Scorpionate Ligand - Isolobality

Isolobality

Since the work by Wilkinson and others on ferrocene a vast amount of work has been done on cyclopentadienyl complexes. It was soon understood by many organometallic chemists that a Cp ligand is isolobal to Tp. As many insights into chemistry can be obtained by the study of a series of closely related compounds (where only one feature is changed) a great deal of organometallic chemistry has been done using Tp (and more recently Tm) as a co-ligand on the metal.

The Tp, Tm, trithia-9-crown-3 (a sulfur version of a small crown ether) and cyclopentadienyl (Cp) ligands related ligands and form related complexes. These ligands donate the same number of electrons to the metal, and the donor atoms are arranged in a fac manner covering a face of a polyhedron.

The Tp and Tm ligands are isolobal with the Cp ligands, here is the structure of the Cp manganese tricarbonyl complex. This compound like the others shown in this section can be formed by the reaction of with the anionic ligands, in the case of the thio crown ether a better synthesis would be to react .OTf with the crown in a non coordinating solvent such as dichloromethane.

Below is shown the structure of the tricarbonyl manganese complex of trithia-9-crown-3

While the geometry of the Tp ligands do not allow the formation of simple borane complexes with the metals, the geometry of the Tm ligands (and sometimes their bidentate versions Bm) are such that with late transition metals such as osmium and platinum it is possible to turn the Tm ligand inside out to form a borane to which the metal forms a dative bond.

Here is the manganese complex of Tm with (again three carbonyls).