Abstract:
The bispidinone (3,7-diazabicyclo[3.3.1]nonan-9-one) structure satisfies the criteria for a good chelating ligand for the synthesis of stable transition metal complexes. The bicyclic structure is comprised of two fused piperidin-4-one rings joined via the α-position. The bispidinone framework can easily be substituted at the α- (1,5), β- (2,4,6,8) or γ- (3,7) positions making the bicyclic structure ideal as the basis of a versatile ligand system. The synthesis of the bispidinones is a double Mannich condensation reaction via a Schiff's base.
A novel class of bicyclo[3.3.1]nonan-9-ones has been synthesized with nitrogen and phosphorus at the γ- positions, and variations in substitution at the α and β positions. These nitrogen-phosphorus heterobidentate ligands take advantage of the different ligating properties of nitrogen and phosphorus, creating two very different binding sites on the opposite side of the metal.
The new P-N heterobidentate ligands were made in a two-step synthesis. The double Michael addition of phenylphosphine to a substituted l,5-diphenylpenta-l,4-dien-3-one afforded a phosphorinan-4-one. The second ring was constructed through a Mannich reaction affording the 6,8-bis(4-dimethylaminophenyl)-3-R-7-phenyl-3-aza-7-phospha-9-oxobicyclo[3.3.1]nonane-l,5-dicarboxylic acid dimethyl ester I (R = a. ethyl, b. 2-methylpropyl, c. Me, d. (5)-l-napthylethyl).
An X-ray crystallographic investigation of Ic (R = Me) confirmed the molecular structure and established the twin-chair conformation that optimizes the formation of stable metal complexes.
