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Highly Reactive, General and Long-LivedCatalysts for Palladium-CatalyzedAmination of Heteroaryl and Aryl
Chlorides, Bromides, and Iodides: Scopeand Structure-Activity Relationships
Qilong Shen, Tokutaro Ogata, and John F. HartwigCurrent LiteratureBryan Wakefield
5/30/08
Bryan Wakefield @ Wipf Group Page 1 of 14 6/15/2008
A Brief History:Who came first the Buchwald or the Hartwig?
Neither was first, the originalreport that inspired both Hartwig and Buchwald wasmade by Kameyama, Kosugi,And Migita in the early 1980’s
Hartwig, J. F. Synlett, 2006, 1283
Bryan Wakefield @ Wipf Group Page 2 of 14 6/15/2008
Mechanism of the Buchwald-Hartwig Coupling
Bryan Wakefield @ Wipf Group Page 3 of 14 6/15/2008
Mechanism of Oxidative Insertion
Sterically hindered phosphineligands lead to coordinativelyunsaturated palladium complexes which readily undergo oxidative insertion
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Reductive Elimination of Amines
Reductive elimination Occurs most quickly From 3-coord. Pd-complex
Reductive elimination occurs mostquickly when electron rich aminesin Pd complexes with electron withdrawing ligands
Bryan Wakefield @ Wipf Group Page 5 of 14 6/15/2008
Reductive Elimination of Amines
Sterically hindered ligandsreduce the amount of β-hydride elimination.
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General Scope of Buchwald-Hartwig Amination
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Current Work: Coupling to Heteroaryl Halides
Catalysts generatedfrom Pd(dba)2 or PdCl2(PhCN)2 werenot effective The relative rate ofamidation of aryl halides: Br>Cl>I.
Bryan Wakefield @ Wipf Group Page 8 of 14 6/15/2008
Comparision of Ligands commonly used forAmination
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Amination of Aryl Halides
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Comparision of Ligands commonly used forAmination
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Catalyst SAR
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Why is this ligand good?
• The rigid backbone of the ligand allows for tight binding ofpalladium that prevents displacement by primary amines andbasic heterocycles.
• The ligand is strongly electron donating, which promotesoxidative addition to less reactive haloarenes.
• The ligand’s steric bulk disfavors diarylation, facilitates thegeneration of the (chelate)Pd(0) intermediate, and promotesreductive elimination.
Bryan Wakefield @ Wipf Group Page 13 of 14 6/15/2008
Conclusion
• This work describes the use of very low loadings of Pd incombination with the CyPF-tBu ligand to achieve amination ofheteroaryl and aryl halides.
• These low loadings could increase the use of this method inindustry by lowering cost and easing the removal of Pd from thefinal product.
• The catalysts using the CyPF-tBu ligand were shown to havehigher Turnover numbers and selectivity than those with thecommonly used Xphos.
• Systematic variation of the ligand structure showed whichfeatures are necessary.
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