Historical Perspective of the Heck Reaction

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It was used Pd-G-3 [8,9] as catalyst in the Heck reactions shown in Scheme 2. Typically, 10 mM each of the reactants and 20 mM triethylamine were taken up in toluene and the mixture was heated to reflux for 24 h in the presence of 10 mg (2- 10-3 mol %) Pd-G-3. Pd-G-3 is soluble in toluene and, hence, reactions 1 and 2 occur under homogeneous catalytic conditions. After the reaction, toluene was removed in a rotavapor and the residue extracted with ether. The turnover numbers (TON ) mol product/mol catalyst) and turnover frequencies (TOF ) mol product/mol catalyst/hour) given in Scheme 2 were calculated from isolated product yields. The reaction with ethyl acrylate proceeded with good yield, although that with styrene was low. The TON and TOF, however, are very high for both reactions. This, coupled with the absence of side products, indicates that the yields could be improved by using slightly higher amounts of Pd-G-3. In most Pd catalyzed reactions, 0.5-2 mol % catalyst is generally used and this is 100-1000 times higher than what we have employed here. The catalytic properties of the Pd nanoparticles dispersed in BMI. PF6 were tested in the coupling of aryl halides with n-butylacrylate at different temperatures (Table 1). First, we tested different bases (NaOAc, NEt(iPr)2, DABCO, and Na2CO3) in the reaction of iodobenzene with n-butylacrylate at 80 oC ([PhI]/[Pd] ) 1000). A mixture of the aryl halide (1.0 mmol) and n-butyl acrylate (1.2 mmol) with the Pd nanoparticles dispersed in 0.5 mL of ionic liquid gave a light-yellow solution in the presence of NEt(iPr)2 and suspensions in the presence of the other bases. 16
Figure 2. Possible pathways involved in the Heck reaction promoted by Pd nanoparticles dispersed in imidazolium ionic liquids. Almost complete iodobenzene conversion was observed in the reaction experiment performed with NEt(iPr)2, whereas only 60%). A similar trend was recently observed in Heck reactions promoted by a heterogeneous catalyst precursor where it was proposed that Pd dissolution and reprecipitation are inherent parts of the catalytic cycle. References [1] (a) R. B. Bedford, C. S.J. Cazin, D. Holder, The development of palladium catalysts for C–C and C–heteroatom bond forming reactions of aryl chloride substrates, Coord. Chem. Rev. 248 (2004) 2283–2321; (b) Applied Homogeneous Catalysis with Organometallic Compounds; Edited by B. Cornils, W.A. Hermann, VCH, Weinheim-New York, 1996; (c ) http://en.wikipedia.org/wiki/Heck_reaction [2] (a) R. F. Heck, Jr., J. P. Nolley, Palladium-catalyzed vinylic hydrogen substitution reactions with aryl, benzyl, and styryl halides, J. Org. Chem. 37(14) (1972) 2320–2322. doi:10.1021/jo00979a024. (b) T.Mizoroki, K. Mori, A. Ozaki, Arylation of Olefin with Aryl Iodide Catalyzed by Palladium, Bull. Chem. Soc. Jap. 44 (1971) 581. doi:10.1246/bcsj.44.581. [3] F.Ozawa, A.Kubo, T.Hayashi, Generation of Tertiary Phosphine-Coordinated Pd(0) Species from Pd(OAc)2 in the Catalytic Heck Reaction, Chemistry Lett. (1992) 2177–2180. doi:10.1246/cl.1992.2177. [4] (a) Hagiwara, Hisahiro, Sustainable Mizoroki–Heck reaction in water: remarkably high activity of Pd(OAc)2 immobilized on reversed phase silica gel with the aid of an ionic liquid, Chemical Communications. 23(2005) 2942– 2944. doi:10.1039/b502528a. (b) L. Kiss, T. Kurtan, S. Antus, H. Brunner, Further insight into the mechanism of Heck oxyarylation in the presence of chiral ligands, Arkivoc (2003) GB–653J. http://www.arkat-usa.org/ark/journal/2003/I05_Bernath/GB-653J/GB- 653J.asp. (c) M. Kitamura, D. Kudo, K. Narasaka, Palladium(0)-catalyzed synthesis of pyridines from β-acetoxy-γ,δ-unsaturated ketone oximes, Arkivoc (2005) JC–1563E. http://www.arkat-usa.org/ark/journal/2006/I03_Coxon/1563/1563.asp. [5] J. G. De Vries, The Heck reaction in the production of fine chemicals, Canadian Journal of Chemistry 79 (2001) 1086. doi:10.1139/cjc-79-5-6-1086. [6] J.Dupont, M.Pfeffer, J. Spencer, Palladacycles - An Old Organometallic Family Revisited: New, Simple, and Efficient Catalyst Precursors for Homogeneous Catalysis, Eur. J. Inorg. Chem. (2001) 1917-1927 [7]D. Kovala-Demertzi, P. N. Yadav, M. A. Demertzis, J. P. Jasiski, F. J. Andreadaki, I. D. Kostas, First use of a palladium complex with a thiosemicarbazone-based ligand as catalyst precurs or for the Heck reaction, Tetrahedron Letters ,45 (2004) 2923–2926. [8] C. C. Cassol, A. P. Umpierre, G. Machado, S. I. Wolke, J. Dupont, The Role of Pd Nanoparticles in Ionic Liquid in the Heck Reaction, J. Am. Chem. Soc. 127 (2005) 3298-3299, DOI: 10.1021/ja0430043 17
Page 1 and 2: Dimitra Kovala-Demertzi Section of
Page 3 and 4: Aryl and vinyl halides- Aryl and vi
Page 5 and 6: Solvents-Heck reactions are conduct
Page 7 and 8: Oxidative addition is often the rat
Page 9 and 10: Amino-Heck reaction In the amino-He
Page 11 and 12: All of the palladacycles shown in t
Page 13 and 14: The monoanionic HSal4Et ligand is c
Page 15: 3.3 Palladium nanoparticles as cata

Historical Perspective of the Heck Reaction

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