Zinc halide oxazoline complexes - The quest for structural diversity

Article abstract of DOI:10.1139/V08-174

The synthesis and characterization of 14 ZnX₂ (X = Cl or Br) complexes containing aryl-oxazoline (ox) lig-ands is reported. Eleven of these derivatives have been structurally elucidated in the solid state by single crystal X-ray diffraction met

Full text of DOI:10.1139/V08-174

368
Zinc halide oxazoline complexes — The quest for
structural diversity1
Robert A. Gossage, Paras N. Yadav, Timothy D. MacInnis, J. Wilson Quail, and
Andreas Decken
Abstract: The synthesis and characterization of 14 ZnX2 (X = Cl or Br) complexes containing aryl-oxazoline (ox) lig-
ands is reported. Eleven of these derivatives have been structurally elucidated in the solid state by single crystal X-ray
diffraction methods. The ligands used are 2-(3-R-phenyl)-2-oxazoline (R = Cl or Me), 2-(4-R-phenyl)-2-oxazoline (R =
Cl, F, Me or –OMe), and 2-(anisol-2-yl)-4,4-dimethyl-2-oxazoline (7a). All oxazolines, with the exception of 7a, lead
to the formation of materials identified as ZnX2(ox)2 upon reaction with ZnX2. A distorted tetrahedral coordination mo-
tif around the Zn metal centre is displayed in nine examples that have been characterized by single crystal X-ray dif-
fraction methods. In the case of ligand 7a, an unusual dimeric species (X-ray) of formula [ZnCl2(7a)]2 (7b) is formed
upon reaction with ZnCl2. Compound 7b displays a rare (formally neutral) µ-(Cl)2-(Zn[L]Cl)2 (L = neutral donor
ligand) unit in addition to secondary bonding interactions between the Zn centres and the O-atom of the –OMe group
(ZnLO distance of ~2.56 Å). In contrast, reactions of 7a with ZnBr2 lead to the formation of a monomeric species
containing a chelating molecule of 7a with binding through the oxazoline N-atom and the methoxy (Zn–O distance of
~2.14 Å) group, i.e., ZnBr2(7a-κ2N,OOMe). These complexes are discussed in terms of structurally related Zn species
and some comment is made as to the direction to be explored within this series of materials that may lead to further
unusual structural diversity.
Key words: oxazoline, oxazole, zinc, X-ray crystal structure, coordination complex, Zn(II) halide. 379
Résumé : On rapporte la synthèse et la caractérisation de quatorze complexes de ZnX2 (X = Cl ou Br) contenant des
ligands aryloxazoline (ox). On a élucidé les structures de onze de ces dérivés en faisant appel à des méthodes de dif-
fraction des rayons X à l’état solide. Les ligands utilisés comprennent des 2-(3-R-phényl)-2-oxazolines (R = Cl ou
Me), des 2-(3-4-phényl)-2-oxazolines (R = Cl, F, Me ou OMe) et la 2-(anisoly-2-yl)-4,4-diméthyl-2-oxazoline (7a). Par
réaction avec du ZnX2, toutes les oxazolines, à l’exception du composé 7a, conduisent à la formation de produits iden-
tifiés par la formule générale ZnX2(ox)2. Dans neuf exemples caractérisés par des méthodes de diffraction des rayons-X
par un cristal unique présentent un motif de coordination de tétraèdre déformé autour du centre métallique Zn. Dans le
cas du ligand 7a, il se forme une espèce dimère inhabituelle (aux rayons X) de formule [ZnCl2(7a)]2 (7b). Le composé
7b comporte une unité rare (formellement neutre) µ-(Cl2)-(Zn[L]Cl)2 (L = ligand donneur neutre) en plus des interac-
tions de liaisons secondaires entre les centres Zn et l’atome d’oxygène du groupe –OMe (distance ZnLO de ~2,56 Å).
Par opposition, les réactions du composé 7a avec le ZnBr2 conduit à la formation d’espèces monomères contenant une
molécule chélatante de 7a qui donne des liaisons par le biais de l’atome d’azote de l’oxazoline et du groupe méthoxy
(distance Zn–O de ~2,14 Å), c’est-à-dire ZnBr2(7a-κ2N,OOMe). On discute de ces complexes en fonction d’espèces de
Zn reliées d’un point de vue structural et on fait quelques commentaires concernant la direction qui devrait être explo-
rer dans cette série de produits qui pourrait conduire à une plus grande diversité structurale.
Received 7 April 2008. Accepted 7 October 2009. Published on the NRC Research Press Web site at canjchem.nrc.ca on
29 November 2008.
This manuscript is dedicated to Professor Richard J. Puddephatt in recognition of his outstanding contributions to Canadian
science.
R.A. Gossage.2 Department of Chemistry & Biology, Ryerson University, 350 Victoria Street, Toronto ON M5B 2K3 Canada.
P.N. Yadav3 and T.D. MacInnis.4 The David Upton Hill Laboratories of Inorganic Chemistry, Department of Chemistry, Acadia
University, Wolfville NS B4P 2R6 Canada.
J.W. Quail.5 Saskatchewan Structural Sciences Centre and Department of Chemistry, Thorvaldson Building, 110 Science Place,
University of Saskatchewan, Saskatoon SK S7N 5C9 Canada.
A. Decken.6 Department of Chemistry, University of New Brunswick, Fredericton NB E3B 6E2 Canada.
1Oxazoles XIX. This article is part of a Special Issue dedicated to Professor R. Puddephatt.
2Corresponding author (e-mail: gossage@ryerson.ca)
3Present address: Central Department of Chemistry, Tribhuvan University, Kirtipur, Kathmandu, Nepal.
