Photochemistry of Carbonyl Complexes

The photosensitivity of metal carbonyls has been known almost as long as the class of coordination compounds itself. Among no other group of inorganic compounds may one find so many light-sensitive materials. Hence photochemical reactions of metal carbonyls have found wide applications for synthetic purposes. However, whereas much research has been done to understand the thermal reactions," the mechanism leading to photochemical reactions of metal carbonyls is not yet well investigated. The papers that have appeared on the photochemistry of metal carbonyls are largely restricted to preparative aspects, although some preliminary attempts have been made to correlate the photochemical reaction with the electronic structure of these compounds. Two excellent reviews of the photochemistry of metal carbonyls are of special importance. 5 In 1964 the first review was published by Strohmeier, who did pioneering work in this field, and in 1969 von Gustorf and Grevels presented a comprehensive survey on this subject. During the last few years considerable progress has been made, particularly in the investigation of primary photochemical steps. However, the lack of sufficient information on the complicated electronic structures of metal carbonyls remains an obstacle to the understanding of their photochemical reactions. Since the metal in most carbonyl complexes, such as Cr(CO)6, has the formal oxidation state, zero, a simple electrostatic picture can not account for the stability of these compounds. Only MO theory provides a model that is in agreement with the chemical and physical properties of metal