Preparation and X-ray structure of a (catecholato)copper(II) complex with a Sch?nberg adduct

Article abstract of DOI:10.1016/j.inoche.2005.12.015

The reaction of metallic copper, triphenylphosphine and 1,2-naphthoquinone leads to the copper(II) catecholate complex bis(4-triphenylphosphoniono) (naphthalene-1,2-dioxolato)copper(II), the first molecular structure of a Sch?nberg adduct coordinated to a metal ion.

Full text of DOI:10.1016/j.inoche.2005.12.015

Inorganic Chemistry Communications 9 (2006) 367–370
www.elsevier.com/locate/inoche
Preparation and X-ray structure of a (catecholato)copper(II)
complex with a Schonberg adduct
¨
a
a,b,
c
c
d
*
´
´
´
, Michel Giorgi , Marius Reglier , Takuzo Funabiki ,
Beata Tapodi , Gabor Speier
e
e
´
´
Laszlo Korecz , Antal Rockenbauer
a
Department of Organic Chemistry, University of Veszpre´m, Wartha V. u. 1, 8201 Veszpre´m, Hungary
b
Research Group for Petrochemistry, Hungarian Academy of Sciences, 8201 Veszpre´m, Hungary
c
ˆ
Laboratoire de Cristallochimie et Laboratoire de Bioinorganique Structurale, Universite´ Paul Ce´zanne Aix-Marseille III, F. S. T. Saint-Je´rome, Service
432, Avenue Escadrille Normandie-Niemen, 13397 Marseille Cedex 20, France
d
Biomimetics Research Center, Dishisha University, Kyo-Tanabe, Kyoto 610-0321, Japan
Chemical Research Center, Institute of Chemistry, Hungarian Academy of Sciences, 1525 Budapest, Hungary
e
Received 6 December 2005; accepted 31 December 2005
Available online 28 February 2006
Abstract
The reaction of metallic copper, triphenylphosphine and 1,2-naphthoquinone leads to the copper(II) catecholate complex bis(4-triphe-
nylphosphoniono)(naphthalene-1,2-dioxolato)copper(II), the first molecular structure of a Scho¨nberg adduct coordinated to a metal ion.
Ó 2006 Elsevier B.V. All rights reserved.
Keywords: Copper; Catecholate; Scho¨nberg adduct
The chemistry of metal catecholate, semiquinone, and
quinone complexes is in the focus of recent research [1,2].
The reason for that is that they have non-innocent ligands
with orbital energy levels close to those of the orbitals of
the central metal ions [3,4]. This gives rise to electron delo-
calization over the whole metal complex, and the phenom-
ena are called as valence tautomerism [5,6] or electromery
[7] (Scheme 1). Due to valence isomerism the chemical
character of the coordinated catecholate ligand is changed,
the catecholate is transformed to a semiquinone and the
metal oxidation state is lowered due to electron transfer
from the ligand to the metal ion. This makes them eligible
to react with dioxygen resulting in quinone or ring-clea-
vaged products as found by catechol oxidase [8,9] or cate-
chol dioxygenase [10] enzymes and their chemical models
(Scheme 1).
Early papers report on the reaction of quinones with
phosphines, where the phosphines attack the quinones in
a nucleophilic manner. The product was first evidenced,
after some uncertainties, as (trialkylphosphoniono)cate-
chols and called as the ‘‘Scho¨nberg adduct’’ (1,2) (Scheme
2) [11–17].
The proof for the structure of the Scho¨nberg adduct 1
has been given only by IR spectroscopy through its proton-
ated form 3, which was independently synthetized through
ether splitting of 4, showing identical absorptions in its IR
spectrum (Scheme 3) [15]. Now we report here the prepara-
tion and X-ray structure of the copper(II) complex ligated
by the Scho¨nberg adduct formed from 1,2-naphthoquinone
and triphenylphosphine.
In our previous studies we have shown that copper sem-
iquinone and catecholate complexes can be prepared easily
from copper metal, an o-quinone and ligands of various
kind [18]. During these reactions one electron is transferred
from the copper to the o-quinone forming copper(I) semi-
quinone complexes (with ligands preferring the Cu(I) oxi-
dation state e.g. phosphines) [19,20] and then another
*
Corresponding author. Tel.: +36 88 624 657; fax:+36 88 624 469.
E-mail address: speier@almos.vein.hu (G. Speier).
1387-7003/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2005.12.015

