kovalademe3 - Dimitra Kovala-Demertzi Section of Inorganic...

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1 Dimitra Kovala-Demertzi Section of Inorganic and Analytical Chemistry, Department of Chemistry, University of Ioannina, 45110 Ioannina, e-mail:[email protected] 1. Suzuki-Miyaura reaction • The coupling of aryl halides with organoboronic acids, is one of the most important palladium-catalyzed cross-coupling reactions of both academic and industrial interest. • First published in 1979 by Akira Suzuki , the Suzuki reaction couples boronic acids (containing an organic part) to halides. The reaction relies on a palladium catalyst such as tetrakis(triphenylphosphine)palladium(0) to effect part of the transformation. The palladium catalyst (more strictly a pre-catalyst) is 4-coordinate, and usually involves phosphine supporting groups. • In many publications this reaction also goes by the name Suzuki- Miyaura reaction . It is also often referred to as "Suzuki Coupling".
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2 • The reaction is the organic reaction of an aryl -or vinyl - boronic acid with an aryl -or vinyl - halide catalyzed by a palladium(0) complex . It is widely used to synthesize poly- olefins , styrenes , and substituted biphenyls , and has been extended to incorporate alkyl bromides. Several reviews have been published [1]. Scheme 1. The Suzuki coupling of aryl chlorides . Vinyl- biphenyl- styrene Starting Materials The cross-coupling reactions of organoboron compounds with organic halides or related electrophiles provide one of the most straightforward methodologies for various carbon–carbon bond formations. The characteristics of organoboron reagents (i.e., high selectivity in cross-coupling reactions, stability, nontoxic nature, and tolerance towards functional groups) often gives the Suzuki coupling a practical advantage over other cross-coupling processes. It has now confirmed that all kinds of carbon–boron bonds including (sp3)C–B, (sp2)C–B, and (sp)C–B bonds are employed as cross-coupling partners in the coupling reactions. Among such organoboron compounds, alkynylborane derivatives were not used in the Suzuki coupling, because they are stronger Lewis acids and easily hydrolyzed in the presence of bases. The reaction also works with pseudohalides , such as triflates (OTf), instead of halides , and also with boron-esters instead of boronic acids. Relative reactivity: R-I > R-OTf > R-Br >> R-Cl Aryl halides (bromides or iodides) and triflates substituted with electron- withdrawing groups (EWGs) are suitable substrates for the cross-coupling reaction. Only aryl bromides and iodides can be used, as the chlorides only react slowly. Byproducts such as self-coupling products, coupling products of phosphine-bound aryls, are often formed. Triflate , more formally known as trifluoromethanesulfonate , is a functional group with the formula CF3SO3-. The triflate anion, CF3SO3- is an extremely stable polyatomic ion , being the conjugate base of triflic acid (CF3SO3H), one of the strongest acids known. It is defined as a superacid , because it is more acidic than pure sulfuric acid .
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3 Solvents, bases and catalysts
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This note was uploaded on 02/17/2011 for the course CHEMISTRY 101 taught by Professor Csr during the Spring '11 term at University of Louisville.

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kovalademe3 - Dimitra Kovala-Demertzi Section of Inorganic...

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