Competition between 3d metals(II) and palladium(II) in the reaction of heterobimetallic complexes Pd(μ-OOCMe)4M(OH2) (M = Ni, Co, Mn) with azobenzene

Article abstract of DOI:10.1016/j.inoche.2009.03.012

The reaction of Pd^II(μ-OOCMe)₄M^II(OH₂) (M = Ni, Co, Mn) with azobenzene under mild conditions produces the homonuclear complex with ortho-metallated azobenzene (PhN = NC₆H₄)₂Pd

Full text of DOI:10.1016/j.inoche.2009.03.012

Inorganic Chemistry Communications 12 (2009) 454–456
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Inorganic Chemistry Communications
journal homepage: www.elsevier.com/locate/inoche
Competition between 3d metals(II) and palladium(II) in the reaction of
heterobimetallic complexes Pd(
with azobenzene
l-OOCMe) M(OH ) (M = Ni, Co, Mn)
4
2
Sergei E. Nefedov, Elena V. Perova, Ilya A. Yakushev, Natalia Yu. Kozitsyna,
*
Michael N. Vargaftik , Ilya I. Moiseev
N.S. Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences, Leninsky prospect 31, 119991 Moscow, Russian Federation
a r t i c l e i n f o
a b s t r a c t
The reaction of PdII(
l-OOCMe) M (OH ) (M = Ni, Co, Mn) with azobenzene under mild conditions pro-
II
Article history:
4 2
Received 28 January 2009
Accepted 22 March 2009
Available online 31 March 2009
6 4 2 2 2
duces the homonuclear complex with ortho-metallated azobenzene (PhN = NC H ) Pd (l-OOCMe) (4)
in higher than 90 % yield as the sole Pd-containing reaction product, while the co-metals are recovered
as the corresponding M acetates.
II
Ó 2009 Elsevier B.V. All rights reserved.
Keywords:
Heterobimetallic paddlewheel complexes
Palladium
Azobenzene
Ortho-metallation
X-ray structure
Recently we synthesized and structurally characterised a series
of Pd -based heterodimetallic tetraacetate-bridged paddlewheel
complexes with divalent 3d-metals [1,2].
temperature treatments. To develop the preparation procedures
of these materials, we studied the chemical behaviour of the start-
ing heterodimetallic complexes during low-temperature treat-
ments in solutions and solid phases, in particular, the
comparative reactivities of the metal partners towards N- and O-
bases.
II
R
R
C
O
Generally, palladium(II) is a better complexation agent for N-
O
C
II
II
II
O
O
O
bases than such 3d-metals as Ni , Co and Mn . However, the tetra-
acetate bridging system is rather strong (providing a very short,
II
II
II
II
II
Pd
O
M
L
(
M = Co , Ni , Mn , Zn , Cu ;
II
O
t
ꢀ2.5 Å, Pd–M distance and difficult accessibility of Pd atom),
C
R
2
L = OH , NCMe; R = Me, Bu ).
O
whereas the axial position of the co-metal coordination sphere is
rather labile and easy accessible to a nucleophilic attack. Earlier,
C
R
0
we found that such N-donors as 1,10-phenanthroline and 2,2 -
bipyridine attach to a co-metal rather than to palladium atom,
keeping almost intact the acetate bridging system [5], whereas pyr-
idine partially decomposes the heterometallic complex to form the
The heterodimetallic complexes are prospective starting com-
pounds for the preparation of mixed-metal materials such as
nanoalloys [3] and catalysts [4] without resorting to severe high-
4 2
pentanuclear bis-paddlewheel compound [Pd(l-OOCMe) Co] (l-
OOCMe) Pd(py) [6].
2
2
II
Here we report on the reaction of the complexes Pd (
l
-OOC-
II
Me)
found that trans-Ph
duce the homonuclear red-brown complex (PhN = NC
OOCMe) (4) in chloroform at ambient temperature as the sole
Pd-containing reaction product [7]:
4
M (OH
2
) (M = Ni (1), Co (2), Mn (3)) with azobenzene. We
readily reacts with complexes 1–3 to pro-
Pd
2 2
N
6
H
4
)
2
2
(l-
*
Corresponding author. Tel.: +7 495 9554865; fax: +7 495 9541279.
2
E-mail address: wahr36@gmail.com (M.N. Vargaftik).
1
387-7003/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2009.03.012