4Present address: Department of Chemistry, University of Victoria, Victoria BC V8W 3V6 Canada.
5Correspondence regarding X-ray structure determinations of compounds 7b and 7c (e-mail: wilson.quail@usask.ca).
6Correspondence regarding X-ray structure determinations of compounds 1b–5b, 2c–4c, and 6c (e-mail: adecken@unb.ca).
Can. J. Chem. 87: 368–379 (2009)
doi:10.1139/V08-174
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Gossage et al.
369
Mots-clés : oxazoline, oxazole, structure cristalline par diffusion des rayons X, complexe de coordination, halogénure
de Zn(II).
[Traduit par la Rédaction] Gossage et al.
Fig. 1. Some of the known structural motifs for (ZnX2[py–R]n)m
complexes.
Fig. 2. Ligands employed in this study (1a–7a) and the structure
of L-573,655 (8).
served that the only structural motif observed (X-ray) was
that of a neutral four-coordinate Zn species with a distorted
tetrahedral coordination mode around the metal centre (2).
Ligation to zinc in our case invariably consisted of two
metal-bound halide atoms and two oxazolines, the latter of
which was shown to bind through the N-atom, as expected
(3). This is in sharp contrast to the complimentary py–R do-
nor series (Fig. 1), in which tetrahedra4l (A), polymeric oc-
tahedral (B), Magnus type salts (C), multi-component salts
(D), and a variety of five-coordinate structures have all been
structurally characterized (4).
A secondary underlying theme of our research is the focus
on biologically relevant metal complexes (5). In this regard,
the lead drug candidate L-573,655 (8: Fig. 2) has been
shown to inhibit Lipid A biosynthesis by selective binding to
an enzyme-bound Zn2+ ion (6). This result emphasises the
biological relevance and importance of the structure and
variability in Zn-oxazoline complexes. In this report, we ex-
pand our fundamental investigations of the solid-state struc-
ture of Zn halide aryl-oxazoline complexes. This study
reveals that although the tetrahedral coordination motif
seems to dominate the coordination chemistry of ZnX2 with
oxazolines, unusual species can be produced from a simple
ortho-substituted aryl oxazoline.
Introduction
Despite the stability of only a single cationic oxidation
state, zinc displays rich and diverse coordination chemistry
in both the natural and artificial (i.e., synthetic) settings (1).
The formal Zn2+ ion binds with a large variety of ligands (1)
including alkyl and aryl anions, halides, P-donor, O-donor,
and N-donor fragments, etc. Many Zn materials have been
isolated with heterocyclic ligands, with substituted pyridines
(py–R) being a particularly noteworthy example. Several
years ago, we reported our initial investigations into the co-
ordination chemistry of the zinc(II) halides (i.e., ZnX2) with
heterocyclic bases containing a single oxazoline (i.e., 4,5-
dihydro-1,3-oxazole) group. In this earlier work, we ob-
Results and discussion
Syntheses and spectroscopic characterization
The synthesis of the materials discussed here is quite
straightforward. Treatment of diethylether solutions of ZnX2
with an excess of oxazoline (ox) ligand (Fig. 2, 1a–7a) typi-
cally leads to the rapid precipitation of a white coloured ma-
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Can. J. Chem. Vol. 87, 2009
terial. This is essentially pure (ZnX2[ox]n)m, which can then
be readily recrystallized from a variety of organic solvents
(e.g., CH2Cl2/petroleum ether mixtures, MeOH/Et2O mix-
tures). Although most of the complexes reported here have
quite low solubility in deuterochloroform, solubility is suffi-
suitability of the crystals for X-ray diffraction analysis. As a
result, the diffraction data could only be used to confirm the
global structure of the molecule(s) in the unit cell. Although
one can discern the general aspects of the atom connectivity,
exact data on bond lengths, bond angles, etc. could not be
obtained within acceptable experimental error. However, a
mononuclear structure of this material was established that
contains a Zn atom with a distorted tetrahedral array of
bonded groups (comprising of two bromide atoms and two
N-bonded oxazoline ligands: Fig.1, cf. A). This is similar to
that observed (2) for ZnX2(2-phenyl-2-oxazoline-κ1N)2
(X = Cl: 9 or Br: 10). The other nine compounds of 2:1
oxazoline-to-metal stoichiometry reported herein (i.e., 1b–
5b, 2c–4c, and 6c) have all been fully characterized by sin-
gle crystal X-ray diffraction. Tables 1 and 3 contain the data
on the ZnCl2 derivatives and Tables 2 and 3 report the re-
sults for the ZnBr2 complexes. ORTEP representations of a
molecule within the unit cell of each of complexes 1b–5b,
2c–4c, and 6c appear in Figs. 3 to 11. Of this group, all are
structural analogues of the previously reported parent mate-
rials 9 or 10 (2). This bonding motif involves two metal-
bound halide atoms and two N-bound oxazolines forming a
distorted tetrahedral coordination motif around the zinc atom
(Scheme 1). There is little variability in the Zn–N bond
lengths (Table 3), which all lie in the range of 2.03–2.08 Å
and can be compared with similar bond distances of
2.026(2) and 2.050(2) Å reported for 9, and 2.025(3) and
2.053(3) Å for 10 (2). In five of the nine novel complexes,
the narrowest bond angle containing the Zn atom is the
N-Zn-N angle, and perhaps not surprisingly, the larger
halide atoms (vs. that of N) occupy the fragment with the
larger E-Zn-E (E = donor atom) angle (Table 3 and Supple-
mentary Data).7 The exceptions to this trend are found with
complexes 5b, 2c, and 3c. All three of these compounds
contain at least one N-Zn-X angle that is identical in magni-
tude (within experimental error) to that of the X-Zn-X angle.
