Mix and match : templating chiral Schiff base ligands to suit the needs of the metal ion

One-pot reactions of 2,2′-bipyridine-6-carbaldehyde, (1S,2S)-(−)-1,2-diphenyl-1,2-diaminoethane and FeCl2·4H2O or Zn(OAc)2·2H2O (2[thin space (1/6-em)]:[thin space (1/6-em)]1[thin space (1/6-em)]:[thin space (1/6-em)]1) at room temperature in MeOH lead to [Fe{(S,S)-5}2][PF6]Cl or [Zn{(S,S)-5}2][PF6]2 in which (S,S)-5 contains an imidazolidine ring, produced by intramolecular cyclization. This has been confirmed with the single-crystal structure of 2{P-[Fe{(S,S)-5}2][PF6]Cl}·H2O. The diastereoselectivity observed in the solid state has been confirmed by NMR spectroscopy for solutions of [Fe{(S,S)-5}2][PF6]Cl and [Zn{(S,S)-5}2][PF6]2. At room temperature, a minor product competes with the formation of [Fe{(S,S)-5}2][PF6]Cl, and the preference for these complexes is switched by carrying out the reaction in MeOH at reflux. In this case the major product is M-[Fe2{(S,S)-4}2][PF6]4 in which (S,S)-4 is the hexadentate Schiff base ligand formed by condensation of two equivalents of 2,2′-bipyridine-6-carbaldehyde with (1S,2S)-(−)-1,2-diphenyl-1,2-diaminoethane; the single-crystal structure of 4{M-[Fe2{(S,S)-4}2][PF6]4}·8Me2CO·5MeCN·3H2O confirms the assembly of a double helicate. When pyridine-6-carbaldehyde replaces 2,2′-bipyridine-6-carbaldehyde in the iron(II)-templated reaction with (1S,2S)-(−)-1,2-diphenyl-1,2-diaminoethane, the product is [Fe{(S,S)-7}2][PF6]2 (3[thin space (1/6-em)]:[thin space (1/6-em)]2 mixture of diastereoisomers in solution) in which (S,S)-7 is an asymmetrical Schiff base, formed by reaction of only one of the amine groups in (1S,2S)-(−)-1,2-diphenyl-1,2-diaminoethane. The solid state structure of P-[Fe{(S,S)-7}2][PF6]2·MeCN is presented.