This proposal is a planning grant to develop a research program which probes the mechanisms by which cyclometalation takes place. Issues to be addressed include how the C-H bond approaches the metal atom, how the metal center prepares itself for subsequent insertion into the C-H bond, whether the mechanism involves an unsaturated metal site, how steric effects determine which C-H bond participates in the reaction, and whether there is a difference between intermolecular and intramolecular mechanisms. Chromium and tungsten phosphines and arsines will be studied. Reactions will also be studied by flash photolysis to detemine whether thermal and excited state reactions proceed by the same mechanisms. %%% This is a planning grant to investigate the mechanism of a very widespread type of reaction -- cyclometalation. The reaction is of considerable commercial importance and a better understanding of it would be important to many industrial processes.
