Iridium complexes aliphatic amines

The most conspicuous property of aliphatic amines, apart from their fishy smell, is their high basicity, which usually precludes N-alkylations under acidic reaction conditions (last reaction, Scheme 6.3). Hence, alkylation of amines with tertiary alkyl groups is not usually possible without the use of highly stabilized carbocations which can be formed under basic reaction conditions. Rare exceptions are N-alkyla-tions of amines via radicals (Scheme 4.2), copper-catalyzed propargylations (Scheme 6.3), and the addition of amines to some Michael acceptors and allyl palladium or iridium complexes. Better strategies for the preparation of tert-alkylamines include the addition of Grignard reagents to ketone-derived imines [13] or the reduction of tert-alkyl nitro compounds. 

In 2010, Bruneau and co-workers described an unprecedented cascade N- and C(3)-dialkylation of unactivated cyclic amines with benzylic and aliphatic alcohols using a new (arene)mthenium (II) complex 7 bearing a phosphinosulfonate ligand as the catalyst (Eq. 17) [94]. In 2012, they achieved a three-component N- and C-dialkylation reaction of the easily accessible anilines, diols, and aldehydes through tandem hydrogen transfer reactions in the presence of iridium complex 8 (Eq. 18) [95]. 

In 2011, Fujita, Yamaguchi and co-workers reported a water-soluble Cp Iridium complex (33)-catalyzed base-free A(-alkylation of amines with alcohols in water (Scheme 34) [183]. Since the catalyst is air-stable, the reactions could be readily carried out under air. Primary and secondary benzylamines, aliphatic amines, cyclic amines, anilines, as well as benzylic, aliphatic, secondary alcohols can be used to synthesize secondary and tertiary amines. Cyclic amines could also be achieved by A -alkylation of amines with diols. The authors also proposed a mechanism with hydrogen transfers from alcohols to form [Ir-H] complexes and finally to the product amines. 

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