Iron tetracarbonyl complex

Insertion of isocyanide carbon atoms into the Cr—carbene bond of [(CO)5CrC(OMe)Me] gave aziridinylcarbene complexes (CIV), some reactions of which are summarized in Scheme 2 28, 198). Cyclic carbene groups (CV)-(CVIII), in which the carbene carbon atom is part of an aromatic six-electron Tr-system, have been reported to form pentacarbonyl chromium and tetracarbonyl iron complexes 383, 384). Related to carbene... 

The tetracarbonyl iron complex of methyl acrylate, methyl 2-chloroacrylate ° and methyl crotonate react in a similar fashion. Although the resulting jj -alkyliron complexes are stable (requiring treatment with trifluoroacetic acid followed by a oxidant to free the organic group from the iron), they are not well characterized. 

Scheme 4-73. Reactions of neutral ri -alkene(tetracarbonyl)iron complexes with nucleophiles.

Cationic ri -allyl(tetracarbonyl)iron complexes are powerful electrophiles that react with nucleophiles primarily to T -alkene(tetracarbonyl)iron complexes. Those species are rather labile and decompose during workup to afford substituted alkenes. This methodology has been described for the first time by Pearson using organocadmium nucleophiles. Similarly, Ti -allyl(dicarbonyl)(nitrosyl)iron complexes, despite the lacking positive charge, also smoothly react with various nucleophiles. As... 

Cationic ri -allyl(tetracarbonyl)iron complexes can also be employed in electrophilic aromatic substitution reactions. This allylation reaction is limited to electron-rich arenes and heteroarenes. Unsymmetrically substituted allyl complexes react with good to excellent regioselectivity and excellent stereoselectivity (Scheme 4—87). ... 

Diaryl thioketones are converted by diiron enneacarbonyl into products of orthometallation.141 Oxidative or photochemically induced deligation of these complexes provides an unusual and valuable synthetic entry into compounds in the uncommon isobenzothiophene category142,151 (Scheme 84). Moreover, the photochemical procedure provides the novel complex, (tetracyanoethylene)tetracarbonyl iron. The orthometallated complexes (68) can also be used to prepare isobenzofurans (see Section IV,B,5). 

Iron tetracarbonyl and various related unsaturated iron complexes show a remarkably rich diversity of spin-forbidden chemistry. Various reactions of these species have been the object of a large number of experimental studies, including many careful studies of reaction kinetics. These experiments provide an excellent set of data with which to evaluate the power of computation to rationalize observations in a qualitative way, as well as to account in a more quantitative way for experimental observations. The computational work described above is largely drawn from our own published work (23-27), including some unpublished data for some of the reactions (85,87). Nevertheless, many other groups have carried out insightful ab initio and DFT studies of many of the species and processes described. 

The reductive dehalogenation of haloalkanes has also been achieved in high yield using polymer supported hydridoiron tetracarbonyl anion (Table 11.15). In reactions where the structure of the alkyl group is such that anionic cleavage is not favoured, carbonylation of the intermediate alkyl(hydrido)iron complex produces an aldehyde (see Chapter 8) [3]. 

Carbonvlation of Benzyl Halides. Several organometallic reactions involving anionic species in an aqueous-organic two-phase reaction system have been effectively promoted by phase transfer catalysts(34). These include reactions of cobalt and iron complexes. A favorite model reaction is the carbonylation of benzyl halides using the cobalt tetracarbonyl anion catalyst. Numerous examples have appeared in the literature(35) on the preparation of phenylacetic acid using aqueous sodium hydroxide as the base and trialkylammonium salts (Equation 1). These reactions occur at low pressures of carbon monoxide and mild reaction temperatures. Early work on the carbonylation of alkyl halides required the use of sodium amalgam to generate the cobalt tetracarbonyl anion from the cobalt dimer(36). 

While a great number of tricarbonyl( -diene)iron complexes have been reported and their reactivity investigated, much less is known of the corresponding heterodiene complexes. In recent years, synthesis of several tricar-bonyl(heterodiene)iron systems involving r] coordination of the heterodiene unit has been achieved. Among the tetracarbonyl(/ -olefin)iron complexes prepared by Weiss was tetracarbonyl(cinnamaldehyde)iron, which converts on heating to the //-bonded tricarbonyl(cinnamaldehyde)iron. The preparation and synthetic utility of (benzylideneacetone)tricarbonyl iron, an analogous complex of an ar,/9-unsaturated ketone, are reported here. 

