Rationalizing the Low‐Spin Products Observed for the Reactions M+CH₃CN (M=V, Nb,Ta) Through a Non‐Spin Flip Scheme.

Abstract

Results emerging from a CASSCF‐MRMP2 study are used to explain the products observed under matrix isolation conditions for the interactions M + CH3CN (M=V(4F), Nb(6D), Ta(4F)). A two‐reaction scheme is proposed to rationalize the low‐spin inserted species detected for the niobium and tantalum interactions, mainly the quadruplet CH3‐Nb‐NC and the doublet CH2=Ta‐(H)NC compounds, respectively. According to this scheme, the radicals CH3 + M‐NC are formed in each case from the ground state of the reactants. As these radical fragments remain trapped in the matrix they can recombine themselves in a second reaction, which evolves to the low‐spin observed products. The absence of inserted products for the vanadium reaction is also explained in terms of this scheme. The picture attained for the investigated reactions fits better with the available experimental data than previous descriptions based on spin‐flip models.

Applying a Nonspin-Flip Reaction Scheme to Explain for the Doublet Sulfide Oxides SMO2 Observed for the Reactions of SO2 with V(4F), Nb(6D), and Ta(4F)

“…Recently, we studied theoretically the interactions of acetonitrile with group V transition metal atoms [19]. In accord with the results in reference 19, the products determined under matrix-isolation conditions for these reactions can be explained in terms of a nonspin flip scheme consisting of two sequential reactions involving the radical species M-NC + CH 3 .…”

“…In a previous contribution, the results obtained from matrix-isolation determinations for the reactions of V, Nb, and Ta with CH 3 CN were described in terms of a similar reaction scheme involving the radical species CH 3 + MNC [19]. As for the reactions with SO 2 discussed here, the products determined for those reactions evolve from the doublet channel activated by the rebounding of radical fragments with opposite spin.…”

Low‐Energy Pathways Found for the NH3 Activation and H2 Elimination by the Werner‐Type Complexes M(NH3)4+ (M=Fe, Ru and Os).

“…For the same reason, reactions along these channels evolve independently to their corresponding products. A similar two‐step reaction scheme has been used to rationalize the shift in the spin multiplicity between the reactants and the observed products for other interactions [33–38] …”

“…A similar two-step radical reaction scheme has been used in previous contributions to explain for the observed products in other reactions. [33][34][35][36][37][38] Although mass-spectrometry determinations on these reactions have inspired the present study, this investigation is mainly focused on the analysis of the factors that could be relevant in determining the role of the metal-ligand interactions on the NH 3 activation by the ammine complexes yielded by sequential addition of NH 3 ligands to the metallic center. However, even when our reaction models do not consider the experimental conditions of the spectroscopic determinations, there is a good agreement between the results presented herein and those obtained by mass spectrometry for the investigated interactions.…”

“…A similar two-step reaction scheme has been used to rationalize the shift in the spin multiplicity between the reactants and the observed products for other interactions. [33][34][35][36][37][38] In Figure 4 are shown the potential energy plots for these recombination reactions. As it is seen in Figure 5, the product Ru(NH 3 ) 3 (H)NH 2 + evolving from the doublet pathway is more stable than that corresponding to the quadruplet one by 38.7 kcal/mol (for both multiplicity-channels a NH 3 ligand is expelled out when the NH 2 group is been attached to the metallic center).…”