2 ) 2 }(THF)] and [Y{(2,6-Et 2 C 6 H 3 ) 2 N 2 NMe}( o -C 6 H 4 CH 2 NMe 2 )] were shown by X-ray crystallography to be trigonal bipyramidal, where the amine donor and coordinated THF molecule in [Y(Mes 2 N 2 NMe){N(SiHMe 2 ) 2 }(THF)] and both amine donors in [Y{(2,6-Et 2 C 6 H 3 ) 2 N 2 NMe}( o -C 6 H 4 CH 2 NMe 2 )] occupy axial positions. All complexes catalyze intramolecular hydroamination of aminoalkynes and aminoalkenes. Those having bis(trimethylsilyl)amido or ( o -C 6 H 4 CH 2 NMe 2 ) ligands show significantly higher activity than the complex containing the bis(dimethylsilyl)amido ligand, whose activity is impeded by sluggish initiation and not by THF coordination. While [Y(Mes 2 N 2 NMe)( o -C 6 H 4 CH 2 NMe 2 )] decomposes by a first-order rate law with t 1/2 = 348 ± 8 min at 25 °C, the corresponding 2,6-diethylphenyl- and 2,6-dichlorophenyl-substituted complexes are significantly more thermally stable. The electron-withdrawing effect of the dichlorophenyl substituents increases the stability of the catalyst toward protonolysis, as exemplified by a superior activity in the cyclization of pent-4-enylamine and 5-phenylpent-4-ynylamine. Ring-closing of 1-methylpent-4-enylamine proceeds with high trans selectivity and good activity ( trans: cis = 22:1 and TOF = 7.8 h - 1 at 25 °C for [Y(Mes 2 N 2 NMe)( o -C 6 H 4 CH 2 NMe 2 )]). Bicyclization of 2-allyl-2-methylpent-4-enylamine was achieved at 60 °C, giving a mixture of endo, exo - and exo, exo -2,4,6-dimethyl-1-aza-bicyclo[2.2.1]heptane.