The influence of secondary interactions on the [Ni(O₂)]⁺ mediated aldehyde oxidation reactions

A rate enhancement of one to two orders of magnitude can be obtained in the aldehyde deformylation reactions by replacing the -N(CH₃) groups of [Ni^III(O₂)(Me₄[12]aneN₄)]⁺ (Me₄[12]aneN₄ = 1,4,7,10-tetramethyl-1,4,7,10-tetraazacyclododecane) and [Ni^III(O₂)(Me₄[13]aneN₄)]⁺ (Me₄[13]aneN₄ = 1,4,7,10-tetramethyl-1,4,7,10-tetraazacyclotridecane) complexes by -NH in [Ni^III(O₂)([12]aneN₄)]⁺ (2; [12]aneN₄ = 1,4,7,10-tetraazacyclododecane) and [Ni^III(O₂)([13]aneN₄)]⁺ (4; [13]aneN₄ = 1,4,7,10-tetraazacyclotridecane). Based on detailed spectroscopic, reaction-kinetics and theoretical investigations, the higher reactivities of 2 and 4 are attributed to the changes in the secondary-sphere interactions between the [Ni^III(O₂)]⁺ and [12]aneN₄ or [13]aneN₄ moieties, which open up an alternative electrophilic pathway for the aldehyde oxidation reaction. Identification of primary kinetic isotope effects on the reactivity and stability of 2 when the -NH groups of the [12]aneN₄ ligand are deuterated may also suggest the presence of secondary interaction between the -NH groups of [12]aneN₄ and [Ni^III(O₂)]⁺ moieties, although, such interactions are not obvious in the DFT calculated optimized structure at the employed level of theory.