Nickel double-bond migration

Replacement of halides with deuterium gas in the presence of a surface catalyst is a less useful reaction, due mainly to the poor isotopic purity of the products. This reaction has been used, however, for the insertion of a deuterium atom at C-7 in various esters of 3j -hydroxy-A -steroids, since it gives less side products resulting from double bond migration. Thus, treatment of the 7a- or 7j5-bromo derivatives (206) with deuterium gas in the presence of 5% palladium-on-calcium carbonate, or Raney nickel catalyst, followed by alkaline hydrolysis, gives the corresponding 3j3-hydroxy-7( -di derivatives (207), the isotope content of which varies from 0.64 to 1.18 atoms of deuterium per mole. The isotope composition and the stereochemistry of the deuterium have not been rigorously established. 

In aqueous medium, the reduction of nickel(II) acetate with NaBFLt produces nickel boride66. This fine black precipitate, designated P-1 nickel, is a more active catalyst than Raney nickel for double-bond hydrogenations. The P-1 nickel catalyst produces less double-bond migration than standard Raney nickel, it is not pyrophoric and is more readily prepared than Raney nickel. 

The first manufacturing route of the GEM side-chain relied on a-cyanoketone 125 however, the number of chemical steps from 125 to the final side-chain was reduced by one step (Noh et ah, 2004a). The sequence began with a selective hydrogenation with Raney nickel followed by double bond migration to enamine 131 (Scheme 4.25). The amino functionality of 131 was then monoprotected, and the double bond was reduced under hydrogenation conditions to afford pyrrolidine-3-one 133. Treatment of 133 with methoxylamine yielded methoxyoxime 129. Deprotection of the carbamate functionality was achieved with methanesulfonic acid to afford the C7-side-chain as the bis-methansulfonate salt. 

The addition-elimination mechanism, however, is strongly preferred for monohydride systems such as [HCo(CO)4]187 and the Vaska complex193,194 promoting extensive isomerization. Hydroformylation of 2-pentenes in the presence of [HCo(CO)4], for instance, yields mainly the nonbranched aldehyde resulting from double-bond migration.195 Nickel hydride complexes are one of the most active... 

When the transfer reaction competes successfully with further insertion, as in the case of nickel, dimerization becomes the dominant transformation. When metal hydride elimination, in turn, is slow relative to insertion, polymeric macromolecules are formed. Ligand modification, the oxidation state of the metal, and reaction conditions affect the probability of the two reactions. Since nickel hydride, like other metal hydrides, catalyzes double-bond migration, isomeric alkenes are usually isolated. 

One of the earliest studies of n-butene hydrogenation was that reported by Twigg [121] who observed that, for the reaction of l butene with hydrogen over a nickel wire between 76 and 126°C, both hydrogenation and double-bond migration occurred. Hydrogenation and double-bond migration followed the same kinetic rate law, namely... 

Conclusive evidence for the participation of 7r-allylic intermediates in double bond migration has been obtained from a study of the nickel-catalysed hydrogenation of the isomeric olefinic esters methyl oleate and methyl elaidate using tritium as a tracer [147]. It was also concluded that in this system cis—trans isomerisation occurred by an addition—abstraction mechanism. 

Complexes of many transition metals including cobalt, rhodium, iridium, iron, nickel, palladium, and platinum have been found to catalyze double-bond migration in terminal olefins. Evidence for a mechanism of the following type, which is probably also applicable to some of the other catalysts, has been obtained by Cramer 24, 27) for the rhodium chloride-catalyzed reaction (Reaction 37). 

The CO2 fixation into (perfluoroalkyl)iodoalkanes, (perfluoroalkyl)-iodoalkenes and (perfluoroalkyl)alkenes, catalyzed by electrogenerated nickel complexes, afforded perfluoroalkyl carboxylic acid derivatives. The electrocarboxylation of perfluoroalkyl olefins proceeded with double bond migration and loss of an allylic fluorine atom. 

The electrochemical incorporation of CO2 into perfluoroalkyl derivatives has been explored in the case of (perfluoroalkyl)alkyl iodides and (perfluoroalkyl)alkenes, with an electrochemical system based on the use of consumable anodes combined with organometallic catalysis by nickel complexes. Iodide derivatives have been functionalized to the corresponding carboxylic acids by reductive carboxylation. Interesting and new results have been obtained from the fixation of CO2 into perfluoroalkyl olefins. Good yields of carboxylic acids could be reached by a carefull control of the reaction conditions and of the nature of the catalytic system. The main carboxylic acids are derived from the incorporation of carbon dioxide with a double bond migration and loss of one fluorine atom from the CF2 in a position of the double bond. 

Imidazolines can exist as the 2-, 3-, or 4-isomers ((5)- 7)), and whereas (5) can exist as a pair of tautomers, any proton shift in (6) will give (7) by rearrangement. Hydrolysis of A(-unsubstituted 3-imidazolines (6) to a-aminoketones presumably occurs via (7). Nickel boride , prepared in situ, transforms 3-imidazolines into 2-imidazolines by double-bond migration <86H(24)287l>. 

Hydrogenation catalyst. C. A. Brown1 has compared P-1 nickel boride with W-2 Raney nickel as hydrogenation catalysts and finds that the former is somewhat more active and produces less double-bond migration. In addition it is not... 

Conn and Twigg (91) found that no exchange occurred between ethylene and ethylene-di on a nickel catalyst. Twigg (92) further showed that double bond migration in the case butene I—> butene II occurred on his nickel catalyst, but only in the presence of hydrogen. 

Double-bond migration of terminal alkenes forms more of the Z-isomer than corresponds to thermodynamic equilibrium. A study of the exchange and isomerisation of 1-pentene-1,2- 2 on various types of nickel catalyst has shown that this is due to crowding at the active centre, so that the pentyl radical on losing a... 

Hardening of fats is also a three phase catalytic hydrogenation. On nickel or palladium, saturation of the double bonds occurs simultaneously with cis-trans-isomerization and double bond migration. As shown by the example of Figure 13, all these reactions influence the melting point of the treated fat. This very delicate hydrogenation is operated batchwise in stirred tank reactors. Trickle-bed operation is very rare. 

An older method,which also retains the double bond in its original location, utilizes the fact that thioketal formation from A" -3-ketones does not induce bond migration. Subsequent desulfurization with Raney nickel gives the A" -olefin (see section XI-D). 

L = P(OPh)3] formed by oxidative addition of DCN to ML4, coordinates one of the two double bonds of the diene. The coordination is followed by a cw-migration of the coordinated deuterium, producing a jr-allyl nickel complex in which a further cw-migration of the cyanide gave the two products 10 and 11. 

---