Copper(II) and Sodium(I) Complexes based on 3,7‐Diacetyl‐1,3,7‐triaza‐5‐phosphabicyclo[3.3.1]nonane‐5‐oxide: Synthesis, Characterization, and Catalytic Activity

Abstract

Abstract The reaction of 3,7‐diacetyl‐1,3,7‐triaza‐5‐phosphabicyclo[3.3.1]nonane (DAPTA) with metal salts of Cu II or Na I /Ni II under mild conditions led to the oxidized phosphane derivative 3,7‐diacetyl‐1,3,7‐triaza‐5‐phosphabicyclo[3.3.1]nonane‐5‐oxide (DAPTA=O) and to the first examples of metal complexes based on the DAPTA=O ligand, that is, [Cu II (μ‐CH 3 COO) 2 (κ O ‐DAPTA=O)] 2 ( 1 ) and [Na(1κ OO′ ;2κ O ‐DAPTA=O)(MeOH)] 2 (BPh 4 ) 2 ( 2 ). The catalytic activity of 1 was tested in the Henry reaction and for the aerobic 2,2,6,6‐tetramethylpiperidin‐1‐oxyl (TEMPO)‐mediated oxidation of benzyl alcohol. Compound 1 was also evaluated as a model system for the catechol oxidase enzyme by using 3,5‐di‐ tert ‐butylcatechol as the substrate. The kinetic data fitted the Michaelis–Menten equation and enabled the obtainment of a rate constant for the catalytic reaction; this rate constant is among the highest obtained for this substrate with the use of dinuclear Cu II complexes. DFT calculations discarded a bridging mode binding type of the substrate and suggested a mixed‐valence Cu II /Cu I complex intermediate, in which the spin electron density is mostly concentrated at one of the Cu atoms and at the organic ligand.