Revisit of Unusual Ruthenium(III) Dichloro Complex

Abstract

Diverse oxidation chemistry associated with polypyridyl ruthenium complexes emerged. 1 Especially oxo-metal reagents in high oxidation state have been found to be versatile stoichiometric and/or catalytic oxidants toward a variety of organic and inorganic substrates via electron transfer, oxygen atom transfer, hydride transfer, and proton-coupled electron transfer pathways. 2 Among multiple ruthenium species appeared in the syntheses and mechanistic studies, Ru(III) complex is quite interesting material to investigate. However, there is a complication since Ru(III), once formed, undergoes disproportionation reaction to give Ru(II) and Ru(IV).Ammonium A yellow solid with 54% yield was isolated by suction filtration followed by washing with water and methanol. 5 Broad resonance peaks between −8 and 18 ppm for bipyridyl protons in the 1 H NMR spectrum for the product are observed, which suggest the existence of a paramagnetic material. The peak at 145 ppm in the 31 P NMR spectrum shown as sharp septet indicates the phosphorous atom in the PF 6 anion salt. In the ESR spectrum of the prepared complex, the g-tensor values are well matched with those of other Ru(III) complexes previously studied. 4b,6 Single crystals were grown from acetonitrile solution added to diethyl ether. A prismatic crystal of the Ru(III) of approximate dimensions of 0.3 × 0.2 × 0.2 mm was mounted and a Rigaku Rapid R-axis diffractometer equipped with graphite-monochromated Mo-Kα radiation (λ = 0.7107 Å) was employed for data collection. 7 A total of 11232 (2715 independent) reflections were collected, which yielded 1244 reflections observed for I > 2σ(I). The final agreement factors were R[F 2 > 2σ(F 2 )] = 0.0208 and wR(F 2 ) = 0.0474.The crystal structure of this salt is composed of mononuclear cationic ruthenium complex in six-coordinate with four nitrogen atoms of the bpy ligands and two chlorine atoms cis each other balanced by hexafluorophosphate anion. Figure 1 shows the perspective view of the cis-[Ru III (bpy) 2 Cl 2 ][PF 6 ] compound with atom labeling. The ruthenium atom in this molecule has an imposed two-fold rotational symmetry and there is a unique chloride and a unique bpy ring per molecular unit. Because of the ionic nature of the Ru(III), neither stacking interactions nor close contacts are observed in the lattice.As shown in Table 1, the Ru(III)-Cl bond length is 2.337(1) Å, which might otherwise have been expected in a compound of this type. 8,9