Direct ortho-C-H Aminoalkylation of 2-Substituted Pyridine Derivatives Catalyzed by Yttrium Complexes with N,N'- Diarylethylenediamido Ligands

摘要

A mixed ligated amidoyttrium complex, Y(NBn_(2))(L1 )(THF)_(2) (8 , L1 = N ,N’ -bis(2,6-diisopropylphenyl)ethylenediamine), served as a catalyst for addition of the ortho -pyridyl C(sp~(2))—H bond of 2-substituted pyridines to nonactivated imines; complex 8 showed superior catalytic performance compared with Y[N(SiMe_(3))_(2)]_(3) (1 ) and Y[N(SiMe_(3))_(2)]_(2)(NBn_(2))(THF) (2 ). Concerning the reaction mechanism, we conducted a stoichiometric reaction of an alkylyttrium complex, Y(CH_(2)SiMe_(3))(L1 )(THF)_(2) (7 ), with 2-ethylpyridine (4e ), giving a mixture of (η~(3)-pyridylmethyl)yttrium complex 9 and (η~(2)-pyridyl)yttrium complex 10 along with elimination of SiMe_(4). Furthermore, addition of N -(tert -butyl)-2-methylpropan-1-imine (5i ) to the mixture of 9 and 10 afforded (pyridylmethylamido)yttrium complex 11 as a single product, and the catalytic activity of 11 was comparable to that of complex 8 . Kinetic analysis of the aminoalkylation reaction in the presence/absence of HNBn_(2) revealed that the reaction rate in the presence of HNBn_(2) was four times faster than that without HNBn_(2) due to acceleration of the product-eliminating step from complex 11 by HNBn_(2) to regenerate amidoyttrium complex 8 and the product. In addition, we determined that the catalytic reaction obeyed a first-order rate dependence on the catalyst concentration, independent of the imine concentration, and a second-order rate dependence on the concentration of the pyridine substrate in the reaction system, both with and without HNBn_(2). An enantiomerically pure N ,N’ -diaryl-1,2-diphenylethylenediamido ligand was applied for the C(sp~(2))—H aminoalkylation reaction in combination with Lu(CH_(2)SiMe_(3))_(3)(THF)_(2) to give chiral aminoalkylated products in moderate yield with good enantioselectivity.