Iron pentacarbonyl systems

This paper reviews the recent studies in the field of radical reactions of organobromine compounds. A special attention is paid to the use of metal-complex systems based on iron pentacarbonyl as catalysts this makes it possible to perform the initiation and chain transfer reactions selectively at C-Br bond. 

There have been several reports of homogeneous systems which catalyze the shift reaction in the absence of the synthesis reaction. Probably the first example of such a system was that reported by Reppe and Reindl in 1953 based on iron pentacarbonyl (74). They suggested that in the presence of a suitable base the following catalytic cycle could be established ... 

Analogous carbonylation reactions using nickel and iron carbonyl based systems also produce alkanecarboxylic acids [11, 13, 14]. The mechanism of the conversion of benzyl halides into arylacetic acids using iron pentacarbonyl is not as well defined as it is for reactions promoted by nickel or molybdenum carbonyl complexes. Iron... 

UFPs of the Fe-N system can be synthesized from iron pentacarbonyl Fe(CO)s] and NH3 as reactants by a IOOO-W continuous wave C02 laser irradiation. The NH, gas is the absorbent of the laser beam in this case. At the lower synthesis temperature, below 650°C, UFPs of y -Fe4N with particle size of 10-25 nm grew dominantly. Above 1150°C, however, the growth of y-Fe UFPs with larger particle size of 30-100 nm was predominant (73). Iron carbonitride (lCN) UFPs were also synthesized from the ternary reactants of Fe(CO)s, NH3, and C2H i. The structure oflCN UFPs was hexagonal with e-Fe3(N,C) phase. A large saturation magnetization up to 142 emu/g was obtained and was ascribed to the carbon layer on 1CN UFPs (74). 

Iron-Pentacarbonyl. The FeVIII(CO)5 molecule is equally fundamental to organometallic chemistry and electrochemistry, and, like Feu(Cp)2, is a diamagnetic 18-electron system. It exhibits (a) an irreversible two-election oxidation and (b) an irreversible two-electron reduction (Figure 13.1e). In each case Fe(CO)5 has a synergistic effect on (1) the reduction of residual H20 and (2) the oxidation of solvent molecules ... 

An uncommon ring system formed by an unusual reaction, and the only ring system dealt with here which has eight heteroatoms in its two rings is represented by the [l,3,2,6]oxazadiborino[5,4-f7][l,3,2,6]-oxazadiborine derivative (508) which is formed when two molecules of the three-mem-bered ring precursor (507) are irradiated in presence of iron pentacarbonyl at — 30 °C <90AG(E)900>. 

DIBAL-H/n-butyllithium, in cyclic and acyclic systems with iron pentacarbonyl, in cyclodecanes with lithium dihydrodimethoxyaluminate(III)/copper(I) iodide, and in cyclohexane and cyclopentane systems with NaH/sodium r-butylpentyl/Ni(OAc)2. ° The monoreduction of 1,3-diketones can be carried out under similar conditions, as illustrated by the reaction of a substituted cyclohexane-1,3-dione with oxalyl chloride to give the corresponding 1-chlorocyclohexenone, which was subsequently reduced to the enone with zinc-silver couple (Scheme 45). Kropp et al. have reported the photolytic reduction of vinyl iodides in acyclic systems however, when an a-hydrogen is present, formation of the diene product is a limiting side reaction (Scheme 46). For a more extensive discussion of vinyl halide reductions, see the preceding chapter in this volume. 

Tetracarbonylcobaltate anion, generated under PTC conditions, catalyzes the reaction of aryl halides with excess methyl iodide under a CO atmosphere [122]. The reaction produces aryl methyl ketones and carboxylic acids as the main products. Stoichiometric or catalytic iron pentacarbonyl can also be used for the carbonylation of organohalides under PTC conditions [123-128]. For example, reactions of alkyl and arylalkyl halides with CO in aqueous-organic systems using catalytic amounts of Fe(CO)5 and a PT agent afford alkyl- and arylacetic acids as the main products [127]. 

In this reaction iron pentacarbonyl was found to add CF3I to form the first (trifluoromethyl)iron derivative reported (20). The oxidative-addition route has proven to be successful in a number of systems in which d or dt0 metal complexes have been employed as reagents, but ineffective with substrates in which the metal had an alternative delectron count (1 -4). 

In a well-ventilated hood a 1-1. three-necked flask is immersed in an oil bath and fitted with a mechanical stirrer and condenser with aT-piece at the top with one lead connected to a nitrogen supply and the other to a gas bubbler. The flask is charged with 60 g. (0.49 mole) of c/i-3,4-dichlorocyclobutene (this volume) in 250 ml. of benzene, and the system is flushed with nitrogen. A first 50-g. batch of diiron nonacarbonyl (2) is added and the mixture is heated at 50-55° with stirring. After about 15 min. the initial rapid evolution of carbon monoxide becomes greatly diminished and a further 25 g. of Fe2(CO)9 is added. Further 25-g. portions are added until no more carbon monoxide is liberated a total of approximately 275 g. of Fe2(CO)9 is required and the total reaction time is about 5 hrs. The mixture is then filtered with suction through Celite and the Buchner funnel is washed thoroughly with pentane until the filtrate is colorless. Fractional distillation at reduced pressure removes benzene, then iron pentacarbonyl (b.p. 20730 mm.) when the Fe(CO)5 has been removed, cyclobutadieneiron tricarbonyl is collected as a pale yellow oil, b.p. 4773 mm. 

