Halides iron/cobalt

There are few reports of oxidative addition to zerovalent transition metals under mild conditions three reports involving group 10 elements have appeared. Fischer and Burger reported the preparation of aTT -allylpalladium complex by the reaction of palladium sponge with allyl bromide(63). The Grignard-type addition of allyl halides to aldehydes has been carried out by reacting allylic halides with cobalt or nickel metal prepared by reduction of cobalt or nickel halides with manganese/iron alloy-thiourea(64). 

The possibility that substitution results from halogen-atom transfer to the nucleophile, thus generating an alkyl radical that could then couple with its reduced or oxidized form, has been mentioned earlier in the reaction of iron(i) and iron(o) porphyrins with aliphatic halides. This mechanism has been extensively investigated in two cases, namely the oxidative addition of various aliphatic and benzylic halides to cobalt(n) and chromiumfn) complexes. 

The elements iron, cobalt and nickel, and the elements preceding the platinum-iron group, have not as strong a tendency to form covalent complexes in reaction with halides. There are no compounds K2NiGl6 or K4FeCl6. 

Among the electrochemical syntheses related to the change of metal oxidation number, we emphasize obtaining acetylacetonates of divalent iron, cobalt, and nickel [551,623]. The method of alternating-current electrochemical synthesis was applied to isolate Ji-complexes of monovalent copper with allylamines, allylimines, and ally-lurea from the salts of divalent copper [624-628], We note that the same method was used for preparation of analogous ji-complexes with copper(II) halides (X = Cl, Br) [629a]. Other electrochemical syntheses with participation of metal salts and complexes are described in monographs [201,202] and literature cited therein. 

The only other known work along these lines was reported by Scott and Walker (10). The reaction described therein involves the reduction of metal halides with the highly colored addition compounds (9) which are formed when sodium metal is added to polynuclear hydrocarbons in certain active ether media such as 1,2-dimethoxyethane and dimethyl ether. For example, sodium reacts with a solution of naphthalene in 1,2-dimethoxyethane to produce a dark green solution which contains the sodium addition compound of naphthalene, having the empirical formula CioHsNao. If nickel chloride is added to the colored solution, the metal is reduced to the elemental state as a finely divided nickel powder with an average particle size of less than 20 microns. Similarly, iron, cobalt, and other metal powders can be produced by this method. 

Several other nitroso compounds have been investigated by PES. The nitrosyl halides, Hal-NO, are basic inorganic compounds. Of particular inteest for organic chemists are nitrosamines, R2N—NO, and nitrites, RO—NO. The NO group occurs as a ligand in transition metal complexes and PE spectra of complexes of chromium, manganese, iron, cobalt and nickel have been measured. ... 

The cell which holds the molten salt and metal can be made of a variety of materials, such as iron, graphite, fire brick, alumina, magnesia, molybdenum or tantalum. The cathode is usually molybdenum, tantalum or tungsten and sometimes iron, cobalt or nickel. The choice of the cell and cathode materials will depend on the product desired. Graphite is almost always the choice for the anode because it is relatively inert to the halide gases (F2 or CI2) or oxygen liberated at this electrode. 

Reactions of metal halides with ammonia may involve the formation of addition compounds or bring about ammonolysis of one or more of the metal-halogen bonds . The dichlorides of manganese, iron, cobalt and nickel form adducts. Vanadium(III) chloride and vanadium(III) bromide are ammonolysed in liquid ammonia to a mixture of ammonolysis products with the same chemical composition as that of the previously reported hexamine ... 

A quite different process, called Reppe carbonylation, has been used to convert acetylene to acrylic acid esters. The catalysts are carbonyls of iron, cobalt or nickel and the hydrogen source is a hydrogen halide, HX. The process is thought to involve oxidative addition of HX to the metal carbonyl, followed by coordination and insertion of alkyne into the M—H bond and insertion of CO into the M—C bond. The resulting acyl complex is cleaved by alcohol to produce the ester and the metal hydride catalyst. De Angelis et al. have reported a theoretical analysis of the Ni(CO)4 system. 

