Mechanistic study of the photofragmentation of the clusters [Os-3(CO)(10)(diene)] (diene = cis-1,3-butadiene, 1,3-cyclohexadiene): direct observationof the open-triangle primary photoproduct with nanosecond time-resolved infrared and UV-Vis spectroscopy

The photochemistry of the clusters [Os-3(CO)(10)(diene)] (diene = cis-1,3-b utadiene, 1,3-cyclohexadiene) was studied in detail. Upon near-UV irradiati on photofragmentation occurs to give mononuclear [O-3(CO)(3)(diene)]. The s econd fragmentation product [Os-2(CO)(7)] was trapped by reaction with CO, or with alkenes at low temperatures, to produce the dinuclear complexes [Os -2(CO)(7)(L)(2)] (L = CO, ethene, 1-octene). The fragmentation was studied further with nanosecond time-resolved W-Vis and IR spectroscopy and was fou nd to proceed via the initial formation of a triosmium photoproduct with a lifetime of about 100 ns in hexane. From the spectroscopic data we infer th at this intermediate has a coordinatively unsaturated open-triangle structu re with two bridging carbonyl groups, one bridging the split (CO)(4)Os-Os(C O)(2)(diene) bond. (C) 2000 Elsevier Science S.A. All rights reserved.