Mechanism of Isomerization and Methyl Migration in Heterobimetallic Rhenium–Iridium Complexes: Experimental and DFT Study

Investigation of the mechanism of conversion of the bimetallic complex [PNP­(H)­Ir-μ­(CH2)-μ­(O)-Re­(O)2]­[PF6] (1) to its structural isomer [PNP­(Me)­(CH3CN)­Ir-ReO3]­[PF6] (2) by detailed kinetics and DFT computational studies is reported. The reaction proceeds by intramolecular rearrangement of 1 to [PNP­(Me)­Ir-ReO3]­[PF6] (S) via a methyl-bridged [PNP­(H)­Ir-μ­(CH3)-Re­(O)3]­[PF6] (P) intermediate followed by CH3CN coordination. The rate-determining step is the transformation of 1 to P displaying ΔG⧧ of 21.8 kcal/mol. Experimental kinetic results include zero-order dependence on acetonitrile, positive ΔS⧧, and deuteration of the bridging methylidene group in the reaction of 1 with CD3OD. All of these results support the proposed mechanism.