Iron carbonyl complexes, nucleophilic

Syntheses of primary ally lie amines have been reviewed183. The regiochemistry of the reaction of iron carbonyl complexes with nucleophiles such as morpholine has been investigated. The (r 3-crolyl) Fe+(CO)4 BF4- complexes 172 (R1 = H R2 = Me or R1 = Me R2 = H) undergo preferential attack at the less substituted allyl terminus to yield allylic amines 173. The (/j2-crotyl acetate) Fe(CO)4 complex 174, on the other hand, does not react with morpholine184. 

A diene system with unsymmetrical 1,4-disubstitution is converted to the iron carbonyl complex 1 which is resolved into its enantiomers. The aldehyde function is conformationally locked in the transoid position and is diastereofacially shielded from the bottom face. Nucleophiles attack from the top face with high selectivity. Alternatively, chain elongation leads to the triene 2 which is reacted with diazomethane. Cerium(IV) oxidation removes the metal and furnishes the substituted cyclopropane 3. 

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]. 

A hydride is one of the simplest nucleophiles, and Casey ° and Gladysz have prepared kinetically stable formyl complexes by the direct attack of hydride on a number of neutral chromium-, molybdenum-, and iron-carbonyl complexes (Equation 11.2). Although these complexes are relatively electron rich, because they possess zero-valent metal centers, the negative charge in the product can be stabilized by the remaining -ir-ac-cepting CO ligands. 

Several interesting and significant papers concerning ligated CO appeared in 1985. Quantitative aspects of the reaction of OH" and OMe" with M(C0)s and M3(C0)i2 (M = Fe, Ru or Os) have been reported and the implications with regard to the water gas shift reaction were noted.A full account of a method for computing the most favourable initial site for nucleophilic attack on a transition metal complex has been described and applied to reactions of cationic iron carbonyl derivatives. Nucleophilic attack by H2O, OH" and H" on dicationic Ir carbonyl complexes yields cationic hydroxycarbonyl and formyl... 

Iron carbonyl complexes containing 77 -alkyl-77 -allyl coordinated hydrocarbon ligands are obtained in several ways. Nucleophilic addition to cationic iron complexes containing 77 -pentadienyl ligands yields (pentenediyl)iron complexes. Oxidatively-induced reductive elimination of these complexes can be utilized as a means to generate 1,2,3-trisubstituted cyclopropanes.The reaction of cationic cycloheptadienyl complexes (Scheme 22) with appropriate nucleophiles also yields the alkyl-allyliron carbonyl complexes. Fe(CO)s also reacts with a- or /3-pincnc in refluxing dioxane (Scheme 22) to produce an alkyl-allyliron complex. Recently, 1,2- and 1,4-disubstituted [(pentadienyl)Fe(CO)3] cations were shown to react with carbon nucleophiles, such as sodium dimethylmalonate, to yield 77 77 -allyl complexes as products. 

Nucleophilic Aromatic Substitution Involving Iron Carbonyl Complexes... 

In 1989, Thomas reported3 the novel synthesis of tricarbonyl(774-vinylke-tene)iron(O) complexes (221) from the corresponding 774-vinylketones (222). Nucleophilic attack by methyllithium on a carbonyl ligand is thought to produce the anionic complex 223, which then carbonylates to give the rf-... 

Reaction of Z-a./j-unsaturated iron-acyl complexes with bases under conditions similar to those above results in exclusive 1,4-addition, rather than deprotonation, to form the extended enolate species. However, it has been demonstrated that in the presence of the highly donating solvent hexamethylphosphoramide, y-deprotonation of the -complex 6 occurs. Subsequent reaction with electrophiles provides a-alkylated products such as 736 this procedure, demonstrated only in this case, in principle allows access to the a-alkylatcd products from both Z- and it-isomers of a,/j-unsaturated iron-acyl complexes. The hexamethylphosphoramide presumably coordinates to the base and thus prevents precoordination of the base to the acyl carbonyl oxygen, which has been suggested to direct the regioselective 1,4-addition of nucleophiles to -complexes as shown (see Section 1.1.1.3.4.1.2.). These results are also consistent with preference for the cisoid conformations depicted. 

Neither the palladium nor nickel catalyst described will promote the carbonylation of saturated aliphatic halides as noted above. However, this reaction can be catalyzed with cobalt (17) or iron (77) and probably with manganese (18) carbonyl anion salts. These carbonyl anions are strongly nucleophilic species and readily displace halide or other good leaving groups from primary or secondary positions giving alkyl metal carbonyl complexes. 

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-... 

