Acrylonitrile, iron complex

In the recent literature several instances have been reported of the formation of olefin-iron tetracarbonyl complexes. The first example was the preparation of acrylonitrile-iron tetracarbonyl from acrylonitrile and Fe2(CO)9 107). The X-ray data for this complex shows that the iron atom in this complex is bonded to the C=C group rather than to the C=N or to the nitrogen atom 108, 109). 

MAA and MMA may also be prepared via the ammoxidation of isobutylene to give meth acrylonitrile as the key intermediate. A mixture of isobutjiene, ammonia, and air are passed over a complex mixed metal oxide catalyst at elevated temperatures to give a 70—80% yield of methacrylonitrile. Suitable catalysts often include mixtures of molybdenum, bismuth, iron, and antimony, in addition to a noble metal (131—133). The meth acrylonitrile formed may then be hydrolyzed to methacrjiamide by treatment with one equivalent of sulfuric acid. The methacrjiamide can be esterified to MMA or hydrolyzed to MAA under conditions similar to those employed in the ACH process. The relatively modest yields obtainable in the ammoxidation reaction and the generation of a considerable acid waste stream combine to make this process economically less desirable than the ACH or C-4 oxidation to methacrolein processes. 

Catalysts. In industrial practice the composition of catalysts are usuaUy very complex. Tellurium is used in catalysts as a promoter or stmctural component (84). The catalysts are used to promote such diverse reactions as oxidation, ammoxidation, hydrogenation, dehydrogenation, halogenation, dehalogenation, and phenol condensation (85—87). Tellurium is added as a passivation promoter to nickel, iron, and vanadium catalysts. A cerium teUurium molybdate catalyst has successfliUy been used in a commercial operation for the ammoxidation of propylene to acrylonitrile (88). 

Dehydrogenation, Ammoxidation, and Other Heterogeneous Catalysts. Cerium has minor uses in other commercial catalysts (41) where the element s role is probably related to Ce(III)/Ce(IV) chemistry. Styrene is made from ethylbenzene by an alkah-promoted iron oxide-based catalyst. The addition of a few percent of cerium oxide improves this catalyst s activity for styrene formation presumably because of a beneficial interaction between the Fe(II)/Fe(III) and Ce(III)/Ce(IV) redox couples. The ammoxidation of propjiene to produce acrylonitrile is carried out over catalyticaHy active complex molybdates. Cerium, a component of several patented compositions (42), functions as an oxygen and electron transfer through its redox couple. 

Olefins readily displace CO groups from the iron carbonyls, Fe(CO)5, Fe2(CO)9, and Fe3(CO)12, to form complexes in which a C C bond of the olefin takes the place of each displaced CO group, and by donating its ir-electrons preserves the formal inert gas electron configuration of the iron atom in the complex. Acrylonitrile is the only reported example of a monoolefin complexing with iron in this way, but many complexes of iron with polyolefins are known. 

The first investigations on iron-catalyzed Michael reactions utilized Fe(acac)3 as catalyst. However, this metal complex is itself catalytically almost inactive. Yields of only up to 63% could be achieved, if BF3OEt2 is used as a co-catalyst [55], Polystyrene-bound Fe(acac)3 catalysts were also reported to give yields up to 63% [56], FeCl3 was used as a co-catalyst for clay-supported Ni(II). Yields achieved with this heterogeneous system ranged from 40 to 98% [57]. The double Michael addition of acrylonitrile to ethyl cyanoacetate is smoothly catalyzed by a complex generated from [Fe(N2) (depe)2] [depe = l,2-bis(diethylphosphano)ethane]. At 23 °C and after 36h, an 88% yield is obtained with 1 mol% of this Fe(0) catalyst [58]. 

Although ethers have been used less frequently than alcohols, it has recently been reported that tetrahydrofuran (THF) is photocatalytically activated by TBADT, and the alkylation of unsaturated nitriles is obtained in good yield [15]. As an alternative, the C—Br bond in various glycosyl bromides has been homolytically cleaved, and the resulting radical trapped by acrylonitrile to form the corresponding C-glycosides. The halogen abstraction step is initiated by a photolabile iron-based dimeric metal complex [16]. 

