PHOTOCHEMICAL ACTIVATION AND SPLITTING
OF H 2 O, CO 2 , AND N 2 INDUCED BY CT EXCITATION
OF REDOXACTIVE METAL COMPLEXES
ARND VOGLER^1 and HORST KUNKELY
Institut für Anorganische Chemie, Universität Regensburg, 93040 Regensburg, GermanyI. Introduction 346
II. Water Splitting 347
A. Water Splitting by Light with Osmocene as Photocatalyst 349
III. Carbon Dioxide Splitting 353
A. Photoreduction of Carbonate in a Copper(I) Phosphine Complex 354
B. Splitting of Alkyl Carbonates Photocatalyzed by Copper
Hydrotris Pyrazolylborate Complexes 357
IV. Dinitrogen Splitting 360
A. Photoreduction of N 2 in a Binuclear Osmium Complex 361
V. Conclusion 367
VI. Abbreviations 367
Acknowledgment 367
References 367
ABSTRACTThe cleavage of the ubiquitous and abundant molecules H 2 O,
CO 2 (or CO 32 , respectively) and N2 is of is of considerable inter-
est. Owing to their stability this splitting should be facilitated by
light and may thus be applied for solar energy utilization. Under
ambient conditions the direct photocleavage can certainly not be
accomplished but assistance by suitable redox-active metal
complexes is conceivable. Light absorption should induce charge
redistribution between metal and molecules to be split. CT excita-
tion is expected to initiate the generation of redox products in
the first photochemical step. Indeed, the redox couples OsIICp 2 /
OsIVCp 2 with Cp ¼ cyclopentadienyl anion, Cu(I)/Cu(II) and
OsIIN 2 OsIII/OsVI(N) have been successfully applied to photo cleave
H 2 O, CO 32 and N 2 , respectively. Future attempts are directed to
improve the efficiency of these photoreactions. In particular, the
inclusion of such reactions in photocatalytic cycles is a challenging
task.
(^1) Corresponding author.
345
INORGANIC PHOTOCHEMISTRY #2011 Elsevier Inc.
VOLUME 63 ISSN 0898-8838 / DOI: 10.1016/B978-0-12-385904-4.00003-2 All rights reserved