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2.4.10 Method 10: (Arene)tricarbonylchromium(0) Complexes as Catalysts

DOI: 10.1055/sos-SD-002-00214

Kündig, E. P.; Pache, S. H.Science of Synthesis, (20032207.

(Arene)tricarbonylchromium(0) complexes catalyze the 1,4-addition of hydrogen to 1,3-dienes, the hydrogenation of alkynes to Z-alkenes, and the isomerization of 1,4- and 1,3-dienes.[‌323‌,‌324‌] The high chemo-, regio-, and stereoselectivity of these processes make them powerful synthetic tools. All of these processes involve metalarene bond cleavage to generate the catalytically active species [Cr(CO)3S3] (S=solvent). The most active precatalysts are therefore complexes that undergo arene displacement readily, such as tricarbon­yl(naphthalene)chromium(0) (14). Coordinating solvents (tetrahydrofuran, acetone) are best and, in tetrahydrofuran, 1,4-hydrogenation of dienes occurs slowly already at ambient temperature and ambient pressure, although slight warming (50°C) and higher pressure (40100 bar) render the process more efficient. Tricarbonyl(methyl benzoate)chromium(0) (6, M=Cr; R1=CO2Me) is used at ca. 120°C and has a longer induction period. The hydrogenation reaction likely involves a [Cr(H2)(CO)3(diene)] complex in which the diene adopts an s-cis conformation.[‌325‌] In the absence of hydrogen, isomerization of the diene via 1,5-hydrogen migration takes place to form the most stable diene capable of adopting a cisoid conformation.[‌324‌,‌326‌] This process, as well as that of isomerization of 1,4-dienes to 1,3-dienes, presumably occurs via [CrH(CO)3(pentadienyl)] intermediates.[‌327‌,‌328‌] 1,4-Hydrogenation of 1,3-dienes has been applied in prostaglandin[‌329‌] and in pheromone syntheses.[‌330‌] Examples shown in Scheme 55 include the hydrogenation of methyl sorbate (139) to methyl (Z)-hex-3-enoate (140),[‌323‌] the 1,5-addition of hydrogen and CC bond formation in norbornadiene,[‌331‌] the tricarbonyl(methyl benzoate)chromium(0) (6, M=Cr; R1=CO2Me) catalyzed synthesis of a key reagent in the synthesis of ω3 prostaglandins,[‌329‌] and the stereocontrol of the exocyclic alkene in a key intermediate 142 of a prostacyclin analogue.[‌332‌] (Arene)tricarbonylmolybdenum(0) and (arene)tricarbonyltung­sten(0) complexes give products of low regio- and stereoselectivity in this transformation, and ligand substitution in the tricarbonylchromium group often leads to loss of activity. One exception to this is the methyl acrylate complex 130.[‌268‌]

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