In contrast, compound 6c displays an N-Zn-N angle that is
larger than that of the Br-Zn-Br grouping (Table 3). This is
similar to that observed in the complex ZnBr2(4,4-dimethyl-
2-phenyl-2-oxazoline-κ1N)2 reported previously (2). Further
details on the structure of these materials can be found in the
Supplementary Data.7
1
cient to obtain H NMR spectra; attempts to obtain spectra
in DMSO-d6 or MeOH-d4 resulted in ligand displacement by
these solvents. These properties precluded 13C NMR studies
of these compounds. The observed spectroscopic properties
(1H NMR, IR, etc., see Experimental section) of these mate-
rials display the expected behaviour with respect to the free
ligand form (2, 7, 8). Specifically, these data are character-
ized by a lowering of the IR stretching frequency assigned
to the ν(C=N) absorption of the oxazoline ring system and
the appearance of lower frequency bands attributed to Zn-
ligand bonding vibrations (see Experimental section and
refs. 8d and 8e). Other spectroscopic trends of this ligand
class upon coordination to ZnX2 have been discussed previ-
ously in some detail (2, 8e).
Examination of these materials by elemental analysis
strongly suggests that chlorido compounds 1b–6b and the
bromo-containing 1c–6c are characterized by the presence of
two oxazolines per [ZnX2] unit. Hence, a likely structural
motif is that of the distorted tetrahedral array around the Zn
atom, although polymeric materials (Fig. 1, cf., B) cannot be
ruled out by these data. Compounds 7b and 7c, however,
analyse for a 1:1 ratio of the zinc halide unit per oxazoline.
This is a situation that we did not encounter in our previous
investigations (2). Thus, an examination of a number of
these materials by X-ray diffraction methods was obviously
in order (vide infra).
Solid-state crystal structures
Despite the widespread use of oxazolines (9) and their
transition metal complexes (3h), there is surprisingly little
structural information on Group 12 species containing
mono-oxazolines (2, 3a, 3h). As stated earlier, our previous
work (2) had revealed only mononuclear formally Zn2+ ha-
lide complexes with both alkyl- and aryl-oxazolines, all with
similar bonding motifs. Unfortunately during this study,
crystals suitable for X-ray diffraction of compounds 6b and
1c could not be obtained and therefore one can only assign a
2:1 ratio of the oxazolines to the ZnX2 unit based on their
respective elemental analyses. The rest of the compounds re-
ported here yielded crystalline material from CH2Cl2 or
CHCl3 solutions that had been layered with excess Et2O and
(or) petroleum ether.
ZnX2 Complexes possessing a 1:1 oxazoline/Zn ratio
(ZnX2 derivatives of 7a)
The analytical data of complexes 7b and 7c present the
first examples of stoichiometric diversity within the
(ZnX2[ox]n)m series thus far investigated. Both of these ma-
terials contain oxazoline 7a. In terms of the ligand itself, the
primary difference between this compound and other
oxazolines (ref. 2 and this work) is the presence of a poten-
tially donating substituent located on the ortho-position of
the aromatic ring.8 This leads to the formation of 1:1 com-
plexes in both cases, regardless of the use of excess 7a in the
ZnX2 Complexes possessing a 2:1 oxazoline/Zn ratio
The lack of suitable crystals of compounds 6b and 1c
means that we are unable to comment any further with re-
gards to the overall structural nature of these two complexes
(Scheme 1). The crystalline material obtained of compound
5c was invariably of only very poor quality in terms of the
7 Supplementary data for this article are available on the journal Web site (canjchem.nrc.ca) or may be purchased from the Depository of
Unpublished Data, Document Delivery, CISTI, National Research Council Canada, Ottawa, ON K1A 0R6, Canada. DUD 3867. For more
information on obtaining material refer to cisti-icist.nrc-cnrc.gc.ca/cms/unpub_e.shtml. CCDC 684048–684058 contain the crystallographic
data for this manuscript. These data can be obtained, free of charge, via www.ccdc.cam.ac.uk/conts/retrieving.html (Or from the Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax +44 1223 336033; or deposit@ccdc.cam.ac.uk).
8 Our previous work (2) included several examples of oxazoline ligands with methyl groups on oxazoline ring position-4, such as 4,4-
dimethyl-2-phenyl-2-oxazoline and 2,4,4-trimethyl-2-oxazoline.
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Table 2. General crystal data for the zinc bromide complexes reported herein.
