Axial-Site Modifications of Paddlewheel Diruthenium(II, II) Complexes Supported by Hydrogen Bonding

Abstract

The reactions of paddlewheel-type diruthenium(II, II) complexes, [Ru2(II,II)(x-FPhCO2)4(THF)2] (x-FPhCO2(-) = x-fluorobenzoate with x- = o-, m-, p-), with 2,6-diaminopyridine (dapy) and 7-azaindole (azain) afford axially capped discrete compounds, [Ru2(II,II)(x-FPhCO2)4(dapy)2] (x = o-, 1; m-, 2; p-, 3) and [Ru2(II,II)(o-FPhCO2)4(azain)2] (4), respectively. In these compounds, intramolecular hydrogen bonds are observed between NH2 groups for 1-3 or imine NH groups for 4 and oxygen atoms of carboxylate groups. In addition, hydrogen bonds of NH2···F are also observed for 1 and 4 with an o-positioned F atom on benzoate. This coordination mode, i.e., a dual bonding mode with σ-bonding and hydrogen bonding, should assist ligand coordination to the axial position of the [Ru2] unit. The Ru-N bond distance in 1-4 is shorter than that observed in related compounds reported previously. In a similar fashion, reactions with planar M(II) dithiobiuret (dtb) complexes, [M(II)(dtb)2] (M(II) = Pd(II) and Pt(II)), were carried out. One-dimensional alternating chains, [{Ru2(II,II)(o-FPhCO2)4}{M(II)(dtb)2}] (M(II) = Pd(II), 5; Pt(II), 6), were obtained, in which the hydrogen-bonding modes of NH2···O and NH2···F are present, as expected. DFT calculations for the [M(II)(dtb)2] unit revealed that the LUMO of [M(II)(dtb)2] lies at -2.159 and -1.781 eV for M = Pd and Pt, respectively, which is much higher than HOMO energy at -4.184 eV calculated for [Ru2(II,II)(o-FPhCO2)(THF)2], proving that the respective units are essentially electronically isolated in the chains.