Copper(i) complexes based on ligand systems with two different binding sites: synthesis, structures and reaction with O2.

The synthesis of the ligand systems L1 and L2 with two different N3-binding sites linked through a dibenzofuran spacer and their coordination properties towards a variety of CuI precursors are reported. The reaction of L1 with copper halides leads to the formation of a bimetallic species [(L1)(CuICl)2] (1), and metallodimers [((L1)(CuIX)2)2(µ-(Cu)(µ-X)2)] (2: X = Br, 3: X = I) in which two dicopper complexes are bridged by a (µ-(Cu)(µ-X)2)-moiety whereas L2 reacts with copper chloride to afford {[Cu(L2)Cl2]}n (8). Furthermore, starting from L1 in combination with copper(i) salts of weakly coordinating anions the dicopper complexes [(L1)(CuI(NCCH3))2](BF4)2 (4), [(L1)(CuI(NCCH3))(Cu(Y))](Y) (5: Y = OTf, 6: Y = ClO4) and [(L1)(Cu(dppe))](PF6)2 (7) were isolated, and employing L2, the complexes [(L2)(CuI(NCCH3))2](Z)2 (9: Z = PF6, 10: Z = OTf) and [(L2)(Cu(dppe))](PF6)2 (11) were obtained. Complexes 4-6 as well as 9 and 10 react rapidly with O2 to form metastable O2 adducts in acetone at -90 °C, where O2 is bound between the two copper centers within one dicopper molecule, as evidenced by UV/Vis spectroscopy, kinetic investigations, Raman spectroscopy and studies with ligands containing the isolated donor sites. The reactivity of the O2 adducts towards selected substrates was also investigated, showing their ability to act as electrophiles as well as nucleophiles.

O2 activation at a trispyrazolylborato nickel(ii) malonato complex.

To support mechanistic inferences made for an iron-based dioxygenase model, a nickel analogue, i.e. a TpNi-malonate (1) was prepared. 1 proved to represent a rare case of a nickel complex reacting with O2 in a controlled manner - mechanistically different from the iron case - and leads to hydroxylation of the malonate.

A high-spin square planar iron(ii)-siloxide and its tetrahedral allogon - structural and spectroscopic models of Fe-zeolite sites.

The famous α-Fe active sites in Fe-zeolites have recently been revealed to correspond to mononuclear high-spin iron(ii) centres in square planar coordination environments. Here we report a first iron siloxide complex which represents a faithful structural and spectroscopic model of such sites. Notably, also an allogon with a distorted structure exists and could be crystallised.

A Hexanuclear Iron(II) Layer with Two Square-Planar FeO4 Units Spanned by Tetrasiloxide Ligands: Mimicking of Minerals and Catalysts.

A hexanuclear iron(II) siloxide complex has been prepared by reacting an incompletely condensed silsesquioxane first with NaOMe and then with Fe(OTf)2. In the process of product formation, the siloxane framework undergoes a transformation and it was shown that this happens already upon addition of base: Treatment of the ligand precursor with NaOMe leads to a completely condensed silsesquioxane cage with 12 Si atoms that is composed of 2 equiv of the tetrasiloxide ligands found in the product complex. Its iron centers form a two-dimensional array reminiscent of the situations found in minerals and two-dimensional oxide films caused by segregation of FeOx and silica. As the hexairon(II) assembly contains two high-spin square-planar FeO4 units-suggested to represent the active sites in Fe-zeolites, which react with N2O to generate strongly oxidizing sites-it was treated with Me3NO. This led to the oxidation of two of the iron centers to the oxidation state +III and elimination of one iron ion, so that a pentanuclear, mixed valent iron siloxide was formed. All complexes were fully characterized.