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

Abstract

The electrochemical behaviour of the ruthenium(II) alkyl complexes [Ru(Me)Cp*(L) 2] (Cp*=η 5-C 5Me 5; L=PMe 3 2a, PMe 2Ph 2b), [Ru(CH 2CMe 3)Cp*(PMe 3) 2] ( 3a), and the related [Ru(Me)Cp(PPh 3) 2] ( 4d) (Cp=η 5-C 5H 5) in CH 2Cl 2 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 [FeCp 2] + in benzene to unidentified paramagnetic products which may decompose giving the corresponding alkane. The Cp* compounds react with NOBF 4 affording the monocationic alkylnitrosyl derivatives [Ru(R)Cp*(NO)(L)]BF 4 (R=Me; L=PMe 3 7a, PMe 2Ph 7b. R=CH 2CMe 3; L=PMe 3) and, when in excess of NO +, the ruthenium(II) dicationic complexes [RuCp*(NO)(L) 2](BF 4) 2 (L=PMe 3 5a, PMe 2Ph 5b). The chloro complexes [Ru(Cl)Cp*(L) 2] (L=PMe 3 1a, PMe 2Ph 1b, PPh 3 1d) react analogously with NO + to give [Ru(Cl)Cp*(NO)(L)]BF 4 (L=PMe 3 6a, PMe 2Ph 6b, PPh 3 6d) and [RuCp*(NO)(L) 2](BF 4) 2 (L=PMe 3 5a, PMe 2Ph 5b). In contrast [Ru(Me)Cp(PPh 3) 2] gives only [Ru(Me)Cp(NO)(PPh 3)]BF 4. EPR spectroscopy suggests that these nitrosylation reactions are also oxidative in character proceeding through ruthenium(III) intermediates.