Ethylene and Co

M-NHC catalysts in this area. Metal catalysed carbonylation also provides an alternative synthetic ronte to the prodnction of materials that traditionally reqnire highly toxic precnrsors, like phosgene. This section discnsses carbonylation of aryl hahdes, oxidative carbonylation of phenolic and amino componnds, carbonylation of aryl diazoninm ions, alcohol carbonylation, carbonylative amidation, and copolymerisation of ethylene and CO. 

Ethylene Carbonylation. The classical rhodium catalyzed carbonylation of ethylene to propionic acid (Eqn. 1) used ethyl iodide or HI as a co-catalyst (6). In the presence of excess ethylene and CO the process could proceed further to propionic anhydride (Eqn. 2). While additional products, such as ethyl propionate (EtC02Et), diethyl ketone (DEK), and ethanol were possible (See Eqns. 3-5), the only byproduct obtained when using a rhodium-alkyl iodide catalyst was small amounts (ca. 1-1.5%) of ethyl propionate. (See Eqns. 3-5.)... 

The adsorption of hydrogen, ethylene, and CO on Pt(l 1 1) was extensively studied. Molecular hydrogen dissodatively adsorbs on the catalytic Pt(l 1 1) surface... 

A nonlocal density functional study of the Pdn-assisted copolymerization of ethylene and CO has been published.490 491... 

We note that there are NMR-based kinetic studies on zirconocene-catalyzed pro-pene polymerization [32], Rh-catalyzed asymmetric hydrogenation of olefins [33], titanocene-catalyzed hydroboration of alkenes and alkynes [34], Pd-catalyzed olefin polymerizations [35], ethylene and CO copolymerization [36] and phosphine dissociation from a Ru-carbene metathesis catalyst [37], just to mention a few. 

Fig.l. Co60 y-copolymerization of ethylene and CO. % CO in copolymer vs. % CO in initial gas mixture. Taken from ref. 7 by permission of the publisher, John Wiley Sons, Inc. 

In a similar manner, imines 50 with various ancillary groups X, such as ethoxy-carbonyl, 2-pyridyl, or 2-thiazolyl, are also converted into lactams 51 in mod-erate-to-good yields (Eq. 24) [38]. The [2+2+1] lactam formation using a chiral substrate 52, ethylene, and CO quantitatively furnished the spiro lactam 53 (Eq. 25) [39]. The cycloaddition exclusively took place at the carbon-nitrogen double bond next to the oxazine oxygen atom, although 53 was obtained as a diastereomeric mixture. 

Figure 26 Proposed steps in Pdfllj-catalyzed polyketone formation from ethylene and CO in MeOH.

Similar cts-bis-carbene chelate complexes of palladium(Il) [327,330,331], but without the hydroxy functional groups on the wingtips, were used by the same research group for the copolymerisation of ethylene and CO. Once again, chelating bisphosphane complexes inspired the synthesis and application of their NHC counterparts [332,333]. The actual, defined catalyst precursors were the cationic complexes formed after haUde abstraction with silver salts in acetonitrile as donor solvent. 

Palladium complexes figure prominently as well in the copolymerization of Q -olefins with carbon monoxide. Unlike the low molecular weight photodegradable random copolymers of ethylene and CO produced from a free-radical process, olefin/carbon monoxide copolymers produced from homogeneous palladium catalysts are perfectly alternating, the result of successive insertions of olefin and CO (Figure 19). Consecutive insertion of two similar monomers is either slow... 

In this reaction, the addition of P(p-QH4-CF3)3 was crucial to obtain the product in high yield. Furthermore, 2-acetylpyridines and 2-pyridylimines, together with ethylene and CO, give 2-pyridyl-y-lactones [89] and 2-pyridyl-y-lactams [90], respectively. 

Polyoximes 121) prepared by copolymerisation of ethylene and CO followed by reactirai with hydroxylamine were used as starting material. Reaction with different metal ions like Cu(Il) and Co(Il) in a methanol/dioxane mixture leads to coloured insoluble chelates such as (122) (Eq. 63) After evaluating the IR spectra it is assumed that also other structure elements than normal bis(glyoximato)Cu(II) are present. 

The main side reactions are cyclotrimerization (of the alkyne), co-cyclotrimer-ization (alkyne/alkyne/alkene), and formation of cyclopentadienones 5 and 6. In addition, spirofuranones such as 7 and 8 can form, with the latter being the Diels-Alder product of 7 with ethylene. It is generally observed that high ethylene and CO pressures disfavor the formation of side products. Further details on the side-product formation were given in [4d]. 

Other steps used in the model assume that the heterogeneous conversion of methane is limited to the gas-phase availability of oxygen, O2 adsorption is fast relative to the rate of methane conversion, and heat and mass transports are fast relative to the reaction rates. Calculations for the above model were conducted for a batch reactor using some kinetic parameters available for the oxidative coupling of methane over sodium-promoted CaO. The results of the computer simulation performed for methane dimerization at 800 °C can be found in Figure 7. It is seen that the major products of the reaction are ethane, ethylene, and CO. The formation of methanol and formaldehyde decreases as the contact time increases. 

Later, Berzelius replaced the Daltonian symbols by letters, and here again the letter represented one atom of the element concerned. The modem notation of the symbols shown in Fig. 38 arc H, N, C, O, P, S, for the elements and HO, HN, NO, HC, OC for the compounds. Each of the latter group would now be called a molecular formula, which shows the kind and number of each atom in the molecule which it represents. The corrected molecular formulae for those shown in Fig. 38 arc, in fact HjO (water), NH, (ammonia), NO (nitric oxide) C2H4 (ethylene), and CO (carbon monoxide). 

The free-energy profile with solvent interaction taken into account is shown in Fig. 27. The feature of the entire potential surface is dramatically changed. The large barriers in the reaction from 40 to 42 and from 48 to 40 have disappeared because of the stabilization of the four-coordinate intermediates 41 and 47 by the solvation. The endothermic ethylene and CO insertion reactions became exothermic and the exothermic H2 oxidative addition became endothermic, because the four-coordinate intermediate 43 and... 

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