Theoretical Study of the 15- and 17-Electron Structures of Cyclopentadienylchromium(III) and Cyclopentadienylmolybdenum(III) Complexes. Dichloride and Dimethyl Compounds

International audience; The structure and the energetics of the model systems CpMX2(PH3) + PH3 ⇄ CpMX2(PH3)2 (Cp = cyclopentadienyl; M = Cr, Mo; X = Cl, CH3) are studied by performing Møller−Plesset second order (MP2) and density functional theory (DFT) calculations. Extended basis sets are employed in the geometry optimizations. The results indicate that the structural preference can be traced back to the competition between electron pairing stabilization and M−P bond dissociation energy along the spin doublet surface. At all levels of calculation, the energy splitting, a measure of the cost of pairing the electron during the promotion process from the quartet ground state to the excited d…