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}{sup 5}-C{sub 5}H{sub 5})Ru(CO)(PPh{sub 3})H (1) undergoes a chemically irreversible oxidation at +0.39 V vs the ferrocene/ferrocenium couple. Oxidation of 1 with ({eta}{sup 5}-C{sub 5}H{sub 5}){sub 2}Fe{sup +}PF{sub 6}{sup {minus}} (3) in dichloromethane-d{sub 2} yields the known dihydrogen complex ({eta}{sup 5}-C{sub 5}H{sub 5})Ru(CO)(PPh{sub 3})({eta}{sup 2}-H{sub 2}){sup +} (4) as a primary decomposition product. Ferrocenium oxidation of 1 in acetonitrile-d{sub 3} yielded ({eta}{sup 5}-C{sub 5}H{sub 5})Ru(CO)(PPh{sub 3})(NCCD{sub 3}){sup +} (2-d{sub 3}), HRu(CO)(PPh{sub 3})(NCCD{sub 3}){sub 3}{sup +} (5-d{sub 9}), and cyclopentadiene. Cyclopentadiene and 5-d{sub 9} were generated via the prior formation of dihydrogen complex 4. Solutions of independently prepared 4 in acetonitrile-d{sub 3} were observed to decompose to yield some 2-d{sub 3}, but mostly 5-d{sub 9} and cyclopentadiene. The results are discussed in terms of an initial proton transfer from cation radical 1{sup {sm bullet}+} 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.