Publications (8) View all
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Article: Sulfination by Using Pd-PEPPSI Complexes: Studies into Precatalyst Activation, Cationic and Solvent Effects and the Role of Butoxide Base.
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ABSTRACT: The activation of PEPPSI precatalysts has been systematically studied in Pd-catalysed sulfination. Under the reactions conditions of the sulfide and KOtBu in toluene, the first thing that happens is exchange of the two chlorides on the PEPPSI precatalyst with the corresponding sulfides, creating the first resting state; it is via this complex that all Pd enters the catalytic cycle. However, it is also from this same complex that a tri-Pd complex forms, which is a more persistent resting state. Under standard reaction conditions, this complex is catalytically inactive. However, if additional pyridine or a smaller base (i.e., KOEt) is added, this complex is broken down, presumably initially back to the first resting state and it is again capable of entering the catalytic cycle and completing the sulfination. Of note, once the tri-Pd complex forms, one equivalent of Pd is lost to the transformation. Related to this, the nature of the cation of the sulfide salt and solvent dielectric is very important to the success of this transformation. That is, the less soluble the salt the better the performance, which can be attributed to lowering sulfide concentration to avoid the movement of the Pd-NHC complex into the above described off-cycle sulfinated resting states.Chemistry 01/2013; · 5.93 Impact Factor -
Article: The Development of Bulky Palladium NHC Complexes for the Most-Challenging Cross-Coupling Reactions.
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ABSTRACT: Palladium-catalyzed cross-coupling reactions enable organic chemists to form CC bonds in targeted positions and under mild conditions. Although phosphine ligands have been intensively researched, in the search for even better cross-coupling catalysts attention has recently turned to the use of N-heterocyclic carbene (NHC) ligands, which form a strong bond to the palladium center. PEPPSI (pyridine-enhanced precatalyst preparation, stabilization, and initiation) palladium precatalysts with bulky NHC ligands have established themselves as successful alternatives to palladium phosphine complexes. This Review shows the success of these species in Suzuki-Miyaura, Negishi, and Stille-Migita cross-couplings as well as in amination and sulfination reactions.Angewandte Chemie International Edition 01/2012; 51(14):3314-32. · 13.45 Impact Factor -
Article: Carbon-sulfur bond formation of challenging substrates at low temperature by using Pd-PEPPSI-IPent.
Chemistry 09/2011; 17(42):11719-22. · 5.93 Impact Factor -
Article: Pd-PEPPSI-IPent: low-temperature negishi cross-coupling for the preparation of highly functionalized, tetra-ortho-substituted biaryls.
Angewandte Chemie International Edition 02/2010; 49(11):2014-7. · 13.45 Impact Factor -
Article: Pd-PEPPSI-IPent: an active, sterically demanding cross-coupling catalyst and its application in the synthesis of tetra-ortho-substituted biaryls.
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ABSTRACT: Incredible Bulk: A series of N-heterocyclic carbene catalysts (see picture) were prepared and evaluated in the Suzuki-Miyaura reaction. A variety of sterically encumbered tetra-ortho-substituted biaryl products were formed from unreactive aryl chlorides using the isopentyl-substituted catalyst at temperatures ranging from 65 degrees C to room temperature. The cyclopentyl-substituted catalyst was virtually inactive, demonstrating that "flexible bulk" is essential to promote these transformations.Angewandte Chemie International Edition 03/2009; 48(13):2383-7. · 13.45 Impact Factor
