An Organotransition-Metal Complex with Pentagonal-Pyramidal Structure

摘要

It was Alfred Werner in the late 19th century, who first suggested that six ligands should adopt an octahedral (OC-6) geometry around a given central atom. This geometrical arrangement minimize? repulsive effects between six ligands (LCP model) as well as between six valence-electron pairs (VSEPR model). It is no wonder, then, that the many myriads of six-coordinate compounds prepared ever since, almost invariably show an OC-6 geometry. There are, however, some examples of alternative geometries currently known (Scheme 1). Thus, a number of compounds containing dithiolato ligands [M(S2C2R2)3]~(q-) as well as a few homoleptic organo-transition-metal complexes [MR6]~(q-) , that show trigonal-prismatic (TPR-6) structures. Hexagonal-planar (HP-6) structures have been found in [Ni(EtBu)6] compounds (E = P, As), where the nickel center is hosted by a cyclic hexadentate framework. Pentagonal-pyramidal (PPY-6) structures have been found mainly in post-transition-element compoundsincluding the fascinating species [XeOF5] The PPY-6 geometry is less frequent in transition-metal compounds, where it has been found mainly associated to either pentadentate ligands or to bidentate ligands of the peroxo type as in CrO(O2)2py (py = pyridine). Here we report on what we consider to be the first organo-transition-metal complex with PPY-6 structure.