8054 sition metals. Oxidation cyclooctasulfur produces the bicyclic cation 7.46 Further examples of such transanular oxidations ?+ s-s-s 7 \ and oxidative-additions may be anticipated. Abstract: Although [IrCIH2(PPh3)3], mer-[IrH,(PPh3)3], andfac-[IrH3(PPh3)3] will not lose hydrogen under a variety of thermal conditions, irradiation with ultraviolet light readily induces elimination of Hz. Irradiation of [ IrCIH2(PPh3)3] with ultraviolet light or sunlight gives formation of [IrCI(PPh3)3] with a 254-nm quantum yield of 0.56 & 0.03. Irradiation of mer-[IrH3(PPh3)3] and fac-[IrH3(PPh3)3] leads to Hz loss with subsequent formation of internally metallated [ I m P h * ) -(PPh3)2]. The results reported herein suggest that photoinduced elimination of H2 is a general process for di-and polyhydride complexes of iridium. The lack of production of H D upon photolysis of an [IrCIH2(PPh3)3]-[IrClD~(PPh3)3] mixture demonstrates that the photoelimination of H2 from [IrCIH2(PPh3)3] proceeds in a concerted fashion. A molecular orbital description of the complexes is proposed, and the photoactive excited state is believed to involve population of an iridium-Hz antibonding orbital. The [IrCIH2(PPh3)3]-[lrCI(PPh3)3] system is an attractive model for hydrogen storage and energy storage.

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