Abstract:
A series of ferrocenyl (Fc = ferrocenyl; fc = ferrocen-1,1'-diyl) and biferrocenyl (Bfc = 1',1''-biferrocenyl; bfc
= 1',1''-biferrocen-1,1'''-diyl) mono- and biscarbene tungsten(0) complexes of the type [(CO)5W=C(OMe)R] (1, R = Fc; 3, R
= Bfc) and [(CO)5W=C(OMe)-R'-(OMe)C=W(CO)5] (2, R' = fc; 4, R' = bfc) were synthesized according to the classical
synthetic methodology by reacting W(CO)6 with LiR (R = Fc, fc, bfc), followed by a subsequent alkylation using methyl
trifluoromethanesulfonate. Electrochemical investigations were carried out on these complexes to get a closer insight into the
electronic properties of 1 - 4. The ferrocenyl and biferrocenyl moieties in 1 – 4 show reversible one electron redox events. It
was further found that the Fischer carbene unit is reducible in an electrochemical one electron transfer process. For the
tungsten carbonyl moieties, irreversible oxidation processes were found. In addition, charge transfer studies were performed on 1
- 4 by the use of in situ UV-Vis-NIR and infrared spectroelectrochemical techniques. During the UV-Vis-NIR investigations
typical low energy transitions for the mixed-valent biferrocenyl unit were found. A further observed high energy NIR
absorption is attributed to a metal-metal charge transfer transition between the tungsten carbonyl fragment and the
ferrocenyl/biferrocenyl group in the corresponding oxidized states, which can be described as class II systems according to
Robin and Day. This assignment was verified by infrared spectroelectrochemical studies. The electrochemical investigations
are supported by DFT calculations. The structural properties of 1 - 4 in the solid state were investigated by single-crystal Xray
diffraction studies showing no substituent effects on bond lengths and angles. The biferrocenyl derivatives exhibit synconformation
of the ferrocenyl and carbene building blocks.
