Synthesis, Structure, and Electrochemistry of Fischer Alkoxy- and Aminocarbene Complexes of Tungsten: The Use of DFT To Predict and Understand Oxidation and Reduction Potentials

Reactions of Fischer alkoxycarbene
complexes [W­(CO)5{C­(OEt)­Ar}] (Ar = 2-thienyl (1), 2-furyl (2)) with ethylenediamine led to the formation
of two different reaction
products: an aminolysis product (5 or 6)
where the ethoxy substituent of the carbene ligand is replaced by
the ethylenediamine moiety and a chelated product where aminolysis
and substitution of one carbonyl ligand had taken place, yielding 7 or 8. Aminolysis of 1 and 2 with cyclohexylamine (CHA) produced the aminocarbene complexes 3 (Ar = 2-thienyl) and 4 (Ar = 2-furyl). Complexes 1–8 have been electrochemically investigated
by means of cyclic voltammetry. The relative shifts in the oxidation
and reduction potentials are discussed and related to density functional
theory (DFT) calculated energies. DFT calculations further show that
the oxidation center is located on the metal and the carbonyl groups,
while the reduction center is localized on the carbene moiety and
is strongly influenced by the electronic properties of its substituents.
Crystal structures of 1–4, 6, and 8 are reported.