title: Conformational analysis and synthetic approaches to polydentate perhydro-diazepine ligands for the complexation of gallium(III).
abstract: Synthetic approaches are reported to polydentate ligands based on 6-phenyl-6-amino-perhydro-1,4-diazepine. The synthetic route devised averts ring-opening reactions, allowing the exocyclic N-substituent to be introduced separately and involves a nitro-Mannich condensation, prior to chemoselective RANEY® nickel reduction. Comparison of the solid-state structures of four synthetic intermediates reveals that the seven-membered ring adopts a preferred twist-chair conformer in the solid state. Solution state NMR experiments highlight a conformational preference for the bulky aryl groups to adopt an equatorial site, pre-disposing the ligand to metal binding, by adoption of a conformation that creates a facial array of the ligand nitrogen atoms. This ligand conformation averts the formation of less stable metal complexes with differing ligation modes, notably in the binding of Ga(3+) to related ligands, where a C-methyl substituent replaces the phenyl group at the quaternary centre.
authors.affiliation: Department of Chemistry, Durham University, South Road, Durham, DH1 3LE, UK. david.parker@durham.ac.uk
authors.forename: David
authors.initials: D
authors.lastname: Parker
authors.forename: Bradley P
authors.initials: BP
authors.lastname: Waldron
mesh_terms: D001381:Azepines / Q000737:chemistry*; D018360:Crystallography, X-Ray; D005708:Gallium / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D008968:Molecular Conformation; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis* / Q000737:chemistry*; D011108:Polymers / Q000737:chemistry*
chemical_list: D001381:Azepines; D009942:Organometallic Compounds; D011108:Polymers; D005708:Gallium