Highly Oxidized Ruthenium Organometallic Compounds. The Synthesis and One-Electron Electrochemical Oxidation of [Cp*Ru IV Cl 2 (S 2 CR)] (Cp* = η 5 -C 5 Me 5 , R = NMe 2 , NEt 2 , O i Pr)

Abstract

[Cp*RuIVCl2(S2CR)] (R = NMe 2, NEt2, OiPr) were synthesized by the reaction of [Cp*RuIIICl2]2 with [RC(S)S] 2. One-electron electrochemical oxidation of [Cp*RuCl 2(S2CR)] produces paramagnetic [Cp*RuCl 2(S2CR)]+, which are stable in CH 2Cl2 solution for at least several hours at 233 K. EPR experiments performed at 293 K show isotropic signals (g ≈ 2.035) with clearly defined hyperfine coupling to 99Ru and 101Ru of 25 G and with peak-to-peak line widths of 15 G. At temperatures below 153 K, axial-shaped EPR spectra were obtained with g-values close to 2 (2.050-2.008) and narrow peak-to-peak line widths (15 G). Results from DFT calculations indicate that approximately 70% of the spin density in [Cp*RuCl 2(S2CNMe2)]+ is located on the ruthenium, although there is an increase of only 0.06 in the positive charge of the metal ion as a result of the oxidation. The high spin density on Ru supports the assignment of a formally Ru(V) oxidation state, which is unprecedented in organometallic chemistry. Chemical oxidation of Cp*RuIVCl 2(S2CNMe2) with NO(PF6) in CH 3CN resulted in the isolation of [Cp*RuIV(MeCN) 2(S2CNMe2)]+2 (4), while oxidation with [(4-Br-C6H4)3N](SbCl6) in CH2Cl2 resulted in the formation of chloro-bridged dimeric [Cp*RuIVCl(S2CNMe2)]2+2 (5). When 5 is dissolved in CD3-CN/CH3CN, it immediately converts to 4. Cyclic voltammetric experiments confirmed that in both solvents the chemical oxidation process occurred through the [Cp*RuvCl2(S2CNMe2)] + intermediate.