Unprecedented examples of heterobimetallic cerium(IV) disiloxanediolates

Article abstract of DOI:10.1021/ic701320d

The first disiloxanediolate complexes of cerium(IV) are reported. Starting from the readily available precursor (^tBuO)₃Ce ^IV(NO₃)(THF)₂ (1), we prepared the novel heterobimetallic compounds [{(Ph

Full text of DOI:10.1021/ic701320d

Inorg. Chem. 2007, 46, 8100−8101
Unprecedented Examples of Heterobimetallic Cerium(IV)
Disiloxanediolates
Stephan Giessmann, Steffen Blaurock, Volker Lorenz, and Frank T. Edelmann*
Chemisches Institut der Otto-Von-Guericke-UniVersita¨t Magdeburg, UniVersita¨tsplatz 2,
D-39106 Magdeburg, Germany
Received July 4, 2007
The first disiloxanediolate complexes of cerium(IV) are reported.
Starting from the readily available precursor (tBuO)3CeIV(NO3)(THF)2
bonds is very scarce. To the best of our knowledge, Ce-
(OSiPh3)4(DME)x (0.5 < x < 1)6 and a cerium(IV) metal-
lasilsesquioxane complex7 are the only fully characterized
compounds of this type. We report here the preparation and
structural characterization of two unprecedented examples
of cerium(IV) disiloxanediolates.
(1), we prepared the novel heterobimetallic compounds [
SiO)2O}{K(THF)2
]2Ce(OtBu)2 (2) and [ (Ph2SiO)2O}2{(DME)-KOt-
Ce]2 (3) and structurally characterized them by
{(Ph2-
}
{
Bu}{(Ph2SiO2)K
}
X-ray diffraction.
As a suitable cerium(IV) precursor, we chose the readily
available alkoxide nitrate complex (tBuO)3CeIV(NO3)(THF)2
(1). Mixed-ligand complexes of this type were developed
by Evans et al. as soluble and versatile cerium(IV) reagents.8
Bright yellow (tBuO)3Ce(NO3)(THF)2 (1) is easily made by
allowing ceric ammonium nitrate, (NH4)2[Ce(NO3)6] (CAN),
to react with NaOtBu in a 1:5 molar ratio. In the first
experiment, 1 was treated with (Ph2SiOK)2O (made in situ
by deprotonation of 1,1,3,3-tetraphenyl-1,3-disiloxanediol9,10
with KN(SiMe3)2) in a molar ratio of 1:2 according to
Scheme 1. From this reaction, the novel heterobimetallic
potassium/cerium(IV) disiloxanediolate complex [{(Ph2-
SiO)2O}{K(THF)2}]2Ce(OtBu)2 (2) was isolated in the form
of yellow, block-shaped crystals in 81% yield (Scheme 1).
Its structure was studied by single-crystal X-ray diffraction
(Figure 1).
In the molecule of 2, two potassium disiloxanediolate
ligands are coordinated to cerium(IV) in a slightly bent
coordination geometry. Two t-butoxide ligands remain as
functionalizable groups coordinated to Ce. The central cerium
is in a distorted octahedral coordination environment. A very
similar distorted octahedral coordination of tetravalent cerium
was found in Ce(OSiPh3)4(DME)x.6 One phenyl ring of each
disiloxanediolate ligand is engaged in an intramolecular η1-
π-coordination to potassium (K(1)-C(22) 3.395(4) Å).
Phenyl-π-coordination to K+ has been observed, for example,
Because of their high oxidation potential, cerium(IV)
compounds are widely used in various areas of chemistry
and technology. Important fields of application include
organic synthesis,1 bioinorganic chemistry,2 materials sci-
ence,3 and industrial catalysis (automotive three-way cata-
lysts, oxygen storage, etc.).4 Thus there is a constant demand
for new, well-defined cerium(IV) species. Cerium(IV) alkox-
ides form a well-investigated class of compounds which are
of interest as precursors for the MOCVD production of thin
CeO2 layers.5 In sharp contrast, information about the
homologous cerium(IV) siloxides containing Ce-O-Si
* To whom correspondence should be addressed. E-mail: frank.
edelmann@ovgu.de.
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Published on Web 09/01/2007

