In this study, using density functional theory (DFT), the effect of appended s-block metal ion crown ethers were investigated upon the redox properties of nitridomanganese(V) salen complexes, [(salen)MnV(N)(Mn+-Crown ether)]n+ (salen = N,N’ bis(salicydene)ethylenediamine, where, M = Na+, K+, Ba2+, Sr2+ for 1Na, 1K, 1Ba, 1Sr, respectively; A = complex without Mn+-Crown and B = without Mn+). Calculations explore the impact of non-redox active s-block cations on kinetics and thermodynamics of methane activation. Comparison of NBO analysis of the MnN bond order, bond length and stretching frequencies changes after oxidation for all species support that for A.+ , B.+ and 1Na.+ MnN has more nitridyl character, while a nitride form is more dominant for 1K, 1Ba and 1Sr. Complexes A and B with no alkali or alkaline earth metal ion yield lower oxidation free energies as compared to the complexes with coordinated s-block metal ions. The results reveal that ΔGrxn(e&lt;span style="font-size:10.8333px"&gt;-&lt;/span&gt;) and thus E1/2 are quite sensitive to the point charge (q) of the s-block metal ions (1 for K+/Na+ and 2 for Ba2+/Sr2+). Computations suggest that the degree of delocalization of the HOMO electrons on to the supporting ligand is dictated by the chelated s-block metal ion and is the source of their impact upon the properties of the resulting complexes. Methane activation by A, 1K and 1Ba complexes proceeds via a hydrogen atom abstraction (HAA) pathway with reasonable barriers for all complexes with ~ 3 kcal/mol difference in energy.

Effect of s-block metal ion on redox properties of Mn(V) salen-crown ether complexes: Methane activation

2019 Fall National Meeting

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