COLLMAN Carbonylation reagent

Carbonylate anions are the most suitable starting material for the synthesis of silylmetal compounds. A prerequisite for the preparation of compounds with a formal M = Si double bond is the use of metallate dianions like Na2Fe(CO)4 (Collman s reagent) together with the respective dichlorosilanes [96]. 

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]. 

II (dw) 4 [Fe(CO)4]2- Tetrahedral Uncommon oxidation state, but familiar as Collman s reagent Na FefCO),] and other carbonyl anions 1... 

Cycloalkanones. M6rour etaO have reported that Collman s reagent converts a y-ethylenic bromide or tosylate into a cyclohexanone and a -allenic bromide into a cyclopentenone in moderate yield. This carbonylation reaction represents a special O... 

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 most commercially important metal carbonyl anion, [Fe(CO)4]2, contained in Collman s reagent (shown below), can be prepared from the following reaction in dioxane solvent.14... 

Alkylation of the enolate of (138) with methallyliodide gave the product (149) whose stereochemistry was assigned on the basis of equilibration experiment. It was converted to the dione (150) by oxidation with osmium tetrooxide and sodiumperiodate. The aldol cyclization of (150) effected with sodium hydride and trace of t-amyl alcohol in refluxing benzene afforded the enone (151) in 88% yield. Normal protic conditions (sodium hydroxide, ethanol) were not effective in this transformation. All attempts for its conversion to aphidicolin (148) by intermolecular additions proved fruitless and therefore were turned to intramolecular methods. Molecular models show clearly that the top face of the carbonyl group is less hindered to nucleophilic attack than is the bottom face. Thus the reduction of (151) with lithium aluminium hydride afforded the alcohol (152) whose vinyl ether (153) was subjected to pyrolysis for 2 hr at 360 C in toluene solution containing a small amount of sodium t-pentoxide to obtain the aldehyde (154) in 69% yield. Reduction and then tosylation afforded the alcohol (155) and tosylate (156) respectively. Treatment of this tosylate with Collman s reagent [67] (a reaction that failed in the model system) afforded the already reported ketoacetonide (145) whose conversion to aphidicolin (148) has been described in "Fig (12)". 

Acyl transition metal species such as Collman s reagent and the Corey-Hegedus nickel carbonyl system, although also formally acyl anions, have not found wide use in synthesis, possibly... 

Complexation of alkenes to iron carbonyl fragments increases the electrophilicity of the alkene, owing to the electron-withdrawing ability of the carbonyl ligands. The anion of dimethyl malonate will attack the iron tetracarbonyl complex of methyl acrylate 6.295 (Scheme 6.113). " The resulting anion 6.296 is obviously related to the intermediates involved in the reactions of Collman s reagent (Section 4.5.1). Thus, carbonylation and addition of an alkyl halide results in acylation. 

Reduction of all the neutral dinuclear metal carbonyls yields monoanionic mononuclear metal carbonyls such as [Mn(CO)5)] that are very stable, whereas reduction of mononuclear neutral metal carbonyls gives stable dianions such as Collman s reagent [Fe(CO)4] . Some trianions such as [Nb(CO)5] are known to be thermally stable and extremely air-sensitive. Ellis has synthesized a series of multi-anionic metal carbonyls under extreme conditions. - Anions of metal-carbonyl clusters are also known. 

CO insertion into a metal-alkyl bond, introduced in Chap. 6, is a well-known and useful method used to introduce a carbonyl into an organic substrate, for example, stoichiometrically with Collman s reagent or catalytically with palladium acetate and... 

Subsequent to oxidative addition of an organic halide on Pd and CO insertion into the Pd -alkyl bond, the intermediate Pd -acyl species can be trapped by a nucleophile NuH which leads to the carbonylated organic product RC(0)Nu and regenerates Pd. This process represents a catalytic version of the carbonylation of organic halides using Collman s reagent ... 

Three neutral carbonyliron complexes of different reactivity are known pentacarbonyliron Fe(CO)5, nonacarbonyldiiron Fc2(CO)9, and dodecacarbonyltriiron Fej(CO)i2. Moreover, the anionic iron(-II) complex disodium tetracarbonylferrate Na2[Fe(CO)4] (Collman s reagent) and die higher analogs Na2[Fe2(CO)g] and Na2[Fej(CO)ii] also represent iron complexes bearing exclusively carbonyl ligands. With... 

The asymmetric carbonylative coupling of two different benzyl halides using disodium tetracarbonylferrate gives 1,3-diarylacetones in moderate to high yields (Scheme 4-17)The first benzyl halide is reacted with Collman s reagent at 0 °C. The second halide is added after 1 h and reacted at room temperature. The ketones can be utilized for the construction of unsymmetrically substituted hexaarylbenzenes. 

Scheme 4-17. Unsymmetrical dibenzylketones by carbonylative coupling of benzyl halides mediated by Collman s reagent.

A.iii. Sodium Tetracarbonyl Ferrate. An extremely useful organoiron reagent is sodium tetra-carbonyl ferrate [Na2Fe(CO)4], usually prepared by reduction of iron pentacarbonyl. The synthetic utility of this reagent lies in its ability to react with alkyl halides in a stepwise manner, including the reaction with two different alkyl halides, as reported independently by Cooke and by Collman and co-workers. - When sodium tetracarbonyl ferrate reacted with 1-bromooctane, a trigonal bipyramidal complex (715) was formed... 

From the other side, the carbonylation of alkyl halides needs stoichiometric amounts of iron salt, such as the Collman reagent [Na2pe(CO)4]. The first... 

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