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Title:Palladium-catalyzed reactions of ammonia, carbon monoxide, and cyanide
Author(s):Klinkenberg, Jessica
Director of Research:Hartwig, John F.
Doctoral Committee Chair(s):Hartwig, John F.
Doctoral Committee Member(s):Denmark, Scott E.; Rauchfuss, Thomas B.; Girolami, Gregory S.
Department / Program:Chemistry
Degree Granting Institution:University of Illinois at Urbana-Champaign
carbon monoxide
Abstract:The reductive eliminations of primary arylamines from a series of bisphosphine-ligated arylpalladium(II) parent amido complexes countered several established trends. In contrast to arylamido and alkylamido complexes of the aromatic bisphosphines DPPF and BINAP, parent amido complexes did not form or undergo reductive elimination of monoarylamines. However, arylpalladium parent amido complexes ligated by the alkylbisphosphine CyPF-t-Bu formed in good yield and underwent reductive elimination. Despite the basicity of parent amido ligand and the typically faster reductive elimination from complexes containing more basic amido ligands, the CyPF-t-Bu-ligated arylpalladium parent amido complexes underwent reductive elimination much more slowly than the analogous complexes containing arylamido or alkylamido ligands. Moreover, the parent amido complexes formed more rapidly and are more stable thermodynamically in a series of exchange processes than the arylamido complexes. Computational studies supported the overriding influence of steric effects on the stability and reactivity of the parent amido complex. The slow rate of reductive elimination caused the arylpalladium amido complex to be the resting state of the coupling of aryl halides with ammonia catalyzed by CyPF-t-Bu-ligated palladium, and this resting state contrasted the Pd(0) or arylpalladium(II) resting states of reactions of aryl halides with amines catalyzed by most palladium complexes. CyPF-t-Bu-ligated palladium complexes also catalyzed the aminocarbonylation of aryl bromides and aryl iodides with ammonia and carbon monoxide. Primary benzamides formed in good yields from aryl bromides and aryl iodides with 2 mol % of Pd[P(o-tol)3]2 and CyPF-t-Bu under 3 atm total of ammonia and carbon monoxide. The resting state of the catalyst was identified as the Pd(0) di-carbonyl complex (CyPF-t-Bu)Pd(CO)2, which dimerized to [(CyPF-t-Bu)2Pd2(μ-CO)] upon isolation. These complexes did not undergo oxidative addition of aryl chlorides and aryl tosylates. The effect of added CO on the oxidative addition steps was demonstrated. In addition, the intermediacy of an arylpalladium acyl complex in the formation of the benzamide products was demonstrated. A method for the palladium-catalyzed cyanation of aryl chlorides and aryl tosylates was developed. The catalyst formed from the combination of Pd[P(o-tol)3]2 and CyPF-t-Bu formed aryl nitriles via reaction with Zn(CN)2 in high yields with an unprecedented catalyst loadings of 0.8-1 mol %. LiCl was shown to influence the transmetalation of arylpalladium chloride complexes with Zn(CN)2. In addition, the isolation and characterization of arylpalladium cyanide complexes that undergo reductive elimination to form arylnitriles have been demonstrated. The rates of reductive elimination from a series of arylpalladium cyanide complexes reveal that the electronic effects on the reductive elimination from arylpalladium cyanide complexes are distinct from those on reductive eliminations from arylpalladium alkoxo, amido, thiolate, and enolate complexes. Arylpalladium cyanide complexes containing aryl ligands with electron-donating substituents undergo faster reductive elimination of aromatic nitriles than complexes containing aryl ligands with electron-withdrawing substituents. In addition, the transition state for the reductive elimination of the aromatic nitrile is much different from that for reductive eliminations that occur from most other arylpalladium complexes. Computational studies indicate that the reductive elimination of an arylnitrile from Pd(II) occurs through a transition state more closely related in structure and electronic distribution to that for the insertion of CO into a palladium-aryl bond.
Issue Date:2012-06-27
Rights Information:Copyright 2012 Jessica Klinkenberg
Date Available in IDEALS:2014-06-28
Date Deposited:2012-05

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