Cyclohexadiene complexes with iron

Cycloheptene complexes with gold, 12 348 Cyclohexadiene complexes with cobalt, 12 286 with group VIB metals, 12 225-227 with group VIIB metals, 12 240, 241 with iron, 12 264 with palladium, 12 313 with ruthenium, 12 278 with silver, 12 340... 

Selective reduction of the methyl ester to the corresponding aldehyde using DIBAL at low temperature and subsequent reductive amination with iodopiperonyl-ammonium chloride affords the tricarbonyliron-cyclohexadiene complex with the secondary alkylamine in the side chain. Iron(O)-mediated oxidative cydization... 

Herberich, G.E., Raabe, E. Syntheses with l-phenylbora-2,5-cyclohexadiene. Complexes of Iron, Cobalt and Nickel with Partially Hydrogenated Borabenzene Ligands . J. Organomet. Chem. 1986, 309, 143-156. 

Oxidative cyclisation of tricaibonyliron-cyclohexadiene complexes with an alkylamine side-chain to iron-complexed substituted indole derivatives was reported to be easily accon lished in high yield using single-electron transfer (SET) oxidising agents such as ferricenium hexafluorophosphate. The method was employed as a synthetic approach to the framework of mitomycin antibiotics. 

Alkenes in (alkene)dicarbonyl(T -cyclopentadienyl)iron(l+) cations react with carbon nucleophiles to form new C —C bonds (M. Rosenblum, 1974 A.J. Pearson, 1987). Tricarbon-yi(ri -cycIohexadienyI)iron(l-h) cations, prepared from the T] -l,3-cyclohexadiene complexes by hydride abstraction with tritylium cations, react similarly to give 5-substituted 1,3-cyclo-hexadienes, and neutral tricarbonyl(n -l,3-cyciohexadiene)iron complexes can be coupled with olefins by hydrogen transfer at > 140°C. These reactions proceed regio- and stereospecifically in the successive cyanide addition and spirocyclization at an optically pure N-allyl-N-phenyl-1,3-cyclohexadiene-l-carboxamide iron complex (A.J. Pearson, 1989). 

D. Tricafbonyl[(2,3,4 ,5-ri)-2,4-cyclohexadien-l-one]iron. The mixture of tetrafluoroborate from Part C (21 g., 0.062 mole) is heated on a steam bath for 1 hour in 450 ml. of water, during which time orange crystals separate. After cooling, the mixture is extracted three times with 100-ml. portions of ether into which most of the solid dissolves. (The aqueous layer is used in Part E.) The extracts are dried over anhydrous magnesium sulfate, and the ether is evaporated to yield the yellow crystalline dienone complex, 7-7.5 g. (47-51%) (Note 22). 

More recently, an environmentally benign method using air as oxidant has been developed for the oxidative cyclization of arylamine-substituted tricarbonyl-iron-cyclohexadiene complexes to carbazoles (Scheme 19). Reaction of methyl 4-aminosalicylate 45 with the complex salt 6a affords the iron complex 46, which on oxidation in acidic medium by air provides the tricarbonyliron-complexed 4a,9a-dihydrocarbazole 47. Aromatization with concomitant demetalation by treatment of the crude product with p-chloranil leads to mukonidine 48 [88]. The spectral data of this compound are in agreement with those reported by Wu[22j. 

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-... 

Electrophilic aromatic substitution of 5-hydroxy-2,4-dimethoxy-3-methylaniline by reaction with the iron complex salts affords the corresponding aryl-substituted tricarbonyliron-cyclohexadiene complexes. O-Acetylation followed by iron-mediated arylamine cydization with concomitant aromatization provides the substituted carbazole derivatives. Oxidation using cerium(IV) ammonium nitrate (CAN) leads to the carbazole-l,4-quinones. Addition of methyllithium at low temperature occurs preferentially at C-1, representing the more reactive carbonyl group, and thus provides in only five steps carbazomycin G (46 % overall yield) and carbazomycin H (7 % overall yield). 

