X-ray structure of an amide-appended chloromercurated derivative of 2-phenylquinoline

Article abstract of DOI:10.1134/S0022476615050182

Reaction of the morpholine amide derivative of 2-phenyl-4-quinolinecarboxylic acid with mercury(II) acetate and lithium chloride results in chloromercuration at the ortho position on the phenyl ring; the complex was characterised by ESI mass spectrometry

Full text of DOI:10.1134/S0022476615050182

Journal of Structural Chemistry. Vol. 56, No. 5, pp. 948-952, 2015.
Original Russian Text © 2015 C.-Y. Lin, W. Henderson, B. K. Nicholson.
X-RAY STRUCTURE OF AN AMIDE-APPENDED
CHLOROMERCURATED DERIVATIVE
OF 2-PHENYLQUINOLINE
C.-Y. Lin, W. Henderson, and B. K. Nicholson
UDC 541.6:547.13:546.49
Reaction of the morpholine amide derivative of 2-phenyl-4-quinolinecarboxylic acid with mercury(II)
acetate and lithium chloride results in chloromercuration at the ortho position on the phenyl ring; the
complex was characterised by ESI mass spectrometry and an X-ray structure determination.
DOI: 10.1134/S0022476615050182
Keywords: synthesis, mercury complexes, orthometallation reactions, crystal structure.
INTRODUCTION
Organomercury compounds have found to be versatile reagents for the synthesis of a wide range of cycloaurated
gold(III) complexes through transmetallation reactions [1]. The transmetallation synthesis of cycloaurated gold complexes
has been applied to a wide range of systems, including substituted pyridines, azobenzenes, oxazolines, and N,N-
dimethylbenzylamines among others [1, 2]. One of the precursors that has been orthomercurated and converted to
a cycloaurated gold complex is the methyl ester of 2-phenyl-4-quinolinecarboxylic acid 1 [3]. We are interested in the
chemistry of this precursor because it offers an opportunity to easily modify the solubility characteristics via the carboxylic
acid functionality. This is significant because some cycloaurated gold(III) complexes can have relatively poor solubilities in
common solvents. To date, only the methyl ester of 2-phenyl-4-quinolinecarboxylic acid has been converted (via
orthomercurated precursor 2) into cycloaurated gold(III) complex 3. In this paper, the feasibility of orthomercurating amide
derivatives is exemplified by the synthesis and structural characterization of a mercurated morpholine derivative of 2-phenyl-
4-quinolinecarboxylic acid 1.
EXPERIMENTAL
Electrospray mass spectra were recorded in a dichloromethane-methanol solution using a Bruker MicrOTOF
instrument, calibrated with NaHCO2, and employing a capillary exit voltage of 150 V. NMR spectra were recorded in
a CDCl3 solution on Bruker AVIII400 using the Topspin 3.0 software. Elemental microanalyses were from the Campbell
Microanalytical Laboratory, University of Otago. 2-Phenyl-4-quinolinecarboxylic acid (Aldrich), mercury(II) acetate (BDH),
lithium chloride (BDH), morpholine (Aldrich), and thionyl chloride (Riedel de Häen) were used as supplied.
Synthesis of 4. The following reaction was carried out using a Schlenk line with a supply of dry nitrogen gas.
2-Phenyl-4-quinolinecarboxylic acid 1a (3.28 g, 13.2 mmol) was refluxed in thionyl chloride (5 ml, excess) for 1 h. The
Department of Chemistry, School of Science, University of Waikato, Hamilton, New Zealand;
w.henderson@waikato.ac.nz. The text was submitted by the authors in English. Zhurnal Strukturnoi Khimii, Vol. 56, No. 5,
pp. 1006-1009, September-October, 2015. Original article submitted February 03, 2014.
948
0022-4766/15/5605-0948 © 2015 by Pleiades Publishing, Ltd.

