Ligand substitution reactions iron complexes

Iron hydride complexes can be synthesized by many routes. Some typical methods are listed in Scheme 2. Protonation of an anionic iron complex or substitution of hydride for one electron donor ligands, such as halides, affords hydride complexes. NaBH4 and L1A1H4 are generally used as the hydride source for the latter transformation. Oxidative addition of H2 and E-H to a low valent and unsaturated iron complex gives a hydride complex. Furthermore, p-hydride abstraction from an alkyl iron complex affords a hydride complex with olefin coordination. The last two reactions are frequently involved in catalytic cycles. 

Ligand Substitution Reactions of ij Heptafluorocyclooctatetraenyl Complexes of Iron... 

Peroxo-diiron(III) complexes can undergo not only redox but also ligand substitution reactions. Liberation of H202 was observed in the reactions with phenols and carboxylic acids leading also to the respective phenolate or carboxylate iron(III) complexes.86 Hydrolysis of a peroxo-diiron(III) complex results in an oxo-diiron(III) species and hydrogen peroxide. Such reaction is responsible for the autoxidation of hemerythrin, but is very slow for the native protein due to hydrophobic shielding of the active site (Section 4.2.3).20 The hydrolysis of iron(III) peroxides is reversible, and the reverse reaction, the formation of peroxo intermediates from H202 and the (di)iron(III), is often referred to as peroxide shunt and is much better studied for model complexes. 

The rapidity of substitution reactions at a metal surrounded by a porphyrin or corrin group seems to be connected with r-delocalization and a strong in-plane ligand field which is not present in normal complexes. The substitution reactions (4) of five-co-ordinate neutral dithiolen complexes (where M is iron or cobalt and L and [M(S2CaPh2)2X] + L—> [M(S2C2Ph2)2L] + X (4)... 

Two of the papers presented at the Fifth International Conference on Non-aqueous Solvents are of direct relevance to this Report. They deal with solvent effects on kinetics, in the areas of ligand substitution reactions at labile centres, and of preferential solvation in such systems." Another review on preferential solvation and its consequences deals primarily with chromium(iii) complexes, such as the [Cr(NCS)6] anion, in binary aqueous mixtures, but also mentions other groups of inorganic substrates such as low-spin iron(ii) complexes. A short article on the effectiveness of a solvent in catalysis considers such topics as affinities for nf-electrons and polarization potentials. ... 

As part of ongoing research into the behavior of (vinylcarbene)iron complexes,119120 Mitsudo and Watanabe found that the trifluoromethyl-substituted vinylcarbene 174 exhibited a reactivity different from that of both 166 and 169.107 Upon treatment of the complex 174 with triphenylphos-phine the vinylketene complex 175 is formed, a reaction identical to that seen in the series of vinylcarbene complexes 166 (R = H). However, when the vinylcarbene 174 is exposed to a high pressure of carbon monoxide, it is converted cleanly to the ferracyclopentenone 176. Remember that when the vinylcarbene complex 166 (R = H) was treated in the same manner, conversion stopped at the vinylketene complex 167 Even when exposed to a pressure of 80 atmospheres of CO(g), no further reaction was seen to occur. An electron donating ligand (L = PR3) is required for conversion to cyclopentenone structure 168. Conversely, when the more electron-rich vinylcarbene 169 is exposed to carbon monoxide in the same manner, the pyrone complex 172 is formed. 

Substitution reactions of hexadentate diimine complexes of iron(II) are generally slow, thanks to the combination of the strongly binding diimine groups and the chelate effect, even when the ligand contains only two diimine units of the less strongly bonding py—CH=N— type k2(OH)... 

---