Iron carbonyl halides

We were able to prepare (63) iron carbonyl halides of lower carbon monoxide content, Fe(CO)2X2, which are formally related to the long-known platinum carbonyl compounds (62), e.g.,... 

My co-worker H. Lagally showed that the thermal decomposition of Fe(CO)4I2 afforded successively Fe(CO)2I2, Fe(CO)2I, and CO-free Fel. For these decomposition products of Fe(CO)4I2 a polymeric structure with iodine bridges is postulated. A study of the reaction FeI2 + 4 CO Fe(CO)4I2, also in collaboration with Lagally, further established the metastable or labile nature of iron carbonyl halides (63). 

The iron carbonyl halides are light-sensitive water converts them to the corresponding Fe (11) salt solutions (the chloride and bromide react instantaneously, the iodide only upon heating). The thermal decomposition of iron carbonyl halides is a convenient way to produce fine powders of anhydrous Fe(II) halides. 

When Fe(lll), dppm, and LiAlH4 were reacted in the presence of CO, various iron carbonyl-halide complexes were formed. Reactions are depicted in Scheme 51 and Equation (72). ... 

Iron carbonyl halides have not been extensively examined in the past decade for their own sake, but rather most studies where both CO and halide ions are bound to iron have focused on preparing derivatives with other ligand types bound to Fe. Examples of these have already been described in the appropriate sections above. The reader is referred to Equations 54, 75, 76, 78, 79, 105, Schemes 21, 46, 51, 55, 74, 75, 82, 83, and structure 36. General routes to these compounds include substitution reactions of Fe(CO)4X2 complexes and carbonylation of iron halide coordination compounds. 

High selectivity is observed, and in aromatic compounds other substituents (C02R, OR, CN, halide) are not affected. Dinitro aromatics could be sequentially hydrogenated to nitroamines and diamines (105). [Some ruthenium and iron carbonyls were less effective (104)]. 

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... 

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... 

Selected examples of the conversion of benzyl halides into arylacetic acids using iron carbonyl complexes... 

A recent report( ) on the use of iron carbonyl and potassium carbonate in a similar carboxyalkylation scheme to prepare methyl phenylacetate prompted us to examine the use of carbonate on alumina in a similar manner. It was suggested that if the amount of free base was less than the amount of iron carbonyl than ether formation would not occur being that iron carbonyl was a better electrophile than benzyl halide. Under our conditions, the metal carbonyl anion... 

Orgel (23). Subsequently, Hubei and co-workers (24) obtained, among other products, tricarbonyl-7r-tetraphenylcyclobutadiene iron by the reaction of tolane with iron carbonyls. More recently, a general synthesis of tetra-phenylcyclobutadiene-metal complexes using ligand transfer from tetra-phenylcyclobutadiene palladium(II) halides (25) to a metal carbonyl has been described (26). It is also possible to obtain complexes containing... 

Carbonyl halide complexes of platinum(IV) are less common. The reaction of [Pt(CO)2]s with chloride ion in an aqueous solution of iron(HI) ions gives Pt(CO)H2Cl2, which adds chloride to give Pt(CO)H2ClJ.313,314 Addition of chlorine to a thionyl chloride solution of Pt(CO)2Cl2 at room temperature results in the rapid formation of Pt(CO)Cl (equation 106), which shows a carbonyl stretch at 2191 cm-1. The yellow-orange compound is stable toward Cl- but reacts with water to form C02.315... 

In other variations ketones are produced. The acyliron monoanion may be alkylated again with another alkyl halide to form a transient acyl-alkyl iron intermediate, which rapidly decomposes into ketone and the polynuclear iron carbonyl complex. This reaction is limited, however, because only very reactive alkylating agents such as methyl, allyl, and benzyl halides will react with the weakly nucleophilic acyliron monoanions ... 

Addition of nucleophiles to a carbon monoxide ligand of pentacarbonyliron provides anionic acyliron intermediates which can be trapped by electrophiles (H+ or R—X) to furnish aldehydes or ketones [18]. However, carbonyl insertion into alkyl halides using iron carbonyl complexes is more efficiently achieved with disodium tetracarbonylferrate (Collman s reagent) and provides unsymmetrical ketones (Scheme 1.2) [19, 20]. Collman s reagent is extremely sensitive towards air and moisture, but offers a great synthetic potential as carbonyl transfer reagent. It can be prepared by an in situ procedure starting from Fe(CO)5 and Na-naphthalene [20]. 

The mercury compounds HgFe(CO)4 and Fe(CO)4(HgX)2 (X = C1, Br, I), which were the first representatives of non-ionic metal derivatives of iron carbonyl hydrides, were discovered by Hock and Stuhlmann (V, 36). During investigations into the preparation of cobalt carbonyls from cobalt halides under CO pressure, in the presence of another metal as a halogen acceptor, we discovered the mixed metal carbonyls M[Co(CO)4]2 (M = Zn, Cd, Hg, Sn) and M[Co(CO)4]3 (M = In, Tl) (44), e.g.,... 

Almost simultaneously with our first investigations About Reactions and Derivatives of Iron Carbonyl (Section II,A) we concerned ourselves at Heidelberg with the effect of halogens on iron pentacarbonyl, initially in the expectation of obtaining a pure surface-active iron(II) halide. However, to our surprise at the time, reaction occurred according to the equation... 

Carbonyl derivatives of iron(II) exist. Pentacarbonyl-iron(O) is oxidized by halogens to give carbonyl halide complexes (equation 35). The stability of these compounds with respect to thermal decomposition and hydrolysis increases in the sequence Cl < Br < I. 

Of considerably greater interest is 77-allyl ligand transfer from one metal to another. Although the examples of such reactions are rather few they have been studied in detail. The first example of a 7r-allyl ligand transfer from one metal to another was reported by Nesmeyanov, Rubezhov, and Gubin (156). Iron carbonyls were found to react with some substituted binuclear 77-allylpalladium halides in benzene at room temperature, giving the respective 77-allyliron derivatives ... 

Applications of carbonylaie reactions in organic synthesis are numerous. Particularly noteworthy are schemes involving tetracarbonylferrate( - ID (referred to as Collman s reagent), which can be isolated as a. sodium salt, NanFe(CO)4-1.5 dioxane, and is commercially available. The highly nucleophilic [Fe(CO)4p reacts readily with alkyl halides to yield alkyl iron carbonylates ... 

The carbonyls are in general volatile compounds with an extensive chemistry which presents many problems as regards valence and stereochemistry. Some are reactive and form a variety of derivatives, as shown in Chart 22.1 for the iron compounds, while others are relatively inert, as for example, Cr(CO)6 etc. and Re2(CO)iQ. This rhenium compound, although converted to the carbonyl halides by gaseous halogens, is stable to alkalis and to concentrated mineral acids. A few carbonyls may be prepared by the direct action of CO on the metal, either at atmospheric pressure (Ni(C0)4) or under pressure at elevated temperatures (Fe(CO)s, Co4(CO)i2)- Others are prepared from halides or, in the case of Os and Re, from the highest oxide. The polynuclear carbonyls are prepared photo-synthetically, by heating the simple carbonyls, or by other indirect methods. 

---