Mechanisms of norbornadiene dimerization to Binor-S using cationic CoI, Rh,Iand IrIcatalysts

We investigated the transition metal-catalyzed reaction mechanisms of NBD dimerization to Binor-S using cationic Co(I), Rh(I), and Ir(I) catalysts, using mPW1PW91, mPW1K, and B3LYP density functional methods. Our results indicate that the monomeric metal center has the ability to bind with four double bonds of two NBD molecules with a syn spatial geometry to form a penta-coordinated complex. We designed three possible pathways, but found two of them blocked. The favored pathway involves three steps from the reactant precursor to the product precursor: the first step is the formation of a single bond to connect two NBD units, the second is the alkene insertion leading to the formation of the three-membered ring structure, and the final step is the formation of the final product precursor. Orbital analysis showed metal...C-C sigma agostic interaction in the product precursor, which is in agreement with the previous experimental findings. In addition, we found that the solvent and counter-ions had significant effects on the dimerization reactions.