Copper ( I ) – Terpyridine , an Efficient Catalyst for the Synthesis of Symmetrical

Symmetrical diaryl trithiocarbonates were readily synthesized in excellent yields by reaction of carbon disulfide and various aryl halides under mild reaction conditions in the presence of Copper(I) – Terpyridine as an efficient catalyst. This method allows the synthesis of symmetrical diaryl trithiocarbonates in short times without the use of highly toxic starting materials.

In recent years, transition-metal catalysis has intensely changed the face of modern organic chemistry by introducing a variety of novel synthetic methods.Transition metal catalysis of carbon-heteroatom bond formation are of great demand in general organic synthesis as well as the pharmaceutical industry and material science application. 16Among them C(aryl)-S bond formation by the direct coupling of arylhalides and thiols or an in situ generated thiolate moiety 17 has received wide attention. 18In the other hand, the tridentate 2,2':6',2''-terpyridines (tpys) have been of great interest over the last few years, mostly because of their ability to chelate transition metals. 19Herein, according our previous study, 20 we report an efficient catalytic system for the synthesis of Symmetrical Diaryl Trithiocarbonates by using CuI and 4'-(4-methoxyphenyl)-2,2':6',2''-terpyridine (Mtpy) under mild reaction conditions.
To optimize the reaction with respect to catalyst, molar ratios of the catalyst aqnd ligang, base, and temperature we initially examined the reaction of iodobenzene and carbon disulfide as a model reaction, at various conditions under an aerobic atmosphere (Table 1).
As expected, the model reaction did not occur in the absence of catalyst (Table 1, entry 6) while only a 54% yield was obtained after 4 h in the absence of the ligand (Table 1, entry 13).Among the screened copper salts, copper(I) iodide resulted in the best performance (Table 1, entries 1, 7-10).Among the tested organic and inorganic bases, CsOH.H 2 O was found to be the most suitable base (Table 1, entries 1-5).Then, different copper iodide (0.5, 1 and 2 mol%) and ligand (0.5 and 1 mol%) concentrations were investigated (Table 1, entries 1, 11, 12 and 14); among them, 1 mol% of each were found to be the best (Table 1, entry 1).
After optimization, a variety of other ArX were shown to undergo the reaction smoothly, giving the desired products in high to excellent yields (Table 2).
When carbon disulfide (1 mmol) was added to the solution of CsOH.H 2 O (1 mmol) in DMSO (1 ml), and the mixture was stirred vigorously, the colorless mixture turned blood red immediately, indicating the formation of trithiocarbonate anion (CS 3 2-); in situ arylation with ArX for the appropriate times (Table 2) afforded the corresponding symmetrical trithiocarbonates in the presence of copper(I)-Mtpy as a catalyst.With progress of the reaction, the color of the solution changed from blood red to yellow.
The structures of all the known products were established from their analytical and spectral (IR, 1 H, and 13 C NMR) properties.Reactions of various aryl iodides such as iodobenzene, 4-iodoanisole, 2iodotoluene, 2-iodoanisole, 4-iodobenzonitrile, and 1-iodonaphthalene were studied under the above optimized conditions (Table 2).The reactions proceeded well, and the corresponding diaryl trithiocarbonates were obtained in high yields.2-Iodothiophene as a heterocyclic aryl iodide was found to react successfully, and the desire trithiocarbonate was produced in 93% yield (  In conclusion, copper(I)-terpyridine has been introduced as a potential catalyst for the synthesis of symmetrical diaryl trithiocarbonates.The specific advantages of this methodology include: mild reaction conditions, simple reaction work-up, short reaction times and high to excellent yield of the products without using large excess amount of toxic carbon disulfide.

Procedures
All chemicals were purchased from Merck.All products were identified by comparison of their spectral and physical data with those of the known samples.
IR spectra were obtained using an ABB FTLA 2000 instrument. 1 H NMR (400 MHz) and 13 C NMR (100 MHz) spectra were recorded on a Bruker DRX-400 Avance instrument with CDCl 3 as solution and the chemical shifts are determined by reference to residual CHCl 3 in CDCl 3 .All compounds were characterized by comparing their physical data with those in the literature.

a
Isolated yields.b References are provided for known compounds.