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Structural Design for Molecular Catalysts
Published in Qingmin Ji, Harald Fuchs, Soft Matters for Catalysts, 2019
Qingmin Ji, Qin Tang, Jonathan P. Hill, Katsuhiko Ariga
Phosphines have attracted considerable attention and have allowed for the development of catalytic systems possessing a wide scope. Buchwald et al. developed important sets of phosphines (biaryl phosphines and cyclometallated biaryl phosphines) as excellent supporting ligands for organometallic catalyst systems [24′27]. The effectiveness of these systems was attributed to a combination of electronic and steric properties of the ligands, which favor both the oxidative addition and reductive elimination steps in the catalytic cycle. They may also be used as convenient air- and moisture-stable catalyst for aryl amination reactions. It has been suggested that the biaryl group in Buchwald’s phosphines may contribute to the stabilization of ligand–metal complexes by establishing π interactions with the Pd(0) center. Based on Pd(dba)2 using biaryl phosphine ligand as catalyst, Buchwald and Martin showed highly catalytic efficiency for Kumada–Corriu reactions even at temperatures as low as −65°C [28]. The Pd-catalyzed Kumada–Corriu cross-coupling reaction manifests a broad substrate scope. Ortho-, meta-, and para-substituted biaryls could all be efficiently prepared. In addition, a variety of functional groups were tolerated, including nitriles, amines, esters, heterocycles, and a benzylic acetal. Moreover, the process showed excellent chemoselectivity toward aryl halide substituents, like chlorides, fluorides, and even bromides making them available in many reactions, for further functionalization via conventional cross-coupling techniques.
Introduction to Organometallics
Published in Samir H. Chikkali, Metal-Catalyzed Polymerization, 2017
Samir H. Chikkali, Sandeep Netalkar
The reversal of oxidative addition is reductive elimination. In other words, a reaction in which the oxidation state and the coordination number of a metal are reduced by two (sometimes one) units is called as reductive elimination. Reductive elimination involves the elimination or expulsion of two anionic ligands coordinated to the metal in a complex accompanied by reduction of the formal oxidation state of the metal and the coordination number by two units (Figure 1.21). Reductive elimination leads to coordinative unsaturation at the metal center.
Synthesis and structural characterization of palladium(II) 2-(arylazo)naphtholate complexes and their catalytic activity in Suzuki and Sonogashira coupling reactions
Published in Journal of Coordination Chemistry, 2019
Sathya Munusamy, Premkumar Muniyappan, Venkatachalam Galmari
Steric bulk of the ligand is believed to increase the rate of reductive-elimination to regenerate the active catalyst. Despite the bulky ligand increasing the reductive elimination rate, the rate of the oxidative addition step can be dramatically affected by the increasing size of the ligand. According to these points a balance between the steric and electronic properties of the ligand is an essential requirement. Though many reports are available on azo ligands with ruthenium and osmium, less research has been reported for palladium(II) arylazo complexes. We are therefore interested in continuing our studies on synthesis of catalysts derived from inexpensive and easily synthesized ligand sets.