Chiral Macrocyclic N₂P₂ Ligands and Iron(II): A Marriage of Interest

The N2P2 macrocyclic ligands (5S,8S,13E,14aS,18aS,19E)-5,8-diphenyl-5,6,7,8,14a,15,16,17,18,18a-decahydro­tribenzo­[b,f,l]­[1,4,8,11]­diaza­diphospha­cyclotetradecine ((1S,4S,9S,10S)-1a) and (5E,7R,8R,9E,15S,18S)-7,8,15,18-tetraphenyl-7,8,15,16,17,18-hexahydro­dibenzo­[f,l]­[1,4,8,11]­diaza­diphospha­cyclotetradecine ((1S,4S,9R,10R)-1b) were prepared by condensing the new, enantiomerically pure synthon 2,2′-((1S,1′S)-ethane-1,2-diylbis­(phenylphosphinediyl))­dibenzaldehyde ((S,S)-8), prepared in six steps from (2R,4S,5R)-3,4-dimethyl-2,5-diphenyl-1,3,2-oxaza­phospholidine-2-borane (3)), with (1S,2S)-cyclohexane-1,2-diamine and (1R,2R)-1,2-diphenylethane-1,2-diamine under high-dilution conditions. The opposite enantiomers of the diamines gave oligomeric products. The stereospecificity of the macrocyclization reaction is explained by conformational analysis based on the X-ray structures of (1S,4S,9S,10S)-1a and (1S,4S,9R,10R)-1b. The corresponding diamino macrocycles (1S,4S,9S,10S)-2a and (1S,4S,9R,10R)-2b were prepared by reduction of the imine moiety of (1S,4S,9S,10S)-1a and (1S,4S,9R,10R)-1b, respectively. Macrocycles (1S,4S,9S,10S)-1a, (1S,4S,9R,10R)-1b, and (1S,4S,9S,10S)-2a react with [Fe­(OH2)6]­(BF4)2 in acetonitrile to give the corresponding stable, diamagnetic bis­(acetonitrile) complexes [Fe­(MeCN)2(1)]­(BF4)2 (9a and 9b) and [Fe­(MeCN)2(2a)]­(BF4)2 (10a). Complex 9a exists as a 3:1 mixture of trans and Λ-cis-β isomers, whereas 9b and 10a adopt the Λ-cis-β configuration exclusively. The bis­(acetonitrile) complexes are versatile precursors and were used to prepare the bromocarbonyl analogues [FeBr­(CO)­(1)]­BPh4 (11a and 11b).