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Iron-catalyzed Cross Coupling reactions: From Rust to a Rising Star
Weijun Liu
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Transition metal catalyzed cross couplings have seen incredible advances and applications, have wide scope and compatibility. But…..typically use palladium and nickel which are generally toxic and expensive. Expensive and/or sensitive ancillary ligands are required. Alkyl iodides, bromides and triflates are best. With special ligands alkyl chlorides may be used.
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Iron: A More Practical Alternative
Iron is one of the most abundant metals on earth. (5.6% of earth’s crust. 4th most abundant element after oxygen, silicon, and aluminum. Nickel is %, palladium is %, gold is % of Earth’s continental crust.) 2. Cheap •PdCl2: $4005/150g $26.70/g •NiCl2: $98.40/250g $0.39/g •FeCl3: $30.40/1kg $0.03/g 3. nontoxic •Prevalent in biological systems
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Content: Early Examples 2. Alkenyl Derivatives as Substrates
3. Aryl Derivatives as Substrates 4. Alkyl Derivatives as Substrates 5. O, N, S-Arylation 6. Oxidative Cross-coupling
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Early Examples J. Kochi, J. Am. Chem. Soc. 1971, 93, 1487
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Kochi, J. J. Org. Chem. 1976, 41, 502
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2. Alkenyl Derivatives as Substrates
NMP as cosolvent Cahiez, G. Synthesis 1998, 1199
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Cahiez, G. Synthesis 1998, 1199
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60% 60% Cahiez, G.; Knochel, P. Synlett 2001, 1901
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3. Aryl Derivatives as Substrates
Furster, A. Angew. Chem., Int. Ed. 2002, 41, 609
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Proposed Formal Catalytic Cycle
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4. Alkyl Derivatives as Substrates
Furster, A. Angew. Chem., Int. Ed. 2004, 43, 3955
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Furster, A. Angew. Chem., Int. Ed. 2004, 43, 3955
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Furster, A. Angew. Chem., Int. Ed. 2004, 43, 3955
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Only tertiary halides and alky chlorides were found be inert.
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Nakamura, E. J. Am. Chem. Soc. 2004, 126, 3686
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Hayashi, T. Org. Lett. 2004, 6, 1279
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Cossy, J. Angew. Chem., Int. Ed. 2007, 46, 6521
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51% Chai, C.L.L. Adv. Synth., Catal. 2007, 349, 1015
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5. O, N, S-Arylation Bolm, C. Angew. Chem., Int. Ed. 2007, 46, 8862
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Bolm, C. Angew. Chem., Int. Ed. 2007, 47, 586 Bolm, C. Angew. Chem., Int. Ed. 2008, 47, 2880
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6. Oxidative Cross-coupling
Iron-Catalyzed Homo-Coupling FeI/FeIII or Fe0/FeII Fe-II/Fe0 Cahiez, G. Org. Lett. 2005, 7, 1943
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Cahiez, G. J. Am. Chem. Soc. 2007, 129, 13788
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Oxidative Heterocoupling
Cahiez, G. Angew. Chem., Int. Ed. 2009, 43, ASAP
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Iron-Catalyzed Direct Arylation through Directed C-H Bond Activation
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Nakamura, E. J. Am. Chem. Soc. 2008, 130, 5858
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Iron-Catalyzed Chemoselective ortho Arylation of Aryl Imines by
Directed C-H Bond Activation Nakamura, E. Angew. Chem., Int. Ed. 2009, 48, ASAP
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Li, Z.-P.; Li, C.-J. Angew. Chem., Int. Ed. 2007, 46, 6505
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X = N, O, S Li, Z.-P. Angew. Chem., Int. Ed. 2008, 47, 7497
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Summary 1. Iron catalysts activate alkenyl, aryl, and alkyl derivatives. 2. Iron catalysts activate aryl chlorides, triflates and tosylates under ligand free conditions. 3. Iron-catalyzed cross-coupling shows excellent functional group tolerance. 4. Iron-catalyzed cross-coupling needs only short reaction (typically 5-30 min) time and are performed at low temperatures (typically -20 oC to 0 oC). 6. Iron salts has been successfully applied in the C-H bond activation and oxidative coupling reactions But the iron-catalyzed cross coupling is not nearly as mature as its palladium and nickel counterparts. And the reaction mechanisms are needed to be proved.
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