Furan, tetrahydro-, iron complex

C4H602, 2-Propenoic acid, methyl ester platinum complex, 26 138 C4H7NO, 3-Butenamide nickel complex, 26 206 C4HsO, Furan, tetrahydro-iron complex, 26 232 magnesium complex, 26 147 neodymium and samarium complexes, 26 20... 

OC4H, Furan, tetrahydro-, actinide and lanthanide complexes, 28 289, 290 iron complex, 26 232 lanthanide complexes, 28 293-295 lanthanide-lithium complexes, 27 170... 

For iron(IlI)-porphyrinato complexes, strong-held ligands lead to low-spin (5 = 2) complexes. A pair of identical weak-held ligands, such as tetrahydro-furan, leads to intermediate-spin (5 = ) species. Five-coordinate species are, with few exceptions, high-spin (5 = f), with all hve 3d electrons in separate orbitals. Spin equilibria 5 = i 5 = f and 5 = 15 = i are not unusual. Specihc examples of these spin systems are given in Table 4.4. Higher oxidation states are found in some other hemoproteins. Fe(V)-porphyrin systems actually occur as Fe(IV)-porphyrin cation radical species, and Fe(I)-porphyrin systems exist as Fe(II)-porphyrin anion radical species. 

These reactions are extremely sensitive to conditions, e.g., temperature, solvent, etc. The best one is the reaction of the palladium complex (XXXVII) with iron pentacarbonyl to give (XIII). At 80° C the yield ranges from 87% in benzene, cyclohexane, or 1,2-dichloroethane, to 17% in tetrahydro-furan-diglyme and is zero in carbon tetrachloride (77). The reaction of (XXXVII) with molybdenum hexacarbonyl only occurs in aromatic hydrocarbon solvents and since the complex (XL) is obtained in the same yield starting from either molybdenum hexacarbonyl or benzenemolyb-denum tricarbonyl, it is reasonable to assume the latter to be an intermediate in this reaction. 

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