Aluminum complexes containing cyclohexane-1,2-diyl linked bis(ketiminato) ligands and proton-promoted demethylation

Abstract

A series of cyclohexane-1,2-diyl linked bis(ketiminato)aluminum complexes were synthesized. Reaction of a mixture of cis- and trans-diaminocyclohexane and 2,4-pentanedione gave a mixture of cis- and trans-cyclohexane-1,2-diyl linked bis(ketimine) ligands (cis-1 and trans-1), which can be separated by fractional recrystallization. Reactions of trans-1 with 1 and 2 equiv. AlMe3 gave monoaluminum complex trans-C6H10[(NCMeCHCMeO)AlMe 2](NHCMeCHCMeO) (2) and dialuminum complex trans-C6H 10[(NCMeCHCMeO)AlMe2]2 (3), respectively. Contrarily, when 1 equiv. or excess cis-1 reacted with AlMe3, only five-coordinate, linked bis(ketiminato) aluminum complex cis-C6H 10[(NCMeCHCMeO)2AlMe] (4) could be isolated in moderate yield. Heating complex 2 at reflux in a toluene solution resulted in the elimination of 1 equiv. methane to generate a five-coordinate, linked bis-(ketiminato)aluminum complex, trans-C6H10[(NCMeCHCMeO) 2AlMe] (5). Complex 2 reacts with allyl alcohol and 2,6-dimethylphenol to form dimeric aluminum complexes [trans-C6H 10(NCMeCHCMeO)2Al]2(μ-O-CH 2CH=CH2)2 (6) and trans-C6H 10(NCMeCHCMeO)2Al(O-C6H3-2,6-Me 2) (7), respectively. All the complexes have been characterized by 1H and 13C NMR spectroscopy and X-ray diffractometry. © Wiley-VCH Verlag GmbH & Co. KGaA, 2008.