Recoverable Palladium-Catalyzed Carbon-Carbon Bond Forming Reactions under Thermomorphic Mode: Stille and Suzuki-Miyaura Reactions.

Chiao-Fan Chiu,Zong-Lin Tsai,Eskedar Tessema,Ka Long Chan,Chia-Rui Shen,Vijayanath Elakkat,Norman Lu,Han-Chang Su

doi:10.3390/molecules26051414

Abstract

The reaction of [PdCl2(CH3CN)2] and bis-4,4′-(RfCH2OCH2)-2,2′-bpy (1a–d), where Rf = n-C11F23 (a), n-C10F21 (b), n-C9F19 (c) and n-C8F17 (d), respectively, in the presence of dichloromethane (CH2Cl2) resulted in the synthesis of Pd complex, [PdCl2[4,4′-bis-(RfCH2OCH2)-2,2′-bpy] (2a–d). The Pd-catalyzed Stille arylations of vinyl tributyltin with aryl halides were selected to demonstrate the feasibility of recycling usage with 2a as the catalyst using NMP (N-methyl-2-pyrrolidone) as the solvent at 120–150 °C. Additionally, recycling and electronic effect studies of 2a–c were also carried out for Suzuki-Miyaura reaction of phenylboronic acid derivatives, 4-X-C6H4-B(OH)2, (X = H or Ph) with aryl halide, 4-Y-C6H4-Z, (Y = CN, H or OCH3; Z = I or Br) in dimethylformamide (DMF) at 135–150 °C. At the end of each cycle, the product mixtures were cooled to lower temperature (e.g., −10 °C), and then catalysts were recovered by decantation with Pd leaching less than 1%. The products were quantified by gas chromatography/mass spectrometry (GC/MS) analysis or by the isolated yield. The complex 2a-catalyzed Stille reaction of aryl iodides with vinyl tributyltin have good recycling results for a total of 8 times, with a high yield within short period of time (1–3 h). Similarly, 2a–c-catalyzed Suzuki-Miyaura reactions also have good recycling results. The electronic effect studies from substituents in both Stille and Suzuki-Miyaura coupling reactions showed that electron withdrawing groups speed up the reaction rate. To our knowledge, this is the first example of recoverable fluorous long-chained Pd-catalyzed Stille reactions under the thermomorphic mode.

Highlights

This article is an open access articleCarbon-carbon bond forming reactions are among the most useful and most widely studied synthetic transformations
As shown in Scheme 2, the Pd-catalyzed Stille arylation of vinyl tributyltin (3) with aryl iodides was selected to demonstrate the feasibility of recycling usage with 2a as the catalyst using NMP (N-methyl-2-pyrrolidone) as the solvent under thermomorphic mode, at ca 120 ◦ C for 1–8 h varying in each run for different substituents
The amount of Pd leaching of catalyst (2a) in the product solution of Stille reaction after centrifugation from the two randomly selected specific runs from each table were determined by inductively coupled plasma mass spectrometry (ICP-MS)

Summary

Introduction

Carbon-carbon bond forming reactions are among the most useful and most widely studied synthetic transformations. We have a more complete thermomorphic survey of a series of the chain length of Pd complexes and a related fluorous compound (see Figure 1 below) This type of fluorous long-chained palladium complexes 2a–c features on homogeneously catalyzing at high temperature in common polar organic solvent and turning to the heterogeneous precipitation at lower temperature. Taking their good catalytic ability and good thermal stability into consideration, these catalysts could be regarded as a very good alternative to homogeneous complexes in sustainable catalysis

Catalyst Synthesis

Thermomorphic Property Study

Aryl Iodides

Aryl Bromides

Purification of Crude Product Mixture from Pd-Catalyzed Stille Reaction

Aryl Iododes

Detection of Metal Recovery by ICP-MS

General Procedures

Starting Materials

Preparation of Palladium Complexes

Analytical Data for the Ligands and Pd Metal Complexes

Procedures in Catalytic Stille Reaction and Recovery