S.E. Nefedov et al. / Inorganic Chemistry Communications 12 (2009) 454–456
455
these conditions even after 12 h. Generally, the efficiency of
H3C
C
CH3
II
ortho-palladation depends on the solvent and Pd complex
CH3
C
O
Ph
N
2ꢂ
O
C
(PdCl4 , PdCl
2 3
/NaOOCCH , etc.), normally producing the ortho-met-
O
O
O
O
O
O
PhN=NPh
allated azobenzene or relative N-aryl in 50–60% yield upon rather
long staying or heating [10a–c]. The highest yield (91%) was
N
Pd
M
OH2
Pd
Pd
CHCl3, rt, 4 h
yield >90%
N
O
O
C
O
N
achieved in the reaction of Pd
3
(OOCCH
3
)
6
with azobenzene for 6 h
O
CH3
C
at 50 °C in acetic acid [10d].
C
Ph
CH3
II
Our results demonstrate a benefit of the Pd -based heterome-
tallic vs. homometallic complexes in ortho-metallation reactions.
The nature of this effect is still unclear. Our preliminary kinetic
study [14] suggested a complicated reaction mechanism of the for-
mation of heterometallic complexes 1–3.
1
- 3 CH3
4
CH3
CH3
H3C
C
O
C
C
O
O
O
O
O
PhN=NPh
yield <5%
Pd
Pd
Pd
CHCl3, rt, 12 h
O
O
O
C
Acknowledgements
O
O
O
C
C
H3C
CH3
CH3
We thank for financial support the Russian Foundation for Basic
Research (Projects Nos. 08-03-01063, 08-03-90455, 08-03-01150
and 09-03-00514), the Foundation of President of the Russian Fed-
eration (program for support of leading Russian scientific schools
NSh-1733.2008.3) and the Foundation of the Russian Academy of
Sciences (programs for Basic Research ‘‘Purposeful synthesis of
inorganic substances and creation of related functional materials”
and ‘‘Theoretical and experimental investigation of the nature of
chemical bonding and mechanisms of important reactions and
processes”).
The co-metals form no N-containing reaction products but the cor-
responding acetate complexes.
The X-ray diffraction [8] showed that the ortho-metallated azo-
benzene molecules in complex 4 are attached to two Pd atoms
II
0
(
Pdꢁ ꢁ ꢁPd 2.9032(3) ÅA ) that are linked by a couple of acetate bridges.
II
The Pd atoms have a typical square-plane environment of the ace-
tate O atoms as well as the N and C atoms of the ortho-palladated
azobenzene ligand (Fig. 1).
Appendix A. Supplementary material
In conclusion, two points are worthy of notice. First, in the metal
pairs comprising complexes 1–3, palladium confidently wins the
competition with co-metals for azobenzene, while the 3d-metals
turned to be inactive in ortho-metallation and transform into the
corresponding M acetates. This fact seems to be not unexpected,
although nickel(II) is known as the historically first metallating
agent for azobenzene [9]. Another point is that heterometallic com-
CCDC 718271 contains the supplementary crystallographic data
for 4. These data can be obtained free of charge from The Cam-
bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/da-
ta_request/cif. Supplementary data associated with this article
can be found, in the online version, at doi:10.1016/
j.inoche.2009.03.012.
II
plexes 1–3 react with Ph
2 2
N much easier than homometallic
Pd (OOCCH , while the latter gives only traces (<5 %) of 4 under
3
3 6
)
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1346m, 1308m, 1261m, 1243m, 1168w, 1159w, 1019m, 918m, 860m, 840m,
762s, 759s, 708s, 689vs, 622s, 594s, 550m, 433w.

4
56
S.E. Nefedov et al. / Inorganic Chemistry Communications 12 (2009) 454–456
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[
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> 2
r(I),
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= 1.367 cm
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[
(