4th EucheMs chemistry congress

Poster Session 1
s951
chem. Listy 106, s587–s1425 (2012)
Poster session 1 - inorganic Chemistry
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vALenCe tAutoMeriC quinonoid CoBALt
CoMPLexeS with PhotoACtive CiS-trAnS
iSoMerizABLe LiGAndS
A. witt 1 , f. heineMAnn 1 , M. KhuSniyArov 1
1 Friedrich-Alexander-University Erlangen-Nuremberg, Chemie
und Pharmazie, Erlangen, Germany
The recently proposed ligand-driven light-induced spin
change (LD-LISC) is one possible approach to achieve magnetic
bistability at room temperature. It is based on the possibility to
reversibly change the ligand field of a transition metal complex
by photoisomerization of the ligands to such an extent, that
the metal ion undergoes a spin transition. [1] In this contribution
we adopt the LD-LISC concept to the well explored valence
tautomeric quinonoid transition metal complexes [2] which
are known to exhibit different optical, electronic and/or
most importantly magnetic properties due to a reversible
interconversion between their electronic isomers.
Well studied 4-phenylazopyridine (4-papy) and
4-styrylpyridine (4-stpy), which undergo a reversible cis-trans
isomerisation upon irradiation, are incorporated into a redox
active Co(3,5-DBTSQ)(3,5-DBTCat) framework as photoactive
ligands, where 3,5-DBTSQ- and 3,5-DBTCat2- are the
semiquinonate and catecholate forms of 3,5-di-tert-butyl-o-
-benzoquinone, respectively.
As confirmed by EPR spectroscopy in frozen solution at
14 K, the electronic structure of complexes [Co(3,5-DBTSQ)(3,5-
DBTCat)(4-papy) ] 1 and [Co(3,5-DBTSQ)(3,5-DBTCat)(4-stpy) ]
2 2
2 consists of a ligand π-radical attached to a low-spin Co(III) ion.
Cyclic voltammogram of 1 at RT reveals several typical (partially)
reversible redox processes. Magnetochemical data of 1 in solid
state shows a low-spin Co(III) electronic structure at T < 240 K;
however, the observed gradual increase of the effective magnetic
moment at higher temperatures may indicate a thermally induced
transition to a high-spin Co(II) state. Upon irradiation with UV
light at RT in solution a trans-to-cis isomerization of the
photoactive ligands both in 1 and 2 is suggested by electronic
absorption spectroscopy.
references:
1. M.-L. Boillot, J. Zarembowitch, A. Sour, in Topics in
Current Chemistry, Vol. 234 (Eds.: P. Gütlich,
H. A. Goodwin), Springer Berlin / Heidelberg, 2004,
pp. 786–786.
2. D. N. Hendrickson, C. G. Pierpont, in Topics in Current
Chemistry, Vol. 234 (Eds.: P. Gütlich, H. A. Goodwin),
Springer Berlin / Heidelberg, 2004, pp. 786–786.
Keywords: Cobalt; Valence isomerization; Spin crossover;
Magnetic properties; UV/Vis spectroscopy;
4 th EucheMs chemistry congress
P - 0 1 8 1
CoMPAriSon of C-h hydroGen AtoM trAnSfer
reACtionS MediAted By MAnGAneSe(iv)-oxo
CoMPLexeS with tuned eLeCtroniC
ProPertieS
o. CuSSó 1 , i. GArCiA-BoSCh 1 , A. CoMPAny 1 ,
x. riBAS 1 , M. CoStAS 1
1 Universitat De Girona, Departament de Química, Girona,
Spain
Oxidation of C-H bonds mediated by transition metal
complexes are fundamental steps in fine and industrial chemistry,
and in many biochemical transformations. One of the most
commonly metal used is iron, usually adopting high valent
iron(IV)-oxo species. [1] The comparison of manganese systems
with their iron analogues have also attracted the attention of
different authors, trying to shed light into the Fe/Mn duality found
in nature. It is known that there are some oxidative enzymes that
can be both iron and manganese dependent. While several highvalent
iron complexes are currently known, this is not the case for
the manganese metal, for which mononuclear high-valent
oxo-complexes are rather uncommon, likely because of their
tendency to dimerize. [2] Manganese(V)-oxo species and their role
in C-H oxidation reactions have been also explored, [3] also it have
been studied in other oxidative transformations such as sulfide
oxidations and epoxidations.
In this work, we have studied the reaction of C-H oxidation
of dihydroanthracene as model substrate mediated by
[ RPyTacn-Mn IV (OH) ] and [ 2 RPyTacn-Mn IV (OH)(O)] species
containing different electronic groups on the pyridine ligand. [4]
A comparative analysis of the kinetic parameters of these
reactions, as well as the thermodynamic driving forces for such
reactions have been performed.
references:
1. M. Costas, M. P. Mehn, M. P. Jensen, L. Que, Jr., Chem.
Rev. 2004, 104, 939
2. G. Yin, A. M. Danby, D. Kitko, J. D. Carter,
W. M. Scheper, D. H. Busch, J. Am. Chem. Soc. 2008,
130, 16245
3. J. T. Groves, J. Lee, S. S. Marla, J. Am. Chem. Soc. 1997,
119, 6269.
4. I. Garcia-Bosch, A. Company, C. W. Cady, S. Styring,
W. R. Browne, X. Ribas, M. Costas, Angew. Chem., Int.
Ed. 2011, 50, 5648.
Keywords: C-H activation; Kinetics; Manganese;
AUGUst 26–30, 2012, PrAGUE, cZEcH rEPUbLIc