Iron olefin

A family of cyclopentadiene(Cp)-containing iron-olefin complexes has been pioneered by Jonas [13-15]. The complexes 38-40 (Scheme 7) can be obtained in a large scale from ferrocene 37 under reducing conditions in the presence of suitable coordinating olefins. Complex 38 is a highly air-sensitive, crystalline material, whereas complexes 39 and 40 are more robust due to their cyclooctadiene (cod)... 

Let us return to the thermal decomposition of Fe(CO)(l,3-C4H6)2. Once the calibration constant is known, the enthalpy of the net process 9.10 can be calculated as the product of s and the area (A + B). The next step is to correct this value to 298.15 K by using heat capacity data. This exercise is, however, complicated by the cyclobutadiene polymerization. Brown et al. analyzed the reaction products by mass spectrometry and found several oligomers, in particular the dimer (C4H6)2 and the trimer (C4H6)3 [163]. With such a mixture, it is difficult to ascribe the observed enthalpy change to a well-defined chemical reaction. This is discussed in the paper by Brown and colleagues, who were nevertheless able to recommend a value for the standard enthalpy of formation of the iron-olefin... 

D. L. S. Brown, J. A. Connor, M. Y. Leung, M. I. Paz-Andrade, H. A. Skinner. The Enthalpies of Thermal Decomposition of Iron-Olefin Complexes, and the Strengths of Iron-Olefin Bonds. J. Organometal. Chem. 1976, 770,79-89. 

The straight chain congeners of GT-2208 and GT-2209 were synthesized from aldehyde 49 which is readily available from urocanic acid. Wittig chemistry provides the cis olefin 50 from 49 (Figure 24). The irons olefin 51 is obtained from Na (lig. NH3) reduction of acetylene 52 (Figure 24). 

B. Iron-Olefin and Alkali Metal-Iron-Olefin Complexes... 

Olefin-coupling reactions of Tj -allyliron complexes with a variety of cationic iron-olefin complexes (ethylene, propene, styrene, etc.) were utilized to give cationic bimetallic complexes with cr,7r-hydrocarbon bridges (80,81). The condensation of simple [FpColefin)]" substrates with Fp(allyl) precursors was extended to the reaction with Fp(l,3-butadi-ene)+. Initial attack at C-1 or C-4 leads to the formation of dinuclear complexes with cr-coordinated and 7r-coordinated Fp fragments, which by subsequent intramolecular condensation could give either cyclohexenyl or cyclopentenyl intermediates. Attack at C-2 yields a dinuclear complex incapable of further intramolecular reaction [Eqs. (6-8)]. 

Reduction of iodohydrins. In Cornforth s stereospecific synthesis of a cis or irons olefin, an intermediate is a chlorohydrin of predictable configuration which cannot be reduced directly to the olefin. The conversion is accomplished by three strictly stereospeciflc steps formation of the epoxide, cleavage with HI (Nal—AcOH—EtCOgH), and reduction of the resulting iodohydrin with stannous chloride, phosphoryl chloride, and pyridine. 

Solutions of many of the iron-olefin complexes in MeCN are observed to undergo substitution to give free olefin and the cationic acetonitrile complex [Fp(MeCN)] see P. M. Treichel, R. L. Shubkin, K. W. Barnett, D. Reichard,/norg. C/iem., 5, 1177 (1966). 

Cationic iron-olefin complexes have been prepared - by displacing isobutene from [Fe(/y -Cp)(CO)2(isobutene)][BF4] ... 

The reaction is rapid, being complete in about 10 min, and may be monitored by the evolution of isobutene. The products involve the formation of only one iron-olefin bond so the [Fe(> -Cp)(CO)2] cation may be used as a protecting group for one double bond of a polyolefin ... 

The iron- olefine complexes Fe(olXCO)4 can be prepared by the thermal reaction of the olefin with FeXCG) in benzene at modest temperatures. The reaction does not formally involve carbonyl displacement it is a bridge splitting reaction in which Fc2(CO)9 is cleared into two moieties Fe(CO)5 and Fe(CO)4 ... 

Iron-olefin complexes have been prepared photochemically from Fe(CO)5, Fe CCO), and FesCCO) ... 

Some of the classic studies of nucleophilic, attack on coordinated olefins were conducted with iron(II) species. Rosenblum reported the reactions of (ti -cyclopentadienyl) iron-olefin complexes with a wide range of carbanion and enamine nucleophiles. These reactions produce stable o-alkyliron complexes (Equation 11.22). The stereochemistry is cleanly trans. However, the regioselectivity of reactions of complexes of imsymmetrical olefins depended on the nucleophile. 

The relative iron-olefin bond strength is evidenced by the ease of olefin substitution by phosphines. For complexes which contain olefins possessing a,j5 carbonyl substituents, the rate of olefin and carbonyl group substitution by PPh3 increases according... 

Keywords metathesis, polymerization, dendrimer, arene, iron, olefin... 

Figure 2.49. Relative magnitudes of H- H coupling constants in cis and Irons olefins.

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