Inorganica Chimica Acta 324 (2001) 131 – 140
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Copper(I) tris(pyrazolyl)methane complexes and their reactivity
towards dioxygen
Milivoje Cvetkovic, Stuart R. Batten, Boujemaa Moubaraki, Keith S. Murray *,
Leone Spiccia
School of Chemistry, PO Box 23, Monash Uniersity, Victoria 3800, Australia
Received 5 June 2001; accepted 28 June 2001
Abstract
The reactivity towards dioxygen has been explored for two copper(I) tris(pyrazolyl)-methane complexes, [Cu
I
((3,5-Me
2
-
pz)
3
CH)(MeCN)](PF
6
)
2
(1) and [Cu
I
((3,5-Me
2
-4-Br-pz)
3
)(MeCN)](PF
6
)
2
(2). Reversible oxygenation of 1 occurs in CH
2
Cl
2
solution at 7 °C to yield a 2:1 -
2
2
-peroxo complex [((3,5-Me
2
-pz)
3
CH)
2
Cu
2
(-O
2
)](PF
6
)
2
. Equilibrium studies, made using
manometric techniques over the temperature range 258 – 278 K and at two equilibration times, 2 and 30 min, yielded best-fit
thermodynamic constants of K
21
=32 M
-2
(at 298 K), H° =-110 5 K J mol
-1
, S ° =-340 18 J K
-1
mol
-1
(30 min)
which have been compared to values for other CuO
2
adducts. Thermal decomposition of this -peroxo species yields crystals of
a di--hydroxo complex [((3,5-Me
2
-pz)
3
CH)
2
Cu
2
(-OH)
2
](PF
6
)
2
(3), whose crystal structure and magnetism (J =-298 cm
-1
) are
described. Complex 3 can also be made by reaction of 1 with iodosylbenzene. Complex 2 does not form a dioxygen adduct but
slowly oxidizes in CH
2
Cl
2
to form [Cu
II
((3,5-Me
2
-4-Br-pz)
3
CH)
2
](PF
6
)
2
·2CH
2
Cl
2
(4), the crystal structure of which is described.
Complex 4 was also formed by the reaction of 2 with iodosylbenzene. © 2001 Elsevier Science B.V. All rights reserved.
Keywords: Copper(I); Tris(pyrazolyl)methane; -
2
2
-Peroxo; Crystal structures; Oxygen binding; Magnetism; di--Hydroxo copper(II)
1. Introduction
Studies of dioxygen reactivity in copper(I) complexes
of tris-3,5-substituted-pyrazolyl-hydridoborate ligands,
[Cu(HB(R
2
pz)
3
)(MeCN)], and of related facially coordi-
nating ligands such as N -substituted triazacyclonanes,
[Cu(1,4,7-R
3
-tacn)(MeCN)]
+
, have led to the isolation
of crystalline dioxygen adducts of type [LCu
II
(-
O
2
)Cu
II
L]
n +
. The interconversion of the latter -
2
2
-
peroxo species to form the di--oxo copper(III) analogs
has been examined. The groups of Kitajima [1], Karlin
[2] and Tolman [3] have made major advances in the
synthesis and reactivity aspects of such compounds,
while Solomon et al. [4] have elucidated the spec-
troscopy and electronic structure in great detail. A
number of chemical and structural factors have been
shown to influence the reactivity of the copper(I)
chelate with dioxygen. Such factors include the charge
on the ligand, the size and electronic properties of
substituents on the ligand at both the N-donor and/or
ring positions, the redox potential of the Cu(I) complex
and the solvent, temperature and counteranion used.
Structural subtleties such as variation of the macro-
cyclic ring size in triazacyclodecane and triazacyclodo-
decane copper(I) chelates, in comparison to the
triazacyclononane species, have recently been shown to
influence the relative amounts of -
2
:
2
-peroxo and
bis(-oxo) products obtained upon reaction with O
2
[5].
All these studies on model systems have provided valu-
able data for comparison to related data on copper
oxygenase and oxidase enzymes [6,7].
In the present paper, we report the synthesis and
dioxygen reactivity of two copper(I) chelates of the
little studied tris(3,5-substituted pyrazolyl)methane
tripodal ligands, the neutral analogs of the anionic
tris(3,5-substituted pyrazolyl)hydridoborate(1-) ligands,
much studied by Kitajima et al. [1]. We make compari-
sons with this hydridoborate work and with studies
* Corresponding author. Tel.: +61-39-905-4512; fax: +61-39-905-
4597.
E-mail address: k.s.murray@sci.monash.edu.au (K.S. Murray).
0020-1693/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
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