Bis(imino)pyridines 2-[2,6-(R 1 ) 2 C 6 H 3 NC(CH 3 )]-6-[2,6-(R 2 ) 2 C 6 H 3 NC(CH 3 )](C 5 H 3 N) (1a, R 1 = R 2 = i-Pr; 1b, R 1 = i-Pr, R 2 = CH 3 ; 1c, R 1 = R 2 = CH 3 ) were first alkylated by AlMe 3 and then hydrolyzed to aminoiminopyridines 2-[2,6-(R 1 ) 2 C 6 H 3 NC(CH 3 )]-6-[2,6-(R 2 ) 2 C 6 H 3 NHC(CH 3 ) 2 ](C 5 H 3 N) (3a, R 1 = R 2 = i-Pr; 3b, R 1 = i-Pr, R 2 = CH 3 ; 3c, R 1 = R 2 = CH 3 ). When the aminoiminopyridines were treated with AlMe 3 , the expected methane elimination was not found; alkylation at the imine functional group led to the aluminum complexes {2-[2,6-(R 1 ) 2 C 6 H 3 NC(CH 3 ) 2 ]-6-[2,6-(R 2 ) 2 C 6 H 3 NHC(CH 3 ) 2 ]-(C 5 H 3 N)}AlMe 2 (4a, R 1 = R 2 = i-Pr; 4b, R 1 = i-Pr, R 2 = CH 3 ; 4c, R 1 = R 2 = CH 3 ), which were further hydrolyzed to the bis(amino)pyridines 2-[2,6-(R 1 ) 2 C 6 H 3 NHC(CH 3 ) 2 ]-6-[2,6-(R 2 ) 2 C 6 H 3 NHC(CH 3 ) 2 ](C 5 H 3 N) (5a, R 1 = R 2 = i-Pr; 5b, R 1 = i-Pr, R 2 = CH 3 ; 5c, R 1 = R 2 = CH 3 ). The selective alkylation over elimination may come from the noninnocent property of the conjugated iminopyridine group. New magnesium, yttrium, and zirconium complexes supported by 5a ({2,6-[2,6-(i-(8)) were formed via the alkane elimination method.Since the first independent reports by Gibson, Bennett, and Brookhart that bis(imino)pyridine-supported iron and cobalt complexes were very active for olefin polymerization, 1 tremendous research has been undertaken to understand this efficient system. 2 Studies have shown that the conjugated ligand itself is noninnocent and is involved in a series of transformations such as deprotonation reactions, alkylation, and participation in redox reactions. 3,4 One of the transformations is the monoalkylation of the bis(imino)pyridine 1a to the aminoiminopyridine 3a by AlMe 3 via the aluminum complex 2a as the intermediate (Scheme 1). 3d,5 The aminoiminopyridine 3a has offered a platform to numerous complexes with unique properties and applications. 6 A further straightforward modification to the ligand framework is bis(amino)pyridine, in which both of the imine groups are replaced by amine donors. Bis(amino)pyridines exert quite different electronic and steric environments and have been applied as useful supporting ligands for transition metals which mainly have applications to polymer formation. 4,7,8 While the direct reduction of bis-(imino)pyridine to bis(amino)pyridine by sodium borohydride was previously reported, 9 this method cannot be applied to this ligand frame with bulky steric demands. The starting material was fully recovered when 1a was treated in the same way. Direct alkylation of 1a to bis(amino)pyridine 5a also does not work. 10 A general synthesis of bis(amino)pyridines was achieved by the substitution reaction of 2,6-bis(bromomethyl)-pyridine by amines. 11 We disclose here a convenient way to the bis(amino)pyridine 5 through selective alkylation of 3 by AlMe 3 followed by hydrolysis (Scheme 2). The expected formation of aluminum complex 2 from 3 via methane elimination was not found. ■ RESULT...
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