Chromium dimer spectroscopy

The spirit is to show some of the results, but also to guide users of the approach by pointing to the problems and limitations of the method. The review covers some of the newer applications in the spectroscopy of organic molecules acetone, methylenecyclopropene, biphenyl, bithiophene, the protein chromophores indole and imidazole, and a series of radical cations of conjugated polyenes and polyaromatic hydrocarbons. The applications in transition metal chemistry include carbonyl, nitrosyl, and cyanide complexes, some dihalogens, and the chromium dimer. 

The dimer [CpCr(CO)3]2 has a weak metal-metal bond and dissociates in solution at room temperature to a measurable extent to generate the 17-electron [CpCr(CO)3]. This permitted a detailed kinetic study of CO substitution in the radical, which established a rapid associative mechanism. 15,16 A comparison of these results with reactivity data17-47 for [Cp W(CO)3] suggests that CO substitution by PPh3 in the 17-electron radicals is faster for tungsten than chromium by a factor of ca. 106. Photolysis of [CpFe(CO)2]2 in conjunction with time-resolved infrared spectroscopy was... 

---