Complex
Formula
2c
3c
4c
6c
7c
C18H16N2O2Cl2ZnBr2 C18H16F2N2O2ZnBr2 C20H22N2O2ZnBr2
C20H22N2O4ZnBr2
579.59
C12H15NO2ZnBr2
430.44
Forumal mass
Crystal size (mm)
a (Å)
b (Å)
c (Å)
588.42
555.52
458.67
0.40 × 0.35 × 0.25
14.5424(10)
10.3753(10)
15.4015(14)
90
0.50 × 0.40 × 0.35
14.501(3)
10.360(3)
14.918(4)
90
0.45 × 0.20 × 0.175 0.45 × 0.35 × 0.15 0.15 × 0.15 × 0.10
14.4148(7)
10.4163(7)
15.4021(10)
90
10.5967(16)
16.065(2)
13.488(2)
90
6.9385(2)
20.2638(6)
12.1570(3)
90
α (°)
β (°)
117.283(2)
90
2065.3(3)
1.892
118.104(8)
90
1976.8(9)
1.867
114.098(2)
90
2111.1(2)
1.723
109.624(3)
90
2162.7(6)
1.780
118.756(2)
90
1498.48(8)
1.908
γ (°)
V (Å3)
Dcalc (g/cm3)
Crystal sytem, space group
Z
Monoclinic, C2/c
4
Monoclinic, C2/c
4
Monoclinic, C2/c
4
Monoclinic, P21/c
4
Monoclinic, P21/c
4
F(000)
T (K)
1152
173(1)
1088
173(1)
5.318
1088
213(1)
4.966
1152
173(1)
4.859
840
173(2)
6.965
Absorption coefficient (mm–1) 5.333
2θ range (°)
Limiting indices
2.52–27.49
2.53–27.49
–17 ≤ h ≤ 18
–13 ≤ k ≤ 13
–18 ≤ l ≤ 16
6 624
2 222
2 222
123
1.066
2.49–27.49
–16 ≤ h ≤ 18
–13 ≤ k ≤ 13
–19 ≤ l ≤ 20
7 203
2 379
2 379
124
1.055
2.04–27.49
–13 ≤ h ≤ 12
–20 ≤ k ≤ 20
0 ≤ l ≤ 17
9 531
9 531
9 531
265
0.972
2.77–27.56
–9 ≤ h ≤ 9
–26 ≤ k ≤ 26
–15 ≤ l ≤ 15
21 620
3 431
3 431
168
1.083
–18 ≤ h ≤ 18
–13 ≤ k ≤ 13
–19 ≤ l ≤ 19
6 961
2 305
2 273
Reflections collected
Reflections unique
Reflections I > 2σ(I)
Parameters
155
1.057
GOF on F2
Final R indices I > 2σ(I)
R1 = 0.0205,
R1 = 0.0279,
R1 = 0.0219,
R1 = 0.0489,
R1 = 0.0353,
wR2 = 0.0536
wR2 = 0.0716
R1 = 0.0231,
wR2 = 0.0536
0.937, –0.317
wR2 = 0.0596
R1 = 0.0330,
wR2 = 0.0738
0.498, –0.338
wR2 = 0.1195
R1 = 0.0251,
wR2 = 0.0609
1.014, –0.946
wR2 = 0.0680
R1 = 0.0658,
wR2 = 0.1238
0.582, –0.707
R indices (all data)
ρ
min,max (e Å–3
)
0.415, –0.414
Table 3. Selected bond lengths and angles for the ZnX2 complexes reported herein (standard deviations are given in parentheses).
Bond lengths (Å)
Zn–N
Bond angles (°)
N-Zn-N
Bond lengths (Å)
C=N (oxazoline)
Complex
Zn–X (X = Cl or Br)
X-Zn-X (X = halogen)
1b
2b
3b
4b
2.039(2)
2.2298(9)
2.2371(4)
2.2350(5)
2.2419(10)
2.2317(10)
2.2425(4)
2.3766(3)
2.3746(6)
2.3795(3)
2.4039(6)
2.4060(6)
2.2201(7)a
2.3152(7)d
2.3348(6)
2.3371(6)
112.80(13)
103.54(7)
104.03(7)
109.09(11)
116.82(6)
115.01(3)
113.11(3)
114.26(4)
1.279(4)
1.284(2)
1.284(2)
1.284(4)
1.273(4)
1.285(2)
1.283(2)
1.282(3)
1.288(2)
1.283(4)
1.276(5)
1.285(3)
2.0489(12)
2.0408(11)
2.042(3)
2.041(3)
5b
2c
3c
4c
6c
2.0433(11)
2.0397(14)
2.036(2)
2.0354(14)
2.045(3)
102.94(6)
103.31(8)
103.96(10)
103.59(8)
116.16(11)
112.51(2)
112.42(2)
111.21(3)
110.65(2)
113.77(2)
2.043(3)
2.009(2)
c
7b
7c
n/ab
1.991(3)
2.141(3) f
85.42(11)e
120.01(2)
1.285(5)
aTerminal Zn–Cl.
bn/a = not applicable.
cSee Supplementary Data.7
dBridging Zn–Cl.
eN-Zn-O bond angle.
fZn–O bond length.
© 2008 NRC Canada

Gossage et al.
373
Fig. 3. ORTEP representation of a molecule of complex 1b.
Fig. 4. ORTEP representation of a molecule of complex 2b.
Fig. 7. ORTEP representation of a molecule of complex 5b.
Fig. 5. ORTEP representation of a molecule of complex 3b.
synthetic protocol. The chlorido case, complex 7b, reveals
itself (X-ray) to be a dinuclear species in which two Zn at-
oms are connected via two symmetry-related chloride
bridges (Fig. 12). The residual coordination polyhedron
around the Zn atom contains a second, albeit terminal, chlo-
ride atom. The terminal Zn–Cl bond is distinctly shorter than
that found in the complimentary bridging halide (Table 3,
~2.22 vs. ~2.32 Å). In addition, a single N-bonded oxazoline
is coordinated to each Zn atom. This latter ligand also dis-
plays secondary bonding interactions between the metal nu-
cleus and the O-atom of the –OMe group contained on the
aromatic ring. The ZnLO bond distance is a respectable
2.56 Å. Of particular interest in the structure of 7b is the
presence of a µ-(X)2-(M[L]X)2 unit (M = Group 12 element,
X = halogen, L = neutral donor ligand).
