The first sideways-bonded peroxo complex for a tetraaminecobalt(III) species

Article abstract of DOI:10.1021/ic040044z

Cobalt(II) salts react with H₂O₂ in the presence of 2 equiv of tetramethylethylenediamine (tmen) to produce a stable sideways bonded mononuclear peroxo complex [Co(tmen)₂O₂]ClO₄ which has been characterized chemically and by a single crystal X-ray determination. This is the first such tetraaminecobalt(III) complex, indeed, the first for any tetraaminemetal ion complex. The mononuclear peroxo complex can also be synthesized by O₂^2- anation of cis-[Co(tmen) ₂(OH₂)₂]³⁺. This reaction is reversed in acid, and this offers the potential to develop Co(III) catalyzed oxidation reactions.

Full text of DOI:10.1021/ic040044z

Inorg. Chem. 2004, 43, 7558−7560
The First Sideways-Bonded Peroxo Complex for a Tetraaminecobalt(III)
Species
A. F. M. Mokhlesur Rahman,† W. Gregory Jackson,*,† and Anthony C. Willis‡
School of Physical, EnVironmental and Mathematical Sciences, UniVersity College, The UniVersity
of New South Wales, ADFA, Canberra ACT, Australia 2600, and Research School of Chemistry,
Australian National UniVersity, Canberra ACT, Australia 0200
Received March 24, 2004
Cobalt(II) salts react with H
tetramethylethylenediamine (tmen) to produce a stable sideways
bonded mononuclear peroxo complex [Co(tmen) ]ClO which
has been characterized chemically and by a single crystal X-ray
determination. This is the first such tetraaminecobalt(III) complex,
2
O
2
in the presence of 2 equiv of
bridging dinuclear species is not formed. Rather, with use
-
of the ClO
tmen)
complex was derived (quantitatively) by treating cis-[Co-
4
salt, red-brown crystals of composition [Co-
5
(
O
2 2
4 2
]ClO ‚2H O are produced in good yield. The same
2
O
2
4
3
+
5
(tmen)
2 2
(OH )
2
]
2 2
with H O .
The single crystal X-ray structure (Figure 1) revealed the
indeed, the first for any tetraaminemetal ion complex. The
6
mononuclear sideways bonded peroxo complex. The promi-
nent structural features are the small bite angles for the tmen
five-membered rings, 83.2°, a feature of tmen complexes
which is becoming the norm, the O-O bond length (1.457
Å) which is typical for a sideways bonded peroxide, and
the distortion from octahedral geometry arising from the
mononuclear peroxo complex can also be synthesized by O 2
-
2
2 2 2
anation of cis-[Co(tmen) (OH )
]3+. This reaction is reversed in acid,
and this offers the potential to develop Co(III) catalyzed oxidation
reactions.
2
triangular CoO moiety with a small bite angle of 45.7°. The
Air is usually a good enough oxidant to raise cobalt(II)
salts, in the presence of amines under neutral to slightly basic
conditions, up to the cobalt(III) state. The immediate
product is commonly the characteristic brown, bridging
geometry of the complex could also be described as distorted
trigonal bypyramidal, if the center of the chelating peroxo
ligand is regarded as a monodentate entity (trigonal plane
bond angles 131°, 131°, and 98°). The complex nonetheless
has the spectroscopic properties of a diamagnetic, octahedral
cobalt(III) complex. Despite having two tmen ligands in cis
1,2
peroxo complex containing the entity [(amine)
5
Co(III)-
2-
4+
2-
O
2
-Co(III)(amine)
5
]
or [X(amine)
4
Co(III)-O
2
-Co-
m+
-
(
III)(amine)
with CoCl
intermediate brown [Cl(en)
decomposed by HCl to yield the well-known trans-[Co-
en) Cl ]Cl complex and H
Pure O and H are sometimes used as oxidants when
the (amine) Co(III)/Co(II) potential is too high, or Co(III)
starting materials such as Na [Co(OCO ] or trans-[Co-
]Cl are employed to make Co(III) complexes.
