Synthesis and characterisation of κ2-N,O-oxazoline-enolate complexes of nickel(ii): explorations in coordination chemistry and metal-mediated polymerisation

Article abstract of DOI:10.1039/c8ra10304f

The synthesis and characterisation (UV-Vis, IR, X-ray diffraction, etc.) of a series of Ni(ii) complexes derived from both known and novel 2-acylmethyl-2-oxazolines (2a-g: i.e., (Z)-1-R-2-(4,4′-dimethyl-2′-oxazolin-2′-yl)eth-1-en-1-ol; R =-Ph,-2-furanyl,-

Full text of DOI:10.1039/c8ra10304f

RSC Advances
View Article Online
View Journal | View Issue
PAPER
Synthesis and characterisation of k2-N,O-
oxazoline-enolate complexes of nickel(II):
explorations in coordination chemistry and metal-
mediated polymerisation†‡
Cite this: RSC Adv., 2019, 9, 3956
a
Jeanette A. Adjei,a Alan J. Lough§b and Robert A. Gossage
*
The synthesis and characterisation (UV-Vis, IR, X-ray diffraction, etc.) of a series of Ni(II) complexes derived
from both known and novel 2-acylmethyl-2-oxazolines (2a–g: i.e., (Z)-1-R-2-(4,40-dimethyl-20-oxazolin-
20-yl)eth-1-en-1-ol; R ¼ –Ph, –2-furanyl, –p-NO2-Ph, –t-Bu, –2-thiofuranyl, p-NC-Ph, –CF3) is reported.
These Ni materials (3a–g) represent the first group 10 metal complexes of this ligand class. All derivatives
reported are paramagnetic (S ¼ 1) compounds of formulae Ni(k2-N,O-L)2 where L represents an enolate
of structure (Z)-1-R-2-(40,40-dimethyl-20-oxazolin-20-yl)eth-1-en-1-ate formed via proton loss from 2.
The air- and moisture-stable metal complexes feature a less typical distorted seesaw-shaped disposition
of binding atoms around the metal centre for six structurally characterised (X-ray) examples. Preliminary
investigations indicate that 3a (R ¼ –Ph) is a useful catalysts for olefin polymerisation in the presence of
alkylaluminum reagents.
Received 15th December 2018
Accepted 10th January 2019
DOI: 10.1039/c8ra10304f
rsc.li/rsc-advances
that can be easily ne-tuned and ideally are air-stable. Azole
heterocycles typically meet all of these pre-requisites
Introduction
(Scheme 1). Our use of azole ligands is directed towards
a number of applications in coordination2 and medicinal
chemistry,3 ligand design strategies4 and catalysis.5 In terms of
metal-mediated polymerisation, our investigations of Ni-based
trinuclear coordination complexes has revealed active catalytic
systems for the synthesis of polymers such as syndio-tactic
polystyrene.6 Sometime ago, we began a parallel investigation
Polymerisation chemistry, specically involving the use of
transition metal (TM) catalysts, has been an arena of academic
and industrial importance for many decades.1 The application
of rst row transition metals, such as Ni, has enabled the
development of cheaper protocols for the formation of not only
atactic polymers but also stereo-regular macromolecules.1
Nickel-based mediators represent an interesting avenue in
modern catalyst design as the metal itself is relatively inex-
pensive (cf. Zr, Pd, etc.) and the ambient stability hallmarks
a system that is inherently easy-to-handle. Nickel(II) complexes
exhibit rich coordination chemistry and redox behaviour, facets
that are oen exploited in catalyst and property directed
systems.1 Ligands are the linchpin of controlling and modifying
reactivity at the active metal centre and with this in mind, we
have been inclined to use bi- or multi-dentate ligand scaffolds
into
a sub-class of azoles, the 2-acylmethyl-2-oxazolines
(A; Scheme 1).7 These materials, and their analogues, have
been primarily studied as sources of reactive enols in organic
syntheses and/or as potential medicinal agents.7–15
Oxazolines of general structure A (Scheme 1), referred to by
us as Tohda's ligands, had few scattered examples8 until the
pioneering synthetic work on this class of organics by Yasao
aDepartment of Chemistry & Biology, Ryerson University, 350 Victoria Street, Toronto,
ON M5B 2K3, Canada. E-mail: gossage@ryerson.ca
bDepartment of Chemistry, University of Toronto, 80 St. George Street, Toronto, ON
M5S 3H6, Canada. E-mail: alough@chem.utoronto.ca
† This work was presented, in part, at the 68th meeting of the Japan Society for
Coordination Chemistry and at the 43rd International Conference on
Coordination Chemistry (Sendai, Japan, 2018).
‡ Electronic supplementary information (ESI) available. CCDC 1884791–1884796
have been assigned to the structural data for 3a–c and 3e–g, other
crystallographic data, .cif les; meff calculations, DFT calculations, polymer
characterisation data. For ESI and crystallographic data in CIF or other
electronic format see DOI: 10.1039/c8ra10304f
Scheme 1 Azole heterocycles: 1,3-oxazole (top, left); 1,3-benzox-
azole (top, middle); 4,5-dihydro-1,3-oxazole (i.e., 2-oxazoline: top,
right); 2-acylmethyl-2-oxazoline (A: bottom; enol tautomer shown).
§ Contact for queries on crystallography.
3956 | RSC Adv., 2019, 9, 3956–3964
This journal is © The Royal Society of Chemistry 2019

View Article Online
Paper
RSC Advances
Tohda and co-workers beginning in the mid-1980s.9–12 Since
that time, other studies have explored the tautomeric nature of
compounds A (Scheme 1: R ¼ aryl or alkyl group)7–14 and
a number of alternative synthetic methodologies to these and
related species have been probed.13–15 In 2013, we reported the
rst TM coordination compound derived from these materials;
a formally Cu(II) complex B (eqn (1)).
(1)
Scheme 2 The general synthetic scheme for 2a–g; R1 ¼ –Ph (a), 2-
furanyl (b), –Ph-p-NO2 (c), –t-Bu (d), 2-thiofuranyl (e), –Ph-p-CN (f);
R2 ¼ –CF3 (g).
This compound results from the de-protonation of A (R ¼
Ph) and k2-N,O-coordination of the resulting enolate. Herein, we
expand the coordination chemistry of these ligands into the
realm of Ni(II) chemistry. This work reveals aspects of the rich
bonding potential of these enolate sources. In addition, one of
the resulting air-stable Ni(II) complexes is shown to be useful
catalytic precursors for olen polymerisation in the presence of
MAO (MAO ¼ methyl-alumoxane).
complexes are novel and are air- and moisture-stable.
Elemental analyses, IR and UV-Vis spectroscopies are all
consistent with materials of general formulae Ni(2–H)2 (see
Experimental section). Measurement of meff for 3a
conrmed the presumed paramagnetic S ¼ 1 spin state sug-
gested by UV-Vis spectroscopy (meff
¼
3.31 B.M.).‡16
Complexes 3a–g represent the rst group 10 TM examples of
this ligand class.
Results and discussion
The synthesis of the 2-acylmethyl-2-oxazolines described
herein is directly based on known methodologies (Scheme 2)
previously developed by Tohda et al.9–12 This involves the
reaction of commercial 2,4,4-trimethyl-2-oxazoline (C) and
acid chlorides (NEt3/MeCN) forming the key intermediate
amides 1a–f.9 Treatment of these materials with KOH (MeOH)
gives 2a–f. Good yields are obtained for all materials with the
exception of 1f which could not be isolated in pure form; hence
it was formed in situ and thereaer treated with KOH (MeOH)
to yield 2f (see Experimental section).9,11,12 Alternatively, C can
be reacted with triuoromethylacetic anhydride (pyridine/
MeCN: 0 ꢀC) to give 2g (Scheme 2).10,12 The synthesis of 1e,
2e and 2f has not been previously reported and hence these are
novel compounds. The materials are, however, obtained using
the Tohda protocols with little modication.