Although this dimeric structure is well-known in the case
of M = Cd or Hg, zinc derivatives with such a bridging motif
are surprisingly rare.9 Structurally characterized examples
include the phosphine or arsine compounds µ-(I)2-
9 See the Cambridge structural database (CSD) at http://www.ccdc.cam.ac.uk/products/csd. Further information on Cd and Hg compounds
containing the µ-(X)2-(M[L]X)2 structural unit can be found in Comprehensive coordination chemistry. Vol. 5. Edited by G. Wilkinson.
Elsevier, Toronto, Ont., Canada, 1987. Chaps. 56.1–56.2 and Comprehensive coordination chemistry II. Vol. 6. Edited by J.A. McCleverty
and T.J. Meyer. Elsevier, Toronto, Ont., Canada, 2003.
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Can. J. Chem. Vol. 87, 2009
Fig. 6. ORTEP representation of a molecule of complex 4b.
Fig. 8. ORTEP representation of a molecule of complex 2c.
Fig. 9. ORTEP representation of a molecule of complex 3c.
Fig. 10. ORTEP representation of a molecule of complex 4c.
ligand. This organic group is found to chelate to the ZnBr2
fragment via bonding of the oxazoline N-atom and the O-
atom of the –OMe group (i.e., a κ2N,OOMe bonding pattern).
This is the only member of the series with a distinct chelate
(Zn–O distance = ~2.14 Å) and the only one with an NOX2
atomic composition of the Zn-binding set. Not surprisingly,
compound 7c displays a narrow N-Zn-O bond angle (~85°)
to accommodate the chelating ligand; this is accompanied by
a slightly shorter (with respect to 1b–5b, 2c–4c, 6c, 9, and
10) Zn–N bond length (~1.99 Å). The Zn–Br bond lengths
are also the shortest in this series (~2.33 Å). These data can
be compared with another ZnBr2 species with the NOX2 Zn-
(ZnI[P{NMe2}3])2 (10a), µ-(I)2-(ZnI[PEt3])2 (10b), and µ-
(I)2-(ZnI[AsEt3])2 (10c), in addition to the tetranuclear
nitrido complex 11 (10d), bridged oxo compound 12 (10e),
tin-containing 13 (10f), the unusual iron carbonyl (10g) spe-
cies 14 (Fig. 13), amongst others (10h, 10i). Hence, our
material 7b is the first oxazoline (and, in fact, imine) exam-
ple of this structural motif in Zn chemistry.
The bromide analogue of complex 7b (viz., complex 7c)
is not a structural relative of the chlorido congener (Fig. 14).
With the heavier halogen, a mononuclear complex is re-
vealed and as expected it contains only a single oxazoline
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Gossage et al.
375
Fig. 13. Some previously characterized relatives of complex 7b
Fig. 11. ORTEP representation of a molecule of complex 6c.
Fig. 12. ORTEP representation of a molecule of complex 7b.
Fig. 14. ORTEP representation of a molecule of complex 7c.
binding set, viz. 2-picoline-6-carbaldehyde-κ2N,O zinc(II)
bromide (15). As observed for 7c, complex 15 (11) contains
a six-membered chelate ring with a similarly narrow N-Zn-
O bond angle (80.3(6)°) and similar metal-ligand bond
lengths (Zn–N: 2.05(2) Å, Zn–O: 2.10(1) Å; Zn–Br:
2.314(3) and 2.334(4) Å).
In terms of potential future work in relation to the above
investigations, the presence of a sterically bulky group on
oxazoline ring position-2 seems to be a potential gateway for
the discovery of other structural classes of Zn materials. Our
intentions are to survey ligands such as 2-t-butyl-2-oxazoline
in this regard. In terms of other bulky 2-aryl-2-oxazolines,
the use of ortho-substituted aromatic groups may also lead
to novel structural forms, especially if such substitution con-
tains groups that are unlikely to form a stabilization interac-
tion with Zn (e.g., Me, Ph, t-Bu, etc.). As a variety of
nucleophiles are known to readily replace the –OMe group
from 7a (12), this is an obvious avenue for our continued in-
vestigations into ligand design strategies and coordination
chemistry in general (13). Two further aspects that we have
yet to vary are the effect of solvent(s) and the replacement of
–
–
the halides for other anionic sources (e.g., NO3 , ClO4 , etc.)
on the structural nature of the resulting products (Fig. 1, cf.,
D). These facets will also be included in some of our future
synthetic endeavours.
Conclusions
The results reported herein greatly expand the number of
structurally characterized ZnX2 oxazoline complexes, al-
though unfortunately the structural elucidation of com-
pounds 6b and 1c has thus far eluded us. Generally
speaking, 2-aryl-2-oxazoline ligands have demonstrated little
structural diversity with the Zn(II) halides, regardless of the
presence of electron-withdrawing (1a, 2a, and (or) 3a) or
electron-donating groups (4a, 5a, and (or) 6a) located meta
or para within the arene framework (Scheme 1). Although
admittedly only represented here by ligand 7a, the formation
of novel binuclear Zn-imine complex 7b or ligand chelation
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Can. J. Chem. Vol. 87, 2009
Scheme 1. A summary of the products synthesized herein.
Synthesis of bis-(2-[p-chlorophenyl]-2-oxazoline-␬1N)
zinc chloride (2b)
(7c) has been realised with an appropriately basic ortho-
functionality (Scheme 1).
Complex 2b was produced in a manner similar to that of
1b using of ZnCl2 (0.068 g, 0.50 mmol) and oxazoline 2a
(0.218 g, 1.20 mmol). The yield of cream coloured product
was 0.28 g (96%), mp 198–200 °C (decomp). IR (cm–1):
1635 (s, ν[C=N]), Zn–L vibrations: 300 (s), 285 (s), 232
(m). 1H NMR δ: 4.30 (t, J = 9.0 Hz, 2H, NCH2), 4.50 (t, J =
9.0 Hz, 2H, OCH2), 7.40 (d, J = 8.4 Hz, 2H, ArH), 7.83 (d,
2H, ArH). Anal. calcd. for C18H16N2O2Cl4Zn (%): C 43.28,
H 3.23, N 5.61; found: C 43.30, H 3.37, N 5.24.
