Tetracarbonyliron complexes

Neutral ri2-alkene-tetracarbonyliron complexes can be prepared from the corresponding alkene and nonacarbonyldiiron via a dissodative mechanism. The organic ligand in the alkene-iron complex is more easily attacked by nucleophiles than the corresponding free alkene due to the acceptor character of the tetracarbonyliron fragment. The reaction principle is demonstrated in Scheme 1.8 [30],... 

As a reversible protection measure, complexation with a Fe(CO)4 moiety appeared to be most promising. The monoene 68 was indeed found to react smoothly with Fe(CO)s at room temperature to give the tetracarbonyliron complex 73b in 75% yield after crystallization. The complex 73b proved to be stable for days in air as a solid and in solution (CHCl3, benzene), and its ligand 68 can be conveniently liberated under mild oxidative conditions [Ce(N03)4/ MeOH/THF] at room temperature (Scheme 14) [77]. Although the use of metal complexation as a protection method for such compounds with highly pyramidalized double bonds works well for the monoene 68 and the diene 70, the complexation of more highly unsatu-... 

Di-rerr-butylcycloprop-2-enylidene)mesitylphosphane reacted with pentacarbonyltun-gsten(0)-tetrahydrofuran complex in tetrahydrofuran or with nonacarbonyldiiron in pentane to form a pentacarbonyltungsten or a tetracarbonyliron complex, respectively. ... 

Intramolecular Rearrangement in Olefin-Tetracarbonyliron Complexes. Importance of Olefin Rotation on the Barrier for Rearrangement, L. Kruczyn-ski, L. K. K. Lishingman, and J. Takats, J. Amer. Chem. Soc., 96,4(X)6(1974). 

Fe(0)-stabilized carbonium ions are normally prepared by protonation of Fe(0)-diene complexes with HBF in the presence of carbon monoxide [Eq. (21)] or by protonation of diene-tetracarbonyliron complexes [Eq. (25)] (Gibson and Vonnahme, 1974). 

The instability of monoolefin complexes limits the use of this means of protection, although tetracarbonyliron complexes of olefins containing electron-withdrawing groups usually show increased stability (Herberhold, 1974 Kemmitt, 1972) and the derivatives of a,) -unsaturated ketones are reported to lose their normal high reactivity toward nucleophiles (Nesmeyanov et al., 1974). Further work in this area is needed. 

Standard methods of resolution of complexes can be used when appropriate groups are present. For example, tetracarbonyliron complexes of acrylic and fumaric acids can be resolved by crystallization of the diastereoisomeric brucine salts (Paiaro et al., 1965 Paiaro and Palumbo, 1967). Tricarbonyl(trcrnj-// owj-2,4-hexadienoic acid)iron is similarly resolved via the diastereoisomeric... 

Carbon-carbon bond formation by the addition of soft nucleophiles such as malonate enolates to 7r-allyl metal complexes continues to be a productive area. Various neutral tt-ally 1-iron complexes can be used to prepare esters (85) in this way while the tetracarbonyliron complex of methyl a-chloroacrylate undergoes a double addition to give polyester (86). Trost s group has shown that TT-ally 1-palladium complexes react completely stereoselectively as, for example, in the conversion of butyrolactone (87) into the tricarboxylate (88). ... 

Sequential addition of stabilized anions and alkyl iodides to tetracarbonyliron complexes of methyl acrylate and methyl crotonate affords products consistent with regiospecific generation and alkylation of an organoironcarbonylate anion intermediate. The tetracarbonyliron group in this example is therefore serving as a control element for effecting regiospecific introduction of two carbon-carbon bonds into an acrylate ester (Scheme 13). ... 

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