An iron tetracarbonyl complex (295) ° and a platinum bis(triphenylphosphine) complex of thiete 1,1-dioxide have been prepared. Platinum complexes of 3-phenyl- and 3-(p-bromophenyl) thiete 1,1-dioxide also have been prepared. No complex was obtained with the 3-t-butyl derivative. The pale-yellow, crystalline iron complex decomposes in refluxing hexane in the presence of excess sulfone to Fe2S2(CO)9, indicating a drastic structural rearrangement. Other carbon-containing fragments were not observed. The bis(triphenylarsine)platinum complex of 3-02-bromophenyl) thiete sulfone is decomposed photochemically to the thiete sulfone. The same result is achieved on treatment of the complex with tetra-cyanoethylene. ... 

The use of sonolytic activation of Fe2(CO)9 in an inert solvent has proved to be a general process in the synthesis of a large number of (Ti-allyl)tricarbonyliron lactone complexes and provides an alternative route to those already established in the literature. Diiron nonacarbonyl failed to react with alkenyl epoxide (over a period of up to two weeks) in the absence of ultrasonication. Sonication may aid the breakdown of the diiron nonacarbonyl allowing generation of the highly reactive, coordinatively unsaturated tetracarbonyl iron species which after initial complexation to the double bond of the alkenyl epoxide can form the lactone complex. other pathways cannot, however, be ruled out. 

Jt-Allyltricarbonyliron lactone complexe s are useful precursors for organic synthesis. They were first reported in 1964 [254] and have since been shown to be available from a variety of substrates [255]. For example, they may be prepared from alkenyl epoxides or various butenediols [256] and their derivatives by treatment with tetracarbonyl iron [257]. Work in our laboratories had shown that these were useful precursors for a wid5.,range of naturally occurring p and 5-lactones and lactams [258] (Scheme 123). 

Cationic alkene-Fp complexes are rather stable and easier to handle than their neutral alkene(tetracarbonyl)iron congeners. Due to their positive charge, they are inert towards electrophiles and, thus, can be employed as protecting groups for olefins. Bromination and hydrogenation of other double bonds in the molecule leaves them unaffected. On the other hand they readily react with various nucleophiles such as enamines, enolates, silyl enol ethers, phosphanes, thiols, and amines to give alkyl-Fp... 

The first ri -allyliron complex was obtained by Emerson and Pettit treating ri -butadiene(tricarbonyl)iron with Bronsted acid such as tetrafluoroboric acid to obtain the coordinatively unsaturated cationic T -allyl(tricarbonyl)iron complex. In the presence of carbon monoxide, tricarbonyl(T -diene)iron complexes can be protonated to give tetracarbonyl(Ti -aIlyl)iron complexes (Scheme 4-77). ... 

Borst et al. <2005CEJ3631> conducted a study on the synthesis of strained bicyclic phosphirane and phosphirene iron-tetracarbonyl complexes (Scheme 11). It was shown that, depending on the ring size of the resulting heterocycle, electrophilic phosphinidene [Ri-PrNP=Fe(CO)4] could be trapped intramolecularly with both double and triple bonds (compounds 146-150). The phosphinidene addition was found to be reversible at room temperature and when using phenylacetylene as solvent, exchange between phenylacetylene and the phosphinidene group took place. Compound 151 was isolated as the dimer, compound 152. 

A variety of experimental methods has been used to study the thermal chemistry of the unsaturated iron fragments produced by photolysis. For example, regeneration of 1Fe(CO)s was observed upon heating low-temperature matrices in which Fe(CO)5 had been photolyzed (35). These condensed-phase reactions are rather complex, as in some cases, components of the inert matrix may form adducts Fe(C0)4L or Fe(CO)sL (L = N2, Xe, CH4), so that the reaction observed is not simply CO addition to an unsaturated iron tetracarbonyl fragment. The same reactions were studied in the gas phase, using flash... 

In a similar manner, Jt-allyl complexes of manganese, iron, and molybdenum carbonyls have been obtained from the corresponding metal carbonyl halides [5], In the case of the reaction of dicarbonyl(r 5-cyclopentadienyl)molybdenum bromide with allyl bromide, the c-allyl derivative is obtained in 75% yield in dichloromethane, but the Jt-allyl complex is the sole product (95%), when the reaction is conducted in a watenbenzene two-phase system. Similar solvent effects are observed in the corresponding reaction of the iron compound. As with the cobalt tetracarbonyl anion, it is... 

Similar pyrone complexes were isolated by Semmelhack97a as the products of the reaction between tetracarbonyl[ethoxy(alkyl)carbene]iron(0) complexes and various acetylenes. Vinylketene complexes are proposed as key intermediates in the mechanism of this conversion, which closely matches analogous reactions with cobalt carbenes51 (see Section V,B), while showing crucial differences with the analogous reaction of a chromium carbene (see Section II,B). 

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