Dissertation

|1.10 Intramolecular Photoredoxcatalysts|
O
N
N
N
N
N
2+
N
Ru
N
N
N
3+
Cl
Rh
Cl
N
a: TON = 30
(4h)
t-Bu
N
N
N
2+ N
Ru
N
Ru
N
HO
N
O
b: TON = 4.8
(10h)
2+
N
Pt
N
Cl
Cl
N O BF
O N 3+ 2
O
Co
N
F 2 B N O
d: TON = 103
(15h)
N
OH 2
N
O
N
N
N
2+
N
Ru
N
N
t-Bu
t-Bu
N
N
N
2+
N
Ru
N
N
N
N
N
N
2+
Pd
Cl
Cl
N
N 2+ N
Ru
N N
N
t-Bu
c: TON = 56
(29h)
Figure 33: Representative systems for the intramolecular hydrogen evolution, reported by the
workgroups of BREWER (a) [84] , SAKAI (b) [82] , RAU (c) [80] and ARTERO (d) [85, 86] . The dyads and triads
typically contain a [Ru(bpy) 3 ] 2+ -type photocenter (orange). A second NN-chelated metal center
(blue) provides redox activity and coordination sites for catalytic hydrogen evolution. Covalent
bridges (bold) constitute the framework of the substructures.
(distance control) and activity in ET and EnT processes. [83] Especially the amide linked bridge
in the Sakai system represents a very flexible bridge which may flip back and forth (allow for
outer sphere ET). The Rau system, based on tpphz, exhibits a very rigid π-system with high
distance control between the metals (forces inner sphere mechanism). [82, 80] Very short distances
with high electronic communication between the metals are achieved in the Brewer system
(metal-metal interaction) whereas the Artero system exhibits the largest distance between the
metal centers (through-bond versus outer sphere mechanism). [84, 87] In addition, the type of the
coordinative bond will influence the integrity (e.g. reversible redox behavior, photostability) of
the supramolecular scaffold during the high energy processes. For historical and photochemical
reasons, typically N-donor ligands are used to bind the photocenter metal in the different redox
states. Catalysis experiments with the P B C Red systems are very similar to previous
experiments with intermolecular systems in set up and analysis. Usually, a sacrificial electron
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