Olefin Dimerization and Polymerization The homogeneous catalytic dimerization of olefins, e.g., ethylene to butene, is another important reaction that can proceed via the addition, insertion, cleavage sequence. Among the catalysts that effect ethylene dimerization are RhCl3, PdCl2, and combinations of alkylaluminum halides with divalent iron, cobalt, and nickel compounds. The rhodium system has been thoroughly studied (177) and almost certainly proceeds by the sequence shown below (S = solvent). The nickel system probably functions similarly, but other mechanisms have been considered for the iron-, cobalt-, and palladium-catalyzed reactions. 

Cobalt is a bluish silvery metal, exhibits ferromagnetism, and can exist in more than one crystal form it is used in alloys for special purposes. Chemically it is somewhat similar to iron when heated in air it gives the oxides C03O4 and CoO, but it is less readily attacked by dilute acids. With halogens, the cobalt(II) halides are formed, except that with fluorine the (III) fluoride, C0F3, is obtained. 

Perfluoroalkyl or -aryl halides undergo oxidative addition with metal vapors to form nonsolvated fluonnated organometallic halides and this topic has been die subject of a review [289] Pentafluorophenyl halides react with Rieke nickel, cobalt, and iron to give bispentafluorophenylmetal compounds, which can be isolated in good yields as liquid complexes [290] Rieke nickel can also be used to promote the reaction of pentafluorophenyl halides with acid halides [297] (equation 193)... 

Structural types for organometallic rhodium and iridium porphyrins mostly comprise five- or six-coordinate complexes (Por)M(R) or (Por)M(R)(L), where R is a (T-bonded alkyl, aryl, or other organic fragment, and Lisa neutral donor. Most examples contain rhodium, and the chemistry of the corresponding iridium porphyrins is much more scarce. The classical methods of preparation of these complexes involves either reaction of Rh(III) halides Rh(Por)X with organolithium or Grignard reagents, or reaction of Rh(I) anions [Rh(Por)] with alkyl or aryl halides. In this sense the chemistry parallels that of iron and cobalt porphyrins. 

The preparation of carbonylmetals by treating a transition metal halide either with carbon monoxide and zinc, or with iron pentacarbonyl is well-known and smooth. However, a violent eruptive reaction occurs if a methanolic solution of a cobalt halide, a rhodium halide or a ruthenium halide is treated with both zinc and iron pentacarbonyl. 

Low-valent cobalt pyridine complexes, electrogenerated from CoCl2 in DMF containing pyridine and associated with a sacrificial zinc anode, are also able to activate aryl halides to form arylzinc halides.223 This electrocatalytic system has also been applied to the addition of aryl bromides containing an electron-withdrawing group onto activated alkenes224 and to the synthesis of 4-phenylquinoline derivatives from phenyl halides and 4-chloroquinoline.225 Since the use of iron as anode appeared necessary, the role of iron ions in the catalytic system remains to be elucidated. 

Synthesis of 2,6-Bis(imino)pyridine Iron(II) and Cobalt(II) Halides. 110... 

Bis(imino)pyridine Iron Halide/MAO and Cobalt Halide/MAO Catalysts. 120... 

Typically, the synthesis of the precursor iron(II) and cobalt(II) halide complexes proceeds by treatment of an anhydrous or hydrated divalent iron or cobalt halide (e.g. MX2 jcH20 or MX2 X = Cl or Br) with 1 (and also 2-4) in... 

Scheme 2 Synthesis of bis(arylimino)pyridine iron(II) and cobalt(II) halides...

The capacity of bis(arylimino)pyridine iron(II) (5) and cobalt(II) halides (6) to act as precatalysts for the polymerisation and oligomerisation of ethylene was first demonstrated when toluene solutions of 5 or 6 were treated with excess MAO... 

The active species generated when bis(arylimino)pyridine iron (5) and cobalt (6) halides are activated with MAO was, by analogy with metallocene catalysts, initially considered to be a highly reactive mono-methylated cobalt(II) or iron(II) cation of the form LM-Me+ bearing a weakly coordinating counter-anion such as [X-MAO]-(X = halide, Me). To examine this theory a number of spectroscopic investigations have been directed towards identifying the active species (vide infra). 

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