Theoretical Studies of Inorganic and Organometallic Reaction Mechanisms. 10. Reversal in Stability of Rhodium and Iridium η2-Ethene and Hydridovinyl Complexes

Abstract

Ab initio quantum mechanical calculations were used to examine models for the reaction [η3-HB(X)3](CO)M(η2-CH2CH2) → [η2-HB(X)3](CO)M(η2-CH2CH2) → [η3-HB(X)3](CO)M(H)(CHCH2), for which it is known that the equilibrium lies toward the hydridovinyl product for iridium, with X = 3-trifluoromethyl-5-methylpyrazol-1-yl, and lies toward the η2-ethene reactant for rhodium, with X = 3,5-dimethylpyrazol-1-yl, and most other related systems. The ligand models tested correspond to X = NHNH2, NHNCHF, N2C3H3 (pyrazol-1-yl), N2C3H2F (3-fluoropyrazol-1-yl), N2C3H2F (5-fluoropyrazol-1-yl), N2C3H2CH3 (3-methylpyrazol-1-yl), and N2C3H2CF3 (3-(trifluoromethyl)pyrazol-1-yl). For the iridium complexes, the restricted Hartree−Fock (RHF) optimized geometries are similar to the Moller−Plesset second-order (MP2) ones and the energy calculations at the MP2//RHF, MP2//MP2, and MP4SDQ//MP2 levels give reasonable results. For the rhodium complexes, although the RHF energies appear to be in qualitative accord with the calculated resul...