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Recent Advance in Silver-Mediated Chemistry Special edition on coinage metals, Chem. Rev. 2008, 108, 2793-3442. A Larger Picture of Silver Ag (Latin: argentum, from the ancient greek: argentos, from argeis, "white, shining" ) Oxidation state : +1, +2, +3 Borderline between main group elements and transition metals. Low Solubility Strong interactions with halogens, but low solubility of the corresponding salt. Alkynophilicity Due to d10 electronic configuration, with low-lying empty orbitals of π systems. Reinforced by f orbitals. Price For 1 mmole of the corresponding chloride (Aldrich, in CHF): IrCl3 (93.9) > RhCl3 (72.6) ~ AuCl3 (70.5) > PtCl4 (64.5) > PdCl2 (23.5) > AgCl (1.3) A Larger Picture of Silver Lewis acidity Can act both as σ−Lewis acid and π-Lewis acid. σ-Coordination preferred over π-coordination, with a preference for nitrogen over oxygen donor. Figure 2. Computed heats of formation (B3LYP/SDD, kcal mol-1) of various substrates with AgCl Yamamoto. Y., J.Org.Chem. 2007, 72, 7817. A Larger Picture of Silver: Oxidation Processes - Ag-Alumina: Industrial formation of ethylene oxide, precursor to ethylene glycol. 7 H2C=CH2 + 6 O2 → 6 C2H4O + 2 CO2 + 2 H2O Industrial formation of formaldehyde. 2 CH3OH + O2 → 2 H2CO + 2 H2O - Tollen’s reagent: Ag(NH3)2NO3 (test for aldehyde) Positive result: formation of Ag (s) Topics of This Review Part 1 Coupling Reactions Promoted by Silver Salts Part 2 Asymmetric Reactions Part 3 Group-transfer Reactions Νο π-Lewis acid mediated reaction of silver will be discussed here (discussed previously by P. Mateo). Part 1: Coupling Reactions Promoted by Silver Salts Two main applications of silver salt in coupling reactions: (i) They can abstract halides from organometallic intermediates, rendering the metal (Pd) more electropositive and opening a vacant site in the coordination sphere. In these cases, the main role is thus to form insoluble silver halides while activating the actual catalytic species. Common additives in Heck, Suzuki, Sonogashira, Stille, Hiyama coupling (ii) They can produce organosilver species, which can either react as such or more often be transmetalated to various metals or organometallics, especially organopalladium intermediates. Weibel, J.-M.; Blanc, A.; Pale, P., Chem. Rev. 2008, 108, 3149. Heck Coupling Promoted by Silver Salts insoluble silver halides Complexation facilited by cationic palladium Weibel, J.-M.; Blanc, A.; Pale, P., Chem. Rev. 2008, 108, 3149. Heck Coupling Promoted by Silver Salts Selectivity achieved through complexation of the second double bond: (1) Weibel, J.-M.; Blanc, A.; Pale, P., Chem. Rev. 2008, 108, 3149. (2) Madin, A.; Overman, L. E. Tet. Lett. 1992, 33, 4859. Suzuki Coupling Promoted by Silver Salts Acceleration effect of silver salt in the transmetalation: (1) Weibel, J.-M.; Blanc, A.; Pale, P., Chem. Rev. 2008, 108, 3149. (2) Kishi, Y. et al., J. Am. Chem. Soc. 1987, 109, 4756. Sonogashira Coupling Promoted by Silver Salts Formation of a alkynyl silver complex proposed: (109Ag NMR) (1) Weibel, J.-M.; Blanc, A.; Pale, P., Chem. Rev. 2008, 108, 3149. (2) Bertus, P.; Dillinger, S.; Pale, P. Org. Lett. 2001, 3, 1661. Part 2: Asymmetric Reactions σ- and π-Lewis acidity of silver can easily be used, mostly through the use of N-containing chiral ligand. Figure 2. Computed heats of formation (B3LYP/SDD, kcal mol-1) of various substrates with AgCl Potential in any reactions which involve N-complexation of a Lewis acid prior to reaction. (1) Naodovic, M., Yamamoto, H., Chem. Rev. 2008, 108, 3132. Asymmetric [3+2] Cycloaddition Endo selective Amino phosphine ligands (1) Complexation of the chiral silver catalyst to the imino ester, (2) Deprotonation (3) [3+2] Cycloaddition (1) Naodovic, M., Yamamoto, H., Chem. Rev. 2008, 108, 3132. (2) Chen, C.; Li, X.; Schreiber, S. L. J. Am. Chem. Soc. 2003, 125, 10174. Asymmetric [3+2] Cycloaddition Reversal of selectivity through Hbonding with the dipolarophile (1) Lie, Y.