Dienes, Versatile Reactants in the Photochemistry of Group 6 and 7 Metal Carbonyl Complexes

Publisher Summary This chapter describes the preparative aspects of the photochemistry of carbonyls of the group 6 and group 7 elements and some key derivatives, with the exception of technetium with conjugated and cumulated dienes. Not only carbonyl substitution reactions by the dienes but also C–C bond formation, C–H activation, C–H cleavage, and isomerizations due to H shifts, have been observed, thereby leading to various types of complexes. With mononuclear transition-metal carbonyls, photochemically induced substitutions of one or two carbonyl ligands by a diene can be expected to be the only reactions. Although complexes with C–H–metal three-center, two-electron bonds were first observed several years ago, they have received increasing attention recently as model systems for C–H activation by transition-metal complexes. Ultraviolet irradiation of [Cr(CO) 3 (η 6 -l,3,5-cycloheptatriene)] in the presence of conjugated dienes causes no CO evolution. No simple η 2 - or η 4 -diene complexes could be detected from the reaction of tricarbonyl-η 5 -cyclopentadienylmethylmolybdenum with 1,3-butadiene.Ultraviolet activation of the complexes hexacarbonylbis (η 5 cyclopentadienyl) dimolybdenum and –ditungsten has been studied in detail. When decacarbonyldimanganese is irradiated photochemically at 253 K with 1,3-butadiene in n-hexane solution, four dinuclear reaction products are observed by analytical high performance liquid (HPL) chromatography.