Co(tmen) Cl ]Cl is prepared by the latter routes, because
does not oxidize Co(II) plus tmen. However, H
react with Co(II)/tmen, but curiously, the usual peroxo
4
X] (X ) Cl or OH
2
). Such a reaction occurs
positions, there is none of the strain apparent in the tris
2
and ethylenediamine, for example, and the
3+
complex, [Co(tmen) ] , manifested in elongated C(tert)-
3
2
CoO Co(en) Cl]Cl complex is
2
2
2
4
C(tert) and Co-N bonds, and pronounced trigonal twisting.
Ancilliary ligands such as phosphines or arsines were
(
2
2
2 2
O .
2-
required for Co(III) to bind O
2
as a three-membered ring
2
2 2
O
(
5) The diaqua complexes cis-[Co(tmen)2(OH2)2]NO3(ClO4)2 and cis-[Co-
n
(tmen)2(OH2)2](ClO4)3 were prepared as described elsewhere (ref 3).
3
2 3
)
Addition of a fifth volume of 32% H2O2 (excess) to a saturated aqueous
solution of the diaqua complex followed by a fifth volume of 5 M
NaClO4 yielded pink crystals of [Co(tmen)2O2]ClO4‚2H2O essentially
quantitatively. The same complex was obtained by addition of H2O2
(excess) to a solution of Co(ClO ) ‚6H O in water containing tmen‚
1
,2
4 2
(py) Cl
[
O
2
2
3,4
2
2 2
O does
4
2
2
2HNO3 (2 equiv) and NaOH (2 equiv). The crystals were recrystallized
twice from water by careful addition of 5 M NaClO4. Yield: 65%.
Anal. Calcd for CoC12H36N4ClO8: C, 31.4; H, 7.9; N, 12.2; Cl, 7.7.
Found: C, 31.4; H, 8.0; N, 12.2; Cl, 7.8%.
*
To whom correspondence should be addressed. E-mail: g.jackson@
adfa.edu.au.
(6) Crystal data: [Co(tmen)2O2]ClO4‚2H2O, M ) 458.82, monoclinic,
†
3
The University of New South Wales.
space group C2/c, dark red block crystal (0.30 × 0.20 × 0.12 mm ),
‡
Australian National University. E-mail: willis@rsc.anu.edu.au.
1) Shibata, M. In Topics in Current Chemistry; Springer-Verlag: Berlin,
983; Vol. 110, p 1.
a ) 11.108(3) Å, b ) 18.6362(6) Å, c ) 10.4397(2) Å, â ) 105.488-
3
-3
(
(
(2)°, V ) 2082.69(10) Å , Z ) 4, Dc ) 1.463 Mg m , µ ) 0.996
-1
1
mm , 295 K, 18449 reflections measured, 2397 independent, Nonius
KappaCCD diffractometer, Mo KR (λ ) 0.71070 Å), ω-2θ scans,
θmax 27.59°. The structure was solved by heavy-atom methods and
refined by full-matrix least-squares procedures based on F. Non-H
atoms were refined with anisotropic displacement parameters. H atoms
were refined positionally. Refinement with 173 parameters converged
at R ) 0.035, Rw ) 0.041 for 1888 reflections with I > 3σ(I)
2) Buckingham, D. A.; Clark, C. R. In Middle Transition Elements;
Gillard, R. D., McCleverty, J. A., Eds.; Pergamon: New York, 1987;
Vol. 4; p 635.
(3) Jackson, W. G.; Rahman, A. F. M. M.; Wong, M. A. Inorg. Chim.
Acta 2004, 357, 665.
(4) Hendry, P.; Ludi, A. HelV. Chim. Acta 1988, 71, 1966.
7558 Inorganic Chemistry, Vol. 43, No. 24, 2004
10.1021/ic040044z CCC: $27.50
© 2004 American Chemical Society
Published on Web 10/27/2004

COMMUNICATION
+
s to yield the cis-[Co(tmen)
2 2
(OH )
2
]3 complex, as shown
1
13
by H and C NMR spectroscopy and using an authentic
sample of the independently synthesized and known cis-
3
diaqua complex in deuterated media. On a larger scale, the
-
liberated H
titrated against S
. Also, as demonstrated by NMR studies, reaction of
the diaqua complex with excess H yielded >90% peroxo
2
O
2
was treated with excess I and the resultant
2-
I
2
O
2 3
to confirm 0.985 equiv of generated
2 2
H O
2 2
O
complex, together with a little protonated free ligand,
3
established by adding an authentic specimen to the NMR
tube. The acid catalyzed release of H
and a green complex can be rapidly crystallized by adding
cold 70% HClO to a saturated aqueous solution of the
2 2
O is not instantaneous,
4
peroxo species. This species proved insufficiently stable to
characterize. It reverted to the starting material on washing
with alcohol and ether, and presumably, it was a protonated
peroxo species. We have been unable to obtain crystals
suitable for X-ray structural analysis to ascertain the detailed
structure.