It was determined that carbon nucleophiles derived from carbon acids with p/fa > 22 or so are sufficiently reactive to combine with the diene ligand rapidly at —78°C to produce an anionic intermediate (Scheme 25). With a few exceptions, the regioselectivity favors formation of the homoallyl anionic complex from addition at C-2, by kinetic control. This intermediate can be quenched with protons to give the terminal alkene, or can react with excess CO to produce an acyl iron intermediate. Following the recipes of Collman s reaction, the acyl iron intermediate can lead to methyl ketones, aldehydes, or carboxylic acids. The processes are illustrated with the 1,3-cyclohexadiene complex (Scheme 25). ... 

Nucleophilic attack on neutral complexes of ii -diene ligands is less common than attack on cationic complexes of these ligands but is known. In one case, Semmelhack reported the reactions of iron complexes of acyclic ii -dienes with reactive carbanions such as LiC-MCjCN and LiCHPhj (Equation 11.47). At -78 °C, the reaction is rapid, and kinetically controlled. Attack occurs at an unsubstituted, internal position to give an unstable o-alkyl Ti -olefin complex. This addition is reversible below 0 °C, and the more stable product is then generated from nucleophilic addition at a terminal position of the diene to give the thermodynamically more stable T -allyl complex. Cyclohexadiene complexes are similarly alkylated by a range of carbanions. ... 

The reactions of Ru3(CO)i2 with diolefins to give (diene)Ru(CO)3 derivatives does not proceed as well as the corresponding reactions of Fe3(CO)i2f since the ruthenium triangle is more stable than the iron triangle. Nevertheless, the 1,3-cyclohexadiene complex C6H0Ru(CO)3 can be prepared in reasonable yield by heating 1,3-cyclohexadiene with RU3(CO)j2 (221). Cyclooctatetraene reacts with RU3(00) 2 boiling... 

Ironcarbonyl compounds are liable to form 7r-complexes with unsaturated compounds such as monoenes, butadiene, cyclobutadienes, and cyclopentadiene. In the case of diene, the two double bonds of 1,5-cyclooctadiene are able to coordinate to the metal, without a sterical strain as shown in Table 15.2. The two double bonds of 1,4-cyclohexadiene are difficult to bond to iron without strain, so 1,4-cyclohex-adiene isomerized to 1,3-cyclohexadiene. The iron atoms have such a high reactivity with diene compounds that the isomerization of the diene occurs [13,19,20,25]. 

Cyclic Dienes - A number of optically active tricarbonyl iron ic-complexes with unsymmetrical cyclohexadiene and cyclohexadienyl ligands have been prepared from diols available by the oxidation of arenes by Pseudomonas putida. The circular dichroism spectra of the metal complexes were shown to provide an empirical guide for the assignment of absolute configuration from chiroptical data for this class of compounds. 

What appear to be perfluorodiene-Fe(CO)3 complexes have been obtained from the reaction of periluorodienes with iron carbonyls. Thus, as indicated in Eq. 6, the complex (LXVII) has been obtained from the reaction of either perfluoro-l,3-cyclohexadiene 81) or perfluoro-l,4-cyclo-hexadiene (55). The latter reaction involves a fluorine shift reminiscent of the hydrogen shift observed in the analogous reaction with 1,4-cyclo-hexadiene 43). 

Bridged bicyclo[3.2.1]octenes and bicyclo[3.3.1]nonenes are obtained when this reaction is carried out in an intramolecular mode. The nucleophiles are generated in appropriately functionalized side chains at C5 of the tricarbonyl( n -cyclohexadiene)iron complexes. Acyclic (Ti -l,3-butadiene)Fe(CO)3 complexes with fimctionalized side chains at the terminal position of the diene ligands provide fused bicyclo[3.3.0]octanones and bicyclo[4.3.0]nonanones (Scheme 4-121). Up to four new stereogenic centers are established in a controlled way in the course of this reaction. ... 

Scheme 4-124. Double cyclization of (ri -cyclohexadiene)iron complexes with pendent conjugated dienes.

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