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-decahydro-tribenzo[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, I] [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 (IS,45,9R,10R)-1b, respectively. Macrocycles (1S,4S,9S,10S)-1a, (1S,4S,9R,10R)-1b, and (IS,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)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 Lambda-cis-beta isomers, whereas 9b and 10a adopt the Lambda-cis-beta configuration exclusively. The bis(acetonitrile) complexes are versatile precursors and were used to prepare the bromocarbonyl analogues [FeBr(CO)(1)]BPh4 (11a and 11b).