Nucleophilic Addition and α-C–H Substitution Reactions of an Imine Mediated by Dibutylmagnesium and Organolithium Reagents

Abstract

A series of nucleophilic addition reactions and α-C–H substitution reactions of an imine-containing ligand 2-(2-((((1H-pyrrol-2-yl)methylene)amino)methyl)-1H-pyrrol-1-yl)-N,N-dimethylethan-1-amine (HL1) were reported. The reactions of HL1 with 0.5 and 2 equiv of nBu2Mg, respectively, gave two complexes of compositions [Mg(L1)2] (1) and [Mg2(L2)2] (2) (H2L2 = N-((1-(2-(dimethylamino)ethyl)-1H-pyrrol-2-yl)methyl)-1-(1H-pyrrol-2-yl)pentan-1-amine). The nucleophilic addition of nBu2Mg to the C═N bond of the HL1 ligand occurred in the process for the formation of 2. Treatment of HL1 with 2 and 1 equiv of nBuLi generated [Li2(L3)2] (3) (HL3 = 2-(2-(((1-(1H-pyrrol-2-yl)pentylidene)amino)methyl)-1H-pyrrol-1-yl)-N,N-dimethylethan-1-amine) and [Li2(L1)2] (4). An α-C–H substitution of the HC═NR moiety of the HL1 ligand triggered by nBuLi was discovered in the preparation of 3. The formation of 3 demonstrates a new concept for the C–C coupling that involved inert C–H bond activation of HC═NR skeleton. The reactions of HL1 with MeLi, sec-BuLi, and tert-BuLi, respectively, were also examined. The products for both the nucleophilic addition of organolithium reagents to the C═N bond and α-C–H substitution of the HC═NR moiety of the HL1 ligand were determined. The mechanisms for the formations of 2 and 3 were rationalized by DFT calculations. The hydroboration reactions catalyzed by 2 were investigated, and these reactions characterize ample substrate scope, very good yields, and high selectivity.