resulting bright yellow solution was evaporated to dryness under reduced pressure to give carboxylic acid chloride as a bright
yellow solid which was used without further purification. The acid chloride was cooled in an ice bath and morpholine (5 ml)
was added dropwise with stirring. After the addition, hexane (5 ml) and dichloromethane (5 ml) were added with stirring,
followed by an additional portion of morpholine (5 ml). The mixture was stirred for 5 days, giving a milky white solution,
which was then evaporated to dryness in the air; subsequent operations were carried out in the air. The product was
crystallized from a hot ethanol-water mixture (70:30), with excess sodium chloride added to aggregate the milky precipitate
formed. A second recrystallization from the hot ethanol-water mixture (70:30) produced an off-white solid of 4 (3.24 g,
77 %). Found (%): C 75.19, H 5.71, N 8.76. C20H18N2O2 requires (%) C 75.46, H 5.70, N 8.80. M.p. 128-130 °C. Positive-ion
+
ESI MS, [MH] (m/z 319.227, calculated 319.144), [MNa] (m/z 341.214, calculated 341.126), [M2Na] (m/z 659.418,
+
+
1
calculated 659.263). H NMR (CDCl3), δ 3.22-3.26 (m, 2H, CH2), 3.53-3.58 (m, 2H, CH2), 3.86-3.92 (m, 2H, CH2), 4.03-
4.06 (m, 2H, CH2), 7.47-7.61 (m, 5H), 7.76-7.86 (m, 5H), 8.15-8.18 (m, 1H), 8.21-8.23 (m, 1H).
Synthesis of 5. To compound 4 (2.00 g, 6.29 mmol) in ethanol (40 ml) was added mercury(II) acetate (2.00 g,
6.28 mmol), and the mixture was refluxed for 14 h to give a milky-white cloudy solution. The hot mixture was filtered into
a solution of lithium chloride (0.38 g, 8.90 mmol) in ethanol (5 ml), immediately giving a white solid. The mixture was
refluxed for 2 h, cooled to room temperature and allowed to stand for 16 h. Water (200 ml) was added and the white solid
filtered and washed with water. Recrystallization by vapour diffusion of pentane into a dichloromethane solution gave solid
+
product 5 (1.93 g, 55 %). M. p. 226-230°C. Positive-ion ESI MS, [MNa] (m/z 577.064, calculated 577.057). Found (%):
1
C 44.55, H 3.04, N 5.11. C20H17N2O2HgCl requires (%) C 43.41, H 3.10, N 5.06. NMR, δ 3.23-3.27 (m, 2H, CH2), 3.54-3.59
(m, 2H, CH2), 3.87-3.92 (m, 2H, CH2), 4.05-4.07 (m, 2H, CH2), 7.43-7.66 (m, 4H), 7.77-7.86 (m, 5H), 8.14-8.17 (m, 1H),
8.24-8.25 (m, 1H).
X-ray crystal structure determination of 5. The compound was recrystallized by vapour diffusion of diethyl ether
into a chloroform solution at room temperature, giving colourless single crystals suitable for an X-ray diffraction study. Data
(21919 reflections collected, 4825 independent reflections, Rint 0.0391) were collected on a crystal with dimensions of
0.60×0.13×0.06 mm at 89(2) K on a Bruker SMART CCD diffractometer and processed using the standard software.
2
An absorption correction was carried out using SADABS [4]. The structure was solved using SHELX-97 and refined on F
using SHELXL-97 [5] operated under WinGX [6], giving final R indices R1 0.0360, wR2 0.0656 for data with [I > 2σ(I)] and
R1 0.0335, wR2 0.0694 (all data). All non-hydrogen atoms were treated anisotropically and hydrogen atoms were included
3
with a riding model with d(C–H) 0.95 Å, Uiso = 1.2Ueq(C) for aromatic hydrogen atoms. Residual electron density (e/Å )
max/min: 2.496/–1.712.
Crystal data: C20H17ClHgN2O2, M = 553.40, triclinic, space group P-1, a = 9.5893(4) Å, b = 9.8519(4) Å,
3 3
c = 10.1798(5) Å, α = 107.494(2)°, β = 92.149(2)°, γ = 102.002(2)°, V = 892.01(7) Å , Z = 2, Dc = 2.060 g/cm ,
–1
μ(MoK ) = 8.794 mm , F(000) = 528.
α
A CIF file containing complete information on the studied structure was deposited with CCDC, deposition number
976914, and is freely available from the web page http://www.ccdc.cam.ac.uk/data_request/cif.
RESULTS AND DISCUSSION
2-Phenyl-4-quinolinecarboxylic acid 1 was converted into its morpholine amide derivative 4 by a two-step
procedure involving conversion to the acid chloride, followed by reaction with excess morpholine, as summarised in
Scheme 1. The compound shows unexceptional spectroscopic features; the CH2 protons of the morpholine group appear as
four distinct multiplets, due to the typical restricted rotation about the C(O)–N moiety. Although compound 4 has been
previously prepared [7] it has not been orthomercurated. Mercuration was achieved by the standard procedure, involving
