Photolytic hydride elimination

Photocatalysis of alkene isomerizations and related processes has also been noted for a number of other common carbonyls including Fe(CO)s, Fe(CO)4PPh3, Mo(CO)6, W(C0)6, Ru(CO)4PPh3 and Ru3(CO)i2 [61,74,79-82], In some cases quantum yields substantially in excess of unity have been reported consistent with the photolytic formation of a catalytically active species capable of numerous turnovers. The photocatalysis of 1-pentene hydrogenation by Fe(CO)s is accompanied by isomerization of the substrate to 2-pentene [57], Such a pathway could occur via a -hydride elimination pathway comparable to the reverse of step 2 in Scheme I, but a more likely pathway would be via a C-H insertion reaction of the intermediate Fe(CO)3(alkene) to give an alkyl hydride intermediate as in eq. 20. 

Transition metal hydride complexes of the second- and third-row transition are common, and frequently thermally stable under ambient conditions. They can be synthesized by reactions involving hydrides, protons, or by the oxidative addition of hydrogen to a low valent complex. Hydride complexes of these metals will often undergo reductive elimination of hydrogen under photolytic conditions, which is the reverse of the oxidative addition reaction that can be used in their synthesis ... 

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