The desired Ni complexes (3: eqn (2)) were obtained by the
reaction of NiBr2$3(H2O) with two equivalents of 2 in a solu-
tion consisting of NEt3 and 95% EtOH (see Experimental
section).{ The addition of base was required to give suitable
yields; this is in contrast to the Cu(II) derivative B (eqn (1))
which forms directly in the absence of external nucleophiles.7
Metal chelation is thus presumed to occur once 2 is converted
into a more reactive enolate form. Complexes 3a, b, 3d and 3f
are green coloured crystalline solids while 3c and 3e are
brown in colour. Complex 3g is a shade of lavender in the
solid-state; however, when 3g is dissolved in a variety of
solvents, the colour of the solution is distinctly green. All Ni
(2)
X-ray crystallography
Crystals of complexes 3a–c and 3e, f, suitable for X-ray diffrac-
tion study, were obtained by slow crystallisation aer dissolving
the compounds in 95% EtOH and layering the solvent with
hexanes followed by slow evaporation in open air. The crystals
of 3g were grown by recrystallization from acetone solution. All
attempts to obtain suitable quality crystals of 3d were unsuc-
cessful. Crystallographic parameters and a list of selected bond
lengths and angles for 3a–c and 3e–g can be found in Tables 1
and 2, respectively.‡
In all cases, these data conrm that the materials are four-
coordinate Ni complexes with a high degree of tetrahedral
distortion around the metal centre (Scheme 3). Two deproto-
nated ligands 2, in the enolate conguration, are chelated to the
formal Ni2+ ion.17 Bond lengths between Ni and N or O are
typical for Ni(k2-N,O-L)2 complexes and are thus unsur-
prising.18,19 In all materials studied, the O–Ni–N bond angles
ranged from 91.5 to 94.3ꢀ (chelate) and 102.81 to 113.07ꢀ. The
N–Ni–N and O–Ni–O bond angles range from 114.5 to 127.1ꢀ
and 109.8 to 142.0ꢀ, respectively (Table 2). In the vast majority of
cases, complexes with
a
Ni(k2-N,O-L)2 composition have
{ Reduced yields were noted employing [Ni(OH2)6](NO3)2 or [Ni(OH2)6]Cl2.
This journal is © The Royal Society of Chemistry 2019
RSC Adv., 2019, 9, 3956–3964 | 3957

View Article Online
RSC Advances
Paper
Table 1 Crystal and refinement data for complexes 3a–3c and 3e–3g
Complex
3a
3b
3c
3e
3f
3g
Formula
C
26H28N2NiO4
C22H24N2NiO6
471.14
Monoclinic
P21/c
C26H26N4NiO8
581.22
Triclinic
ꢀ
P1
C22H24N2NiO4S2
503.26
Monoclinic
P21/n
C28H26N4NiO4
541.24
Triclinic
ꢀ
P1
C16H18F6N2NiO4
475.03
Orthorhombic
Pbca
Molar mass (g molꢁ1
Cryst. syst.
Space group
T/K
)
491.21
Monoclinic
P21/c
150
150
150
150
150
150
˚
a (A)
12.0764(17)
9.6715(15)
20.657(4)
90
92.155(5)
90
2411.0(7)
4
1.353
10.2574(8)
11.7648(9)
23.418(2)
90
95.190(3)
90
2127.9(3)
4
1.471
9.5476(10)
10.5561(12)
14.4705(16)
74.720(3)
70.961(3)
70.689(3)
1281.1(2)
2
9.8995(5)
14.7668(8)
16.2988(9)
90
104.652(2)
90
2305.1(2)
4
1.450
6.9179(6)
9.6038(10)
20.210(2)
103.140(3)
94.606(3)
98.490(3)
1284.2(2)
2
11.1193(4)
18.3316(8)
19.0410(8)
90
90
90
3881.2(3)
8
1.626
˚
b (A)
˚
c (A)
a (ꢀ)
b (ꢀ)
g (ꢀ)
3
˚
V (A )
Z
Density (calc.; Mg mꢁ3
)
1.507
1.400
Absorption coefficient
0.839
0.953
0.815
1.054
0.797
1.081
(mmꢁ1
)
Crystal size (mm3)
0.150 ꢂ 0.150 ꢂ
0.040
0.71073
1.001
24.999
35 050
0.180 ꢂ 0.160 ꢂ
0.050
0.71073
1.001
27.559
33 572
0.0562
284
0.200 ꢂ 0.180 ꢂ
0.110
0.71073
1.024
27.698
31 731
0.0333
356
0.280 ꢂ 0.240 ꢂ
0.220
0.71073
1.052
27.519
31 003
0.0282
321
0.250 ꢂ 0.080 ꢂ
0.050
0.71073
1.024
27.673
52 010
0.0449
338
0.300 ꢂ 0.150 ꢂ
0.050
0.71073
0.993
27.524
26 354
0.0721
294
˚
l (MoKa: A)
Goodness-of-t-on F2
Max. 2q (ꢀ)
Reections
R(int)
0.1140
302
Param.
R1[I > 2s(I)]
wR2 (all data)
0.0438
0.08686
0.0324
0.0714
0.0301
0.0733
0.0264
0.0667
0.0305
0.0692
0.0386
0.0789
Table 2 Selected bond angles (ꢀ) and bond lengths (A˚) for 3a–3c, and 3e, 3f; estimated standard deviations are in parentheses
Descriptor
3a
3b
3c
3e
3f
3g
O(3)–Ni(1)–O(1)
O(3)–Ni(1)–N(2)
O(1)–Ni(1)–N(2)
O(3)–Ni(1)–N(1)
O(1)–Ni(1)–N(1)
N(2)–Ni(1)–N(1)
Ni(1)–O(3)
Ni(1)–O(1)
Ni(1)–N(2)
Ni(1)–N(1)
131.15(9)
92.44(10)
112.04(10)
113.07(10)
92.62(10)
117.71(11)
1.912(2)
1.917(2)
1.937(3)
1.937(3)
140.61(6)
92.89(6)
102.81(6)
110.44(6)
94.29(6)
117.02(7)
1.9272(13)a
1.9325(13)
1.9531(16)
1.9560(16)
141.83(5)
93.04(5)
104.36(5)
107.53(5)
92.16(5)
121.31(6)
1.9377(11)b
1.9362(11)b
1.9597(14)
1.9547(14)
137.71(5)
93.18(5)
110.04(5)
106.88(5)
93.58(5)
117.17(6)
1.9253(11)
1.9214(11)
1.9479(14)
1.9437(14)
138.36(5)
92.11(5)
106.42(5)
109.82(5)
91.51(5)
122.31(6)
1.9282(11)
1.9276(11)
1.9338(14)c
1.9381(13)
123.24(7)
92.62(8)
111.40(8)
113.00(8)
92.58(XX)
127.11(8)
1.9284(16)
1.9185(17)
1.940(2)
1.941(2)
a
b
Bonds are labelled Ni(1)–O(4); additional O atom originates from the furan functionality. Bonds are labelled Ni(1)–O(5) and Ni(1)–N(3);
additional O atoms originate from the nitro group. c Bonds are labelled Ni(1)–N(3); additional N atom originates from the cyano group.