Experimental
General
All reactions were carried out using standard bench top
techniques employing commercially available, reagent grade
solvents. Zinc bromide and 7a (Fig. 2) were purchased and
used as received. Commercial zinc chloride was purified as
detailed previously (2). Ligands 1a–6a (Fig. 2) were synthe-
sized using published protocols (7, 8, 14), and their purity
Synthesis of bis-(2-[p-fluorophenyl]-2-oxazoline-␬1N)
zinc(II) chloride (3b)
1
checked by a combination of mp and H NMR spectroscopy
1
(7, 8). The H NMR spectra (300 MHz) were recorded at
Complex 3b was produced in a manner similar to that of
1b using of ZnCl2 (0.068 g, 0.50 mmol) and oxazoline 3a
(0.198 g, 1.20 mmol). The yield of cream coloured product
was 0.18 g (78%), mp 229–231 °C (decomp). IR (cm–1):
1633 (s, ν[C=N]), Zn–L vibrations: 296 (s), 286 (s), 232
room temperature (RT) using a Bruker Avance 300 NMR
spectrometer using CHCl3-d as solvent (except where
noted); chemical shifts are reported vs. that of external
SiMe4 (δH = 0.00 ppm), which is, in turn, referenced to re-
sidual non-deuterated solvent resonance. IR data (CsCl or
CsI plates) was recorded using a PerkinElmer 283B IR spec-
trometer and (or) a Nicolet Avatar 300 FT-IR spectrometer.
Elemental analyses were carried out by the Analyst Centre
(University of Toronto, Canada), the Analytical Services De-
partment of the University of Saskatchewan, and by
Lakehead University Centre for Analytical Services (Thun-
der Bay, Canada).
1
(w). H NMR δ: 4.33 (m, 2H, NCH2), 4.48 (m, 2H, OCH2),
7.10 (m, 2H, ArH), 7.91 (m, 2H, ArH). Anal. calcd. for
C18H16N2F2O2Cl2Zn (%): C 46.33, H 3.46, N 6.00; found: C
46.01, H 3.48, N 5.67.
Synthesis of bis-(2-[p-tolyl]-2-oxazoline-␬1N) zinc(II)
chloride (4b)
Complex 4b was produced in a manner similar to that of
1b using of ZnCl2 (0.068 g, 0.50 mmol) and oxazoline 4a
(0.193 g, 1.20 mmol). The yield of cream coloured product
was 0.18 g (79%), mp 206–209 °C (decomp). IR (cm–1):
1628 (s, ν[C=N]), Zn–L vibrations: 296 (s), 288 (s). 1H
NMR δ: 2.44 (s, 3H, CH3), 4.30 (m, 4H, CH2CH2), 7.21 (d,
J = 8.1, 2H, ArH), 7.71 (d, J = 8.1, 2H, ArH). Anal. calcd.
for C20H22N2O2Cl2Zn (%): C 52.37, H 4.83, N 6.11; found:
C 51.94, H 4.88, N 6.06.
Synthesis of bis-(2-[m-chlorophenyl]-2-oxazoline-␬1N)
zinc(II) chloride (1b)
A sample of ZnCl2 (0.068 g, 0.50 mmol) was dissolved in
Et2O (10 mL) and stirred at RT for 20 min. The mixture was
filtered and a solution (10 mL of Et2O) of 1a (0.218 g,
1.20 mmol) was added. The product began to precipitate al-
most immediately. Stirring was continued for 24 h (RT) and
the resulting solid was isolated by filtration and washed with
Et2O (15 mL) and then allowed to dry in open air. The yield
of cream coloured product was 0.26 g (95%), mp 217–
220 °C (decomp). IR (cm–1): 1631 (s, ν[C=N]), Zn–L (L =
Synthesis of bis-(2-[m-tolyl]-2-oxazoline-␬1N) zinc(II)
chloride (5b)
1
ligand) vibrations: 295 (m) 230 (w). H NMR δ: 4.39 (m,
Complex 5b was produced in a manner similar to that of
1b using of ZnCl2 (0.068 g, 0.50 mmol) and oxazoline 5a
(0.193 g, 1.20 mmol). The yield of cream coloured product
was 0.19 g (85%), mp 175–177 °C (decomp). IR (cm–1):
2H, NCH2), 4.57 (m, 2H, OCH2), 7.33 (m, 1H, ArH), 7.55
(m, 1H, ArH), 7.62 (m, 1H, ArH), 7.77 (s, 1H, ArH). Anal.
calcd. for C18H16N2O2Cl4Zn (%): C 43.28, H 3.23, N 5.61;
found: C 43.32, H 3.12, N 5.43.
1
1634 (s, ν[C=N]), Zn–L vibrations: 295 (m), 230 (w). H
© 2008 NRC Canada

Gossage et al.
