Synthesis of Copper(I) Thiolate Complexes in the Thioetherification of Aryl Halides

Abstract

The copper(I) thiophenolato complexes 1–3 containing 1,10-phenanthroline (phen) and 2,9-dimethyl-1,10-phenanthroline (Me2phen) were isolated in excellent yields from reactions of [CuOtBu]4 with the dative ligands and subsequent addition of 1 equiv of arylthiol and characterized spectroscopically. X-ray structural analysis of a single crystal of [(phen)Cu(µ-SC6H5)]2 (1) revealed that this complex adopts a neutral dimeric form with a weak Cu–Cu bonding interaction. These complexes were found to react with iodoarenes to form aryl sulfide products. The intermediacy of such complexes in copper-catalyzed thioetherification of aryl halides was demonstrated by the reactivity with p-tolyl iodide and o-tolyl iodide to form two aryl thioethers with selectivities similar to those of catalytic reactions conducted with the same two iodoarenes.

Understanding the Heteroatom Effect on the Ullmann Copper-Catalyzed Cross-Coupling of X-Arylation (X = NH, O, S) Mechanism

“…The Gibbs energies computed for the formation of the complexes [(phen)Cu I (XPh)] follow the trend according to the pK a of the nucleophiles, i.e., pK a (PhNH 2 ) = 27.0, pK a (PhOH) = 9.95, and pK a (PhSH) = 6.5. In concordance with the experiments outcomes [60,65] [66,67], Chen et al [42], and Zhang et al [59][60][61]. Our results show that this disproportionation is unfavorable in nonpolar solvents while it becomes favored when the dipolar constant of the solvent increases, in good agreement with previously reported results [59][60][61].…”

“…The Cu-NHPh bond distance is within the range of distances reported for the Cu I -amido complexes (~1.865 Å). As expected, the Cu-O and Cu-S bond distances are shorter than those found for the dimer, i.e., 2.066 Å [66] and 2.340 Å [42] for Cu-O and Cu-S bonds, respectively. Additionally, the Cu-S distance is also slightly longer than those measured by Kaim and co-worked for thiolate copper complexes (ca.…”

“…While most of the evidence collected so far has shown that the active catalyst is a ligand-copper(I)-nucleophile [(L)Cu I (Nu)] species, there is no such agreement on the way this catalyst activates the aryl halide (ArY, Y = Cl, Br and I). The most invoked routes are based on either one-electron redox processes through the radical intermediate Cu I /Cu II catalytic cycle namely Single Electron Transfer (SET) and Halogen Atom Transfer (HAT) [4,[39][40][41][42], or on two-electron redox processes via a Cu I /Cu III catalytic cycle like Oxidative Addition-Reductive Elimination (OA-RE) or σ-bond Metathesis (MET) (Scheme 1) [37,38,[43][44][45][46][47][48][49][50]. Scheme 1.…”

“…They clearly showed that the aryl halide activation occurs by the [(L)Cu I (Nu)] complexes. In this regard, Hartwig et al were able to isolate and characterize a number of copper imidate, amidate, amino, phenoxide, and thiophenoxide complexes which are chemically competent to couple a variety of aryl halides [40,42,56]. The studies carried out on the reactivity of these complexes, including kinetic studies and radical clock experiments, argued against pathways involving radical intermediates.…”

Theoretical Study on Copper-Catalyzed S-Arylation of Thiophenols with Aryl Halides: Evidence Supporting the LCu(I)-SPh Active Catalyst and Halogen Atom Transfer Mechanism

“…23 Later, studies of our own also confirmed that for Ullmann O-arylation of phenols with aryl bromides a similar bromine atom transfer mechanism is the most favored among several commonly proposed mechanisms. 24 As to the S-arylation mechanism, there is one experimental study concerning the preparation and reactivity studies of a few Cu(I)-thiophenolato complexes reported by Weng and Hartwig et al 25 Cheng et al reported an ESI-MS study that characterized several Cu-thiolate intermediates during the Ullmann S-arylation reaction developed by Venkataraman et al 26 However, the mechanism is still vague and elusive. Up to now, Ullmann S-arylation has generally escaped detailed computational study.…”