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B. Tapodi et al. / Inorganic Chemistry Communications 9 (2006) 367–370
Scheme 1.
Scheme 2.
Fig. 1. The room temperature EPR spectra of 5 in MeCN and 7 in the
solid state.
2.0050, aCu = 9.25, aP(2) = 1.42. aH(5) = 1.32 G. From the
reaction mixture, on standing at room temperature, dark
crystals of 7 separated which were suitable for single crystal
X-ray structure determination and spectroscopic investiga-
tions. To our surprise the EPR spectrum of the solid sam-
ple showed a characteristic feature of copper(II) with the
parameters gzz = 2.264, gxx = 2.052, Azz = 175, Axx = 28,
and AP(2) = 13 G. (Fig. 1b). No absorptions indicative of
the presence of the semiquinone ligand could be seen.
The complex is paramagnetic at room temperature with
lB = 2.00 characteristic for Cu(II). The UV–vis spectrum
in CH2Cl2 exhibited bands at 408 (4.2), 263 (4.5) and
230.5 nm (loge 4.6). In the IR spectrum, characteristic
Scheme 3.
electron may be transferred to give copper(II) catecholate
complexes (with N-ligands preferring the Cu(II) oxidation
state) [21]. Following this line we extended the scope of this
reaction to 1,2-naphthoquinone.
The color of 1,2-naphthoquinone in its reaction with
copper powder and triphenylphosphine in acetonitrile
changed very soon to dark and the amount of the copper
powder diminished [22]. The EPR spectrum of the reaction
mixture showed the presence of CuI(PPh3)2(1,2NSQ)
(1,2NSQ = 1,2-naphthosemiquinone) (Fig. 1a) with g =
˚
Fig. 2. The molecular structure of 7. Selected bond distances (A) and angles (°): Cu(1)–O(1) 1.9165(4); Cu(1)–O(2) 1.9303(3); O(1)–C(3) 1.3386(6); O(2)–
C(4) 1.3099(6); C(3)–C(4) 1.4048(7); P(1)–C(1) 1.7615(5); O(1)–Cu–O(2) 93.683(15), O(1)–Cu–O(2) 86.32(2), O(1)–Cu–O(1) 93.683(14).

