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

New diamidoamine yttrium complexes [Y(Mes2N2NMe){N(SiHMe2)2}(THF)] (Mes2N2NMe2- = (2,4,6-Me3C6H2NCH2CH2)2NMe2-), [Y(Ar2N2NMe){N(SiMe3)2}], and [Y(Ar2N2NMe)(o-C6H4CH2NMe2)] (Ar2N2NMe2- = (ArNCH2CH2)2NMe2- with Ar = 2,4,6-Me3C6H2, 2,6-Et2C6H3, 2,6-Cl2C6H3) were prepared by transamination or arene elimination reactions starting from the corresponding trisamido or trisaryl yttrium complexes. The structures of [Y(Mes2N2NMe){N(SiHMe2)2}(THF)] and [Y{(2,6-Et2C6H3)2N2NMe}(o-C6H4CH2NMe2)] were shown by X-ray crystallography to be trigonal bipyramidal, where the amine donor and coordinated THF molecule in [Y(Mes2N2NMe){N(SiHMe2)2}(THF)] and both amine donors in [Y{(2,6-Et2C6H3)2N2NMe}(o-C6H4CH2NMe2)] occupy axial positions. All complexes catalyze intramolecular hydroamination of aminoalkynes and aminoalkenes. Those having bis(trimethylsilyl)amido or (o-C6H4CH2NMe2) 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(Mes2N2NMe)(o-C6H4CH2NMe2)] decomposes by a first-order rate law with t1/2 = 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(Mes2N2NMe)(o-C6H4CH2NMe2)]). 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.