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

摘要

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 Cs_2CO_3. 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 Cs_2CO_3 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 CuI catalyst.