Die ambidenten Ligandeigenschaften der Gruppe 15 Heteroarene in Übergangsmetallkomplexen

The ambident ligand properties were studied in this work. The possible eta1 and eta6 group 15 heteroarene complexes with transition metals were investigated by using theoretical methods. The long-lasting experimental work by the groups of Ashe III and Elschenbroich had given important insights of the bonding modi of the group 15 heteroarenes transition metal complexes. These works are the starting point for our own investigations. However, we will undertake a systematic investigation of the bonding situation in these complexes. The possible study of experimentally unknown compounds is one major advanced of modern, theoretical methods. 1. eta1-Bindungsmodus 1. eta1 bonding mode In this work we confermed the experimentally detected uniqueness of the phosphabenzene compared to the other heteroarenes and the low stability of the pyridine complexes. More over, the arsabenzen could be identified as the second stronges eta1 ligand within the heteroarenes. The pyridine bonding modes differ qualitatively from the other heavier heteroarenes. 2. eta6 bonding mode The investigation of the eta6 heteroarene complexes with elements of the chromium group were undertaken with special focus on the preferred rotational conformere. Experimentally the synperiplanar rotamer is the observed one. However, theoretically we found only for the pyridine that the antiperiplanar configuration is the preferred one. For all others the syn-conformation is energetically lower. Ashe III postulated a secondary bonding between the heavier heteroatoms to be the reason for the preference for the syn-rotamer. However, we have identified a quantum chemical source for the as the origin for the rotational conformation preference. It is an increasing heteroatom-metal-interaction, if the heteroatom is an heavier element, which could be interpreted as a 3-center-2e-bond. 3. eta1 vs eta6 bonding mode The comparison of the different bonding modi, eta1 vs eta6, have show that firstly the without entropic effects only a few number of eta6 complexes would be stable compared to the eta1 complexes. However, considering entropic corrections the picture is reversed and only the phosphabenzene complexes have a reasonable stability of the eta1 complexes.