Ligand design for the assembly of polynuclear complexes: Syntheses and structures of trinuclear and tetranuclear aluminum alkyl complexes bearing tripodal diamidoselenophosphinito ligands and a comparison to related tripodal triamidophosphine complexes

Reactions of the triaminophosphines P( CH2NHArR)(3) ( 1a- c, where Ar-R) 3,5-(CF3)(2)C6H3 for a; Ar-R) Ph for b, Ar-R)3,5- Me2C6H3 for c) with selenium afford the triaminophosphine selenides SedP( CH2NHArR) (3) (2a- c). The phosphine selenides 2a- c react with 4 equiv of AlMe3 at room temperature to generate the triangular trinuclear aluminum complexes [ P( CH2NArR)(2)Se](AlMe2)(3) (3a- c). The byproduct of the formation of 3a was hydrolyzed and provided CH3CH2N( H)- 3,5-( CF3)(2)C6H3. When 2a- c are treated with excess AlMe3, the corresponding tetranuclear Lewis acid- base adducts Me3Al center dot [P( CH2NArR) Se-2]( AlMe2)(3) ( 4b, c) are isolated. The reaction of P(CH2NHArR)(3) (1a-c) with 2 equiv of AlMe3 produces the dinuclear aluminum complexes P( CH2NArR)(3)Al2Me3 ( 5a- c). When 1b, c are reacted with excess AlMe3, the Lewis acid- base adducts Me3Al center dot P( CH2NArR)(3)Al2Me3 ( 6b, c) are isolated. Solid- state molecular structures were determined for complexes 2a, 2b, 2c, 3a, 3c, 4b, 5a, and 6b by X- ray crystallography.