Olefin-iron carbonyl complex

The olefin-iron carbonyl complexes were first introduced by two entirely different synthetic methods. In 1930 Reihlen and co-workers (I) obtained butadiene-iron tricarbonyl by a reaction of butadiene with iron penta-carbonyl and in 1953 Reppe and Vetter (2) reported organoiron compounds, since shown to be diene-iron carbonyl complexes, following reaction of acetylene with iron carbonyls. 

Subsequent developments in this area have produced a large number of new organoiron complexes the greater majority of these are found to be olefin-iron carbonyl complexes, hence their inclusion in this review. 

Although the reaction responsible for the generation of the hydride is not specified, it is assumed that it arises from a disproportionation of iron carbonyl complexes. The hydride presumably adds after ir-complexing to form the c-bonded complex which then splits out the metal hydride in either direction. The ir-complexed olefin may then be displaced by another olefin or undergo another hydride addition-elimination sequence. The second path involves olefin complexing with the deficient Fe(CO)3 species and formation of a jr-allyliron hydride intermediate ... 

A review of diene-iron carbonyl complexes has recently appeared (5) metal complexes of di- and oligoolefinic ligands have also been reviewed (6). A general review of olefin, acetylenic, and 7r-allylic complexes of transition metals is due to Guy and Shaw (7). 

Photochemical activation (15) and thermal activation (11,16, 17) of iron carbonyl complexes In various zeolites have been reported. Part of our study Is to use Mossbauer spectroscopy to Investigate the behavior of Fe(C0)5 on several zeolites when activated photochemically and thermally. Another part of our study Is to Investigate the novel preparation method of Scherzer and Fort (18) that Introduces iron Into (in their study) zeolite NH Y as an anionic complex. Finally, we will report the preparation of ferrocene sublimed onto zeolite ZSM-5. The photochemical and thermal activation of these systems will be reported as well as preliminary results of the photochemical isomerization of olefins by Fe(C0)5 zeolites and the thermal activation of Fischer-Tropsch catalytic systems. It also should be noted here that our Mossbauer studies involve an in-situ pretreatment cell which can be heated to 500°C under various gaseous atmospheres. 

In 2012 Ryu and his colleagues reported the iron-catalyzed decarbonylation of aliphatic carboxylic acids to a-olefins (Scheme 11.7) [32]. In their mechanism study, they found the formation of CO but not CO2. If the reaction was carried out under low or no pressure (0-5 bar) of carbon monoxide, internal an olefin was observed [33]. In the proposed reaction mechanism, the reaction starts from acid anhydride, which was produced from the reaction of substrate and AC2O. Then it reacts with the in situ-formed iron-carbonyl complex, which was generated by FeCl2, phosphine ligand, KI, and CO, and decarbonylation occurred under high temperatures. Notably, Fe2(CO)9, Fe3(CO)i2, [Fe(CO)2Cp]2 did not give the decarbonylation product. 

Two new reagents have been introduced for the reduction of lactones. A modification of Red-al by addition of one equivalent of ethanol provides a method for reduction of lactones to lactols, and the easily prepared iron carbonyl complex NaHFe2(CO)g is useful for the reduction of the olefinic bond in a)3-unsaturated lactones, as well as in unsaturated esters and amides. ... 

Since 1958 a considerable amount of research activity has centered around these systems, both in the acetylene-iron carbonyl reactions and the direct reactions of olefins with iron carbonyls. The types of unsaturated ligands which are now known to occur in stable iron carbonyl complexes include substituted and nonsubstituted cyclic, acyclic, and nonconjugated dienes as well as some aromatic systems. Furthermore, what may be formally regarded as dienyl cations as well as allyl cations and radicals are found to... 

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. 

Perfluoroethylene was first thought to react with iron carbonyl to give the iron(O) olefin complex [Fe(CO)3(C2F4)2] 213). It has since been shown that the product is a heterocyclic derivative of iron(II) (structure XII) 150, 214) and not a true olefin complex. 

Both conjugated and nonconjugated olefins form complexes with the transition-metal carbonyls. Despite the fact that the first known complex, Zeises salt K(PtC2H4Cl3), discovered in 1827, was that of a simple olefin, complexes of monoolefins are rather limited in number. However, nonconjugated diolefins (L) react with group-VI carbonyls to form complexes of the type LM(CO)4 an example is provided by tetracarbonyl-bicyclo-(2,2, l)hepta-2,5-diene chromium (2) (Fig. 1). In contrast, the iron carbonyls... 

Consequently, the elements to the left of the noble metals show strongest (ft)-character in their zero-valent oxidation state. Thus iron(O), cobalt(O) and nickel(O) are typically (b), forming inter alia strong carbonyl complexes, while the higher oxidation states of these elements have no marked ( )-character at all. Elements in zero-valent state in fact display (b) -character as far left in the periodic system as chromium, or even vanadium, which in higher oxidation states behave as very typical (a)-acceptors. To the right of the noble metals, on the other hand, the metals in their zero-valent states do not show any marked (6)-character they do not form e.g. carbonyl or olefin complexes. 

We have reported here the preparations and treatment conditions that are needed to reduce Iron Ions to metallic Iron In zeolites. Although we have not Isolated highly-dis-spersed superparamagnetic Iron particles In zeolites, we have shown that these iron-containing zeolites are active catalysts in Fischer-Tropsch and in olefin isomerization reactions. The added insight that stems from the use of in-situ Mossbauer experiments has led to the preparation of new active catalysts that can be selectively activated. We presently are studying photochemical reactions of other metal carbonyl complexes in zeolites and believe that increased selectivity is a major benefit in these types of reaction. 

Even though the X-ray data suggest the presence of two a bonds and one 7T bond between metal and olefin as was postulated for the butadiene-iron carbonyls, the UV spectra of the triphenyltropone complexes closely resemble that of the free olefin (80) suggesting that the bonding of the complex may indeed be intermediate between that of structure (96) and simple rr bonding to two olefinic double bonds (80). This concept is more fully discussed in the section on cobalt (Section VII, A). 

Bis(phosphine) derivatives of pentacarbonyliron are starting materials for the synthesis of several organometallic iron complexes. " Iron carbonyl phosphine complexes have attracted attention because of their relevance to photochemical catalysis of olefin hydrosilation. Though Fe(CO)3(PR3)2 complexes are used widely in organotransition metal chemistry, an efficient preparation of these compounds has not been reported. Clifford and Mukherjee describe two methods for the synthesis of tricarbonyl-bis(triphenyphosphine)iron(0). They report that direct reaction between Fe3(CO)j2 and triphenylphosphine in THF solvent gives a mixture of Fe(CO)3[P(C6Hs)3]2 (27%) and Fe(CO)4[P(C5H5)3] (34%). The second... 

Olefins are usually carbonylated in the presence of metal carbonyls, such as nickel, cobalt, and iron carbonyls under homogeneous conditions, and the mechanism of these carbonylations has been established in several cases. On the other hand, isolation or formation of true palladium carbonyl has not been reported. Since palladium is an efficient and versatile catalyst for various types of the carbonylation mentioned above, the mechanisms of the carbonylation of olefin-palladium chloride complexes and of metallic palladium catalyzed carbonylations seem to be worth investigating. 

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