Slow atmospheric oxidation of diphenylzinc: Di-μ-phenoxido-bis[(diethyl ether)phenylzinc(II)]

Article abstract of DOI:10.1107/S0108270107057514

The title compound, [Zn₂(C₆H₅) ₂(C₆H₅O)₂(C₄H ₁₀O)₂], was isolated from a solution of diphenylzinc in diethyl ether that had been exposed to air. The molecules are dinuclear, with a distorted tetrahedral coordination geometry around the Zn atoms and with molecules situated about a crystallographic inversion centre. Molecules associate via three sets of C-H...π (arene) interactions, leading to a network structure.

Full text of DOI:10.1107/S0108270107057514

metal-organic compounds
Acta Crystallographica Section C
Crystal Structure
Communications
November 2006; Allen 2002). Only 11 structures were found
containing a Zn±OEt2 fragment. Among these, two examples
of organozinc complexes, bis[(ꢁ2-chloro)(1,1-dichloro-2,2,2-
tri¯uoromethyl)(diethyl ether)zinc(II)] (Behm et al., 1993)
and tris(diethyl ether)(ethyl)zinc(II) tetrakis(penta¯uoro-
phenyl)borate (Walker et al., 2001), as well as one example of
a zinc aryloxide, bis[(diethyl ether)(2,6-diphenylphenoxy)]-
zinc(II) (Darensbourg et al., 1999), are found.
ISSN 0108-2701
Slow atmospheric oxidation of
diphenylzinc: di-l-phenoxido-
bis[(diethyl ether)phenylzinc(II)]
Anders Lennartson* and Mikael HaÊkansson
Department of Chemistry, Goteborg University, SE-412 96 Goteborg, Sweden
È
È
Correspondence e-mail: anle@chem.gu.se
Received 11 October 2007
Accepted 9 November 2007
Online 14 December 2007
The title compound, [Zn2(C6H5)2(C6H5O)2(C4H10O)2], was
isolated from a solution of diphenylzinc in diethyl ether that
had been exposed to air. The molecules are dinuclear, with a
distorted tetrahedral coordination geometry around the Zn
atoms and with molecules situated about a crystallographic
inversion centre. Molecules associate via three sets of CÐ
HÁ Á Áꢀ(arene) interactions, leading to a network structure.
Several crystal structures for zinc aryloxides and organozinc
aryloxides have been published and are reported in the CSD,
but none of the structures are closely related to (I). 146
structures are found to contain two Zn atoms bridged by two
aryloxide groups. Most of these structures include complex
aryloxide groups, having, for example, N-donor substituents
coordinating to Zn, e.g. bis{[ꢁ2-2-(diethylaminomethyl)phen-
oxo](ethyl)zinc(II)} (Hunger et al., 2005). Structures having a
monodentate neutral ligand at Zn, as for (I), are rare. There is
Comment
Organozinc reagents are known to be highly sensitive towards
atmospheric O2, as noted by Edward Frankland during his
pioneering work on organozinc compounds (see, for example,
Frankland, 1852, 1855; Seyferth, 2001). This forced Frankland
to develop several ingenious apparatuses in order to synthe-
size, purify and analyse the highly reactive compounds he had
discovered (Frankland, 1855). Low molecular weight dialkyl-
zinc compounds (ZnMe2, ZnEt2 and ZnPr2) ignite sponta-
neously when exposed to air (Boersma, 1982a). Slow oxidation
of organozinc reagents by low concentrations of O2 is known
to give rise to the corresponding alkoxides, with zinc
organoperoxides as intermediates (Boersma, 1982b). The
formation of alkoxides by the action of O2 on dialkylzinc
compounds was ®rst reported in the case of diethylzinc by
Frankland (1855), who identi®ed zinc ethoxide as one of the
products obtained in the reaction of diethyl zinc and O2.
The title compound, (I), was isolated from a diethyl ether
solution of diphenylzinc (standing in a Schlenk tube) after a
period of 3.5 years, during which the solution had partially
attacked the silicon grease on the stopcock, causing a minute
leak of atmospheric O2 into the tube. Compound (I) is a
dinuclear zinc complex, situated about a crystallographic
inversion centre (Fig. 1). The coordination geometry around
Zn1 is highly distorted tetrahedral, with a Zn1ÐC1 distance of
Ê
1.964 (2) A, ZnÐO bond lengths of 1.9898 (14), 2.0008 (14)
Ê
Figure 1
A view of (I), showing the atomic numbering scheme; atoms labelled with
and 2.0939 (15) A, and angles about the Zn centre ranging
the suf®x
A indicate symmetry-related equivalents. Displacement
from 79.31 (6) to 130.39 (7)ꢀ. The coordination of diethyl
ether to zinc is, perhaps surprisingly, rare among the structures
in the Cambridge Structural Database (CSD; Version 5.28 of
ellipsoids are drawn at the 30% probability level and H atoms are
included with radii of an arbitrary size. [Symmetry code: (A)
x ‡ 1; y ‡ 1; z.]
m10 # 2008 International Union of Crystallography
DOI: 10.1107/S0108270107057514
Acta Cryst. (2008). C64, m10±m12

