Sites of Protonation and Ligand Migration in Bimetallic Organometallic Complexes Roger L. DeKock, Department of Chemistry, Calvin College, Grand Rapids, MI 49546 Background/Introduction Sites of Protonation (Rh/Os Complex) Results We have found seven sites of protonation as shown in the accompanying graphic. The most stable is shown as structure 2. The least stable is structure 8, at 27 kcal/mol higher in energy. An intermediate structure, 6, is 8 kcal/mol higher in energy. We have examined the migration pathway of the hydrogen atom to go from bridging between the two metal atoms, 6, to formation of an agostic methyl group, 2. We have found that movement of the hydrogen atom directly between the two metals results in a transition state with an energy of about 41 kcal/mol. This is exceptionally high and is unlikely to occur under experimental conditions. This report focuses on a computational chemistry study of [RhOs(CO)3PH3(μ-CH2)(dhpm)2]+,, where dhpm is the dihydrodiphosphinomethane ligand. The purpose of this work is to examine fundamental catalytic conversions that occur at the Rh/Os center. After finding the sites of protonation, pathways of hydrogen transfer were investigated. Although sites of protonation agreed well with experiment, intriguing questions arose over the pathway by which the hydrogen reaches its final experimental position. Computational Methodology Optimization of structures was done using the hybrid functional B3LYP . The cc-pVDZ basis set was used for most atoms, while the LANL2DZ basis set was used to generate pseudopotentials for the transition metals. To understand mechanisms, we studied transition states using Gaussian 03’s QST3 function. Using B3LYP, cc-pVDZ, and LANL2DZ QST3 uses Synchronous Transit-Guided Quasi-Newton (STQN) methods to find the saddle points. Conclusions The hydrogen migration between the two metals is high in energy (41 kcal/mol) and therefore an unlikely pathway. Other mechanisms that bring the hydrogen around the metals are now being explored.