Inhaltszusammenfassung

The clusters (mu-3-PR)Fe3(CO)10 produce adducts with chalcogenocyanates XCN- (X = S, Se, Te) which, when alkylated with Et3O+, lead to the carbonyl clusters (mu-3-PR)(mu-3-X)Fe3(CO)9 (1) or their isonitrile substitution products (mu-3-PR)(mu-3-X)Fe3(CO)8(CNEt) (2), respectively. One or two CO groups of the clusters 1 can be substituted by trimethylphosphite (TMP) by means of thermal activation. In the case of the monosubstituted products (mu-3-PR)(mu-3-X)Fe3(CO)8(TMP) (3), the isomer which cr...The clusters (mu-3-PR)Fe3(CO)10 produce adducts with chalcogenocyanates XCN- (X = S, Se, Te) which, when alkylated with Et3O+, lead to the carbonyl clusters (mu-3-PR)(mu-3-X)Fe3(CO)9 (1) or their isonitrile substitution products (mu-3-PR)(mu-3-X)Fe3(CO)8(CNEt) (2), respectively. One or two CO groups of the clusters 1 can be substituted by trimethylphosphite (TMP) by means of thermal activation. In the case of the monosubstituted products (mu-3-PR)(mu-3-X)Fe3(CO)8(TMP) (3), the isomer which crystallizes is that in which one of the CO-groups at the apical iron of the square-pyramidal cluster 1 is substituted. In solution a slow isomerisation (on the NMR timescale) occurs to give substitution products in which the TMP ligand is bound to an equatorial iron. Only two of the three geometrically different ligand positions at the equatorial iron centre are markedly populated. The rapid exchange of the TMP ligand between these two positions is frozen out at 210 K. Activation barriers of about 50 kJ mol-1 for this isomerisation process can be calculated from the coalescence temperature of the P-31 NMR resonances. For the disubstituted products 4 a solid state structure is observed in which one TMP ligand is bound to the apical iron, and the second occupies an axial position at an equatorial iron. The P-31 NMR spectra of solutions of 4 demonstrate a dynamic equilibrium between all substitution patterns, in which both TMP ligands are bound separately to an iron centre of the cluster. Exchange between the positions at the apical iron and those at the equatorial iron centres appears to be slow on the NMR timescale. The exchange process between positions at the equatorial iron centres takes place rapidly and is frozen out at 200 K. Activation barriers of about 60 kJ mol-1 for the corresponding exchange phenomena can be deduced from the coalescence temperatures. The compounds 1 and all their substitution derivatives 2-4 show two reversible reductions in the cyclovoltammogram. The observed sequence of the reduction potentials corresponds to the nature of the substituents. The compounds 4 which are most difficult to reduce also show a reversible oxidation peak. The results reported herein are documented by the conventional spectroscopic and analytical data as well as by seven X-ray diffraction studies. » weiterlesen» einklappen

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