a reaction with mercury(II) acetate in refluxing ethanol, followed by conversion to the chloride complex with LiCl
(Scheme 1), giving 5 as a white solid. The complex gave the expected NMR spectroscopic properties, and the positive ion
+
ESI mass spectrum showed [MNa] ions, with good agreement between the observed and calculated m/z values, with the
expected isotopic pattern due to the presence of polyisotopic mercury.
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Scheme 1. Synthesis of organomercury derivative 5.
To fully characterize mercury complex 5, an X-ray structure determination was carried out; there have been several
structure determinations on ortho-mercurated 2-phenylpyridine 6 [8, 9] and derivatives thereof [10], and phenyl-substituted
1,10-phenanthroline [11], but there have been no prior determinations on orthomercurated 2-phenylquinolines. The structure
is shown in Fig. 1, together with selected bond lengths and angles. The structure determination confirms chloromercuration at
the ortho position of the phenyl ring, analogous to the previous reactivity in the ester analogue.
The Hg(1)–C(11) mercury-carbon bond distance is 2.066(4) Å, which is typical, compared to, e.g., chloromercurated
2-phenylpyridine 6 (2.069(13) Å and 2.070(13) Å), in two independent Hg centres [8, 9]. In 5 the Hg(1)–Cl(1) bond is
2.3166(10) Å, compared to the distances of 2.314(4) Å and 2.335(4) Å in 6. There is the typical weak interaction between the
quinoline nitrogen N(1) atom and the mercury atom, with Hg(1)⋯N(1) being 2.635(3) Å. The phenyl and quinoline ring
systems are not coplanar, with an interplanar angle of 15.30°; by comparison, the two independent molecules in 6 have
interplanar angles between the phenyl and pyridyl rings of 9.00° and 23.68° [8, 9]. As a consequence, the mercury atom in 5
is displaced only by 0.016 Å from the phenyl ring plane, but by 0.799 Å out of the least-squares plane of the quinoline ring
system, though this does not appear to change the Hg⋯N distance compared to 6 (2.673(12) Å and 2.627(12) Å in the two
independent molecules) [8, 9]. The C(11)–Hg(1)–Cl(1) bond angle is 175.01(10)°, with the chloride being displaced away
from the quinoline ring as a result of the Hg⋯N interaction.
The amide substituent is approximately planar, with an angle of only 4.4° between the C(31)–N(2)–C(34) and O(1)–
C(1)–C(23) planes, however the amide is not coplanar with the quinoline ring, which can be demonstrated by the O(1)–C(1)–
C(23)–C(22) torsion angle of 123.1(5)°. This distortion presumably minimizes steric interactions between the CH2 group and
the hydrogen atom on carbon C(25) on the quinoline ring. The morpholine ring system has the typical puckered chair
conformation.
A previous structure determination of orthomercurated 2-phenylpyridine 6 [8, 9] showed dimeric units assembled
through weak Hg⋯Cl interactions, these then further assembling to form a tetramer. However, the examination of the
structure of 5 reveals that the molecules of 5 do not form the same aggregates, with the closest intermolecular Hg⋯Cl contact
being very long, at 5.880(1) Å. In 5 the molecules stack on top of each other in a head-to-tail fashion, with a distance of about
3.7 Å between the adjacent stacked molecules. The difference is presumably due to the larger aromatic systems of 5, which
promote π⋯π interactions at the expense of Hg⋯Cl interactions.
950

Fig. 1. Molecular structure of 5 showing the atom numbering scheme;
thermal ellipsoids are shown at the 50 % probability level, with the
exception of hydrogen atoms shown as small open circles. Selected bond
lengths (Å) and angles (deg): Hg(1)–C(11) 2.066(4), Hg(1)–Cl(1)
2.3166(10), Hg(1)⋯N(1) 2.635(3), N(1)–C(21) 1.324(4), N(1)–C(29)
1.365(5), N(2)–C(1) 1.348(5), N(2)–C(31) 1.456(5), N(2)–C(34)
1.465(5), O(1)–C(1) 1.227(5), C(1)–C(23) 1.509(5), C(11)–Hg(1)–Cl(1)
175.01(10), C(11)–Hg(1)–N(1) 74.10(13), O(1)–C(1)–N(2) 123.9(3),
O(1)–C(1)–C(23) 117.7(3), N(2)–C(1)–C(23) 118.4(3).
The University of Waikato is acknowledged for financial support of this work, Pat Gread for assistance with mass
spectrometry studies, and Dr. Tania Groutso (University of Auckland) for the X-ray data collection. W. Henderson thanks
Prof. Paul Low (University of Durham) for generously providing facilities for writing this manuscript.
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