Preparation of chiral diimino- and diaminodiphosphine ligands and their Cu^I and Ag^I complexes. X-ray crystal structures of [Cu(1S,2S-cyclohexyl-P₂N₂)][PF₆] and [Ag(1R,2R-cyclohexyl-P₂N₂H₄)][BF₄]

The interaction of optically pure 1R,2R-diammoniumyclohexane mono-(+)-tartrate and 1S,2S-diammoniumcyclohexane mono-(-)-tartrate with 2 equiv. of o-(diphenylphosphino)benzaldehyde in the presence of 2 equiv. of potassium carbonate in a refluxing ethanol/water mixture gave the optically pure condensation products N,N′-bis[o-(diphenylphosphino)benzylidene]-1R,2R-diiminocyclohexane [1R,2R-cyclohexyl-P₂N₂, (R,R)-I] and N,N′-bis[o-(diphenylphosphino)benzylidene]-1S,2S-diiminocyclohexane [1S,2S-cyclohexyl-P₂N₂, (S,S)-I], respectively, in good yield. Reduction of optically pure (R,R)-I and (S,S)-I with NaBH₄ in ethanol gave the optically pure reduced products N,N′-bis[o-(diphenylphosphino)benzylidene]-1R,2R-diaminocyclohexane [1R,2R-cyclohexyl-P₂N₂H₄, (R,R)-II] and N,N′-bis[o-diphenylphosphino)benzylidene]-1S,2S-diaminocyclohexane [1S,2S-cyclohexyl-P₂N₂H₄, (S,S)-II], respectively, in good yield. The coordination behaviour of I and II toward salts of Cu^I and Ag^I have been examined. The interaction of [Cu(CH₃CN)₄][X] (X = ClO^-₄, PF^-₆) with 1 equiv. of optically pure L₄ [L₄ = (R,R)-I, (S,S)-I, (R,R)-II and (S,S)-II] gave the corresponding optically pure [CuL₄][X] complexes, III-VI [IIIa, L₄ = (R,R)-I, X = PF^-₆, IIIb, L₄ = (R,R)-I, X = ClO₄, IV, L₄= (S,S)-I, X = PF^-₆; Va, L₄ = (R,R)-II, X = PF^-₆, Vb, L₄ = (R,R)-II, X = ClO^-₄, VI, L₄ = (S,S)-II, X = PF^-₆], in good yield. For the Cu^I complexes, the L₄ ligand acted as a tetradentate ligand. However, a variable-temperature ³¹P [¹H] NMR study of IIIb shows that at ambient temperature one of the imino groups of the tetradentate ligand undergoes rapid dissociation to form a tridentate ligand. The interaction of AgBF₄ with 1 equiv. of optically pure L₄ [L₄ = (R,R)-I, (S,S)-I, (R,R)-II and (S,S)-II] gave the corresponding optically pure [AgL₄][BF₄] complexes, VII-X [VII, L₄ = (R,R)-I; VIII, L₄ = (S,S)-I; IX, L₄ = (R,R)-II; X, L₄ = (S,S)-II], in good yield. For the Ag^I complexes, the L₄ ligand acted as a tetradentate ligand with the two amino groups coordinated unsymmetrically to the silver. A variable temperature ³¹P [¹H] NMR study of VII suggests that at high temperature the complex exists as a tri-coordinated complex. The structures of IV and IX were established by X-ray diffraction studies.