Discriminating role of bases in diketonate copper(i)-catalyzed C–O couplings: phenolversus diarylether

Abstract

The mechanism of the formation of phenol from PhI and CsOH catalysed by copper(I) ligated to the 1,3-diketonate ket′⁻ generated from 2,2,6,6-tetramethyl-3,5-heptanedione (TMHD) has been investigated by DFT calculations associated with experimental techniques: cyclic voltammetry, ¹H NMR, and ESI-MS. Weak halogen bonding between the negatively charged O atom of [(ket′)Cu^I–OH]⁻ and PhI leads to an oxidative addition that gives (ket′)Cu^III(Ph)–OH. The latter undergoes a faster reductive elimination that delivers (ket′)Cu^I(PhOH) from which PhOH is released. PhOPh is formed in the presence of an extra base Cs₂CO₃. The two catalytic cycles of formation of PhOH or PhOPh are branched at the level of (ket′)Cu^I(PhOH) that can either afford PhOH in the presence of CsOH or be deprotonated by Cs₂CO₃ to generate [(ket′)Cu^I–OPh]⁻. The oxidative addition of [(ket′)Cu^I–OPh]⁻ to PhI leads to (ket′)Cu^III(Ph)–OPh involved in a faster reductive elimination that delivers PhOPh and the Cu^I catalyst.