a square planar arrangement of donor atoms around the Ni As deviation from square planar is an atypical bonding motif for
centre and are diamagnetic (S ¼ 0).20 Some of these materials complexes such as these, we have further modelled the mate-
24
also subsequently bind opportunistic solvent molecules (water, rials by calculating their s4 values.k This parameter gives
acetone, etc.) leading to the formation of high spin octahedral a quantitative measure of the degree of distortion from ideal-
or square pyramidal Ni complexes.21–23 With the materials ised square planar (s4 ¼ 0.00) to truly tetrahedral (s4 ¼ 1.00) by
herein, we observe none of these typical characteristics. Despite examining the larger bond angles between the ligating atoms
the wide variety of substituents on the enolate skeleton (steric,
EDG, EWG), these groups appear to have little inuence on the
k N.b., the structural characterisation of the apparent distorted tetrahedral
resulting solid-state structures of these Ni compounds. This is
true in both an intramolecular sense (bond lengths/angles
around Ni) and in the lack of propensity for formation of
noticeable long-range intermolecular character (e.g., m O/S
furan/thiophene binding: 3b and 3e; Ni/NC interactions: 3f).
complex
bis(5-bromo-N-cyclohexylsalicylideneaminato)-nickel(II),
in
the
orthorhombic crystal system (Y.-X. Sun, G. Yang, G. Chen, M. Sun and H.-L.
Zhang, Acta Cryst., 2005, E61, m1103–m1104), has been challenged (C. M.
Wandtke, M. Weil, J. Simpson and B. Dittrich, Acta Cryst., 2017, B73, 794–804).
A related complex (X.-F. Zhao, Acta Cryst., 2007, E63, m704–m705) has since
been withdrawn from the literature (Acta Cryst., 2017, E73, 926).
3958 | RSC Adv., 2019, 9, 3956–3964
This journal is © The Royal Society of Chemistry 2019

View Article Online
Paper
RSC Advances
Scheme 3 ORTEP representations of unit cell molecules of 3a (top, left), 3b (top, middle), 3c (top, right), 3e (bottom, left), 3f (bottom, middle) and
3g (bottom, right).
such conditions. As expected, a large excess of MAO was
required for catalytic activity; no polymerisation was observed
Table 3 Calculated s4 values of 3a–c and 3e–g
in the absence of the Ni promoter. Although not vigorously
active, 3a does gives reasonable conversions to narrow
dispersed polystyrene products at 60 ꢀC in toluene solution
a
Complex
s4
3a
3b
3c
3e
3f
0.79
0.73 (Table 4). Examination of this material revels it is atactic in
0.69
0.74
0.70
nature.‡ This preliminary examination was designed to show
the proof-of-principle activity of these complexes for olen
activation. A more detailed study of the polymerisation char-
0.77
3g
acteristics of these Ni systems will be the subject of a subse-
a
Calculated using s4 ¼ [360ꢀ ꢁ (a + b)ꢀ]/141ꢀ; where a and b are the two
quent submission.
largest L–Ni–L bond angles.24
and the metal. The calculated values are displayed in Table 3.
All six complexes give similar s4 values in the range of 0.70–0.79.
Although oen simply referred to using the generic term dis-
torted tetrahedral in nature,18,19 these complexes are best
described as having a distorted seesaw coordination disposition
of ligating atoms around Ni. This latter descriptor is found in
idealised systems with s4 ¼ 0.64.24 Scheme 3 contains ORTEP
representations of a unit cell molecule of each complex.
Experimental
General considerations
All reactions were carried out under ambient atmosphere
conditions unless otherwise stated. Chemical reagents were
purchased commercially and used as received. Reaction
Table 4 Aspects of the polymerisation of styrene by 3aa
Al : Ni
(mol ratio)
Polymer
yield (%)
Activity
Molecular
weight (Da)
Catalytic activity of 3a
Run
(TON hꢁ1
)
PDI
We rst tested Ni complex 3a for possible activity in C–C bond
formation under standard Suzuki cross-coupling conditions
using PhI and PhB(OH)2.25,26 Unfortunately, 3a shows no activity
for biphenyl formation in this regard. However, structurally
related Ni materials are known to mediate olen polymerisation
in the presence of alkyl-Al reagents such as MAO.27 Therefore, 3a
was tested as catalyst for the polymerisation of styrene under
1
2
3
4
0
0
97
93
65
0
n/a
n/a
1.1
1.1
1.2
500 : 1
800 : 1
1000 : 1
1.3 ꢂ 103
1.2 ꢂ 103
8.4 ꢂ 102
1.5 ꢂ 104
2.8 ꢂ 104
1.0 ꢂ 104
a
Polymerisation conditions: 1 h at 60 ꢀC; 20 mmol of 3a in 2 mL of C7H8;
3 mL (2.7 g; 0.026 mol) of styrene in 7 mL C7H8.
This journal is © The Royal Society of Chemistry 2019
RSC Adv., 2019, 9, 3956–3964 | 3959

View Article Online
RSC Advances
Paper
solvents were further puried by an mBraun Solvent Purica- solution was cooled and solvents removed by rotary evapora-
tion System (SPS) or as received. NMR spectra were recorded on tion. To the resulting residue as added 50 mL of water and this
a Bruker AV400 spectrometer using CDCl3 as solvent (chloro- aqueous mixture extracted with DCM (3 ꢂ 20 mL). The organic
form-d) at 400 MHz (1H), 100 MHz (13C) and 376 MHz (19F) at layer was then isolated, washed with 10% aq. Na2CO3 and then
room temperature (RT). In all the spectra, chemical shis were dried over MgSO4. Evaporation of the solvents revealed an
1
adjusted to the solvent peak (7.26 ppm for CHCl3 for H and orange-coloured oil. This crude material was recrystallized
77.16 ppm for CDCl3 for 13C). Elemental analysis was performed using 1 : 1 (v : v) hexanes–toluene as solvent affording a white
by Atlantic Microlab, Inc. of Norcross, GA (USA). Time-of-ight coloured product. The yield of this solid was 4.1 g (82%). Mp:
mass spectrometry analyses were performed using a JMS- 171–174 ꢀC. 1H NMR: dH ¼ 7.71 (d, 3J ¼ 4 Hz, 1H), 7.68 (d, 3J ¼
T1000LC mass spectrometer (JEOL Inc., Peabody, MA [USA]) 4 Hz, 1H), 7.42 (d, 3J ¼ 4 Hz, 1H), 7.11 (t, 3J ¼ 4 Hz, 1H), 7.07 (d,
equipped with a direct analysis in real time (DART) ionization 3J ¼ 4 Hz, 1H), 6.94 (t, 3J ¼ 2 Hz, 1H), 5.35 (s, 1H), 4.32 (s, 2H),
source (DART-SVP, Ionsense Inc., Saugus, MA, USA) located at 1.61 (s, 6H). 13C {1H} NMR: dC ¼ 179.3, 162.0, 161.4, 147.5,
the University of Toronto. The DART source was operated with 137.1, 133.7, 133.5, 131.4, 128.7, 128.0, 127.7, 84.7, 79.8, 63.4,
He (g), and the temperature was adjusted in the range 100– 22.8. Selected IR (cmꢁ1): 1671 (m, C]O), 1625 (m, C]C).
