Oligomeric reduction

Reductive elimination is the reverse reaction of oxidative addition (CN, VE, and ON reduce by two). A practical, most important example of the reductive elimination step is the elimination of alkane product from the catalyst in alkene hydrogenation (X = alkyl, Y = H). In ethylene oligomerization, reductive elimination plays an important role in the liberation of the 1-alkene product from the chromium metallacyclic intermediate. As this process combines several elementary steps, it is shown in Scheme 6.16.8 below to sum up this topic. 

Nickel plays a role in the Reppe polymeriza tion of acetylene where nickel salts act as catalysts to form cyclooctatetraene (62) the reduction of nickel haUdes by sodium cyclopentadienide to form nickelocene [1271 -28-9] (63) the synthesis of cyclododecatrienenickel [39330-67-1] (64) and formation from elemental nickel powder and other reagents of nickel(0) complexes that serve as catalysts for oligomerization and hydrocyanation reactions (65). 

Diaminopropane Processes. 1,2-Propylenediamine can be produced by the reductive amination of propylene oxide (142), 1,2-propylene glycol [57-55-6] (143), or monoisopropanolamine [78-96-6] (144). 1,3-Propanediol [504-63-2] can be used to make 1,3-diaminopropane (143). Various propaneamines are produced by reducing the appropriate acrylonitrile—amine adducts (145—147). Polypropaneamines can be obtained by the oligomerization of 1,3-diaminopropane (148,149). 

Further reductions can be achieved by taking symmetry into account, an approach that holds promise for the analysis of large oligomeric proteins such as virus capsids [14]. 

For oligomeric samples with well defined peaks as shown in Figure 5, the relative percentage for each conq)onent can be obtained by integrating the area under each peak via a gas chromatography data reduction package also resident on the NOVA minicomputer I5]. 

FIGURE 6.32 Configurationally different spiro tetramers 44a and 44b formed by spiro tetramerization of l,3-bis(5-tocopheryl)propane (43) in a 15 1 ratio in agreement with theory. Reduction of each of the tetramers provides c s-l,2-c s-4,5-tetrakis(5-tocopheryl)cyclohexane (45). The dashed lines separate the two former units of 43, indicating where bond formation during the spiro oligomerization process occurred. 

UV-vis and DRS measurements on Fe-ZSM-5 catalysts with variable amounts of isolated, oligomeric and heavily aggregated Fe3+ oxo sites, led to the development of a unified concept of the active Fe sites in these reactions, according to which isolated Fe sites catalyse both SCR reactions while oligomeric sites, though also involved in the selective reduction path, limit the catalyst performance by causing the total oxidation of the reductant [23],... 

This process contrasts with the elemental-silicon processes sometimes used for alkyl silicates (8) and the elemental-silicon processes generally used for oligomeric and polymeric organosi-loxanes ( ,7) Since the silicon in these processes is obtained from quartz, these processes entail, in terms of bond cleavage, the destruction of four silicon-oxygen bonds per silicon and the subsequent reformation of the required number of such bonds. In terms of oxidation number, they entail the reduction of the silicon from four to zero and then its reoxidation back to four, Figures 2 and 3. 

Benzyl Alcohols. Benzyl alcohols of nearly all kinds undergo reduction when treated with acid in the presence of organosilicon hydrides. The most obvious exception to this is the behavior of benzyl alcohol itself. It resists reduction by the action of trifluoroacetic acid and triethylsilane, even after extended reaction times.26 Reducing systems consisting of triethylsilane and sulfuric acid/acetic acid or p-toluenesullonic acid/acetic acid mixtures also fail to reduce benzyl alcohol to toluene.134 As previously mentioned, substitution of boron trifluoride for trifluoroacetic acid results in the formation of modest yields of toluene, but only when a very large excess of the silane is used in order to capture the benzyl cation intermediate and suppress Friedel-Crafts oligomerization processes.129,143... 

Reductive decoupling, 181, 187 Reductive elimination, 171-174, 190-197 refined catalytic cycle, 206-211 and selectivity, 212-214 steric and electronic factors, 202-205, 217 Retro-Wittig decomposition, 37, 78, 79-83 thiobetaines, 57-58, 60, 65 Ring cleavage, 105, 276, 281 Ring closure in oligomerization, 172, 174, 190-197... 

Tellurium sources, 22-24 Thermodynamics in cyclo-oligomerization, 185-186 butadiene insertion, 187-188 reductive elimination, 193, 194 selectivity control, 212 polysilane isomerisation, 158-160 see also Stability Thermolysis, 135, 136, 158 THF (tetrahydrofuran), 97, 150, 153 Thio-Wittig reaction, 37 Tin, 121... 

Figure 3.1. Schematic representation of dimensional reduction for a framework of corner-sharing MX6 octahedra. The M and X atoms are represented by black and white spheres, respectively. In a) though d), reaction with AbX incorporates additional X atoms into the M—X framework, progressively reducing the connectedness and effective dimensionality of the M—X framework. In d), after incorporating n units of AbX (n > 2), the structure is reduced to isolated oligomeric or monomeric components. For clarity, the A atoms are not shown in the figure. [Adapted with permission from [Ref. 16]. Copyright 2001 American Chemical Society.]...

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