Decarbonylation, and metal

Stable mononuclear transition-metal germylene complexes with a formal triple bond between the Ge and metal atoms (Cr, Mo, W, 56-62) have been synthesized by a combination of salt-elimination and decarbonylation reaction (equation 44)150,151. The decarbonylation process for the Cr and W intermediates 61 and 62 can involve either a thermal or a photochemical reaction the molybdenum germylyne complexes 56 and 57 were obtained directly, even at low temperatures. 

It is convenient to note here that a common reaction of alcohols with transition metal halides in the presence of phosphine is the decarbonylation and sometimes dehydrogenation to give metal carbonyls. These reactions proceed via alkoxide intermediates which then undergo 8-H transfer ... 

Furfural 69 has been used as a chemical feedstock for the production of furan via two production methods involving the decarbonylation of furfural <2005MI7>. Processes in both the liquid and gas phases were described for the preparation of furan through the decarbonylation of furfural using noble metal and metal oxide catalysts. The results of the study led the authors to state that the research trends for preparing furan based on the decarbonylation of furfural should mainly be concentrated on more effective catalysts and environmentally friendly processes. 

Both decarbonylation and methyl groups loss are characteristic of the next bimetallic complex, Cp(CO)3MoSbMe2Ni(CO)3 (93). Its mass spectrum shows peaks due to Cp(CO) MoSbMe " (n = 0-9, m = 1,2). Sb-N bond cleavage leads to ions of two series, CpMo(CO) SbMe " (n = 0-3, m = 1,2) and Ni(CO) (n = 0-3). Elimination of species containing two metal atoms gives rise to SbMe (m = 0-2) . 

Palladium chloride and metallic palladium are useful for carbonylating olefinic and acetylenic compounds. Further, palladium is active for decarbonylation of aldehydes and acyl halides. Homogeneous decarbonylation of aldehydes and acyl halides and carbonylation of alkyl halides were carried out smoothly using rhodium complexes. An acyl-rhodium complex, thought to be an intermediate in decarbonylation, was isolated by the oxidative addition of acyl halide to chlorotris(triphenylphosphine)rhodium. The mechanisms of these carbonylation and decarbonylation reactions are discussed. 

These reactions may involve either decarbonylation and coordination of a surface oxide to the metal to produce a new metal carbonyl complex attached to the inorganic surface through nonionic bonds or modification of the original carbonyl complex to form an ionic species which attached to the inorganic surface electrostatically. Further reaction at higher temperatures typically leads to further decarbonylation which may be accompanied by hydrogen evolution and oxidation of the metal. Eventually metal oxide particles or dispersed metal crystallites are formed after extended reaction. 

Catalysts of easily reducible metals (such as Ru, Os, Rh, and Ir) can be active both after activation in the 0 region and after activation in the y region followed by reduction. The last treatment should leave a catalyst both completely decarbonylated and zero valent. 

Metal carbonyl clusters on supports are important to the subject reviewed here because they are the best known precursors of structurally simple supported metal clusters, which are formed by decarbonylation of the precursors. The routes for preparation of molecularly or ionically dispersed metal carbonyl clusters on zeolite and metal oxide supports include syntheses from mononuclear precursors on the support surface [5,9]. Ship-in-a-bottle syntheses of this type take place when the clusters formed in zeolite cages are trapped there because they are too large to fit through the apertures. Syntheses in the nearly neutral NaY zeolite are similar to those occurring on the nearly neutral y-Al203 and in nearly neutral solutions. Examples are the syntheses of [Ir4(CO)i2] [8] and of [Ir6(CO)i6] [10] from [Ir(CO)2(acac)] in the presence of CO. Syntheses in the more basic NaX zeolite are similar to those occurring in basic solutions and on the basic surface of MgO, e g., those of [HIr4(CO)ii]-and [Ir6(CO)i5]2- [11]... 

Cyclopropane formation is also observed in transition-metal-mediated conversions of pent-4-enals. This reaction proceeds via oxidative addition of the metal to the aldehyde C —H group, decarbonylation and cyclization of the resulting homoallylmetal complex. 

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