The only practical preparations of cyclopentadienyliron dicarbonyl dimer involve reactions of iron pentacarbonyl with either cyclopentadiene or its dimer at elevated temperatures. Although the use of monomeric cyclo-pentadiene is reported to give a higher yield and possibly a purer product, use of an autoclave is required because of the low boiling point of cyclopentadiene if a reasonable amount of product is to be prepared. For this reason the reaction between iron pentacarbonyl and dicyclopentadiene may well be more convenient since it can be carried out in an open system. The preparation described below involves dicyclopentadiene. 

It has been observed that the isomerization of 1-olefins by palladium complexes shows simultaneous appearance of all the possible internal isomers at comparable rates (55, 59) rather than the stepwise formation shown in the nickel systems. It has been proposed that perhaps the reaction proceeds by some type of 7r-allyl mechanism (60). Two mechanistic schemes have been proposed for the isomerization of olefins by iron pentacarbonyl (61, 62). One is analogous to that of the nickel isomeriza-tions, and the other involves a 7r-allyl intermediate (Fig. 25). 

A [bis(dimethylamino)alumino-oxy]dimethylamino-carbene complex results when iron pentacarbonyl reacts with tris(dimethylamino)alane. ° The compound is dimeric, as determined by n.m.r. data, and it is formulated as containing a four-membered AlgNg ring system (101). The formation... 

Butanol is prepared commercially by the iron carbonyl-promoted hydro-xymethylation of propylene (Reppe and Vetter, 1953). Iron pentacarbonyl and a tertiary amine serve as a good catalyst system. The active species has been shown to be HFe(CO)4 formed from the metal carbonyl and hydroxide ion (Wada and Matsuda, 1974). 

A crucial concept in the definition of stereoisomers given above is "connectivity". In methane or 2,3-dichlorobutane, there is no doubt as to the connectivity of the system. However, there is an innate arbitrariness to the term, and this can lead to some ambiguity about stereoisomerism. For example, do hydrogen bonds count in our list of connectivity No, but consider the implications of this. If hydrogen bonds "don t count", then how do we think about isomerism in double-helical DN A Do we just ignore the interaction of the two strands As a simpler comfortable with a clear connectivity pattern in inorganic complexes such as iron pentacarbonyl or a porphyrin complex. But what about Mg ions complexing a carbonyl When is a bond too weak to be considered relevant for stereoisomerism . Mg" Mgr O 0 V ... 

As early as 1964, Rhone-Poulenc had investigated the hydrodimerization of acrylonitrile yielding adipodinitrile (Equation 39). In a patent they claimed a catalyst system composed of iron pentacarbonyl and an aqueous alkaline solution [42]. 

One of synthetic approaches for the iron nanoparticles is based on the widely used decomposition of iron pentacarbonyl [19, 361, 362], The novelty of the approach is the surfactant system used. Studies with a number of strongly bound surfactants have resulted in decreased magnetic response, due to surface oxidation, disturbing the electronic structure of the surface atoms, or some other mechanism. With this in mind, ones chose to work with a weak surfactant, a p-diketone. P-diketones do have a history as adhesion promoters in bonds between metals and polymers [363], The limited reactivity of p-diketones is as an advantage the P-diketone is much weaker oxidizer than carboxylic acids or alcohols and will not oxidize iron, it is not as nucleophilic as phosphines, yet it is known to be capable of chelating iron. 

Metal tricarbonyl systems, M(CO)3, are usually markedly resistant to further substitution thus only one or two carbonyl groups may readily be displaced from iron pentacarbonyl. 

Figure 7 illustrates the electrochemial redox chemistry in acetronitrile for several coordination complexes of iron [Fe (MeCN)4, Fe CL, and Fe (acac)s (acac = acetylacetonate)] in relation to that for two iron organometallics [Fe (Cp)2 and Fe (CO)s (iron-pentacarbonyl) both stable 18-electron systems]. In MeCN, Fe (MeCN)4" is the only charged species of the group. It is reversibly oxidized (II/III couple E1/2, -I-1.6 V vs SCE). The uncharged Fe Cb molecule is reversibly reduced (Ill/n couple Ei/2, -1-0.2 V vs SCE) to giveFe Cl, which is reduced by an irreversible two-electron process to iron metal (Ep,c -L5 V vs SCE). The more basic Fe (acac)3 molecule is reversibly reduced (ni/n couple Ei/2, -0.7 V vs SCE), but does not exhibit a second reduction peak. The III/II reduction potentials for these three coordination complexes are a measure of their relative electrophilicity (Lewis acidity). 

Many diene iron tricarbonyl complexes are known.f Butadiene iron tricarbonyl was first prepared in 1930 by Reihlen and co-workers [60], by treatment of iron pentacarbonyl with butadiene under pressure. It is a typical diene iron carbonyl complex being a yellow-brown oil which distils slowly at 60° in high vacuum. It is soluble in the common organic solvents and reacts with chlorinated hydrocarbons. The pure oil and its solutions are oxidized in air within hours, forming iron oxides. The diene system resists hydrogenation and does not undergo the Diels-Alder reaction [5]. 

Iron pentacarbonyl reacts with cinnamaldehyde affording the complex 3.33, in which 77-bonding by both the C=C and C=0 systems has been proposed [84]. With acrolein and Mo(CO) , a polymeric complex, 3.34, is... 

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... 

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