Theoretical studies of inorganic and organometallic reaction mechanisms. 20. Carbon-hydrogen and carbon-carbon bond activation of cyclopropane by cationic iridium(III) and neutral rhodium(I) and iridium(I) complexes
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The reactions of cyclopropane with the coordinately unsaturated species produced by mild thermal activation of [Cp*Ir(P(CH3)3)CH3]+L (L = Cl2CH2, OSO2CF3-) and photochemical activation of Cp*Ir(P(CH3)3)L2 and Cp*Rh(P(CH3)3)L2 (L = H2, CO) have been investigated with density functional calculations (B3LYP). The pathway for the production of endo or exo 3-allyl complexes from the reaction of cyclopropane with the IrIII model complex [CpIr(PH3)CH3]+ proceeds through C-H bond activated IrV intermediates and CH4 elimination, followed by ring opening of the iridium cyclopropyl complexes through an iridium carbene vinyl intermediate to their respective 3-allyl products. This unexpected mechanism breaks two C-C bonds simultaneously and then re-forms one en route from the iridium cyclopropane complex to the iridium allyl products. The interconversion between endo and exo 3-allyl can be assisted by solvent through an 1-allyl intermediate. The IrI and RhI model complexes CpIr(PH3) and CpRh(PH3) react with cyclopropane on their respective singlet potential energy surfaces, first forming a -agostic complex followed by a single transition state producing a kinetic product (a hydrido cyclopropyl complex). Thermal rearrangement of the cyclopropyl kinetic product proceeds back through the same -agostic complex, producing the thermodynamically more stable metallocyclobutane complex.
