No abstract

The chemistry of mixed-valence coordination compounds has been investigated extensively during the last 10 years.',2 Starting with the preparation of the Creutz-Taube ion,, much attention has been paid to binuclear complexes containing ruthenium in the formal oxidation states I1 and III.'q2 Electron transfer from Ru(I1) to Ru(II1) can occur thermally or optically by light absorption into intervalence-transfer (IT) bands. However, this photoredox process is apparently not associated with any permanent chemical change. A rapid back electron transfer seems to restore the starting complexe~.~ On the contrary, photoredox reactions following inner-and outer-sphere IT excitation from Fe(I1) and Ru(I1) to Co(II1) are wellWe report here our observation of a photochemical reaction induced by an optical Ru(I1) to Ru(II1) IT transition.Upon (9) [Ru(CN),lk does not absorb above 300 nm.' (10) This reaction proceeds not only photochemically but also thermally.At 20 'C the half-life of the ion pair was 7 X lo4 s in aqueous solution.( 1 It is suggested that photochemical product formation, following IT excitation of the ion pair, can be described by the reaction scheme given by eq 1-5. The starting ion pair is substutitionallyinert. [Ru(CN),]" is kinetically stable and also [Ru(NH3)'Cll2+ is known to undergo only a very slow aquation of C1-with a half-life greater than 10' s.I7 The ion pair, generated by IT excitation (eq l), may diffuse apart (eq 2). [ R u~~( N H , ) , C~] + aquates rapidly (eq 3) with k = 5 s-I.l8 Substitutionally labile [Ru~~(NH,),H,O]~+ l 9 reacts with [RU11(CN)6]4-(eq 4), which is present in large excess. The formation of the binuclear complex is certainly facilitated by the high opposite charges of the reacting ions. Finally, electron transfer (eq 5 ) restores ruthenium to its stable oxidation states, yielding the blue product. The low quantum yield of the overall reaction (@ = 0.002) is most likely determined by the extremely rapid thermal reversal4 of reaction 1, which competes with the diffusion apart from the primary electron-transfer products (eq 2). We tried to detect [RU (CN 1982, 104, 2312-2314 Acknowledgment. Financial support for this research by the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industrie is gratefully acknowledged. We thank a referee for valuable comments.

AbstractUpon charge transfer (Os to carbyne) excitation the carbyne complexes Os(CPh)(CO)(PPh3)2Cl and [Os(CPh)(CO)2(PPh3)2]+ with Ph = C6H5 are converted to the carbene complex Os(CHPh)(CO)(PPh3)2Cl2 in solutions containing HCl. It is suggested that the relaxed CT state can be described as square-pyramidal Os(II) complex containing a bent carbyne ligand which carries a lone pair at the coordinating carbon atom. Product formation occurs by the addition of a proton to the carbyne ligand and by attaching a chloride to the osmium completing an octahedral coordination. The cationic carbene complex thus formed is apparently not stable but undergoes a substitut ion of a CO ligand by chloride.

No abstract

Gemischt-valente Liganden scheinen auch in den 1,2-Dithiolenkomplexen von Ni", Pd" und