12
400 ꢀC. Isotopic distributions for the observed ionic species HRMS-DART (m/z): calculated for
C
1H1614N116O332S2:
16
were calculated using the Mass Center utility (JEOL) and were in 334.05716 ([M + H]+); found 334.05577.
good agreement with the measured spectra. Melting points
Compound 2e. This material was prepared by treating
were determined using a Fisher Scientic melting point appa- a sample of 1e (2.0 g; 6.0 mmol) with 2.0 M solution of meth-
ratus (max. temperature of 300 ꢀC) and are uncorrected. IR anolic KOH. The initial solution was clear and turned to a yellow
spectra were obtained on Agilent Technologies Cary 630 Fourier and then orange solution with the formation of white precipitate
Transform Infrared (FTIR)-Diamond Attenuated Total Reec- over time. Aer stirring the solution overnight, the precipitates
tance (ATR). Ultraviolet-visible (UV-Vis) spectra were obtained were ltered off and water (50 mL) was added to the ltrate. The
on Agilent Technologies Cary Series UV-Vis-NIR Spectropho- mixture was then extracted with 50 mL of DCM. The organic layer
tometer. THF (tetrahydrofuran) and DCM (dichloromethane), was washed with water and then dried over MgSO4. Aer removal
having the onset peaks at 215 nm and 230 nm respectively, were of the solvent (rotary evaporation), the residue was recrystallized
used as solvents. The average molecular weights and properties from hexanes : toluene (4 : 1; v : v) yielding a pale-yellow solid
of the polystyrene produced was determined by gel permeation (0.84 g; 63%). Mp ¼ 100.5–103.5 ꢀC. 1H NMR: dH ¼ 9.67 (s, 1H),
chromatography (GPC) using a Viscotek Triple Model 302 7.50 (m, 2H), 7.41 (d, 3J ¼ 4 Hz, 2H), 7.05 (t, 3J ¼ 4 Hz, 1H), 5.45 (s,
Detector system equipped with a Refractive Index Detector (RI), 2H), 4.14 (s, 2H), 1.42 (s, 6H). 13C {1H} NMR: dC ¼ 180.90, 169.29,
a four-capillary differential viscometer (VISC), a right angle (90ꢀ) 147.17, 129.62, 127.13, 127.15, 79.11, 73.67, 58.60, 27.17. Selected
laser light scattering detector. GPC columns were calibrated IR (cmꢁ1): 3254 (w, O–H), 1610 (m). Anal. calc. for C11H13NO2S: C
versus polystyrene standards (American Polymer Standards). A 59.17, H 5.87, N 6.27; found: C 59.22, H 5.90, N 6.29.
ow rate of 1.0 mL minꢁ1 was used with ACS grade THF as
Compound 2f. The intermediate 1f was prepared in situ but
eluent. GPC samples were prepared using 5 mg of polymer not isolated by the following method. A sample of C (10 mmol)
per mL THF and ltered using a 0.45 mm lter. The University of in MeCN (30 mL) was treated with 4-cyanobenzoyl chloride (30
Toronto X-ray Crystallographic facility was used to obtain the X- mmol) and NEt3 (37.5 mmol). Isolation was initiated as per 1e
ray structural information as previously described.28,29 Data was above and the resulting solids (crude 1f) treated directly with
collected on a Bruker Kappa APEX DUO diffractometer using 2.0 M methanolic KOH. A pale-yellow coloured solid was iso-
monochromated Mo-Ka radiation (Bruker Triumph) and were lated as detailed above for 2e (yield 0.11 g: 14%). Mp ¼ 179–
measured using a combination of f scans and u scans. The data 180 ꢀC. 1H NMR: dH ¼ 9.99 (s, 1H), 7.89 (d, 3J ¼ 8 Hz, 2H), 7.63
was processed using APEX2 and SAINT1. Absorption corrections (d, 3J ¼ 8 Hz, 2H), 5.49 (s, 1H), 4.17 (s, 2H), 1.43 (s, 6H). 13C {1H}
were carried out using SADABS soware 1. The structures were NMR: dC ¼ 184.9, 169.9, 143.9, 132.1, 127.3, 118.7, 113.7, 79.2,
solved using SHELXT2 and rened using SHELXL-20132 for full 74.6, 58.8, 27.1. Selected IR (cmꢁ1): 3235, 2230 (C^N), 1618 (m).
1
matrix least-squares renement that was based on F2. For all HRMS-DART (m/z): calculated for 12C14 H1514N216O2 ([M + H]+):
structures, H atoms were included in calculated positions and 243.11335; found 243.11383.
allowed to rene in a riding-motion approximation with Uꢃiso
tied to the carrier atom as described previously. Molecular
modelling calculations were carried out using the Spartan 16.0
Synthesis of complex 3a
suite of programs as described earlier.‡30 Compounds 1a–1d, Nickel(II) bromide trihydrate (0.45 g, 2.04 mmol) was dissolved
2a–2d, and 2g were synthesised using literature methods.9–12 in 30 mL of EtOH. This was followed by the addition of 2a
Spectroscopic data of these products were consistent within (0.89 g, 4.08 mmol) and NEt3 (1.25 mL, 8.98 mmol). The initial
experimental error to those previously reported.
green coloured solution turned into darker green in colour with
Compound 1e. A sample of 2,4,4-trimethyl-2-oxazoline (C: 15 precipitate(s) being formed. The solution was stirred overnight
mmol) was treated with 2-theonyl chloride (30 mmol) and NEt3 at RT. Volatile components of this mixture were then removed
(37.5 mmol) in MeCN solution (30 mL). The solution turned (vacuo) yielding a green coloured oil. A volume of Et2O was then
orange in colour and yellow-coloured precipitates formed. The used to precipitate the assumed HNEt3Br salt that had formed;
mixture was then heated to reux temperature for 3 h. The this material was ltered off using vacuum ltration. The ltrate
3960 | RSC Adv., 2019, 9, 3956–3964
This journal is © The Royal Society of Chemistry 2019

View Article Online
Paper
RSC Advances
was then collected and the solvent was again evaporated in 423 nm (3 ¼ 3.43 ꢂ 103). Anal. calc. for C28H26N4O4Ni: C, 62.24;
vacuo. The resulting green coloured oil was solidied by titu- H, 4.84; N, 10.35. Found: C, 62.09; H, 4.91; N, 10.35.
ration with aq. EtOH and the resulting green coloured solids
were washed with further aq. EtOH. This afforded a green col-
oured crystalline product (0.77 g, 77%). Mp: 210–212 ꢀC.
Selected IR (cmꢁ1): 1526 (s). UV-Vis: 242 nm (3 ¼ 4.65 ꢂ 104),
319 nm (3 ¼ 3.79 ꢂ 104), 421 nm (3 ¼ 1.37 ꢂ 103). Anal. calc. for
Synthesis of complex 3g
The compound was prepared and puried as for 3a using 2g
(0.25 g, 1.2 mmol) and NiBr2$3H2O (0.16 g, 0.60 mmol). The
product was isolated as green coloured crystalline solid (0.77 g,
C
26H28N2O4Ni: C, 63.57; H, 5.75; N, 5.70. Found: C, 63.42; H,
77%). Mp: 160–162 C (decomp.). Selected IR (cmꢁ1): 1531 (s).
ꢀ
5.85; N, 5.79.
UV-Vis: 274 nm (3 ¼ 1.69 ꢂ 104). Anal. calc. for C16H18N2O4F6Ni:
C, 40.46; H, 3.82; N, 5.90. Found: C, 40.72; H, 3.82; N, 5.94.