377
NMR δ: 2.41 (s, 3H, CH3), 4.31 (m, 4H, NCH2), 4.50 (t, J =
8.9, 2H, OCH2), 7.28 (m, 1H, ArH), 7.31 (m, 1H, ArH),
7.57 (m, 2H, ArH). Anal. calcd. for C20H22N2O2Cl2Zn (%):
C 52.37, H 4.83, N 6.11; found: C 51.67, H 4.82, N 6.03.
cream coloured solid, mp 224–226 °C (decomp). IR (cm–1):
1624 (s, ν[C=N]), Zn–L vibrations: 304 (m), 282 (w), 270
1
(w). H NMR δ: 2.44 (s, 3H, CH3), 4.33 (m, 4H, CH2CH2),
7.19 (d, J = 8.1, 2H, ArH), 7.70 (d, J = 8.1, 2H, ArH). Anal.
calcd. for C20H22N2O2ZnBr2 (%): C 43.87, H 4.05, N 5.12;
found: C 43.50, H 3.98, N 5.10.
Synthesis of bis-(2-[p-anisolyl]-2-oxazoline-␬1N) zinc(II)
chloride (6b)
Synthesis of bis-(2-[m-tolyl]-2-oxazoline-␬1N) zinc(II)
bromide (5c)
Complex 6b was produced in a manner similar to that of
1b using of ZnCl2 (0.068 g, 0.50 mmol) and oxazoline 6a
(0.212 g, 1.20 mmol). The yield of cream coloured product
was 0.24 g (99%), mp 230–232 °C (decomp). IR (cm–1):
1626 (s, ν[C=N]), Zn–L vibrations: 300 (s), 284 (s), 234
Complex 5c was produced in a manner similar to that of
1c, using of ZnBr2 (0.112 g, 0.497 mmol) and oxazoline 5a
(0.193 g, 1.20 mmol). The yield was 0.22g (81%) of a cream
coloured solid, mp 173–175 °C (decomp). IR (cm–1): 1631
1
(w). H NMR δ: 3.89 (s, 3H, CH3), 4.32 (m, 4H, CH2CH2),
1
6.89 (d, J = 8.7 Hz, 2H, ArH), 7.82 (d, J = 8.7 Hz, 2H,
ArH). Anal. calcd. for C20H22N2O4Cl2Zn (%): C 48.96, H
4.52, N 5.71; found: C 48.21, H 4.39, N 5.52.
(s, ν[C=N]), Zn–L vibrations: 324 (w), 310 (w), 262 (m). H
NMR δ: 2.39 (s, 3H, CH3), 4.36 (m, 4H, CH2CH2), 7.28 (m,
1H, ArH), 7.38 (m, 1H, ArH), 7.58 (m, 2H, ArH). Anal.
calcd. for C20H22N2O2ZnBr2 (%): C 43.87, H 4.05, N 5.12;
found: C 43.24, H 3.88, N 5.02.
Synthesis of bis-(2-[m-chlorophenyl]-2-oxazoline-␬1N)
zinc(II) bromide (1c)
Synthesis of bis-(2-[p-anisolyl]-2-oxazoline-␬1N) zinc(II)
bromide (6c)
A sample of ZnBr2 (0.112 g, 0.497 mmol) was dissolved
in Et2O and treated with 1a (0.218 g, 1.20 mmol) dissolved
in 10 mL of Et2O. The cream coloured product (0.21 g,
82%) was isolated as for compound 1b, mp 217–219 °C
(decomp). IR (cm–1): 1630 (s, ν[C=N]), Zn–L vibrations:
Complex 6c was produced in a manner similar to that of
1c, using of ZnBr2 (0.112 g, 0.497 mmol) and oxazoline 6a
(0.212 g, 1.20 mmol). The yield was 0.20 g (69%) of a
cream coloured solid, mp 222–224 °C (decomp). IR (cm–1):
1621 (s, ν[C=N]), Zn–L vibrations: 296 (w), 286 (w), 270
1
286 (s), 274 (m), 240 (m), 232 (m). H NMR δ: 4.47 (m,
2H, NCH2), 4.61 (m, 2H, OCH2), 7.32 (m, 1H, ArH), 7.57
(m, 2H, ArH), 7.77 (s, 1H, ArH). Anal. calcd. for
C18H16N2O2Cl2ZnBr2 (%): C 36.74, H 2.74, N 4.76; found:
C 36.82, H 2.74, N 4.98.
1
(w), 232 (w). H NMR δ: 3.89 (s, 3H, OCH3), 4.37 (m, 4H,
CH2CH2), 6.88 (d, J = 9.0 Hz, 2H, ArH), 7.82 (d, J =
9.0 Hz, 2H, ArH). Anal. calcd. for C20H22N2O4ZnBr2 (%): C
41.45, H 3.83, N 4.83; found: C 41.81, H 3.56, N 4.76.
Synthesis of bis-(2-[p-chlorophenyl]-2-oxazoline-␬1N)
zinc(II) bromide (2c)
Synthesis of ␮-bis-chloro-bis-([4,4-dimethyl-2-{o-
anisolyl}-2-oxazoline-␬1N]zinc monochloride) (7b)10
A 1.0 g sample of ZnCl2 (7.3 mmol) was added to Et2O
(100 mL), and the mixture was stirred until virtually all of
the zinc materials had dissolved. The mixture was then fil-
tered and 1.52 g of 7a (7.41 mmol) was added at RT with
stirring. Within a few seconds, a white solid had precipitated
from the solution. Stirring was continued for 1 h, and then
the product was isolated by filtration and then washed with
Et2O (2 × 50 mL). The yield was 2.18 g (87%). IR (cm–1):
1624 (s, ν[C=N]). 1H NMR (acetone-d6) δ: 1.49 (s, 6H,
CH3), 4.03 (s, 3H, OCH3), 4.29 (s, 2H, OCH2), 7.06 (m, 1H,
ArH), 7.25 (d, 1H, J = 8.4 Hz, ArH)), 7.59 (m, 1H, ArH),
7.80 (m, 1H, ArH). Anal. calcd. for C24H30N2O4Cl4Zn2 (%):
C 42.20, H 4.43, N 4.10; found: C 42.29, H 4.50, N 3.96.
