OXIDATION OF THE RUTHENIUM HYDRIDE COMPLEX (ETA-5-C5H5)RU(CO)(PPH3)H - GENERATION OF A DIHYDROGEN COMPLEX BY OXIDATIVELY INDUCED INTERMOLECULAR PROTON-TRANSFER

Ruthenium hydride (eta-5-C5H5)Ru(CO)(PPh3)H (1) undergoes a chemically irreversible oxidation at +0.39 V vs the ferrocene/ferrocenium couple. Oxidation of 1 with (eta-5-C5H5)2Fe+PF6- (3) in dichloromethane-d2 yields the known dihydrogen complex (eta-5-C5H5)Ru(CO)(PPh3)(eta-2-H2)+ (4) as a primary decomposition product. Ferrocenium oxidation of 1 in acetonitrile-d3 yielded (eta-5-C5H5)Ru(CO)(PPh3)(NCCD3)+ (2-d3), HRu(CO)(PPh3)(NCCD3)3+ (5-d9), and cyclopentadiene. Cyclopentadiene and 5-d9 were generated via the prior formation of dihydrogen complex 4. Solutions of independently prepared 4 in acetonitrile-d3 were observed to decompose to yield some 2-d3, but mostly 5-d9 and cyclopentadiene. The results are discussed in terms of an initial proton transfer from cation radical 1.+ to the Ru center of 1, yielding 4. It is proposed that a reversible, base-catalyzed deprotonation/protonation sequence generates an undetected cationic trans dihydride intermediate from which cyclopentadiene is eliminated.