Synthesis and Reactivity of Bi-, Tri-, and Hexametallic and Zwitterionic Methyl Aluminum Complexes Containing a Phenoxide/Imine Ligand System

Addition of 3 equiv of trimethylaluminum to tris(3,5-di- tert- butyl-2-hydroxyphenyl)methane, 1 H 3, affords the simple, C 3 - symmetric, trimetallic species [ 1 (AlMe 2 ) 3 ], 2 . To disrupt the Al 3 O 3 bridging unit, one of the ortho -alkyl substituents from the tris(2-hydroxyphenyl)methane platform of 1 H 3 was substituted with a reactive aldehyde group to afford the ligands 3-(2,2‘-methylenebis(4-methyl-6- tert -butylphenol)-5-methyl-2-hydroxybenzaldehyde, 3 H 3, and 3-(2,2‘-methylenebis(4,6-di- tert -butylphenol)-5-methyl-2-hydroxybenzaldehyde, 4 H 3, respectively. Benzylamine reacts independently with both 3 H 3 and 4 H 3 specifically at the aldehyde functionality, affording the mixed donor ligands 3-(2,2‘-methylenebis(4-methyl-6- tert -butylphenol)-5-methylsalicylidenebenzylimine, 5 H 3, and 3-(2,2‘-methylenebis(4,6-di- tert -butylphenol)-5-methylsalicylidenebenzylimine, 6 H 3, in high isolable yields. Furthermore, the Salen-type ligand, 7 H 6, can be prepared from the reaction of 1,2-ethylenediamine and 4 H 3 . Two equivalents of trimethylaluminum will react with 5 H 3 and 6 H 3 to produce the binuclear aluminum compounds [( 5 )Al 2 Me 3 ], 8, and [( 6 )Al 2 Me 3 ], 9, respectively. If an additional equivalent of trimethylaluminum is added to 9, the trimetallic species [( 6 )Al 3 Me 6 ], 10, albeit as a slightly impure material, is observed, while 7 H 6 reacts in an analogous manner to afford [( 7 )Al 6 Me 12 ], 11 . Treatment of 8 with 1 equiv of DMSO produces the new complex [( 5 ){AlMe 2 }{AlMe(OSMe 2 )}], 12, wherein the substrate is coordinated to only one of a possible two aluminum centers. In contrast to this simple transformation, the separate reactions of 8 and 9 with either cyclopentanone or cyclohexanone afford the zwitterionic mononuclear complexes [( 5 H) + AlMe - ], 13, and [( 6 H) + AlMe - ], 14 . Solid-state structures are reported for 2, 6 H 3, 7 H 6, and 9 − 13 .