Palladium‐Catalyzed Polycondensation for the Synthesis of Poly(Aryl)Sulfides

Abstract

the sulfur atom in one transformation is the most desirable process, however, such a reaction is yet unprecedented. A solution to this shortcoming may be the use of hydrogen sulfide surrogates in CS cross couplings to access poly(phenyl)sulfide derivatives according to a polycondensation reaction. We and others have shown that silyl thiol, [35] thiourea [36] or potassium thioacetate [37] offer the unique access to diaryl sulfide derivatives. [36,[38][39][40][41][42] We here report the synthesis of poly(phenyl)sulfide and so far unprecedented poly(thiophene)sulfide through palladium catalyzed CS bond forming polycondensation.Poly (1,4-phenyl)sulfide is insoluble in organic solvents. Therefore, we turned our focus to alkyl-substituted phenylene derivatives to provide enhanced solubility with the aim to investigate the palladium catalyzed polycondensation reaction. 1,4-Dibromo-2,5-bis((2-ethylhexyl)oxy)benzene (1) was synthesized according to literature procedures [43] and was reacted with palladium(0) sources and hydrogen sulfide surrogates.From earlier studies in our group, we knew that the electron-rich [Pd(oTol 3 P) 2 ] complex in combination with the bis(diphenylphosphino)ferrocene ligand (dppf) performed best in the CS cross coupling to form diaryl sulfides. [38][39][40] Accordingly, we turned out attention to the optimization of the H 2 S-surrogate. Whereas thiourea [36] was inactive in the polycondensation, potassium thioacetate (KSAc, 2) was active in the conversion of 1 to polymeric material in the presence of 2 mol% Pd-catalyst (Table 1 entries 1-6). We identified impurities of the polymer after workup, which consisted according to 31 P NMR of phosphine and catalyst decomposition products. Attempted column chromatography did not lead to any improvement, so that we were not able to determine the yields of the reactions. However, NMR-spectroscopy, mass spectrometry and GPC analysis clearly show the synthesis of the poly(phenyl) sulfide polymer. The polymerization reactions displayed strong dependency on the ratio of 2 and the aryl halide. The optimum was determined to 0.94 equivalents (entry 2) as judged from the molecular weights. Such behavior is common for polycondensation reactions and optimization is required for new batches of coupling partners. Next, we studied the impact of catalyst loading on the polymerization. It was found that highest molecular weight was obtained in the presence of 10 mol% [Pd(oTol 3 P) 2 ]/dppf. However, the number average molecular weight (M n ) and the PDI were not dramatically affected by higher catalyst loadings (compare entries 2, 7 and 8 with 2, 4, and 10 mol%). Therefore, we decided to further optimize the reaction with 2 mol% of the palladium complex. Lithium salts The palladium-catalyzed CS cross coupling reaction is investigated as a novel efficient tool for the synthesis of poly(phenyl)sulfide derivatives. The reaction proceeds through the polycondensation of dibromo arenes with a H 2 S-surrogate to yield poly(aryl)sulfides. The reaction is generalized by the sy...

Imidazolyl‐Substituted Benzo‐ and Naphthodithiophenes as Precursors for the Synthesis of Transient Open‐Shell Quinoids

“…The SEM protection of the imidazole moieties was necessary during the whole process because of the poor solubility of the free amines. The double C−S cross‐coupling/cyclization sequence using potassium thioacetate as H 2 S surrogate [7c,f] was initiated by [Pd(dba) 2 ] and Xantphos. This ring closing reaction provided isomerically pure 3 as a dark orange solid in 86 % yield.…”

A Comparative Kinetic and Computational Investigation of the Carbon‐Sulfur Cross Coupling of Potassium Thioacetate and 2‐Bromo Thiophene Using Palladium/Bisphosphine Complexes

“…Only recently, we developed a polycondensation of bifunctional benzene and thiophene derivatives, providing access to poly(phenylene) and poly(thiophenylene) sulfides [11c] . However, we found that the efficiency of the polycondensation was strongly affected by the supporting bisphosphine ligands.…”

Metal-and Oxidant-Free Electrochemical Synthesis of Aryl Sulfides

“…[15][16][17][18][19] It is highly desired to develop concise and effective strategies for synthesizing functionalized aryl sulfides in organic and pharmic synthesis. [20][21][22][23][24] To date, numerous methods have been developed for the construction of the aromatic C-S bond, [25][26][27][28][29] and C-H activation have been widely applied in sulfidation reactions among those methods. [30][31][32][33][34] For example, transition metal catalysis is an effective protocol using C-H activation to build C-S bonds (Scheme 1, Eq.…”