Carbene complexes of iron

One of the limitations concerns the kinetic stabilities of analogous species. For example, in the analogous series of compounds ethylene, carbene complexes of iron tetracarbonyl and its dimer, [Fe2(CO)g] (5-19), the first two are known, but the last is unstable and to date it... 

CYCLOPENTADIENYL-FUNCTIONALIZED N-HETEROCYCLIC CARBENE COMPLEXES OF IRON AND NICKEL... 

Simonneaux G, Le Maux P (2006) Carbene Complexes of Heme Proteins and Iron Porphyrin Models. 17 83-122... 

Heteroatom-substituted (Fischer-type) carbene complexes are mostly used as stoichiometric reagents. For this reason only carbene complexes of reasonably cheap metals, such as chromium, molybdenum, tungsten, or iron have found broad application in organic synthesis. 

In none of the complexes with carbene ground states has any detectable trace of the allene complex been observed. Even benzannelated complexes 335141 and 340144 exist exclusively in the carbene form [Eq. (58)]. Attempts to prepare dibenzannelated complexes of iron analogous to 346 failed.146... 

The first carbene complex of an iron porphyrin was prepared and structurally characterized by Mansuy and co-workers (12, 13) through the reaction of carbon tetrachloride with (TPP)Fe11 under reductive... 

A substantial body of work has been published describing the preparation, properties, and synthetic applications of iron carbenes. These tend to be of the Fischer-type see Fischer-type Carbene Complexes) of carbene species electrophilic and heteroatom-stabilized. However, electrophilic yet unstabilized iron carbenes can be readily prepared and utilized in situ. 

Five types of Fe porphyrin complexes have beenreported, all of which have spin state 5=1 (l)the deep red, five-coordinate ferryl, (Fe =0) +, complexes and the six-coordinate adducts of these ferryl complexes, the (B)(Fe = 0) + complexes (2) the Fe phenyl complex (3) iron(fV) carbene complexes (4) iron(fV) hydrazine complexes and (5) the six-coordinate d complex [TPPFe(OMe)2] mentioned briefly in Section 7 above. The ferryl and Fe - phenyl cases have direct appheation to active states of heme proteins, particularly the cytochromes P450, peroxidases, catalases, and related enzymes. 

A similar type of reaction has been observed in the reactions of iron-carbene complexes with 1,3-dienes. In this case the direction of reductive elimination in the metal hydride intermediate corresponding to (193) is constrained to that which generates a conjugated 1,3-diene however, two isomeric products are also obtained from this reaction which are epimers about the face of the diene to which the iron tricarbonyl group is attached. Tliis reaction produces highly functionalized 1,3-dienyl complexes of iron in high yield under relatively mild conditions and will likely play a role in the development of the... 

Electrophilic carbene complexes of tungsten or iron smoothly transfer their phenylcarbene ligand to electron rich olefins. Pentacarbonyl(phcny]carbcnc)tungsten(0) (4) is generated in situ by acid treatment of the precursor salt 36, while the cationic iron complex 5 is a stable, isolable compound7-10. 

The reactivity of carbonyls of Cr, Mo, and W with alkyl lithium is somewhat lower than that of nickel and iron carbonyls. The most interesting reaction of these metal carbonyls, found and studied extensively by Fischer and his coworkers, is the formation of carbene complexes 98-"). Phenyl or methyl lithium adds readily to W(CO)6 at room temperature to form carbonylate complexes. The tetramethyl ammonium salt of the complex is treated with acid and then with diazomethane to give a neutral complex whose structure was found to be that of a carbene complex. In this way a series of carbene complexes of Cr, Mo, and Mn were synthesized. 

Carbene Complexes of Heme Proteins and Iron Porphyrin Models... 

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