Several aUcene complexes of iron(O) have been reported, of general formula Fe(CO)4(alkene), where the aUcene can be ethylene, acrylonitrile, maleic anhydride, or methyl methacrylate. In these complexes, the original trigonal bipyramidal structure of the pentacarbonyl is retained with one of the equatorial positions now being occupied by the alkene ligand. The tetracarbonyliron(O) complex of fumaric acid has idealized C2 symmetry and has been resolved into its two enantiomers. ... 

Copper chloride complexes can be used as catalysts in a number of organic reactions. Examples include the Wacker process, which is the oxidization of ethylene to acetaldehyde by oxygen and aqueous Cu and Pd precatalysts (or, alternatively using iron catalysts) plus the synthesis of acrylonitrile from acetylene and hydrogen cyanide using CuCl. Cuprous chloride has also been used as a desulfiuizmg and... 

Other Nitrile Complexes. While similar additions of iron (i) and rhodium (11) hydrides to acrylonitrile to form 1-cyanoethylmetal complexes have been reported, 2-cyanoethylmetal complexes also form in certain cases (43, 51). Organotin hydrides may add to acrylonitrile in either direction, depending on the conditions of the reaction (25). Formation of the 2-cyanoalkyltin adduct apparently involves a radical mechanism, whereas a polar mechanism is operative in forming the 1-cyano-alkyl adduct. A four-center transition state was not considered probable in the latter case. 

Yamazaki s complex (Structure 5) contains two alkyne molecules linked together to form a five-membered metallacycle. Arene-solvated cobalt atoms, obtained by reacting cobalt vapor and arenes, have been used by Italian workers to promote the conversion of a,w-dialkynes and nitriles giving alkynyl-substituted pyridines [20]. -Tolueneiron(0) complexes have also been utilized for the co-cyclotrimerization of acetylene and alkyl cyanides or benzonitrile giving a-substituted pyridine derivatives. However, the catalytic transformation to the industrially important 2-vinylpyridine fails in this case acrylonitrile cannot be co-cyclotrimerized with acetylene at the iron catalyst [17]. 

The influence of ammonia on the partial (amm)oxidation of propene was studied over the iron antimony oxide catalyst (Sb/Fe = 2) at 375 °C (see Figure 5). The yield of the partial (amm)oxidation products acrylonitrile plus acrolein decreased with increasing ammonia partial pressure. The yield of the combustion products CO and CO2 first decreased and then increased with increasing ammonia partial pressure. The opposing trends for the yield of both product groups resulted in a complex behaviour of the conversion of propene as a function of the partial pressure of ammonia. The rate of formation of the partial (amm)oxidation products can be easily modelled as a surface reaction ocupying one or two active sites, and ammonia occupying one of the sites. 

A correlation of a high thermal stability with a high ionization potential for a olefin has been observed with iron (O)-olefin complexes of the type Fe(CO)4-(olefin) 96> i.e. poor donor but good acceptor properties increase the stability of the complex. The acrylonitrile complex is one of the most stable, the ethylene complex the least stable and the complexes of styrene or vinyl chloride are of intermediate stability. 

The NMR resonances of the ethylene are shifted upfield to 0.59 ppm below Me4Si. This shift, one of the largest ever reported (27), is another indication of the high electron density on the iron. The ethylene complex and complexes of other unactivated olefins such as propylene and butadiene (which is rj ) undergo a fluxional process on the NMR time scale which equilibrates the four DMPE phosphorus nuclei. Complexes of activated olefins such as acrylonitrile are stereochemically rigid... 

A number of transition metal complexes have been apphed in ATRP process. It has been successful for molybdenum, chromium, rhenium, ruthenium, and iron, rhodiiun, nickel, palladium, and copper complexes. Among these, copper catalysts are superior in terms of versatihty and cost. Styrenes, (meth)acrylates, (meth)acrylamides, and acrylonitrile have been successfully polymerized using copper-mediated ATRP. The polymerization has been foimd to be tolerant to a variety of... 

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