-X., J. Am. Chem. Soc. 2007, 129, 751. (2) Naodovic, M., Yamamoto, H., Chem. Rev. 2008, 108, 3132. Asymmetric [3+2] Cycloaddition With Munchone, exo-selectivity achieved (1) Naodovic, M., Yamamoto, H., Chem. Rev. 2008, 108, 3132. (2) Peddibhotla, S.; Tepe, J. J. Am. Chem. Soc. 2004, 126, 12776. Asymmetric Hetero Diels-Alder Through complexation of the Ag to the imine (1) Naodovic, M., Yamamoto, H., Chem. Rev. 2008, 108, 3132. (2) Josephsohn, N. S.; Snapper, M. L.; Hoveyda, A. H. J. Am. Chem. Soc. 2003, 125, 4018. (3) Yao, S.; Johansenn, M.; Hazell, R.. G.; Jorgensen, K. A. Angew. Chem. Int. Ed. 1998, 37, 3121. (4) Kawasaki, M.; Yamamoto, H. J. Am. Chem. Soc. 2006, 128, 16482. [2+2] Cycloaddition Silver-activation of the alkene/alkyne proposed by the author (1) Naodovic, M., Yamamoto, H., Chem. Rev. 2008, 108, 3132. (2) Sweis, R. F.; Schramm, M. P.; Kozmin, S. A. J. Am. Chem. Soc. 2004, 126, 7442. [2+2] Cycloaddition (1) Naodovic, M., Yamamoto, H., Chem. Rev. 2008, 108, 3132. (2) Nakamura, I.; Nemoto, T.; Yamamoto, Y.; de Meijere, A. Angew. Chem. Int. Ed. 2006, 45, 5176. Asymmetric Mannich Reactions Catalytic enantioselective synthesis of βamino carbonyls (1) Naodovic, M., Yamamoto, H., Chem. Rev. 2008, 108, 3132. (2) Josephsohn, N. S.; Carswell, E. L.; Snapper, M. L.; Hoveyda, A. H. Org. Lett. 2005, 7, 2711. Asymmetric Mannich Reactions - Complexation of the chelated Ag+ to the imine - Addition of the silyl enol ether - Internal desilylation - 1 equivalent of i-PrOH necessary to undergo desilylation (1) Naodovic, M., Yamamoto, H., Chem. Rev. 2008, 108, 3132. (2) Josephsohn, N. S.; Carswell, E. L.; Snapper, M. L.; Hoveyda, A. H. Org. Lett. 2005, 7, 2711. Part 3: Group- Transfer Reactions (1) Carbene New developpement in group-transfer reactions based on: (2) Nitrene (3) Silylene Ambigous mode of activation proposed since silver is oxo-, aza- and carbophilic. (1) Naodovic, M., Yamamoto, H., Chem. Rev. 2008, 108, 3132. (2) Rasika, H. V., Lovely, C. J. Chem. Rev. 2008, 108, 3223. Carbene- Transfer- Buchner Reaction (1) Rasika, H. V., Lovely, C. J. Chem. Rev. 2008, 108, 3223. Carbene- Transfer- Buchner Reaction When conducted in CH2Cl2, 15-25% of this product obtained: CO Et 2 Cl Cl For 11d, 5% of this impureties was obtained: (1) Rasika, H. V., Lovely, C. J. Chem. Rev. 2008, 108, 3223. Cl CO2Et Carbene- Transfer- C-X Addition- Rearrangement (1) Rasika, H. V., Lovely, C. J. Chem. Rev. 2008, 108, 3223. Carbene- Transfer- C-X Addition- Rearrangement (1) Rasika, H. V., Lovely, C. J. Chem. Rev. 2008, 108, 3223. Carbene- Transfer- Catalyzed Cyclopropanation Donor/acceptor carbenoid working in cyclopropanation with silver (1) Rasika, H. V., Lovely, C. J. Chem. Rev. 2008, 108, 3223. (2) Thompson, J. L.; Davies, H. M. L. J. Am. Chem. Soc. 2007, 129, 6090. Nitrene- Transfer- Aziridination Short metal-metal distance Accessible coordination site (1) Naodovic, M., Yamamoto, H., Chem. Rev. 2008, 108, 3132. (2) Cui, Y.; He, C.; J Am. Chem. Soc. 2003, 125, 16202. Nitrene- Transfer- C-H Insertion (1) (2) Naodovic, M., Yamamoto, H., Chem. Rev. 2008, 108, 3132. (2) Cui, Y.; He, C.; Angew. Chem. Int. Ed. 2004, 43, 4210. Silylene- Transfer- Silacyclopropanation (1) Naodovic, M., Yamamoto, H., Chem. Rev. 2008, 108, 3132. (2) Cirakovic, J.; Driver, T. G.; Woerpel, K. A., J Am. Chem. Soc. 2002, 124, 9370. Silylene- Transfer- Silacyclopropanation - Phosphine added in order to study the mechanism - slow the process (10 °C) - Only reversible with bis-cyclic silacyclopropane, with cyclohexane quicker Proved reactive intermediate (1) Naodovic, M., Yamamoto, H., Chem. Rev. 2008, 108, 3132. (2) Driver, T. G.; Woerpel, K. A., J Am. Chem. Soc. 2004, 126, 9993. Silylene- Transfer- Silacyclopropanation (1) Naodovic, M., Yamamoto, H., Chem. Rev. 2008, 108, 3132. (2) Cirakovic, J.; Driver, T. G.; Woerpel, K. A., J Am. Chem. Soc. 2002, 124, 9370. (3) Franz,. A. K.; Woerpel, K. A., Angew. Chem. Int. Ed. 2000, 39, 4295. Silylene- Transfer- Silacyclopropanation (1) Naodovic, M., Yamamoto, H., Chem. Rev. 2008, 108, 3132. (2) Cirakovic, J.; Driver, T. G.; Woerpel, K. A., J Am. Chem. Soc. 2002, 124, 9370. (3) Calad, S. A.; Woerpel, K. A., J Am. Chem. Soc. 2005, 127, 2046. Conclusion High potential for new reactions based on silver, in oxidation, alkene-alkyne activation, metalcatalyzed coupling, assymetric, group-transfer reactions.