Synthesis of complex 3b
Styrene polymerisation
The compound was prepared and puried as for 3a using 2b
(0.25 g, 1.20 mmol) and NiBr2$3H2O (0.16 g, 0.60 mmol). The
product was isolated as green coloured crystalline solid (0.17 g,
61%). Mp: 208–211 ꢀC. Selected IR (cmꢁ1): 1522 (s). UV-Vis:
266 nm (3 ¼ 3.91 ꢂ 104), 322 nm (3 ¼ 4.72 ꢂ 104), 435 nm (3
¼ 1.22 ꢂ 103). Anal. calc. for C22H24N2O6Ni: C, 56.09; H, 5.13; N,
5.95. Found: C, 56.20; H, 5.23; N, 6.08.
Under an N2 atmosphere, a 20 mmol sample of the nickel(II)
complex 3a (dissolved in 2.0 mL C7H8), 3 mL of styrene and
7 mL of toluene were added to a 50 mL three-neck round bottom
ask. The mixture was then degassed for 15 min (N2 purge) and
the temperature subsequently raised to 60 ꢀC for 5 min. A
5.80 mL sample (10% in weight toluene) of MAO was charged
into the system via syringe and stirring was continued. Aer 1 h,
acidic MeOH (VMeOH/Vconc. HCl ¼ 20/1) was added to terminate
the reaction. The resulting PS mixture was then dissolved in
CHCl3 and extracted with water. The organic layer was dried
(MgSO4) and evaporated to give the crude product. This mate-
rial was dissolved in minimal THF and was added dropwise to
a stirring solution of cold MeOH in a 100 mL Erlenmeyer ask.
White precipitates were thus formed and the MeOH was dec-
anted off. The resulting white coloured solids were transferred
to a 50 mL round bottom ask and then dried under vacuum.
The above purication step was repeated two more times and
the PS obtained was then analysed.
Synthesis of complex 3c
The compound was prepared and puried as for 3a using 2c
(0.25 g, 1.20 mmol) and NiBr2$3H2O (0.16 g, 0.60 mmol). The
product was isolated as green coloured crystalline solid (0.15 g,
54%). Mp: 261 ꢀC (decomp.). Selected IR (cmꢁ1): 1514 (s), 1300
(s). UV-Vis: 263 nm (3 ¼ 5.16 ꢂ 104), 368 nm (3 ¼ 2.89 ꢂ 104).
Anal. calc. for C26H26N4O8Ni: C, 53.73; H, 4.51; N, 9.81. Found:
C, 54.00; H, 4.60; N, 9.81.
Synthesis of complex 3d
The compound was prepared and puried as for 3a using 2d
(0.25 g, 1.2 mmol) and NiBr2$3H2O (0.17 g, 0.62 mmol). The
product was isolated as green coloured crystalline solid (0.24 g,
Conclusions
86%). Mp: 215–221 C. Selected IR (cmꢁ1): 2959, 1522 (s). UV-
ꢀ
The synthesis and characterisation of the rst group 10
complexes, specically Ni(II), of the enolates derived from 2-
acylmethyl-2-oxazolines (Tohda's ligands) has been described.
Examination by spectroscopy and X-ray diffraction methods
have shown these materials to be of the less common para-
magnetic Ni(k2-N,O-L)2 formulation with a distorted seesaw
arrangement of bonding atoms around the metal centres. A
preliminary examination of one derivative has shown that it is
an active catalyst, in the presence of excess MAO, for the
formation of low dispersity atactic polystyrene from the
monomer at elevated temperatures.
Vis: 280 nm (3 ¼ 2.11 ꢂ 104), 383 nm (3 ¼ 1.24 ꢂ 103). Anal.
calc. for C22H36N2O4Ni (n.b., a reproducible combustion anal-
ysis for this compound could not be obtained). HRMS-DART (m/
12
z): calculated for
C
1H3714N216O458Ni ([M + H]+): 451.21156;
22
found 451.21068.
Synthesis of complex 3e
The compound was prepared and puried as for 3a using 2e
(0.25 g, 1.20 mmol) and NiBr2$3H2O (0.15 g, 0.60 mmol). The
product was isolated as green coloured crystalline solid (0.21 g,
75%). Mp: 203–206 ꢀC. Selected IR (cmꢁ1): 1511 (s). UV-Vis:
251 nm (3 ¼ 3.16 ꢂ 104), 336 nm (3 ¼ 3.96 ꢂ 104), 435 nm (3
¼ 1.02 ꢂ 103). Anal. calc. for C22H26N2O4S2Ni: C, 52.51; H,
4.89; N, 5.57. Found: C, 51.88; H, 4.84; N, 5.58.
Conflicts of interest
The authors declare no conict of interest.
Acknowledgements
Synthesis of complex 3f
The compound was prepared and puried as for 3a using 2f Ms S. El Sayed and Ms K. L. May are thanked for their contri-
(0.25 g, 1.0 mmol) and NiBr2$3H2O (0.11 g, 0.52 mmol). The butions to this research. The authors acknowledge NSERC
product was isolated as green coloured crystalline solid (0.14 g, (Canada) for funding (Discovery Grant: RAG; NSERC USRA: JAA)
50%). Mp: 160–161 ꢀC (decomp.). Selected IR (cmꢁ1): 2227, 1522 and the generous support of Ryerson University for facilitating
(s). UV-Vis: 248 nm (3 ¼ 4.83 ꢂ 104), 337 nm (3 ¼ 2.73 ꢂ 104), this research (Dean's Research Fund and Dean's Booster Fund:
This journal is © The Royal Society of Chemistry 2019
RSC Adv., 2019, 9, 3956–3964 | 3961

View Article Online
RSC Advances
Paper
RAG; Undergraduate Research Opportunity Award: JAA). We
would also like to thank Prof. B. D. Koivisto and his research
team for access to, and very helpful discussions about, their UV-
Vis spectrophotometer. Further kind acknowledgements go out
and R. A. Gossage, Bioorg. Med. Chem. Lett., 2011, 21, 4512–
4515; F. J. Baerlocher, R. Bucur, A. Decken, C. R. Eisnor,
R. A. Gossage, S. M. Jackson, L. Jolly, S. L. Wheaton and
R. S. Wylie, Aust. J. Chem., 2010, 63, 47–55; A. Decken and
R. A. Gossage, J. Inorg. Biochem., 2005, 99, 664–667.
¨
¨
to Prof. Dr Hans-Beat Burgi (University of Zurich) for very
helpful discussions with respect to the structural aspects of
complex 3a.
´
4 K. Hermasymchuk, J. Huynh, A. J. Lough, L. Roces Fernandez
and R. A. Gossage, Synthesis, 2016, 48, 2121–2129;
R. A. Gossage, Dalton Trans., 2011, 40, 1594–1600;
A. Decken, R. A. Gossage and P. N. Yadav, Can. J. Chem.,
2005, 83, 1185–1189.
