Abstract
A water-soluble PdCl2(NH3)2/cationic 2,2′-bipyridyl system was found to be a highly efficient catalyst for Stille coupling of aryl iodides and bromides with organostannanes. The coupling reaction was conducted at 110 °C in water, under aerobic conditions, in the presence of NaHCO3 as a base to afford corresponding Stille coupling products in good to high yields. When aryltributylstannanes were employed, the reactions proceeded smoothly under a very low catalyst loading (as little as 0.0001 mol %). After simple extraction, the residual aqueous phase could be reused in subsequent runs, making this Stille coupling economical. In the case of tetramethylstannane, however, a greater catalyst loading (1 mol %) and the use of tetraethylammonium iodide as a phase-transfer agent were required in order to obtain satisfactory yields.
Highlights
The palladium-catalyzed cross-coupling of aryl halides or pseudo-halides with organo-stannanes, known as the Stille coupling, is one of the most powerful methods for the straightforward construction of carbon–carbon bonds in synthetic chemistry [1,2,3]
Stille coupling reaction include the stability and functional group tolerance of stannanes, the broad reaction scope of aryl halides and pseudo-halides, and its chemoselectivity; this reaction has been widely applied in natural product synthesis [4,5,6,7,8,9,10], biological research [11], and for pharmaceutical purposes [12]
Several new strategies involving heterogenized homogeneous catalysts have been developed for recycling and reusing catalysts, including the use of Pd complexes supported by silica gel [13,14], polymers [15,16], nanoparticles [17,18], porous metal−organic frameworks [19], bulky proazaphosphatrane ligands [20], mesoporous silica [21,22,23,24,25,26], and metal nanoparticles [27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42]
Summary
The palladium-catalyzed cross-coupling of aryl halides or pseudo-halides with organo-stannanes, known as the Stille coupling, is one of the most powerful methods for the straightforward construction of carbon–carbon bonds in synthetic chemistry [1,2,3]. The development of a recyclable and reusable catalytic system is highly attractive and valuable from the viewpoints of green chemistry and practical application To circumvent this problem, several new strategies involving heterogenized homogeneous catalysts have been developed for recycling and reusing catalysts, including the use of Pd complexes supported by silica gel [13,14], polymers [15,16], nanoparticles [17,18], porous metal−organic frameworks [19], bulky proazaphosphatrane ligands [20], mesoporous silica [21,22,23,24,25,26], and metal nanoparticles [27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42]. Combinations of palladium complexes with several green solvents, such as ionic liquids [43,44,45], polyethylene glycol [46,47,48,49,50], H2 O [51,52,53,54], or H2 O in the presence of surfactants [55,56,57], have been applied as reusable catalytic systems
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