Ab Initio Molecular Orbital Study of Electronic and Geometrical Structures of MCH2+ Complex and its Reactivity with H2, Where M = Co, Rh, and Ir

By using CASSCF (for optimization of geometries) and MR‐SDGI‐CASSCF (for energies) methods we have studied and compared the mechanism of reaction MCH2+ + H2, as well as the electronic and geometrical structure of the MCH2+ complex, where M = Co, Rh, and Ir. It has been found that the mechanisms of reaction MCH2+ + H2 → M+ + CH4 (1) for M = Co and Rh are similar and follow the path: MCH2++H2 → (H2)MCH2+ → [TS1, H2‐activation] → MCH4+ → M+ + CH4. The key step is activation of the H‐H bond, which has a barrier about twice as high for M = Co as for M = Rh; reaction (1) occurs more easily for M = Rh than M = Co. M = Ir completely changes the mechanism of reaction (1), which now follows the path: IrCH2+(3A2) + H2 → (H2) IrCH2+(3A2) → [TS1, H2‐activation] → (H)2 IrCH2+(1A') → [TS2, H‐migration] → HIrCH3+(3A) → [TS3, CH4‐elimination] → IrCH4+(3A2) → Ir+(5F, s1d7) + CH4. The reaction (1) is exothermic for M = Co and Rh, but endothermic for M = Ir. For M = Co and Rh, the reverse reaction M+ + CH4 can give only one product MCH4+ and does not proceed further easily; for M = Co, at elevated temperature CoCH4+may give CoH+ and CoCH3+. However, for M = Ir the reverse reaction can proceed further to give hydridomethyl HIrCH3+ and bishydrido (H)2CH2+ complexes, as well as IrCH4+.