Mechanistic study of the photofragmentation of the clusters [Os3(CO)10(diene)] (diene=cis-1,3-butadiene, 1,3-cyclohexadiene): direct observation of the open-triangle primary photoproduct with nanosecond time-resolved infrared and UV–Vis spectroscopy

The photochemistry of the clusters [Os3(CO)10(diene)] (diene=cis-1,3-butadiene, 1,3-cyclohexadiene) was studied in detail. Upon near-UV irradiation photofragmentation occurs to give mononuclear [Os(CO)3(diene)]. The second fragmentation product [Os2(CO)7] was trapped by reaction with CO, or with alkenes at low temperatures, to produce the dinuclear complexes [Os2(CO)7(L)2] (L=CO, ethene, 1-octene). The fragmentation was studied further with nanosecond time-resolved UV–Vis and IR spectroscopy and was found 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 that this intermediate has a coordinatively unsaturated open-triangle structure with two bridging carbonyl groups, one bridging the split (CO)4OsOs(CO)2(diene) bond.