Dissertation

|3.3 NN-NHC-Ligand bbip: Toward Second Generation Catalysts|
-2.0 -1.0 0 1.0
Fc/Fc +
current / a.u.
-2.0 -1.0 0 1.0
potential / V
Figure 105: Cyclovoltammograms of ruthenium complexes with imidazophenanthroline derived
ligands, measured in a 0.1 M solution of Bu 4 NPF 6 in dry acetonitrile under argon atmosphere,
referenced vs. Fc/Fc + , E 1/2 = 0.00 V. Ru(ip) (—), Ru(bip) (—), Ru(bbip) (—), and Ru(bbip)Ag (—).
azolium salt Ru(bbip) and the carbene complex Ru(bbip)Ag. Furthermore, in all new ruthenium
complexes three independent and quasi reversible redox waves were observed for the three
reductions of the coordinated ligands (E 1/2 (̂LL 1,2,3 ) at roughly -1.8 V, -2.0 V, and -2.2 V respectively.
These findings are in accordance with other trisleptic [Ru(bpy) 3 ] 2+ -type complexes such as
Ru(phen) or [Ru(tbbpy) 3 ] 2+ . Among the complexes, the most significant differences exist between
the first ligand-based reductions which can be attributed to the imidazophenanthroline systems.
While the electron rich complex Ru(ip) exhibits a slightly more negative first reduction potential
(E 1/2 (̂LL 1 ) = -1.89 V), more positive ligand reductions were observed in Ru(bip) (E 1/2 (̂LL 1 ) =
-1.76 V) and Ru(bbip) (E 1/2 (̂LL 1 ) = -1.76 V), respectively. Interestingly, square wave experiments
revealed an unusual behavior of Ru(ip) which could be attributed to irreversible reduction of the
protonated ligand in the reduction wave with formation of neutral Ru(ip) which exhibits a fully
reversible electrochemistry (see figure 106).
Furthermore, the first ligand centered reduction in Ru(bbip) is not fully reversible which
can be explained by reduction and possibly hydrogenation of the imidazolium moiety (see
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