Self-assembled coordination thioether silver(I) macrocyclic complexes for homogeneous catalysis

Zhen Cao,Brigitte Bibal,Aline Lacoudre,Cybille Rossy

doi:10.3762/bjoc.15.239

Abstract

The bis-ortho-thioether 9,10-bis[(o-methylthio)phenyl]anthracene was synthesized as a syn-atropisomer, as revealed by X-ray diffraction. This alkylaryl thioether ligand (L) formed different macrocyclic complexes by coordination with silver(I) salts depending on the nature of the anion: M2L2 for AgOTf and AgOTFA, M6L4 for AgNO3. A discrete M2L complex was obtained in the presence of bulky PPh3AgOTf. These silver(I) complexes adopted similar structures in solution and in the solid state. As each sulfur atom in the ligand is prochiral, macrocycles L2M2 were obtained as mixtures of diastereoisomers, depending on the configurations of the sulfur atoms coordinated to silver cations. The X-ray structures of the two L2·(AgOTf)2 stereoisomers highlighted their different geometry. The catalytic activity of all silver(I) complexes was effective under homogeneous conditions in two tandem addition/cycloisomerization of alkynes using 0.5–1 mol % of catalytic loading.

Highlights

Since the early advances in the late eighties [1,2,3,4,5,6,7,8,9,10], silver(I) catalysis has been widely exploited based on the versatile redox and soft Lewis acid properties of this coinage metal cation
Silver catalysis has proved its effectiveness for numerous transformations involving unsaturated bond activation [11,12,13,14,15,16,17], radical-based reactions [18,19,20] and several applications in asymmetric reactions [21,22]
None of the silver(I) catalysts based on sulfur ligands were reported so far, alkyl thioethers are soft σ-donor ligands such as crown thioethers that were largely developed as macrocyclic ligands for silver(I) [35,36,37,38,39,40,41,42,43]

Summary

Introduction

Since the early advances in the late eighties [1,2,3,4,5,6,7,8,9,10], silver(I) catalysis has been widely exploited based on the versatile redox and soft Lewis acid properties of this coinage metal cation. The two diastereoisomeric macrocycles coexisted, possibly in different ratios as the chemical shift of protons on the 9,10-phenyl and anthracene moieties were found slightly different for three different batches of silver complexes prepared by the same procedure (see Supporting Information File 1, Figure S9). In the presence of the bulky triphenylphosphine silver triflate salt, a monocoordination occurred between Ag(I) and each sulfur atom of ligand 1 leading to a discrete complex (syn1)·(Ph3PAgOTf)2, as revealed by 1H NMR and X-ray (Figure 3).

Results

Conclusion