Complex 2c was produced in a manner similar to that of
1c, using of ZnBr2 (0.112 g, 0.497 mmol) and oxazoline 2a
(0.218 g, 1.20 mmol). The yield was 0.20 g (67%) of a
cream coloured solid, mp 215–217 °C (decomp). IR (cm–1):
1632 (s, ν[C=N]), Zn–L vibrations: 286 (m), 268 (m), 258
(m). 1H NMR δ: 4.37 (t, J = 8.7 Hz; 2H, NCH2), 4.49 (t, 2H,
OCH2), 7.39 (d, J = 8.4 Hz, 2H, ArH), 7.81 (d, 2H, ArH).
Anal. calcd. for C18H16N2O2Cl2ZnBr2 (%): C 36.74, H 2.74,
N 4.76; found: C 36.31, H 2.67, N 4.43.
Synthesis of bis-(2-[p-fluorophenyl]-2-oxazoline-␬1N)
zinc(II) bromide (3c)
Complex 3c was produced in a manner similar to that of
1c, using of ZnBr2 (0.112 g, 0.497 mmol) and oxazoline 3a
(0.198 g, 1.20 mmol). The yield was 0.28 g (99%) of a
cream coloured solid, mp 235–237 °C (decomp). IR (cm–1):
1630 (s, ν[C=N]), Zn–L vibrations: 304 (m), 275 (w), 260
(w), 232 (w). 1H NMR δ: 4.34 (m, 2H, NCH2), 4.49 (m, 2H,
OCH2), 7.10 (m, 2H, ArH), 7.89 (m, 2H, ArH). Anal. calcd.
for C18H16N2F2O2ZnBr2 (%): C 38.92, H 2.90, N 5.04;
found: C 38.92, H 3.02, N 5.32.
Synthesis of 4,4-dimethyl-2-(o-anisolyl)-2-oxazoline-
␬2N,OOMe zinc(II) bromide (7c)10
To a sample of ZnBr2 (1.0 g, 4.4 mmol) was added Et2O
(75 mL), and the mixture was stirred at RT until the Zn ma-
terial had dissolved. This mixture was then filtered and
oxazoline 7a (1.13 g, 5.51 mmol) was added in a single por-
tion. A white solid began to precipitate almost immediately.
This material was isolated by filtration after 1 h of stirring at
RT, and the product was then washed with Et2O (50 mL).
The yield was 1.75 g (92%). IR (cm–1): 1626 (s, ν[C=N]).
1H NMR δ: 1.69 (s, 6H, CH3), 4.00 (s, 3H, OCH3), 4.35
(AB-pattern, 2H, OCH2), 7.25 (m, 2H, ArH), 7.69 (m, 1H,
Synthesis of bis-(2-[p-tolyl]-2-oxazoline-␬1N) zinc(II)
bromide (4c)
Complex 4c was produced in a manner similar to that of
1c, using of ZnBr2 (0.112 g, 0.497 mmol) and oxazoline 4a
(0.193 g, 1.20 mmol). The yield was 0.27 g (99%) of a
10Optimized reaction conditions based on product stoichiometry.
© 2008 NRC Canada

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Can. J. Chem. Vol. 87, 2009
ArH), 7.99 (dd, J = 7.8; 1.8, 1H, ArH). Anal. calcd. for
C12H15NO2ZnBr2 (%): C 33.48, H 3.51, N 3.25; found C
33.53, H 2.96, N 3.15.
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Single crystal X-ray structure determinations
X-ray structures of 1b–5b, 2c–4c, and 6c
Suitable crystals of complexes 1b-5b, 2c–4c, and 6c were
obtained from a CH2Cl2 solution of the compounds that had
been layered with an equal volume of Et2O or petroleum
ether and then set aside for several days at RT. Single crys-
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X-ray structures of 7b and 7c
Suitable crystals of complexes 7b and 7c were obtained
from a CH2Cl2 solution of the compounds that had been lay-
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septum, and then set aside for several days at RT. Data was
collected at –100 °C on a Nonius Kappa CCD diffracto-
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and data reductions used the programs DENZO and
SCALEPACK (22). SIR97 (23) was used to solve the struc-
ture and SHELXL-97 (24) was used to refine the structure.
ORTEP-3 for Windows (25) was used for molecular graph-
ics, and PLATON (26) was used to prepare material for pub-
lication. H atoms were placed in calculated positions with
Uiso constrained to be 1.5 times Ueq of the carrier atom for
methyl protons and 1.2 times Ueq of the carrier atom for all
other H atoms.
For complex 7b, the only checkCIF ALERT is for a high
Hirschfeld test (6.59 s.u.) for Zn1 Cl1A. The Cl1 atom is a
bridge Cl, and this behaviour is commonly found for such
atoms. For complex 7c, the only checkCIF ALERT is at the
C level. The centre of gravity of the molecule is claimed to
be outside the unit cell. To us it appears inside the unit cell
and PLATON does not give a new set of coordinates.
For the molecular representations found in Figs. 12 and
14, a general ORTEP (25) view of the molecule of the title
compound is displayed with non-hydrogen displacement el-
lipsoids drawn at the 50% probability level.
Acknowledgements
The authors are indebted to the generous support of Natu-
ral Sciences and Engineering Research Council of Canada,
Ryerson University, the Canadian Breast Cancer Foundation,
and Acadia University. Laura Botelho is also thanked for her
expert experimental assistance.
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