Notes and references
´
´
5 M. Taghvaee, M. J. Rodrıguez-Alvarez, J. Garcıa-Alvarez, I. del
´
´
1 R. Whyman, Applied Organometallic Chemistry & Catalysis,
Oxford University Press, Toronto, 2001, ch. 6; G. Odian,
Principles of Polymerization, Wiley-Interscience, Hoboken,
4th edn, 2004; S. D. Ittel, L. K. Johnson and M. Brookhart,
Chem. Rev., 2000, 100, 1169–1204; Z. Guan, Chem.–Asian J.,
2010, 5, 1058–1070; T. R. Younkin, E. F. Connor,
J. I. Henderson, S. K. Friedrich, R. H. Grubbs and
D. A. Bansleben, Science, 2000, 287, 460–462; H. Ohtsu and
K. Tanaka, Inorg. Chem., 2004, 43, 3024–3030; H. Ohtsu
and K. Tanaka, Chem.–Eur. J., 2005, 11, 3420–3426;
O. Rotthaus, F. Thomas, O. Jarjayes, C. Philouze, E. Saint-
Aman and J.-L. Pierre, Chem.–Eur. J., 2006, 12, 6953–6962;
T. Storr, E. C. Wasinger, R. C. Pratt and T. D. P. Stack,
Angew. Chem., Int. Ed., 2007, 46, 5198–5201; L. Lecarme,
L. Chiang, C. Philouze, O. Jarjayes, T. Storr and F. Thomas,
Eur. J. Inorg. Chem., 2014, 3479–3487; Y. Shimazaki,
N. Arai, T. J. Dunn, T. Yajima, F. Tani, C. F. Ramogida and
T. Storr, Dalton Trans., 2011, 40, 2469–2479; Y. Shimazaki,
T. D. P. Stack and T. Storr, Inorg. Chem., 2009, 48, 8383–
´
Rıo, A. J. Lough and R. A. Gossage, J. Organomet. Chem., 2017,
´
845, 107–114; J. A. Cabeza, I. da Silva, I. del Rıo,
´
R. A. Gossage, L. Martınez-Mendez and D. Miguel, J.
Organomet. Chem., 2007, 692, 4346–4352; J. A. Cabeza, I. da
´
´
Silva, I. del Rıo, R. A. Gossage, D. Miguel and M. Suarez,
Dalton Trans., 2006, 2450–2455; J. T. Banks, K. M. Button,
R. A. Gossage, T. D. Hamilton and K. E. Kershaw,
Heterocycles, 2001, 55, 2251–2256.
´
6 S. Resanovic, R. S. Wylie, J. W. Quail, D. A. Foucher and
R. A. Gossage, Inorg. Chem., 2011, 50, 9930–9932.
7 R. C. Jones, K. Herasymchuk, T. Mahdi, A. Petrov,
´
S. Resanovic, D. G. Vaughan, A. J. Lough, J. W. Quail,
B. D. Koivisto, R. S. Wylie and R. A. Gossage, Org. Biomol.
Chem., 2013, 11, 3484–3493.
8 A. I. Meyers, D. L. Temple, R. L. Nolen and E. D. Mihelich, J.
Org. Chem., 1974, 39, 2778–2783.
9 Y. Tohda, T. Kawashima, M. Ariga, R. Akiyama, H. Shudoh
and Y. Mori, Bull. Chem. Soc. Jpn., 1984, 57, 2329–2330.
8392; L. Chiang, R. M. Clarke, K. Herasymchuk, 10 Y. Tohda, M. Morikawa, T. Kawashima, M. Ariga and
M. Sutherland, K. E. Prosser, Y. Shimazaki and T. Storr,
Eur. J. Inorg. Chem., 2016, 49–55.
2 P. N. Yadav, T. M. Barclay and R. A. Gossage, J. Nepal Chem.
Soc., 2011, 28, 54–58; R. C. Jones, M. W. Chojnacka,
Y. Mori, Chem. Lett., 1986, 273–274.
11 Y. Tohda, T. Yanagidana, S. Hiramatsu, N. Nishiwaki,
K. Tani, K. Imagawa and M. Ariga, Bull. Chem. Soc. Jpn.,
1997, 70, 2781–2790.
J. W. Quail, M. G. Gardiner, A. Decken, B. F. Yates and 12 Y. Tohda, T. Yanagidani and N. Asaka, Bull. Chem. Soc. Jpn.,
R. A. Gossage, Dalton Trans., 2011, 40, 1594–1600;
2016, 89, 810–822.
R. A. Gossage and H. A. Jenkins, Acta Chim. Slov., 2009, 56, 13 S. Chatterjee, G. Ye, Y. Song, B. L. Barker and C. U. Pittman
´
329–333; I. del Rıo and R. A. Gossage, Acta Crystallogr.,
Jr, Synthesis, 2010, 3384–3394; A. Zhou and C. U. Pittman Jr,
Tetrahedron Lett., 2005, 46, 2045–2048; Y. Song, H. I. de Silva,
W. P. Henry, G. Ye, S. Chatterjee and C. U. Pittman Jr,
Tetrahedron Lett., 2011, 52, 4507–4511.
Sect. E: Struct. Rep. Online, 2009, 65, m103–m104;
R. A. Gossage, P. N. Yadav, T. D. MacInnis, A. Decken and
J. W. Quail, Can. J. Chem., 2009, 87, 368–379; P. N. Yadav,
R. A. Gossage and A. Decken, Anal. Sci., 2008, 24, x301– 14 F. Castan, F. Denonne and D. C. H. Bigg, Synthesis, 1993,
x302; R. A. Gossage, H. A. Jenkins, N. D. Jones, R. C. Jones
and B. F. Yates, Dalton Trans., 2008, 3115–3122; A. Decken,
C. R. Eisnor, R. A. Gossage and S. M. Jackson, Inorg. Chim.
1081–1083; A. Wisniewski Jr, A. R. M. Oliveira, C. Jorge da
Cunha, F. Simonelli and F. A. Marques, J. Braz. Chem. Soc.,
1999, 10, 369–374.
Acta, 2006, 359, 1743–1753; A. Decken, L. Botelho, 15 M. Kawase, M. Teshima, S. Saito and S. Tani, Heterocycles,
A. L. Sadowy, P. N. Yadav and R. A. Gossage, Acta
Crystallogr., Sect. E: Struct. Rep. Online, 2006, 62, o5414–
1998, 48, 2103–2109; M. Kawase, H. Harada, S. Saito, J. Cui
and S. Tani, Bioorg. Med. Chem. Lett., 1999, 9, 193–194;
M. Kawase, N. Motohashi, H. Sakagami, T. Kanamoto,
H. Nakashima, L. Ferenczy, K. Wolfard, C. Miskolci and
´
o5416; T. M. Barclay, I. del Rıo, R. A. Gossage and
S. M. Jackson, Can. J. Chem., 2003, 81, 1482–1491.
´
J. Molnar, Int. J. Antimicrob. Agents, 2001, 18, 161–165.
3 P. N. Yadav, R. E. Beveridge, J. Blay, A. R. Boyd,
M. W. Chojnacka, A. Decken, A. A. Deshpande, 16 G. A. Bain and J. F. Berry, J. Chem. Educ., 2008, 85, 532–536.
M. G. Gardiner, T. W. Hambley, M. J. Hughes, L. Jolly, 17 J. Vicente, Coordination Chemistry of Metal Enolates, in The
J. A. Lavangie, T. D. MacInnis, S. A. McFarland, E. J. New
and R. A. Gossage, Med. Chem. Commun., 2011, 2, 274–277;
Chemistry of Metal Enolates Part 1, ed. J. Zabicky, Wiley,
Mississauga, 2009, ch. 6, pp. 313–353.
E. E. Gordey, P. N. Yadav, M. P. Merrin, J. Davies, 18 D.-S. Xia, W. Chen, Y.-M. Zhao and Q.-F. Zeng, Acta
S. A. Ward, G. M. J. Woodman, A. L. Sadowy, T. G. Smith
Crystallogr., Sect. E: Struct. Rep. Online, 2008, 64, m843;
3962 | RSC Adv., 2019, 9, 3956–3964
This journal is © The Royal Society of Chemistry 2019

View Article Online
Paper
D.-S. Xia, W. Chen, H. Wang and Q.-F. Zeng, Acta Crystallogr.,
RSC Advances
Crystallogr., Sect. E: Struct. Rep. Online, 2007, 63, m3174;
L.-Z. Li and L.-H. Wang, Acta Crystallogr., Sect. E: Struct.