Figure 1. ORTEP diagram of [Co(tmen)2O2]+ showing 30% thermal
ellipsoids. Asterisks indicate atoms generated by crystallographic 2-fold
symmetry. The ∆ enantiomer is arbitrarily depicted. Principal bond lengths
2
The peroxo complex reacts readily with SO to afford a
sulfato species. Normally, a chelated sulfato species would
(
Å) and angles (deg) are the following: O1-O1* 1.457(3), Co1-O1 1.875-
2), Co1-N1 1.988(2), Co1-N2 1.956(2), C1-C2 1.551(3), O1-Co1-
(
result, but the isolated material appears to be trans-[Co-
O1* 45.70(8), N2-Co1-N1 83.22(8), N1-Co1-N1* 97.4(1).
1
3
(tmen)
2
(OH
2
)(OSO
3
)]ClO
4
.
This is a reaction typical of
9
chelate.7,8 A number of such complexes are known for a
range of transition metal ions, but none previously involving
side-on peroxo complexes and attests to the structural
characterization.
9
III
a saturated ligand backbone such as a set of amines. Johnson
The vis-UV spectrum is typical for a Co N
4
O
2
-1
chro-
10
-1
and Geldard have described the synthesis and characteriza-
tion (but no X-ray structure) of a mononuclear tetra-N-donor
peroxocobalt(III) complex which spectroscopically seems to
be an authentic side-on peroxo ion and which comes closest
to ours, but the donors are unsaturated imines. Sideways
bonded dioxygen is also known for the cobalt complexes of
mophore (ꢀmax(527 nm) 107, (ꢀmax(422 nm) 136 M cm ;
3
CH CN), despite the distortion from octahedral geometry
evident from the crystal structure (Figure 1). Also, strong
charge transfer absorptions are observed at 244 and 197 nm
(H O), while a sharp O-O stretch is observed in the IR (KBr
2
-
1
13
disk) at 861 cm . For Me SO-d as solvent, the C NMR
2
6
R
the facially capping tridentate N-donor ligands Tp (monoan-
spectrum shows the expected two C(tert) (δ 62.1, 59.1 ppm)
ionic substituted tris(pyrazoyl)hydridoborate), which have
imine donors.
and four CH resonances (δ 23.0, 23.8, 25.4, 26.3 ppm)
3
characteristic of the C symmetry for the cis-CoN X species,
2
4
2
1
The complex has the stoichiometry Co(TpR)O
2
(un-
while the H NMR spectrum shows four NH doublets (5.41,
3.72, 3.25, 1.16 ppm) and four methyl singlets (1.33, 1.28,
0.97, 0.81 ppm). The NH resonances are unusually sharp
compared to corresponding NH signals of unsubstituted
ethylenediamine species, no doubt due to the absence of
charged); i.e., it is either a Co(III) peroxo or a Co(II)
superoxo species The dioxygen is side-on rather than the
7
n+
usual bent structure for a d M complex, and there are a
number of other unusual aspects of the chemistry of these
complexes attributable to the special properties of these
14
CH-NH coupling, and minimal quadrupolar N broadening.
The geminal NH coupling (JHH ca. 5 Hz) has now become
clear. One of the four NH doublets, likely to be one of the
two axial NH protons, is at very high field (δ 1.16 ppm),
indicating unusual shielding by virtue of its proximity over
1
1
ligands. The complex is paramagnetic, and while the Co-
II)-superoxide description seems more appropriate, alterna-
tive views of the bonding and oxidation state descriptions
(
12
have been presented more recently.
the center of the π system comprising the triangular CoO
moiety (Figure 2).
2
The crystalline peroxo complex is stable indefinitely under
ambient conditions, and despite the normal lability of tmen-
3
Co(III) complexes, the species remains intact in solution.
