photoreactions of the corresponding bismuth corrole catalysts are
shown in Fig. 22 ( 191 ). In this context, it is very interesting to
recall the CT properties of high-valent metal-oxo moieties
(Fig. 19), which could proof to become very versatile tools for
catalyzing the O-O bond formation step in bioinspired artificial
photosynthetic water oxidation schemes (111,193,194).
C.3. Hydrogen atom transfer
Controlled radical reactivity and H-atom abstraction from sub-
strates are common features of many metalloenzymes(112,195).
Photochemical strategies can be successfully applied for
modeling the biocatalytic transformations involving protein
radicals (3,196). For example, one of the possibilities to achieve
CH bond activation of inert compounds under mild and con-
trolled reaction conditions is to create unpaired spin density at
an oxygen atom accessible to the substrate, which should also
be preorganized in the microenvironment of this active site. In
bioinorganic photochemistry, this can be achieved by introducing
oxyl-radical type photoreactivity in low-lying excited states as
discussed in the previous sections (Fig. 19). The fundamental
design criteria for such types of biomimetic systems based on
multielectron transfer (MET) photosensitizers carrying terminal
oxo-functionalities and radical-stabilizing cofactors have already
been described in more detail elsewhere (3,5).
FIG. 22. Structures of hydroperoxo- and oxo-derivatives of bismuth
triphenylcorrole photosensitizers ( 191 ).
274 GÜNTHER KNÖR AND UWE MONKOWIUS