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ChemComm
Table 1 Summary of the photocatalytic activity of different combinations
of PS and WRC, with and without CB8 (as shown in Fig. 2–4)
¨¨
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TON
Without CB8
With CB8
Experiment
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3 + 5
1.26 ꢂ 0.51
3.11 ꢂ 0.01
3.34 ꢂ 1.88
1.65 ꢂ 0.87
11.1 ꢂ 0.11
0
3.72 ꢂ 0.50
0.72 ꢂ 0.05
1.16 ꢂ 0.34
3.77 ꢂ 0.06
3.19 ꢂ 0.49
29.1 ꢂ 0.53
3 + 5 (4 equiv. CB8)
3 + 4 equiv. 5
4 equiv. 3 + 5
3 + 5 (dark)
3 + 5 + Hg
3 + EV
Naph + 5
3 + EV + Ptdmb
Naph + 5 + Irdmb
4 equiv. 3 + 6
—
1.66 ꢂ 0.07
6.43 ꢂ 1.17
—
—
—
—
—
¨
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—
4.23 ꢂ 2.09
¨
(d) M. G. Pfeffer, B. Schafer, G. Smolentsev, J. Uhlig, E. Nazarenko,
¨
¨
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(Fig. 4 and Table S6, ESI‡). In absence of CB8, no change was
observed (4.23 ꢂ 2.09 TONs for 3 + 6, cf. 6.43 ꢂ 1.17 TONs for
3 + 5), which also indicates that the effective increase in total
Pt-concentration has no effect (as expected based on the
stoichiometry experiments for the 3 + 5 mixture, see Table S6,
ESI‡). However, in the presence of CB8, a significant increase
in hydrogen-production was observed when using the bis-Pt
system 6 (29.1 ꢂ 0.53 TONs for 3 + 6 + CB8, cf. 11.1 ꢂ 0.11 TONs
for 3 + 5 + CB8). One possible explanation for this substantial
increase in hydrogen production (+263%) is that the spatial
proximity of the metal-centers is improved by ruling out the
anti-orientation (Table 1).
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In summary, we have reported a supramolecular concept
for the photocatalytic generation of hydrogen from aqueous
solutions. Formation of heteroternary 1 : 1 : 1 complexes of CB8
with naphthol-functionalized PSs and viologen-functionalized
WRCs allowed for an efficient screening of different PS/WRC
combinations, leading to the identification of the Ir/Pt pair as
the best candidate. The initial hit (3 + 5 + CB, 3.11 ꢂ 0.01 TONs)
was systematically investigated and optimized by variation of
stoichiometry and a series of control experiments, finally lead-
ing to the 3 + 6 + CB8 system with a largely increased activity
(29.1 ꢂ 0.53 TONs with 4 equiv. 3, i.e. +935% vs. 3 + 5 + CB8).
Thus, CB8-based supramolecular self-assembly can be an
efficient tool for the formation of bifunctional catalysts in
aqueous solution and we are currently expanding this concept
towards combined transition-metal and organocatalysts.
Funding from MERCUR (AN-2016-007) and the Fonds der
Chemischen Industrie (Liebig-Fellowship) is gratefully
¨
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¨
acknowledged. We thank Prof. Burkhard Konig and Dr.
Andreas Brunschweiger for their support and Jun.-Prof. Jens
Voskuhl for discussions.
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electron transfer can occur through the walls of the host-molecule:
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Conflicts of interest
There are no conflicts to declare.
Notes and references
1 British Petroleum Company, BP Statistical Review of World Energy,
British Petroleum Co, London, 2019.
2890 | Chem. Commun., 2021, 57, 2887ꢁ2890
This journal is The Royal Society of Chemistry 2021