Aluminum Complexes Containing Cyclohexane-1,2-diyl Linked Bis(ketiminato) Ligands and Proton-Promoted Demethylation

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)AlMe2](NHCMeCHCMeO) (2) and dialuminum complex trans-C6H10[(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-C6H10[(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-C6H10(NCMeCHCMeO)2Al]2(μ-O–CH2CH=CH2)2 (6) and trans-C6H10(NCMeCHCMeO)2Al(O–C6H3–2,6-Me2) (7), respectively. All the complexes have been characterized by 1H and 13C NMR spectroscopy and X-ray diffractometry. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)