Iron complexes pentadienyl

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. 

Starting from a single and stereochemically well-defined diene, it is possible to generate enantiomerically pure acyclic ( 7 -pentadienyl)iron complexes that provide a route to enantiomerically enriched substituted dienes. The optically active leukotriene 49 has been synthesized from the acyclic [l-methoxycarbonyl-( 7 -pentadienyl)]iron cation 50 in a key step that involves nucleophilic addition of an organocuprate to the G5 position (Scheme... 

Pentadentate 2,2 6, 2"-terpyridine, 30 107 Pentadiene complexes with iron, 12 255-257 with rhodium, 12 295 with silver, 12 340 Pentadienyl complexes with group VIB metals, 12 224, 225 with group VIIB metals, 12 240 JV,Af,/V,lV",N"-Pentaethyldiethylenetriamine, 42 76... 

The analogous cycloheptadienyl complex (5 equation 1) was similarly prepared by Dauben and Ber-telli,4 but the acyclic pentadienyl systems were a little more difficult to obtain. The triphenylmethyl cation does not remove hydride from tricarbonyl(frans-pentadiene)iron (6 equation 2). The corresponding c/s-pentadiene complex (7 equation 3) cannot be prepared directly from the diene and an iron carbonyl,... 

In principle pentadienyls can bond to transition elements in at least three basic ways, tj3, and tjs (Fig. 1). These can be further subdivided when geometrical factors are considered. If r 5 coordination could be converted to rj3 orr/1, one or two coordination sites could become available at the metal center, and perhaps coordinate substrate molecules in catalytic processes. Little is known about the ability of pentadienyl complexes to act as catalysts. Bis(pentadienyl)iron derivatives apparently show naked iron activity in the oligomerization of olefins (144), resembling that exhibited by naked nickel (13). The pentadienyl groups are displaced from acyclic ferrocenes by PF3 to give Fe(PF3)5 in a way reminiscent of the formation of Ni(PF3)4 from bis(allyl)nickel (144). 

All of the different classes of ligands listed in the table can be treated in this way. The cycL pentadienyl ligands contribute six electrons each and have a formal negative charge, shown in gree which means that the iron in ferrocene is in the +2 oxidation state and will have six valence electroi left. The total for the complex is again eighteen and ferrocene is an extremely stable complex. 

Reasonably similar observations can be made for the complexes bis(2,3,4-trimethyl-pentadienyl)ruthenium and bis(2,4-dimethylpentadienyl)chromium, both of which contain metals larger than iron. Thus, in ruthenocene and chromocene the average M-C bond distances have been found to be 2.196(3) and 2.169(4) A, respectively, whereas for their open analogs, the distances are quite comparable, if not actually shorter, at 2.188(3) and 2.165(4) A, respectively. Thus it does seem that the Fe-C bond distances in Fe(2,4-... 

Complexes (160) (see equation 35) undergo conversion to phenols upon thermolysis. Alternatively, treatment with AICI3 under a CO atmosphere gives an j)" -iron cyclohexadienone complex thermolysis or treatment with CuCl2 affords a phenol as well. Complexes (162), derived from nucleophihc addition to ( ) -pentadienyl)Fe(CO)3+ cations (see equation 37), can be converted to vinyl cyclopropanes by using CAN (equation 41). ... 

Substitution of complexed dienols (244) or dienol acetates with carbon or heteroatom nucleophiles, in the presence of a Lewis acid, occurs with retention of configuration (Scheme 69). (Alkyl aluminum reagents act as both nucleophile and Lewis acid in this process). This reaction is believed to proceed via stereospecific ionization, with anchimeric assistance from the iron, to generate the transoid pentadienyl cation (247) followed by attack of the weak nucleophile on the face opposite to iron. The cross-conjugated pentadienyl cation can also be generated the substitution of (2-acetoxymethyl-l,3-butadiene)Fe(CO)3 (193) has previously been discussed (Section 6.1.1). 

As described in Section 6.3.4, activation of coordinated dienols (by protonation) or coordinated dienol acetates (by treatment with Lewis acid) affords the corresponding (pentadienyl)iron cations (248) (Scheme 69). Since the acyclic pentadienyl cationic complexes do not have the geometrical constraints of their cyclic counterparts, they can potentially adopt either a cisoid ( U ) or transoid ( S , sickle) conformation. Nearly all of the (pentadienyl)iron cations prepared appear to be in the cisoid conformation by H NMR spectroscopy. Only a single, sterically biased transoid pentadienyl cation (269) has been spectroscopically observed, but not isolated (equation 66). Owing to their potential to undergo U to S conformational inversion in solution, and owing to the considerably higher reactivity of the less stable S conformer, the (pentadienyl)iron cations are considerably more sensitive to moisture than their cyclic counterparts. 

Intramolecular C-H insertion reactions of ( -cyclo-pentadienyl)dicarbonyliron carbene complexes can be used to prepare complex polycyclic compounds. Carbon-hydrogen bond insertion using an iron carbene was used as a key step in the synthesis of sterpurene andpentalene (Scheme 81). ... 

The resulting complex salt is so stable that it can be recrystallized from water. In this system, five hybridized carbon atoms are necessarily held in a cissoid configuration. More recently, Pettit and co-workers 192, 193, 194) have studied acyclic systems of this type and have found that there is a strong driving force for a cissoid configuration of the resulting TT-pentadienyl-iron tricarbonyl complexes. 

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