title: Apically linked iron(II) α-dioximate and α-oximehydrazonate bis-clathrochelates: synthesis, structure and electrocatalytic properties.
abstract: Iron(II) α-oximehydrazonate and α-dioximate bis-clathrochelates with apical hydrocarbon linkers were obtained by template condensation on an iron(II) ion followed by H(+)-catalyzed macrobicyclization of the bis-semiclathrochelate precursor with formaldehyde and triethyl orthoformate, and by transmetallation of the triethylantimony-containing clathrochelate precursor with diboron-containing bifunctional Lewis acids, respectively. The geometry of the para-phenylenediboron-capped iron(II) bis-clathrochelate studied by single-crystal X-ray diffraction is intermediate between a trigonal prism and a trigonal antiprism with a distortion angle of 20.4°; the rigidity of its C6H4 linker results in the presence of the expected three-fold pseudo-rotational B···Fe···B···B···Fe···B axis and a staggered conformation of the cyclohexane-containing chelate moieties. The cyclic voltammograms (CVs) for the oximehydrazonate bis-clathrochelates contain single one-electron (for each metallocentre, and therefore, two electrons per molecule) quasi-reversible reduction waves assigned to the redox-processes of Fe(2+/+), and no interaction is observed between the two encapsulated iron(I)-containing metallocenters; six strong electron-withdrawing ethoxy substituents in the 1,3,5-triazacyclohexane capping fragments substantially affect the potential of this reduction. The corresponding waves for the dioximate complexes are irreversible: due to the structural rigidity of the caging tris-dioximate ligands, their reduced dianionic forms are unstable on the CV time scale. The CV for the hexaethoxy bis-clathrochelate complex contains one two-electron reversible oxidation wave assigned to the metal-centered oxidation of Fe(2+/3+), whereas those for its dioximate analogs are quasi-reversible. The relative lability of the ligand cavity in binuclear oximehydrazonates causes a stabilization of both the oxidized and the reduced forms; the reduced iron(I)-containing species are highly electrocatalytically active in the hydrogen-producing 2H(+)/H2 reaction. Their higher activity as compared with that for dioximate bis-clathrochelates was explained by the higher availability of the catalytically active metallocentres for H(+) ions.
authors.affiliation: Nesmeyanov Institute of Organoelement Compounds of the Russian Academy of Sciences, 119991 Moscow, Russia.
authors.forename: Irina G
authors.initials: IG
authors.lastname: Belaya
authors.forename: Semen V
authors.initials: SV
authors.lastname: Svidlov
authors.forename: Alexander V
authors.initials: AV
authors.lastname: Dolganov
authors.forename: Genrikh E
authors.initials: GE
authors.lastname: Zelinskii
authors.forename: Tamara V
authors.initials: TV
authors.lastname: Potapova
authors.forename: Anna V
authors.initials: AV
authors.lastname: Vologzhanina
authors.forename: Oleg A
authors.initials: OA
authors.lastname: Varzatskii
authors.forename: Yurii N
authors.initials: YN
authors.lastname: Bubnov
authors.forename: Yan Z
authors.initials: YZ
authors.lastname: Voloshin
mesh_terms: D002384:Catalysis; D055664:Electrochemical Techniques; D005296:Ferrous Compounds / Q000138:chemical synthesis* / Q000737:chemistry*; D006835:Hydrazones / Q000737:chemistry*; D008958:Models, Molecular; D015394:Molecular Structure; D010091:Oximes / Q000737:chemistry*
chemical_list: D005296:Ferrous Compounds; D006835:Hydrazones; D010091:Oximes