COMMUNICATION
Figure 2. Molecular structure of [{(Ph2SiO)2O}2{(DME)KOtBu}{(Ph2-
SiO2)K}Ce]2 (3). Selected bond lengths (Å): Ce(1)-O(1) ) 2.278(3), Ce-
(1)-O(3) ) 2.248(2), Ce(1)-O(4) ) 2.105(2), Ce(1)-O(5) ) 2.227(2),
Ce(1)-O(6) ) 2.230(2), Ce(1)-O(7) ) 2.318(2), K(1)-O(5) ) 2.743(3),
K(1)-O(5A) ) 3.064(3), K(1)-O(3A) ) 2.742(3).
Figure 1. Molecular structure of [{(Ph2SiO)2O}{K(THF)2}]2Ce(OtBu)2
(2). Selected bond lengths (Å): Ce-O(1) ) 2.279(2), Ce-O(3) ) 2.292-
(2), Ce-O(4) ) 2.102(2), K(1)-O(1A) ) 2.696(2), K(1)-O(3) ) 2.718-
(2), K(1)-C(22) ) 3.395(4).
Scheme 1. Synthesis of Ce(IV) Disiloxanediolates 2 and 3
tion environment. Two disiloxanediolate dianions act as
chelating ligands toward each Ce(IV) and simultaneously
bridge two potassium ions with the cerium. An unusual µ3,µ2-
bridging coordination mode was found for the dianionic
diphenyl-1,1-silane-diolate ligands. One oxygen from each
2-
of the two Ph2SiO2 ligands bridges one Ce and two
potassium ions, while the other oxygen forms a µ2-bridge to
Ce and K. The overall coordination geometry around each
cerium is slightly distorted octahedral. Four t-butoxide groups
originating from precursor 1 are also present in the molecular
structure of 3, two of them bridging (K, K) and the other
two terminally bonded to cerium. Given the high isolated
yield, it is clear that despite its highly unusual structure,
compound 3 is the main product of the reaction of 1 with 3
equiv of (Ph2SiOK)2O. The coordinative unsaturation of the
potassium ions (coordination numbers 4 and 5, respectively)
is relieved by η1- and η2-π-interactions with neighboring
phenyl substituents.11 The respective K‚‚‚C distances are in
the range of 3.173-3.527(4) Å. The fact that the nitrate group
of the starting material was completely eliminated demon-
strates the usefulness of 1 as a precursor for the synthesis of
novel cerium(IV) siloxide species. Because of the remaining
in potassium pyrazolylborates, phosphine(phosphinimino)-
methanides, phenoxides, and thiolates.11
The same reaction carried out in a molar ratio of 1:3 took
a completely different course. In this case, a light yellow
compound could be isolated in high yield (∼70%), which
was shown by X-ray crystallography to be the novel
heterobinuclear potassium/cerium(IV) disiloxanediolate clus-
ter [{(Ph2SiO)2O}2{(DME)KOtBu}{(Ph2SiO2)K}Ce]2 (3, Fig-
ure 1). The X-ray study revealed that, in 3, not only the
expected dianions of 1,1,3,3-tetraphenyl-1,3-disiloxanediol
act as ligands but also the dianions of diphenyl-1,1-silanediol,
which originate from cleavage of the disiloxanediolate. Such
transformations are not uncommon in the chemistry of
silanediolates, disiloxanediolates, and trisiloxanediolates.10
In the unprecedented centrosymmetric cluster molecule 3,
a planar K2O2 ring forms the central structural unit. The
central cerium atoms are in a distorted octahedral coordina-
t
two BuO ligands compound 2 also represents a potentially
useful synthon for other tetravalent cerium species.
Acknowledgment. This work was generously supported
by the Deutsche Forschungsgemeinschaft (SPP 1166 “Lan-
thanoid-spezifische Funktionalita¨ten in Moleku¨l and Mate-
rial”).
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U.; Ruhlandt-Senge, K. Organometallics 1997, 16, 5792. (c) Babu,
R. P. K.; Aparna, K.; McDonald, R.; Cavell, R. G. Organometallics
2001, 20, 1451. (d) Boyle, T. J.; Andrews, N. L.; Rodriguez, M. A.;
Campana, C.; Yiu, T. Inorg. Chem. 2003, 42, 5357. (e) Weinert, C.
S.; Fanwick, P. E.; Rothwell, I. P. Inorg. Chem. 2003, 42, 6089. (f)
Gamer, M. T.; Roesky, P. W. Organometallics 2004, 23, 5540. (g)
Cole, M. L.; Higham, L. T.; Junk, P. C.; Proctor, K. M.; Scott, J. L.;
Strauss, C. R. Inorg. Chim. Acta 2005, 358, 3159. (h) Bieller, S.; Bolte,
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319.
Supporting Information Available: CIF files giving X-ray
structural data for 2 and 3 and experimental details on the
preparation and characterization of 2 and 3. This material is
available free of charge via the Internet at http://pubs.acs.org.
(tBuO)3CeIV(NO3)(THF)2 (1), the novel heterobimetallic compounds
[{(Ph2SiO)2O}2{(DME)KOtBu}{(Ph2SiO2)K}Ce]2 (2) and [{(Ph2-
SiO)2O}{K(THF)2}]2Ce(OtBu)2 (3) have been prepared and struc-
turally characterized by X-ray diffraction.
IC701320D
Inorganic Chemistry, Vol. 46, No. 20, 2007 8101