Organometallic Chemistry
Abstract
Dinuclear pentaispropylcyclopentadienyl complexes [5CpMX]2 and tetraisopropylcyclopentadienyl complexes [4CpMX]2 of nickel and iron react with nucleophiles such as phenolate or aryl anions. Aryl complexes [5CpFeAr] and [4CpFeAr] exhibit interesting magnetic properties and are highly reactive. Oxidation with silver bromide or hexachloroethane yields novel iron(III) complexes [4CpFeBr2] or [4CpFeArCl], respectively.
With Lewis acids rearrangement of σ aryl to π-bonded arene takes place. The Lewis acid coordinates to the ipso position of the aryl ligand.
[5CpFeAr] + AlR3 → [5CpFe(μ,η5:η1-Ar)AlR3)]
The aryl ligand can also be transferred to other metals:
[5CpFeAr] + CuOTf → [5CpFe(OTf)] + 1/4 [CuAr]4
Molecule Magnets
The aryl iron complex shown below behaves like a Single Molecule Magnet.
"High-Spin Cyclopentadienyl Complexes: A Single-Molecule Magnet Based on the Aryl-Iron(II) Cyclopentadienyl Type"
D. Weismann, Y. Sun, Y. Lan, G. Wolmershäuser, A. K. Powell, H. Sitzmann, Chem. Eur. J.2011, 17(17), 4700-4704.
The bis(trimethylsilylamide) iron complex [5CpFeN(SiMe3)2] has four unpaired elektrones and the studies of its magnetic properties are in progress.
Reactive metal complexes with very bulky cyclopentadienyl ligands
The formation of stable, coordinatively saturated complexes can be suppressed by reactions of very bulky cyclopentadienyl anions with transition metal halides. Thus, alkyl cyclopentadienides with three tert.-butyl respectively four or five isopropyl substituents form alkyl cyclopentadienyl halide complexes reacting with iron(II) bromide. Since the formation of ferrocenes is suppressed, highly reactive high spin half sandwich complexes of the type [CpRFe(OAr)] or [CpRFeAr] (CpR = alkyl cyclopentadienyl ligands; Ar = aryl) can be isolated. The aryl complexes rearrange with coordinatively unsaturated metal complexes whereat the σ-aryl ligand undergoes a π-coordination to the iron center and the new added metal atom coordinates to the ipso carbon atom of the aryl ligand. In these dinuclear complexes, the aromatic six-membered ring is not ccordinated symmetric to the iron center, but shows patrially a cyclohexadienyl-ylidene character.
Zirconium complexes
In cooperation with Prof. Dr. M. Tamm and Dr. M. D. Walter (TU Braunschweig) zirconium complexes of the type [(η7-C7H7)ZrCp]with substituted cyclopentadienyl and indenyl ligands are synthesized and studied as model complexes for the quantification of the sterical demand of the cyclopentadienyl ligands.
"How big is a Cp? Cycloheptatrienyl zirconium complexes with bulky cyclopentadienyl and indenyl ligands"
A. Glöckner, H. Bauer, M. Maekawa, T. Bannenberg, C. G. Daniliuc, P. G. Jones, Y. Sun, H. Sitzmann, M. Tamm, M. D. Walter, Dalton Trans. 2012, 41, 6614-6624.
