Synthesis, resolution and reactions of (±)-(2-aminophenyl)methylphenylphosphine. Crystal and molecular structure of (R*,R*, S*, R*)-(±)-(1,3-bis{[2-(methylphenylphosphino)phenyl]amino}propane)nickel(II) perchlorate

Abstract

Asymmetric bidentate (±)-(2-aminophenyl)methylphenylphosphine has been prepared in 80% yield from (2-aminophenyl)diphenylphosphine via the secondary phosphine (±)-(2-aminophenyl)phenylphosphine. The chiral tertiary phosphine has been resolved by the method of metal complexation via the separation by fractional crystallisation of a pair of internally diastereomeric palladium(II) complexes containing the racemic ligand and (S)-[1-(1-ethyl)naphthyl]dimethylamine. The optically pure antipodes of the phosphine have α± 160°(589 nm, CH₂Cl₂). A number of square-planar bis(bidentate ligand) complexes of bivalent nickel, palladium and platinum containing the various forms of the ligand have been prepared and their solution behaviour studied by ¹H and ³¹P-{¹H} NMR spectroscopy. Monodeprotonation of the co-ordinated amino groups in the complexes has also been achieved by reaction with anhydrous sodium carbonate in acetone. The palladium(II) and platinum(II) complexes form cis diastereomers exclusively, whereas trans diastereomers were observed for the nickel(II) analogues. Furthermore, most of the complexes are kinetically labile. Reaction of (±)-(2-aminophenyl)methylphenylphosphine with n-butyllithium and N,N,N′,N′-tetramethylethylenediamine in tetrahydrofuran followed by the addition of 1,3-bis(p-tolylsulfonyloxy)propane gave the quadridentate ligand (R*,R*)- and (R*,S*)-1,3-bis{[2-(methylphenylphosphino)phenyl]amino}propane. The (R*,R*) and (R*,S*) forms of the quadridentate ligand have been separated by complexation to nickel(II). The structure of the nickel(II) complex containing the (R*,R*) form of the quadridentate ligand, viz. (R*,R*,S*,R*)-(1,3-bis{[2-(methylphenylphosphino)phenyl]amino}propane)nickel(II) perchlorate, has been determined by X-ray crystallography.