Oxidative reactions of “half-sandwich” ruthenium compounds: formation of cationic nitrosyl ruthenium(II) derivatives

The electrochemical behaviour of the ruthenium(II) alkyl complexes [Ru(Me)Cp*(L)2] (Cp*=η5-C5Me5; L=PMe32a, 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=PMe37a, PMe2Ph 7b. R=CH2CMe3; L=PMe3) and, when in excess of NO+, the ruthenium(II) dicationic complexes [RuCp*(NO)(L)2](BF4)2 (L=PMe35a, PMe2Ph 5b). The chloro complexes [Ru(Cl)Cp*(L)2] (L=PMe31a, PMe2Ph 1b, PPh31d) react analogously with NO+ to give [Ru(Cl)Cp*(NO)(L)]BF4 (L=PMe36a, PMe2Ph 6b, PPh36d) and [RuCp*(NO)(L)2](BF4)2 (L=PMe35a, 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.