Heterobimetallic catalysts, containing two different metals, have gained increasing attention in recent years. For example, BP’s Cativa process, which converts methanol to acetic acid, utilizes an Ir/Ru catalyst system. Although the roles both Ir and Ru are well understood in this system, the roles of the different metals in most other systems are not. Our group uses well–defined heterobimetallic complexes to determine the roles of the adjacent metals in transformations involving C–C bond formation and C–H activation that are related to the Fischer–Tropsch process. Previous work in the group has explored the Rh/Os and Rh/Ru metal combinations, and has illustrated the much greater propensity of the Rh/Os system towards C–C bond formation than the analogous Rh/Ru system.

Current work in this area is on the Ir/Ru system. One example is the activation of allenes (see Scheme). Depending on the reaction conditions we observe the formation of C–C bonds, the activation of multiple C–H bonds or both. We are currently investigating the mechanisms of these transformations by low–temperature NMR to determine the roles of the different metals.

This study will be extended to include the Ir/Os combination in anticipation that the strong Os–C bonds, coupled with the ability of Ir to activate C–H bonds, will lead to new reactivity patterns not observed with the other combinations. Together with the previous studies, this work should provide additional clues to the roles of the different metals in heterobimetallic systems.

For more information, see Tiffany’s work