The position of the equilibrium between imine and carbonyl may be perturbed by interaction with a metal ion. We saw in Chapter 2 how back-donation of electrons from suitable orbitals of a metal ion may stabilise an imine by occupancy of the jc level. It is possible to form very simple imines which cannot usually be obtained as the free ligands by conducting the condensation of amine and carbonyl compounds in the presence of a metal ion. Reactions which result in the formation of imines are considered in this chapter even in cases where there is no evidence for prior co-ordination of the amine nucleophile to a metal centre. Although low yields of the free ligand may be obtained from the metal-free reaction, the ease of isolation of the metal complex, combined with the higher yields, make the metal-directed procedure the method of choice in many cases. An example is presented in Fig. 5-47. In the absence of a metal ion, only low yields of the diimine are obtained from the reaction of diacetyl with methylamine. When the reaction is conducted in the presence of iron(n) salts, the iron(n) complex of the diimine (5.23) is obtained in good yield. 

Completely different behavior toward liquid NH3 is shown by the three iron carbonyls Fe(CO)s, Fe3(CO)9, and Fes(CO),2 (98, 99) and the two cobalt carbonyls Co2(CO)8 and Co4(CO)i3 (100). Between -21 and 0°C, Fe(CO)5 and liquid NH3 give a homogeneous, pale-yellow solution from which Fe(CO)5 may be recovered on evaporating off the NH3. The solution contains the carbamoyl complex NHJfOC Fe—CONHJ which cannot be isolated and which is formed by nucleophilic attack of an NH3 molecule on a CO ligand, followed by proton release (101). At 20°C after 14 days of reaction, (NHJ FefCOlJ and CO(NH2)2 are obtained (99) ... 

Iron complexes can also catalyze allylic amination [31,32]. Enders et al. have demonstrated the nucleophilic addition of various acyclic and cyclic amines to the optically active l-methoxycarbonyl-3-methyl-(T)3-allyl)-tetracarbonyliron cation 49 formed in high yield from reaction of 48 with iron carbonyls. Oxidative removal of the tetracarbonyliron group by reaction with CAN gives 50 with high optical purity and retention of the stereochemistry (Eq. (12)) [31]. The reaction proceeds well for the different amines, and has been used for the synthesis of a compound showing cytotoxic activity against diverse cell lines [31b]. 

Decomplexation of ArCr CO)3. The chromium carbonyl complexes of arenes are useful for activation of the aryl group to nucleophilic attack (6, 28, 125-126 7, 71-72). Decomplexation has been effected with iodine or by photochemical oxidation with destruction of the expensive Cr(CO)3 unit. A more recent method involves reflux with pyridine to form Py3-Cr(CO)3 in yields of 70-100%. The pyridine complex in the presence of BF3 can be reused for preparation of ArCr(CO)3. Isomerization of 1,3-dienes. Ergosteryl acetate (1) is isomerized by chromium carbonyl to ergosteryl 83 acetate (2) in 81% yield. Under the same conditions ergosteryl 83 acetate (3) is isomerized to ergosteryl 81 acetate (4). 80th reactions involve isomerization of a cisoid diene to a transpid diene. In contrast iron carbonyl isomerizes steroidal transoid 3,5- and 4,6-dienes to 2,4-dienes. ... 

Deprotonated bridging dithiolate ligands in diiron carbonyl complexes of type 101 (R = H, Ph) rearrange intramolecularly by nucleophilic attack on an iron atom while an electron pair is displaced onto a sulfur atom with formation of an Fe—C bond in 102 (76). Neutral derivatives can be formed upon further alkylation, leading to type Ij complexes (Table 1). The bridg-... 

Similar to the reaction course of the allylic substitution, which involves formation of tr-allyl moieties followed by subsequent nucleophilic addition across the Jt-bond, the mononitrosyl iron(—II) complex was expected to be active in transesterifications involving activation of carbonyl group and nucleophilic addition to the electrophilic carbon atom [100]. This assumption could be verified by experimental tests. Under neutral conditions without addition of a ligand co-catalyst, the iron complex 31 exhibited high activity in the transesterification of vinyl acetate. Good to excellent yields were obtained affording a new ester bond, as depicted in Scheme 39. 

The mechanism is similar to that of the allylic substitution, as depicted in Scheme 40. Initially the iron(—11) complex coordinates to the C=0 double bond, which is followed by elimination of the leaving group affording the acyl iron(—I) intermediate. The nucleophile in situ generated by the leaving group attacks the electrophilic carbonyl carbon atom reestablishing the iron(—II) species. Finahy the... 

Synthesis o-f transition metal derivative s. In view o-f the -final goal o-f this survey, that is the catalytic deoxygenation o-f nitro compounds by carbon monoxyde, o-f particular interest are the stoichiometric reactions o-f these compounds with metal carbonyls. Carbonyl ligands coordinated to metal atoms in a high oxydation state should be more susceptible to attack by nucleophiles, than those bound to metal in a low oxydation state. However, the reactivity o-f nitro compounds has been studied in practice only with carbonyl complexes o-f metals in zero or less oxydation states. The -first report in this -field is concernded with the reactions o-f Fe(C0>5 with a series o-f aromatic nitro compounds] 56], leading to dimeric iron-nitroso derivatives[23j ... 

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