Oxidative reactions of half-sandwich ruthenium compounds: Formation of cationic nitrosyl ruthenium(II) derivatives

Article abstract of DOI:10.1016/S0022-328X(01)00680-5

The electrochemical behaviour of the ruthenium(II) alkyl complexes [Ru(Me)Cp*(L)₂] (Cp=η⁵-C₅Me₅; L=PMe₃ 2a, PMe₂Ph 2b), [Ru(CH₂CMe₃)Cp*(PMe₃)₂] (3a), and the related [Ru(Me)Cp(PPh₃)₂] (4d) (Cp=η⁵-C₅H₅) in CH₂Cl₂ involves a one-electron process, yielding the corresponding ruthenium(III) paramagnetic cations, as shown by coupled electrochemical-EPR studies. Compounds 2-4 are oxidised by [FeCp₂]⁺ in benzene to unidentified paramagnetic products which may decompose giving the corresponding alkane. The Cp* compounds react with NOBF₄ affording the monocationic alkylnitrosyl derivatives [Ru(R)Cp*(NO)(L)]BF₄ (R=Me; L=PMe₃ 7a, PMe₂Ph 7b. R=CH₂CMe₃; L=PMe₃) and, when in excess of NO⁺, the ruthenium(II) dicationic complexes [RuCp*(NO)(L)₂](BF₄)₂ (L=PMe₃ 5a, PMe₂Ph 5b). The chloro complexes [Ru(Cl)Cp*(L)₂] (L=PMe₃ 1a, PMe₂Ph 1b, PPh₃ 1d) react analogously with NO⁺ to give [Ru(Cl)Cp*(NO)(L)]BF₄ (L=PMe₃ 6a, PMe₂Ph 6b, PPh₃ 6d) and [RuCp*(NO)(L)₂](BF₄)₂ (L=PMe₃ 5a, PMe₂Ph 5b). In contrast [Ru(Me)Cp(PPh₃)₂] gives only [Ru(Me)Cp(NO)(PPh₃)]BF₄. EPR spectroscopy suggests that these nitrosylation reactions are also oxidative in character proceeding through ruthenium(III) intermediates.