(
13) The pink-brown peroxo complex becomes purple on trituration as a
4
However, it reacts completely with excess HClO within 30
thin paste in SO2(aq) (6% w/v). It was recrystallized from water/
1
NaClO4. The tmen complexes are unusually labile, and the H and
13
(
7) Bosnich, B.; Jackson, W. G.; Lo, S. T. D.; McLaren, J. W. Inorg.
C NMR spectra were indicative of a species having the symmetry
Chem. 1974, 13, 2605.
of the trans-[Co(tmen)2(OS(CD3)2)(OSO3)]ClO4 complex in solution.
In Me2SO-d6, this product slowly reverts to a purple complex having
cis-[Co(tmen)2X2] symmetry, likely containing chelated sulfate. Both
(
(
8) Bosnich, B.; Boucher, H.; Marshall, C. Inorg. Chem. 1976, 15, 634.
9) Gubelmann, M. H.; Williams, A. F. In Structure and Bonding;
Springer-Verlag: Berlin, 1983; Vol. 55, p 1.
2-
2+
species tested positive for SO4 (Ba ). Trans complex data follow.
1
13
(
(
10) Johnson, W. L. I.; Geldard, J. F. Inorg. Chem. 1978, 17, 1675.
11) Hikichi, S.; Akita, M.; Moro-oka, Y. Coord. Chem. ReV. 2000, 198,
H NMR (Me2SO-d6): δ 5.19 d, 3.78 d, NH, 1.20, 1.10 s, CH3.
C
NMR (Me2SO-d6): δ 24.4, 24.0 (CH3), 61.2 (tert C). Chelatedata
1
61.
follow. H NMR: δ 6.43 d, 5.27 d, 4.49 d, 4.01 d, NH.; 1.30 s, 1.20
(
12) Cramer, C. J.; Tolman, W. B.; Theopold, K. H.; Rheingold, A. L.
s, 1.10 s, 1.08 s, CH3. 13C NMR (Me2SO-d6): δ 26.1, 26.0, 23.7,
Proc. Natl. Acad. Sci. 2003, 100, 3635.
23.3 (CH3), 65.7, 61.2 (tert C).
Inorganic Chemistry, Vol. 43, No. 24, 2004 7559

COMMUNICATION
5 2
O
H]3 for example,14
-
an effective oxidant, as has [Co(CN)
the system could well be constructed to be catalytic. The
7
,8
same may prove true for their arsine analogues for which
peroxide addition is also reversible. A particular advantage
of the Co-tmen system is that the complexes are unusually
labile (engendered by the tmen ligand), and that these amine
ancillary ligands are not readily oxidized while the arsine
(and phosphine) analogues are. Mirza et al. have detailed
the conditions necessary for effective catalysis in these metal
1
4
ion/H
O
2 2
systems, and on the basis of these criteria, there
+
is clear potential for the present cis-[Co(tmen)
2 2
O ] ion.
Acknowledgment. This research was supported by an
Australian Research Council grant.
Figure 2. Proton NMR spectrum for [Co(tmen)2O2]ClO4‚2H2O in Me2-
SO-d6. The central spike arises from lattice water.
Supporting Information Available: Crystallographic data
in CIF format. This material is available free of charge via the
Internet at http://pubs.acs.org. This material also available from the
Cambridge Crystallographic Data Centre, CCDC 217508. [Copies
of this information may be obtained free of charge from The
Director, CCDC, 12 Union Road, Cambridge, CB2 1EZ, U.K.
The synthesis for the peroxocobalt(III) complex by two
independent methods is novel, and the stoichiometry for these
reactions appears to be
2
+
+
+
(Fax: +44-1223-336033. E-mail: deposit@ccdc.cam.ac.uk or
2
Co(II) + 3H O f 2Co(III)-O + 2H O + 2H
2 2 2 2
www: http//www.ccdc.cam.ac.uk.)]
3
+
+
2
+
Co(III)-OH2 + H O f Co(III)-O + H O + 2H
IC040044Z
2
2
2
The second reaction is reversible and clearly controlled
by pH. If the Co(III) peroxo complex can be shown to be
(
14) Mirza, S. A.; Bocquet, B.; Robyr, C.; Thomi, S.; Williams, A. F. Inorg.
Chem. 1996, 35, 1332.
7560 Inorganic Chemistry, Vol. 43, No. 24, 2004