Explaining the singlet complexes detected for the reaction Zr(3F) + CH3CH3 through a non-spin flip scheme.

Energy profiles for the lowest lying triplet and singlet electronic pathways that link the reactants Zr + CH3CH3 with the products observed under matrix-isolation conditions were obtained from DFT and CASSCF-MRMP2 calculations. The insertion of the metal into the C-H bond of the organic molecule to yield the oxidative addition product is not favorable for any of the investigated channels. However, the inserted structure H-Zr-CH2CH3 can be obtained from two sequential reactions involving the radical species ZrH and CH2CH3. According to this scheme, a first reaction produces the radical fragments from the ground state of the reactants. Then, the radicals can recombine themselves in a second reaction to form the inserted species H-Zr-CH2CH3. As the triplet and singlet radical asymptotes ZrH + CH2CH3 that vary only in spin of the non-metallic fragment are degenerate, the rebounding of the radicals can occur through both multiplicity channels. It is shown that the low spin channel leads to the most stable structures of the dihydride ZrH2-(CH2)2 and the vinyl metal trihydride complexes ZrH3-CH=CH2 experimentally determined for this reaction under matrix-isolation conditions. The description attained for this interaction does not invoke interactions between the triplet and singlet electronic states emerging from the reactants, as proposed by other authors.