B. Tapodi et al. / Inorganic Chemistry Communications 9 (2006) 367–370
369
up as an interesting catalyst for various reactions and also
a model compound for biomimetic reactions.
Acknowledgements
We thank the Hungarian Research Fund (OTKA) T
´
43414 and Celker Lmtd., for financial support.
Appendix A. Supplementary material
CCD No. 179473 contains supplementary crystallo-
graphic data for this paper. These can be obtained free of
charge at www.ccdc.cam.ac.uk/const/retriving.html or
from the Cambridge Crystallographic Data Centre, 12,
Union Road, Cambridge, CH21EZ, UK (Fax: 44 1223/
336 033; E-mail: deposit@ccdc.cam.ac.uk). Supplementary
data associated with this article can be found, in the online
version, at doi:10.1016/j.inoche.2005.12.015.
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Scheme 4.
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bands at 1540 and 1490 cmÀ1 could be assigned to mCO of
the catecholate ligand coordinated to copper(II) together
with bands (1810, 1253, 1200, 1156, 1090, 960, and
713 cmÀ1) characteristic for the ligand PPh3.
´
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[6] G. Speier, Z. Tyeklar, P. Toth, E. Speier, S. Tisza, A. Rockenbauer,
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The X-ray structure of 7 is shown in Fig. 2 with selected
bond distances and angles [23]. The Cu–O distances
˚
[(1.9165(4) and 1.9303(3) A] and the C–O distances
[7] J. March, Advanced Organic Chemistry, fourth ed., Wiley–Inter-
science, New York, 1992, p. 1134.
˚
[1.3386(6) and 1.3099(6) A] in complex 7 are in agreement
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[18] G. Speier, New. J. Chem. 18 (1994) 143.
with the Cu(II) catecholate formulation [2]. The electro-
chemistry of compound 7 in DMF shows Ered peaks at
À976, 0 and 700 and Eox peaks at À544, 258 and 882 mV
(against Fc/Fc+). The latter may be assigned to the
Cu(II)/Cu(III) oxidation while the other peaks originate
from the redox reactions of the catecholate ligand.
The chemistry of the formation of 7 can be interpreted
as shown in Scheme 4. There are parallel reactions, the
one is the electron transfer from the copper metal to the
quinone resulting in the copper(I) semiquinone complex 5
with two triphenylphosphine. Complexes of this type have
already been prepared in good yield and structurally char-
acterized with 9,10-phenanthrenequinone [18]. The other
reaction route involves first the formation of the Scho¨nberg
adduct 6 by reacting the quinone with triphenylphosphine.
This reacts then further with the copper metal to form the
bis(catecholato)copper complex 7 and possibly dihydrogen
(Scheme 4). The copper complex with the Scno¨nberg
adduct can also be prepared in good yield (ꢀ80%) by the
´
´
´
[19] G. Speier, Z. Tyeklar, L. Szabo II, P. Toth, C.G. Pierpont, D.N.
Hendrickson, in: D.R.H. Barton, A.E. Martell, D.T. Sawyer (Eds.),
The Activation of Dioxygen and Homogeneous Catalytic Oxidation,
Plenum Press, New York, 1993, pp. 423–436.
´
[20] A. Rockenbauer, M. Gyo¨r, G. Speier, Z. Tyeklar, Inorg. Chem. 26
(1987) 3293.
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Dalton Trans. (1992) 837.
reaction of the isolated Scho¨nberg adduct
Cu(OMe)2 in acetonitrile.
6 with
[22] 1,2-Naphthoquinone (1.582 g, 10 mmol), copper powder (0.7 g,
11 mmol), and triphenylphosphine (5.24 g, 20 mmol) were stirred in
acetonitrile (90 mmol) under argon for 4 h and then refluxed for 1 h.
The deposited material was filtered off, dried in vacuum to give a dark
brown solid. It was taken up in dichloromethane (140 ml), the
unreacted copper powder was removed by filtration, and the filtrate
To our knowledge this is the first X-ray structure of a
Scho¨nberg adduct coordinated to a metal ion, and also
of a complex with cationic catecholate ligand, which may
have good solubility properties and probably will show

370
B. Tapodi et al. / Inorganic Chemistry Communications 9 (2006) 367–370
˚
was evaporated to ca. 20 ml. Ether (50 ml) was then added, a brown
precipitate came out which was filtered, washed with ether and dried
in vacuum to give 7 (3.2 g, 43%). m.p.: 174 °C (dec), calcd. for
cell dimensions: a = 9.1970(5), b = 13.8712(8), c = 19.5118(6) A,
3
˚
b = 98.114(3)°, volume: V = 2464.3(2) A , Z = 2, density (calculated):
1.39 g cmÀ3, l(Mo Ka) = 0.98 cmÀ1, 4639 reflections measured, 304
parameters refined on F using 3635 unique reflections to final indices
R[F > 3rF] = 0.054, wR = 0.079 [w = 1/r2(F) + 0.03F2]. The final
residual Fourier positive and negative peaks were equal to 0.52 and
À0.53, respectively.
C
56H40CuO4P2 (902.41): C, 74.53; H, 4.47; Cu, 7.04. Found C, 74.06;
H, 4.63; Cu, 7.04.
[23] Empirical formula: C28H24CuO4P, formula weight: =519.016, tem-
perature: 298 K, crystal system: monoclinic, space group P21/c, unit