Reduction of the NO+ ligand in ‘half-sandwich’ ruthenium derivatives

The reduction of the tetrafluoroborate salts of the ruthenium nitrosyl dicationic [Ru(η5-C5R5)(NO)(L)2]2+ (R=Me, L=PMe3, 1a; PMe2Ph, 1b; R=H, L=PPh3, 2d) and monocationic complexes [Ru(Me)Cp*(NO)L]+ (L=PMe3, 3a; PMe2Ph, 3b) (Cp*=η5-C5Me5) has been studied by electrochemical and spectroscopic (IR, NMR, EPR) techniques. The nitrosyl complexes 1a, 1b and 2d exhibit two successive one-electron cathodic processes due to the sequential reduction of coordinated NO+ to NOradical dot and NO−, respectively. Chemical reduction yields products of rearrangement of the intermediates which have been spectroscopically characterized. EPR studies and theoretical calculations show that in the first one-electron reduction product the electron interacts with the NO nitrogen atom and that the RuNO moiety presents significant distortion from linearity. The X-ray structure of the related [Ir(Me)2Cp*(NO)]BF4 has been determined.