Electron-donating groups and high ring strain promoted ring opening of methylenecyclopropanes catalyzed by rhodium and iridium complexes

The possible ring-opening pathways of X-substituted MCPs (X = NO2, CF3, F, H, Ph, CH3, OH, NH2) promoted by MH(CO)(PY3)(3) (M = Rh, Ir, Y = H, Ph) and Wilkinson's catalyst-[RhCl(PY3)(3)] (Y = H, Ph) were studied by density functional theory. The ring-opening reaction was initiated by the orbital interaction between the transition metal of catalyst and reactant MCP. The strong coordination ability of Ir with C=C double bond and the inertness of complex intermediate caused the difficulty in further reaction steps of catalyst dissociation and hydride transfer, rationalizing that IrH(CO)(PPh3)(3) catalyzed ring-opening reaction occurred at higher temperature (50 degrees C) than the RhH(CO)(PPh3)(3) catalyzed one (room temperature). Without the medium hydride in RhCl(PPh3)(3) catalyst, the C=C bond of MCP cannot insert into the RheH bond and the hydride cannot be borrowed from RhCl(PPh3)(3) like RhH(CO)(PPh3)(3) catalyst, hence making the RhCl(PPh3)(3)-catalyzed reaction much more difficult to occur. The ring-opening step is predicted to be the rate-determining step for MH(CO)(PPh3)(3) catalyst, which is different from the Cp(2)LnH (Ln - La, Lu) catalyzed reactions. Multifaceted factors of substituents including ring strain, electron-donating ability, and the steric effect of the substituents were revealed for MH(CO)(PPh3)(3) catalyzed reactions when M = Rh and Ir. The hydroxyl substituted MCP (X = OH) bears not only higher ring strain but also the stronger electron-donating ability, leading to the lowest activation energy among the studied systems. Understanding of the multifaceted factors of substituents is useful for regulating the ring-opening reaction of substituted MCP promoted by transition metal complexes. (C) 2016 Elsevier B.V. All rights reserved.