The chemistry of singlet oxygen with organometallic compounds and arylphosphines will be explored. Very little research has been accomplished in this area. The basic aims are twofold: (i) To solve a number of fundamental mechanistic questions in oxidation chemistry, and (ii) to find new oxidants derived from the most benign oxidant, i.e. dioxygen. Reactive intermediates in oxygen chemistry are often difficult to detect because they themselves are powerful oxidants. We are trying to find new methods (using singlet dioxygen) to observe and possibly isolate such species and, where applicable, to investigate their potential as oxidants. Specifically, the chemistry of singlet oxygen with metal thiolates, especially S-bound cysteine will be investigated. We will explore the diverse reaction pathways such as formation of sulfenate, sulfinate, C-S bond cleavage or oxidative addition at the metal center. We will determine factors (oxidation state of metal, protic vs. aprotic environment, sterics) that determine the susceptibility of such thiolates toward oxidative damage. Thiolate ligands often serve as bridges in multinuclear complexes, and the chemistry of such species with singlet oxygen will be explored as well. Both ligand oxidation and reaction of dioxygen at the metal center are possible reactive pathways in such systems. We will address the fundamental question of how oxidation at the first metal affects reactivity at the second metal center. We will also investigate the chemistry of singlet oxygen with arylphosphines. Despite the well-known affinity of trivalent phosphorous for oxygen, there have been no previous studies of the chemistry of arylphosphines with singlet oxygen, and intermediates in the oxidation of phosphines by singlet oxygen have never been directly observed. We are planning to study these intermediates and use them as a novel "oxene"-like class of oxygen atom transfer agents.