Rep. Online, 2007, 63, m1791; Y. Elerman, A. Elmani,
I. Svoboda and H. Fuess, Acta Crystallogr., Sect. C: Cryst.
Struct. Commun., 1998, 54, 1076–1078; H.-Y. Liu, F. Gao,
Z.-S. Lu and H.-Y. Wang, Acta Crystallogr., Sect. E: Struct.
Sect. E: Struct. Rep. Online, 2008, 64, m842; Y. Wu, B. Xie,
L. Zou, J.-S. Feng and Z. Hu, Acta Crystallogr., Sect. E:
Struct. Rep. Online, 2007, 63, m2298.
19 Y.-X. Sun and S. W. Ng, Acta Crystallogr., Sect. E: Struct. Rep.
Online, 2005, 61, m323–m324; N. N. Kharabaev, Koord.
Khim., 1991, 17, 579–596; V. S. Psalidas, P. M. Zorkii and
M. A. Porai-Koshits, Vestn. Mosk. Univ., Ser. 2: Khim., 1975,
16, 531–535.
¨
Rep. Online, 2006, 62, m1306–m1308; T. Hokelek,
¨
¨
N. Gunduz, Z. Hayvali and Z. Keliç, Acta Crystallogr., Sect.
C: Cryst. Struct. Commun., 1995, 51, 880–884; B. Kamenar,
´
20 E. Uhlig, Coord. Chem. Rev., 1973, 10, 227–264; A. Blagus,
B. Kaitner and A. Stephanovic, Acta Crystallogr., Sect. C:
ˇ ´
ˇˇ ´
´
D. Cincic, T. Friscic, B. Kaitner and V. Stilinovic, Maced. J.
Chem. Chem. Eng., 2010, 29, 117–138; Y. Zhang, T.-F. Liu
and W.-G. Xu, Acta Crystallogr., Sect. E: Struct. Rep. Online,
2007, 63, m2231; X.-L. Zhang, Z. Kristallogr. - New Cryst.
Struct., 2009, 224, 679–680; J.-X. Ma, Q.-L. Li, P.-P. Li,
J. X. Zhao and L. Zhao, Z. Kristallogr. - New Cryst. Struct.,
2018, 233, 789–791; G. P. Voutsas, K. G. Keramidas,
E. Dova, M. Lalia-Kantouri and M. Hartophylles, Z.
Kristallogr. - New Cryst. Struct., 1999, 214, 33–34; J.-X. Ma,
Q.-L. Li, P.-P. Li, J. X. Zhao and L. Zhao, Z. Kristallogr. -
New Cryst. Struct., 2018, 233, 767–769; X. Dong, Z. Gui and
Y. Li, Z. Kristallogr. - New Cryst. Struct., 2010, 225, 703–704;
B.-W. Li, M.-H. Zeng and S. W. Ng, Acta Crystallogr., Sect.
E: Struct. Rep. Online, 2009, 65, m318; Q. P. Huang,
S. H. Zhang, J. J. Guo, C. Feng and F. S. Tang, Acta
Crystallogr., Sect. E: Struct. Rep. Online, 2011, 67, m1611;
Z.-X. Li, X.-L. Zhang and X.-H. Pu, Acta Crystallogr., Sect. E:
Struct. Rep. Online, 2008, 64, m202; T. C. Jones,
T. N. Waters, B. Kaitner and B. Kamenar, Croat. Chem.
Acta, 1986, 59, 825–831; D. Guan and H. Sun, Acta
Crystallogr., Sect. E: Struct. Rep. Online, 2009, 65, m566;
N. Wang, Acta Crystallogr., Sect. E: Struct. Rep. Online, 2012,
68, m11; F. L. Chen, S. H. Zhang, J. J. Guo, Y. D. Zhang
and C. Feng, Acta Crystallogr., Sect. E: Struct. Rep. Online,
2011, 67, m858; M. R. Fox and E. C. Lingafelter, Acta
Crystallogr., 1967, 22, 943–944; Y. Xiao, Z.-Q. Li and
X. Y. Peng, Acta Crystallogr., Sect. E: Struct. Rep. Online,
2012, 68, m1387; Q. Wang, J. Jiang and P. Zhu, Acta
Crystallogr., Sect. E: Struct. Rep. Online, 2011, 67, m470;
Q. Y. Shi, G.-C. Zhang, C.-S. Zhou and Q. Yang, Acta
Crystallogr., Sect. E: Struct. Rep. Online, 2012, 68, m919;
J. A. Rusanova, E. A. Buvaylo and E. B. Rusanov, Acta
Crystallogr., Sect. E: Struct. Rep. Online, 2011, 67, m222–
Cryst. Struct. Commun., 1990, 46, 1923–1925; H. Bahron,
A. M. Tajuddin, W. N. W. Ibrahim, M. Hemamalini and
H.-K. Fun, Acta Crystallogr., Sect. E: Struct. Rep. Online,
2011, 67, m1010–m1011; H. Bahron, A. M. Tajuddin,
W. N. W. Ibrahim, H.-K. Fun and S. Chantrapromma, Acta
Crystallogr., Sect. E: Struct. Rep. Online, 2014, 70, 104–106;
Y. Elerman, M. Kabak and M. N. Tahir, Acta Crystallogr.,
Sect. C: Cryst. Struct. Commun., 1996, 52, 1154–1156;
S.-Z. Chen and D.-G. Xia, Acta Crystallogr., Sect. E: Struct.
Rep. Online, 2009, 65, m923; A. M. Tajuddin, H. Bahron,
R. M. Hanaah, N. Ibrahim, H.-K. Fun and
S. Chantrapromma, Acta Crystallogr., Sect. E: Struct. Rep.
Online, 2014, 70, 252–255; H. M. Ali, S. J. Nazzatush,
M. R. Rizal and S. W. Ng, Acta Crystallogr., Sect. E: Struct.
Rep. Online, 2007, 63, m3033; Y.-Q. Dang, Acta Crystallogr.,
Sect. E: Struct. Rep. Online, 2009, 65, m1305; B. Kaitner,
ˇ
´
´
E. Mestrovic and G. Pavolic, J. Chem. Crystallogr., 1998, 28,
77–82; Y. Mei, W. Wang and S. Zhang, Z. Kristallogr. - New
Cryst. Struct., 2011, 226, 539–540; D. Britton and
L. H. Pignolet, Acta Crystallogr., Sect. C: Cryst. Struct.
Commun., 1989, 45, 819–821; B. Kamenar, B. Kaitner,
G. Ferguson and T. N. Waters, Acta Crystallogr., Sect. C:
Cryst. Struct. Commun., 1990, 46, 1920–1923; C. Bolm,
K. Weickhardt, M. Zehnder and D. Glasmacher, Helv.
Chim. Acta, 1991, 74, 717–726; A. V. Pestov, P. A. Slepukhin
and V. N. Charushin, Russ. Chem. Rev., 2015, 84, 310–333;
´
´
L. M. Peschel, C. Holzer, L. Mihajlovic-Lalic, F. Belaj and
¨
N. C. Mosch-Zanetti, Eur. J. Inorg. Chem., 2015, 1569–1578;
J. M. Stewart and E. C. Lingafelter, Acta Crystallogr., 1959,
12, 842–845; W. Steurer and W. Adlhart, Acta Crystallogr.,
Sect. B: Struct. Sci., 1983, 39, 344–349; R. L. Braun and
E. C. Lingafelter, Acta Crystallogr., 1966, 21, 546–553;
´
B. Kamenar, B. Kaitner and A. Stefanovic, Acta Crystallogr.,
´
ˇ
´
m223; M. Gavranic, B. Kaitner and E. Mestrovic, Acta
Crystallogr., Sect. C: Cryst. Struct. Commun., 1997, C53,
1232–1234; C. Tang, Acta Crystallogr., Sect. E: Struct. Rep.
