Discriminating role of bases in diketonate copper(I)-catalyzed C-O couplings: phenol versus diarylether.

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, (1)H 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.