The influence of secondary interactions on the [Ni(O)] 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(CH) groups of [Ni(O)(Me[12]aneN)] (Me[12]aneN = 1,4,7,10-tetramethyl-1,4,7,10-tetraazacyclododecane) and [Ni(O)(Me[13]aneN)] (Me[13]aneN = 1,4,7,10-tetramethyl-1,4,7,10-tetraazacyclotridecane) complexes by -NH in [Ni(O)([12]aneN)] (2; [12]aneN = 1,4,7,10-tetraazacyclododecane) and [Ni(O)([13]aneN)] (4; [13]aneN = 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(O)] and [12]aneN or [13]aneN 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]aneN ligand are deuterated may also suggest the presence of secondary interaction between the -NH groups of [12]aneN and [Ni(O)] moieties, although, such interactions are not obvious in the DFT calculated optimized structure at the employed level of theory.