Online, 2009, 65, m1275; Z. Hong, Acta Crystallogr., Sect. E:
Struct. Rep. Online, 2009, 65, m273; X.-X. Gong, R. Xia and
H.-J. Xu, Acta Crystallogr., Sect. E: Struct. Rep. Online, 2008,
64, m494; C. Wang, Acta Crystallogr., Sect. E: Struct. Rep.
Online, 2006, 62, m1754–1755; S. C. Bhatia, V. K. Syal,
Sect. C: Cryst. Struct. Commun., 1990, 46, 1627–1631;
J. C. J. Bart, I. W. Bassi, M. Calcaterra and M. Pieroni,
Inorg. Chim. Acta, 1978, 28, 201–210; R. Vafazadeh,
A. Gorji, S. Ansari and A. C. Willis, Acta Chim. Slov., 2013,
59, 897–903; M. del Mar Conejo, J. Cantero, A. Pastor,
´
E. Alvarez and A. Galindo, Inorg. Chim. Acta, 2017, 470,
113–118; W. Zhao, Y.-L. Qian and J.-L. Huang, Chin. J.
Chem., 2004, 22, 732–737.
R. P. Kashyap, P. C. Jain and C. J. Brown, Acta Crystallogr., 21 G. Watanabe, H. Sekiya, E. Tamai, R. Saijo, H. Uno, S. Mori,
Sect. C: Cryst. Struct. Commun., 1983, 39, 199–200; S. Peng,
C. Zhou and T. Yang, Acta Crystallogr., Sect. E: Struct. Rep.
Online, 2006, 62, m1066–m1068; Y.-G. Li, D.-H. Shi,
H.-L. Zhu, H. Yan and S. W. Ng, Inorg. Chim. Acta, 2007,
360, 2881–2889; W.-C. Hung and C.-C. Lin, Acta
T. Tanaka, J. Maki and M. Kawase, Chem. Pharm. Bull., 2018,
66, 732–740; N. M. Dudarenko, V. A. Kalibabchuk,
M. L. Malysheva, T. S. Iskenderov and E. Gumienna-
Kontecka, Acta Crystallogr., Sect. E: Struct. Rep. Online,
2010, 66, m277–m278; M. Ghorbanloo, N. Shahbakhsh and
This journal is © The Royal Society of Chemistry 2019
RSC Adv., 2019, 9, 3956–3964 | 3963

View Article Online
RSC Advances
Paper
D. Choquesillo-Lazarte, Acta Crystallogr., Sect. E: Struct. Rep.
Online, 2012, 68, m446; V. A. Kalibabchuk, N. M. Dudarenko,
Nat. Rev. Chem., 2017, 1, 25; E. Richmond and J. Moran,
Synthesis, 2018, 50, 499–513.
T. S. Iskenderov, M. L. Malysheva and E. Gumienna- 26 C. R. Eisnor, R. A. Gossage and P. N. Yadav, Tetrahedron,
Kontecka, Acta Crystallogr., Sect. E: Struct. Rep. Online,
2010, 66, m316–m317; A. P. Purdy and R. J. Butcher, Acta
Crystallogr., Sect. E: Struct. Rep. Online, 2014, 70, m18–m19;
R.-Z. Fan, S.-J. Li, W.-D. Song, D.-L. Miao and S.-W. Hu,
2006, 62, 3395–3401; R. A. Gossage, H. A. Jenkins and
P. N. Yadav, Tetrahedron Lett., 2004, 45, 7689–7691
[Corrigendum: R. A. Gossage, H. A. Jenkins and P. N.
Yadav, Tetrahedron Lett., 2005, 46, 5243].
Acta Crystallogr., Sect. E: Struct. Rep. Online, 2010, 66, 27 For example: X. He, Y. Liu, L. Chen, Y. Chen and D. Chen, J.
m897–m898; A. Messai, R. Benali-Cherif, E. Jeanneau and
N. Benali-Cherif, Acta Crystallogr., Sect. E: Struct. Rep.
Online, 2011, 67, m1204; H. Zhou, L. Zhao, R. Huang and
H.-L. Li, Acta Crystallogr., Sect. E: Struct. Rep. Online, 2010,
66, m1068; S. Zheng, S. Cai, J. Fun and W. Zhang, Acta
Crystallogr., Sect. E: Struct. Rep. Online, 2011, 67, m865;
M. Odoko, Y. Muranishi and N. Okabe, Acta Crystallogr.,
Sect. E: Struct. Rep. Online, 2001, 57, m267–m269;
M. R. Fox, P. L. Orioli, E. C. Lingafelter and L. Sacconi,
Acta Crystallogr., 1964, 17, 1159–1166; R. L. Braun and
E. C. Lingafelter, Acta Crystallogr., 1967, 22, 780–787.
22 H.-D. Bian, X.-Q. Zhang, X.-E. Yang, Q. Yu and H. Liang, Acta
Crystallogr., Sect. E: Struct. Rep. Online, 2005, 61, m2237–
m2239.
Polym. Sci., Part A: Polym. Chem., 2012, 50, 4695–4704;
Y.-M. Xu, K. Li, Y. Wang, W. Deng and Z.-J. Yao, Polymers,
2017, 9, 105; X. Hu, S. Dai and C. Chen, Dalton Trans.,
2016, 45, 1496–1503; G.-R. Tang and G.-X. Jin, Chin. Sci.
Bull., 2008, 53, 2764–2769; H. Gao, L. Pei, K. Song and
Q. Wu, Eur. Polym. J., 2007, 43, 908–914; L. Chen,
Z. Zhong, C. Chen, X. He and Y. Chen, J. Organomet.
Chem., 2014, 752, 100–108; G. J. Domski, J. M. Rose,
G. W. Coates, A. D. Bolig and M. Brookhart, Prog. Polym.
Sci., 2007, 32, 30–92; C. Carlini, M. Martinelli,
A. M. R. Galletti and G. Sbrana, J. Polym. Sci., Part A:
¨
Polym. Chem., 2006, 44, 1514–1521; F. Bao, R. Ma, X. Lu,
G. Gui and Q. Wu, Appl. Organomet. Chem., 2006, 20, 32–38.
28 J. Pau, A. J. Lough, R. S. Wylie, R. A. Gossage and
D. A. Foucher, Chem.–Eur. J., 2017, 23, 14367–14374;
M. W. Chojnacka, A. J. Lough, R. S. Wylie and
R. A. Gossage, J. Mol. Struct., 2011, 991, 158–161.
23 Q.-F. He, D.-S. Li, J. Zhao, X.-J. Ke and C. Li, Acta Crystallogr.,
Sect. E: Struct. Rep. Online, 2009, 65, m666.
24 L. Yang, D. R. Powell and R. P. Houser, Dalton Trans., 2007,
955–964.
29 A. Petrov, R. C. Jones, D. G. Vaughan, A. J. Lough and
R. A. Gossage, Crystals, 2011, 1, 229–235.
25 A. Suzuki, Proc. Jpn. Acad., Ser. B, 2004, 80, 359–371;
S. Z. Tasker, E. A. Standley and T. F. Jamison, Nature, 2014, 30 Spartan 16.0, Wavefunction Inc., Irvine, California, U.S.A.,
509, 299–309; I. Maluenda and O. Navarro, Molecules, 2015,
20, 7528–7557; N. Hazari, P. R. Melvin and M. M. Beromi,
2016.
3964 | RSC Adv., 2019, 9, 3956–3964
This journal is © The Royal Society of Chemistry 2019