metal-organic compounds
Figure 2
The structure of (I) has three sets of CÐHÁ Á Áꢀ(arene) interactions. The unit cell of (I) is shown as viewed along the b axis (left, with the H14A
1
2
1
interaction) and along the c axis (right, with the H10 and H15A interactions). [Symmetry codes: (i) x
x ‡ 1; y ‡ 1; z ‡ 1; (iv) x ‡ 12 ; y ‡ 23 ; z ‡ 21.]
;
y ‡ 32 ; z ‡ 21; (ii) x ‡ 32 ; y
;
2
z ‡ 12; (iii)
only one example of an organozinc aryloxide bearing a coor-
dinating ligand at Zn, viz. bis[(ꢁ2-2,6-dimethylphenoxo)(eth-
yl)(pyridyl)zinc(II)] (Boyle et al., 2004). Two structures of
bridged zinc aryloxides having monodentate neutral ligands at
Zn are reported in the CSD, viz. bis[(ꢁ2-2,6-di¯uorophen-
oxo)(2,6-di¯uorophenoxo)(tetrahydrofuran)zinc(II)] and bis-
[(ꢁ2-2,6-di¯uorophenoxo)(2,6-di¯uorophenoxo)(tricyclohexyl-
phosphine)zinc(II)] tetrahydrofuran solvate (Darensbourg et
al., 2000). Another structure somewhat similar to (I) is bis[(ꢁ2-
2,3-dihydro-2,2-dimethylbenzofuranoxide)(chloro)(pyridine)-
zinc(II)] (Sobota et al., 2000). In addition, there are a number
of complexes with three-coordinate Zn atoms. In this category,
tetrakis(ꢁ2-2,2-dimethyl-3,5-hexanedionato)diphenyltetra-
zinc(II), (II) (Boersma et al., 1974). Compound (II) is the only
example in the CSD of a phenylzinc±phenoxide complex. The
ZnÁ Á ÁZn distances in this structure are 3.177, 3.239 and
Ê
Ê
3.171 A, slightly longer than that in (I) [3.0724 (6) A].
The crystal structure of (I) displays three sets of CÐHÁ Á Áꢀ
interactions (Nishio, 2004; Cantrill et al., 2000; Braga et al.,
1998; Viswamitra et al., 1993) (Table 1). The shortest set
involves atom H14A and the (C1±C6)ii phenyl ring [symmetry
code: (ii) x + 1, y, z] and gives rise to chains extending along
the a axis. The second shortest set of CÐHÁ Á Áꢀ contacts
involves atom H10 and the (C1±C6)i phenyl ring [symmetry
1
2
1
2
1
code: (i) x + , y
,
z + ]. These interactions result in
2
layers extending parallel to the (202) set of planes. A third set
of interactions can be identi®ed, viz. atom H15A interacts with
the (C1±C6)iii phenyl ring [symmetry code: (iii) x + 21, y + 32,
1
2
z + ]. These interactions give rise to layers parallel to (202).
The three sets of interactions result in a network structure, and
these interactions are depicted in Fig. 2.
Zinc aryloxides have found use in carbon dioxide activation
and may have future potential as an activator of this green-
house gas. Darensbourg and co-workers reported that zinc
aryloxides catalyse the copolymerization of carbon dioxide
and epoxides (Darensbourg & Holtcamp, 1995; Darensbourg
et al., 1999). Fixation of carbon dioxide by carboxylation of
acetophenone using zinc aryloxide catalysts has also been
reported (Kunert et al., 2000).
there is one example of a base-free zinc aryloxide, viz. bis[(ꢁ2-
2,6-di-tert-butylphenoxo)(2,6-di-tert-butylphenoxo)zinc(II)]
n-pentane solvate (Kunert et al., 2000). Other examples include
bis[(ꢁ2-2,6-di-tert-butylphenoxo)(ethyl)zinc(II)] (Parvez et al.,
1992) and [(ꢁ2-2,6-diisopropylphenoxo)(trimethylsilylmeth-
yl)zinc(II)] (Olmstead et al., 1991). There are no structures of
Zn(OPh)2 complexes in the CSD, but there are eight struc-
tures of derivatives bearing one phenoxide ligand at zinc, e.g.
bis(ꢁ2-phenoxo)[N-isopropyl-2-(isopropylamino)troponimin-
ato]zinc(II) (Herrmann et al., 2004) and bis(ꢁ3-phenoxo)-
Experimental
Bromobenzene (4.1 ml, 0.039 mol) was added to a stirred mixture of
Mg (1.1 g, 0.045 mol) and diethyl ether (40 ml). The mixture was
stirred overnight at ambient temperature. The solution was added
dropwise to a suspension of ZnCl2 (2.6 g, 0.019 mol) in diethyl ether
ꢁ
Acta Cryst. (2008). C64, m10±m12
Lennartson and Hakansson
[Zn2(C6H5)2(C6H5O)2(C4H10O)2] m11
Ê

metal-organic compounds
(10 ml) at 273 K. The reaction mixture was stirred at ambient
temperature overnight, evaporated and sublimated at 10 2 mbar. The
white product was dissolved in diethyl ether (4 ml). After 3.5 years of
storage at 238 K, the silicon grease had been heavily attacked by the
ZnPh2 solution, resulting in leakage of atmospheric O2 into the
Schlenk tube. Large colourless hexagonal prismatic crystals of (I)
were isolated.
Financial support from the Swedish Research Council (VR)
is gratefully acknowledged.
Supplementary data for this paper are available from the IUCr electronic
archives (Reference: GG3123). Services for accessing these data are
described at the back of the journal.
Crystal data
3
Ê
[Zn2(C6H5)2(C6H5O)2(C4H10O)2]
Mr = 619.42
V = 1516.9 (4) A
Z = 2
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Ê
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È
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ꢁ
m12 Lennartson and Hakansson
[Zn2(C6H5)2(C6H5O)2(C4H10O)2]
Acta Cryst. (2008). C64, m10±m12
Ê