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)C p*(L)(2)] (Cp* = eta (5)-C5Me5; L = PMe3 2a, PMe2Ph 2b), [Ru(CH2CMe3)Cp*(PM e3)(2)] (3a), and the related [Ru(Me)Cp(PPh3)(2)] (4d) (Cp = eta (5)-C5H5) in CH2Cl2 involves a one-electron process, yielding the corresponding ruthe nium(III) paramagnetic cations, as shown by coupled electrochemical-EPR stu dies. Compounds 2-4 are oxidised by [FeCp2](+) in benzene to unidentified p aramagnetic products which may decompose giving the corresponding alkane. T he Cp* compounds react with NOBF4 affording the monocationic alkylnitrosyl derivatives [Ru(R)Cp*CNO)(L)]BF4 (R = Me; L = PMe3 7a, PMe2Ph 7b. R = CH2CM e3; L = PMe3) and, when in excess of NO+, the ruthenium(Ir) dicationic comp lexes [RuCp*(NO)(L)(2)](BF4)(2) (L = PMe3 5a, PMe2Ph 5b). The chloro comple xes [Ru(Cl)Cp*(L)(2)] (L = PMe3 1a, PMe2Ph 1b, PPh3 1d) react analogously w ith 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(PP h3)(2)] gives only [Ru(Me)Cp(NO)(PPh3)]BF4. EPR spectroscopy suggests that these nitrosylation reactions are also oxidative in character proceeding th rough ruthenium(III) intermediates. (C) 2001 Elsevier Science B.V. All righ ts reserved.