4th EucheMs chemistry congress

thursday, 30-Aug 2012
s701
chem. Listy 106, s587–s1425 (2012)
inorganic Chemistry plus Young inorganic chemistry day
Young inorganic chemistry day – iii
o - 4 5 3
MoLeCuLAr MetAL-oxideS AS viSiBLe-LiGht
driven SynthetiC oxyGen evoLvinG
CAtALyStS
C. StreB 1
1 Friedrich-Alexander-University Erlangen-Nuremberg, Institute
of Inorganic Chemistry II, Erlangen, Germany
Over the last decades, the activation of small molecules such
as H O has attracted increasing interest from a wide variety of
2
fields of research, as the photochemical splitting of water into
molecular oxygen and hydrogen can be used to convert solar
energy into secondary energy carriers.
Water oxidation is the particularly challenging half-reaction
and the development of highly stable and highly active water
oxidation catalysts (WOCs) based on economically viable
materials is at the forefront of chemical research.
In our work, we focus on the development of
purely inorganic, metal-oxide-based systems, so-called
polyoxometalates, [1] where 3d transition metals are incorporated
as catalytic sites in a redox-active metal-oxide cluster shell.
Conceptually, this incorporation can lead to the stabilization of
catalytic metal centres in high oxidation states [2] which can
subsequently be used as photoactive redox-centres for visiblelight
driven electron transfer reactions. [3]
Here, we show how this concept is employed to access a
manganese vanadium oxide cluster, {Mn V } as a synthetic mimic
4 4
of the oxygen evolving complex (OEC) of Photosystem II. The
{Mn V } unit features a high-valent [Mn O ] 4 4 4 4 6+ cubane which is
stabilized by coordination to a tripodal vanadium oxide cluster,
[V O ] 4 13 6- . The compound can be used as a homogeneous oxygen
evolving catalyst and it is shown that this water oxidation can be
driven photochemically using [Ru(bpy) ] 3 2+ as a visible-light
photosensitizer. The compound shows turnover numbers of ca. 20
and shows high reversible redox-activity and solution stability.
The deactivation mechanism under turnover conditions,
deactivation products and possible stabilization routes are
discussed.
references:
1. D. L. Long, R. Tsunashima, L. Cronin, Angew. Chem.
Intern. Ed. 2012, 49, 1736.
2. C. Streb, Dalton Trans. (Perspective), 2012, 41, 1651.
3. J. Tucher, Y. Wu, L. C. Nye, I. Ivanovic-Burmazovic, M.
M: Khusniyarov, C. Streb, Dalton Trans. 2012, 41, DOI:
10.1039/C2DT30304C
Keywords: water splitting; Photochemistry; Energy
conversion; Sustainable Chemistry; Catalysis;
Young inorganic chemistry day – iii
4 th EucheMs chemistry congress
o - 4 5 4
nuCLeoPhiLiC AryL-fLuorinAtion And
AryL-hALide exChAnGe reACtionS MediAted
By A Cu(i)/Cu(iii) CAtALytiC CyCLe
A. CASitAS 1 , M. CAntA 1 , M. CoStAS 1 , M. SoLA 1 ,
x. riBAS 1
1 Universitat de Girona, Departament de Química, Girona,
Spain
The insertion of a fluorine atom at an aryl group through
halide exchange reactions is a highly desired transformation
because of the importance of fluorinated pharmaceuticals and
agrochemicals. [1] Moreover, the ability to exchange a given halide
in an aryl group for another halide would facilitate the versatility
of many transition metal catalyzed cross-coupling reactions,
[2, 3]
limited for many processes to the most reactive aryl iodide.
Copper-catalyzed halide exchange reactions under very mild
reaction conditions are described for the first time using a family
of model aryl halide substrates. [4] All combinations of halide
exchange (I, Br, Cl, F) are observed using catalytic amounts of
copper(I) in the presence of excess of halide salt in moderate to
high yields. Strikingly, quantitative fluorination of aryl halide
substrates is also achieved catalytically at room temperature, using
common fluoride sources, via the intermediacy of well-defined
aryl-copper(III)-halide complexes. [4, 5] Experimental and
computational data support a redox Cu(I)/Cu(III) catalytic cycle
that involves aryl halide oxidative addition at the copper(I) center,
followed by halide exchange and reductive elimination steps.
Additionally, defluorination of the aryl fluoride model system can
be also achieved with copper(I) at room temperature operating
under a Cu(I)/Cu(III) redox pair.
references:
1. Furuya, T.; Kamlet, A. S; Ritter, T. Nature, 2011, 473,
470–477.
2. Sheppard, T. D. Org. Biomol. Chem., 2010, 7, 1043–1052.
3. Kaplars, A., Buchwald, S. L., J. Am. Chem. Soc., 2002,
124, 14844-14845.
4. Casitas, A.; Canta, M.; Sola, M.; Costas, M.; Ribas, X. J.
Am. Chem Soc. 2011, 133, 19386–19392.
5. Casitas, A.; King, A. E.; Parella, T.; Costas, M.; Stahl, S. S.;
Ribas, X. Chem. Sci., 2010, 1, 326–330.
Keywords: copper; cross-coupling; fluorides; homogeneous
catalysis; hypervalent compounds;
AUGUst 26–30, 2012, PrAGUE, cZEcH rEPUbLIc