Iron 2 2+ with carbanions

Starch dialdehyde also reacts with carbanions. For instance, reaction with nitromethane produces a nitro compound that after reduction with iron(II) hydroxide in ammonia afforded an animated product.539 Molded articles from starch dialdehyde and elemental sulfur were also patented.540... 

Recently, the iron-promoted Barbier-type addition of alkyl halides to aromatic aldehydes has been reported (Equation (26)).326 According to the proposed mechanism, the initial step is the formation of an alkyl radical, which can be reduced to the corresponding carbanion. This carbanion nucleophile can react, while coordinated to the iron pentacarbonyl complex, with the corresponding aldehyde. This stoichiometric method is limited with respect to substrate scope and yield. The same authors have also developed the Reformatsky-type addition of cr-halosub-stituted carbonitriles to aldehydes and ketones in the presence of iron pentacarbonyl.3... 

In 1991, Thomas reported88a that the reaction between vinylketene complexes (221) and several phosphonoacetate anions generated vinylallene complexes (246), in some cases with extremely high stereoselectivity.88,89 This Wadsworth-Emmons type reaction occurs via attack by the phosphonoacetate carbanion at the ketene carbonyl carbon, and product ratios clearly depend on the steric bulk of the R and R substituents. The relative stereochemistry of the major isomers of 246 were determined by X-ray analysis. Upon oxidation of the vinylallene complexes with iron(III) chloride, a range of substituted furanones were isolated.8813,89... 

Deoxygenation of alcohols. Alcohols, particularly tertiary ones that can form stable carbanions, are deoxygenated by reaction with potassium and iron carbonyl in toluene. The reduction proceeds through the potassium alkoxidc.1 Examples ... 

New chelate rings have been formed by the nucleophilic attack of carbanions and nitriles, with both groups being coordinated throughout the reaction to either iron(II) or cobalt(III) (Scheme 61188189 and equation 56).190... 

The original Jager-type complexes can be deacylated by treatment with acid demetallation follows and the free macrocycles can be isolated (Scheme 20).134 These can be converted into iron(II) complexes with acetonitrile coordinated in the axial positions. However, these are unstable in the example with 15- and 16-membered rings and undergo cyclization as a result of carbanion attack on the coordinated acetonitrile (Scheme 21).134 136 A similar reaction occurs with the cobalt... 

Dienes form very stable complexes with a variety of metal caibonyls, particularly Fe(CO)s, and the neutral V-diene metal carbonyl complexes are quite resistant to normal reactions of dienes (e.g. hydrogenation, Diels-Alder). However, they are subject to nucleophilic attack by a variety of nonstabilized carbanions. Treatment of -cyclohexadiene iron tricarbonyl with nonstabilized carbanions, followed by protonolysis of the resulting complex, produced isomeric mixtures of alkylated cyclohexenes (Scheme 15).24 With acyclic dienes, this alkylation was shown to be reversible, with kinetic alkylation occurring at an internal position of the complexed dienes but rearranging to the terminal position under thermodynamic conditions (Scheme 16).2S By trapping the kinetic product with an electrophile, overall carbo-... 

Although alkynes are highly reactive toward a wide range of transition metals, few instances of metal-catalyzed reactions of carbanions with alkynes are known. The most extensively developed system involves cationic iron complexes of internal alkynes. These complexes underwent alkylation by a range of carbanions to produce stable [Pg.582]

Super glue is a polymer of methyl cyanoacrylate. Because both the cyano and carbonyl groups of the monomer help stabilize carbanions, this compound is sensitive to polymerization by the anionic mechanism. The tube of glue contains very pure monomer, which does not polymerize until it contacts an initiator. However, contact with any nucleophile causes rapid polymerization. Therefore, when the tube is opened, polymerization is initiated by water in the air, by SiOH groups on a glass surface, by FeOH groups on an iron surface, or by various nucleophiles that are part of the proteins in skin. The adhesion between the polymer and the surface to which it is applied is very strong because the polymer chains are covalently linked to the nucleophiles that are part of the surface ... 

Treatment of a -unsaturated complex (251) with the basic carbanion LiCH2CN causes a 1,3-migration of the iron... 

By reaction of cationic carbonyl complexes with lithium carbanions, neutral acyl complexes are prepared. Whereas treatment of [> -CpFe(CO)3]BF4 with (a) PhLi gives the expected > -CpFe(CO)2 [C(0)Ph] in 80% yield, with (b) MeLi only traces of > -CpFe(CO)2 [C(0)Me] can be detected . This complex and other phosphane-substituted acyl compounds of the type f -CpM(CO)L[C(0)Me] [M = Fe, Ru L = CO, PPh3, P(hex)j], as well as >/ -CpMo(CO)2P(hex)3[C(0)Me] (prepared by different routes), are protonated with and alkylated with [R3 0]BF4 reversibly, yielding cationic hydroxy- and alkoxy(methyl)carbene complexes, respectively . The formation of the ( + )- and ( —)-acetyl complex / -CpFe(C0)(PPh3)[C(0)Me] from the ( + )-and ( —)-conformers of optically active > -CpFe(C0XPPh3)[C(0)0-menthyl] and MeLi occurs with inversion of configuration at the asymmetric iron atom . 

Reaction of nonstabilized carbanions with [Fp(olefin)] complexes generally results in either displacement of the olefin or reduction of the metal rather than formation of stable (j -alkyliron complexes. This is especially true with simple, nonstabilized organo-magnesium halide or lithio reagents. However, allylmagnesium chloride and phenylmag-nesium chloride react in modest (20-40%) yield with the ethylene, propene and butadiene (1,4 addition) iron complexes. Lithium dimethylcuprate is even more efficient, reacting in up to 70% yield with Fp complexes of styrene, butadiene (1,4 addition) isoprene (1,4 addition) and allene. Complexes of cyclopentene and allene react in low... 

In the former insertion according to (b) yields the endo complex LXII, whereas in the latter direet attack of phenyl carbanion aecording to (a) produces the exo complex LXIV. However, palladium-diene complexes - and the iron complex LXV react with heteroatom nucleophiles according to path (a) even when the nucleophile is partly coordinated to the metal. Thus there is an intrinsic difference between heteroatom nucleophiles and simple carbanions in accordance with the division made in this section. 

The addition of large enolate synthons to cyclohexenone derivatives via Michael addition leads to equatorial substitution. If the cyclohexenone conformation is fixed, e.g. as in decalones or steroids, the addition is highly stereoselective. This is also the case with the S-addition to conjugated dienones (Y. Abe, 1956). Large substituents at C-4 of cyclic aJ-synthons direct incoming carbanions to the Irons-position at C-3 (A.R. Battersby, 1960). The thermodynamically most stable products are formed in these cases, because the addition of 1,3-dioxo compounds to activated double bonds is essentially reversible. 

---