A novel gold(I)-mediated intramolecular transamidation of benzoyl thiourea derivatives to form benzamides via dethiocyanation

Article abstract of DOI:10.1016/j.jorganchem.2020.121359

A novel gold(I)-mediated intramolecular transamidation of thiourea derivatives to yield benzamides via dethiocyanation have been achieved by the reaction of 3-(1,3-benzothiazol-2-yl)-1-(benzoyl)thiourea derivatives in the presence of gold(I) precursors. The compounds have been characterized using IR, NMR, GC-MS and microanalysis. The single crystal XRD of 3-(1,3-benzothiazol-2-yl)-1-(3-bromobenzoyl)thiourea (5), 3-(1,3-benzothiazol-2-yl)-1-(3-methoxybenzoyl)thiourea (6), N-(benzothiazol-2-yl)benzamide (10), N-(benzothiazol-2-yl)-3-chlorobenzamide (11), N-(benzothiazol-2-yl)-4-nitrobenzamide (12), N-(benzothiazol-2-yl)-3-bromobenzamide (14) have been discussed. The novel transformation is thought to proceed by a gold(I)-mediated intramolecular transamidation reaction which releases thiocyanate to yield the benzamide. Density functional theory calculations have been used to support the proposed mechanism for this transformation.

Full text of DOI:10.1016/j.jorganchem.2020.121359

Journal Pre-proof
A novel gold(I)-mediated intramolecular transamidation of benzoyl thiourea
derivatives to form benzamides via dethiocyanation
Felix Odame, Guilliaume Woodcock, Eric C. Hosten, Kevin Lobb, Zenixole R. Tshentu
PII:
S0022-328X(20)30261-8
DOI:
https://doi.org/10.1016/j.jorganchem.2020.121359
JOM 121359
Reference:
To appear in: Journal of Organometallic Chemistry
Received Date: 10 April 2020
Revised Date: 22 April 2020
Accepted Date: 27 May 2020
Please cite this article as: F. Odame, G. Woodcock, E.C. Hosten, K. Lobb, Z.R. Tshentu, A novel
gold(I)-mediated intramolecular transamidation of benzoyl thiourea derivatives to form benzamides
via dethiocyanation, Journal of Organometallic Chemistry (2020), doi: https://doi.org/10.1016/
j.jorganchem.2020.121359.
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A novel gold(I)-mediated intramolecular transamidation of benzoyl
thiourea derivatives to form benzamides via dethiocyanation
Felix Odame,a,b,* Guilliaume Woodcock,b Eric C. Hosten,b Kevin Lobbc,*, Zenixole R.
Tshentub,*
aDepartment of Basic Sciences, University of Health and Allied Sciences, PMB 31, Ho,
Ghana (felixessah15@gmail.com)
bDepartment of Chemistry, Nelson Mandela University, P.O. Box 77000, Port Elizabeth
6031, South Africa (zenixole.tshentu@mandela.ac.za)
cDepartment of Chemistry, Rhodes University, P.O. Box 94, Grahamstown 6140, South
Africa (k.lobb@ru.ac.za)
Abstract
A novel gold(I)-mediated intramolecular transamidation of thiourea derivatives to yield
benzamides via dethiocyanation have been achieved by the reaction of 3-(1,3-benzothiazol-2-
yl)-1-(benzoyl)thiourea derivatives in the presence of gold(I) precursors. The compounds
have been characterized using IR, NMR, GC-MS and microanalysis. The single crystal XRD
of 3-(1,3-benzothiazol-2-yl)-1-(3-bromobenzoyl)thiourea (5), 3-(1,3-benzothiazol-2-yl)-1-(3-
methoxybenzoyl)thiourea (6), N-(benzothiazol-2-yl)benzamide (10), N-(benzothiazol-2-yl)-3-
chlorobenzamide (11), N-(benzothiazol-2-yl)-4-nitrobenzamide (12), N-(benzothiazol-2-yl)-
3-bromobenzamide (14) have been discussed. The novel transformation is thought to proceed
by a gold(I)-mediated intramolecular transamidation reaction which releases thiocyanate to
yield the benzamide. Density functional theory calculations have been used to support the
proposed mechanism for this transformation.
Key words: gold(I), thiourea, intermolecular transamidation, benzamides, dethiocyanation.

Introduction
Thiourea derivatives have been synthesized by different methods for a variety of applications
[1-6]. However, their conversion to benzamides is not extensive in the literature. Odame et.
al. recently discovered a silver(I)-mediated conversion of thiourea derivatives to benzamides
as well as their transformation to dicarbamolyamine [7]. Several methods for the preparation
of amides are known, with the observed reaction being that of amines and different carbonyl
containing functional groups [8-13]. A procedure for the oxidative synthesis of amides from
styrenes and amines has been developed [14]. The synthesis of N-aryl substituted benzamides
has been achieved through the assembly of primary amines and phenylacetic acids in the
presence of copper (II) acetate. The reaction involved a carbon–carbon bond cleavage and the
formation of a C–N yielding secondary benzamides [15]. Benzamides have also been
developed through the cleavage of sp3-sp2 C-Ph bond of methyl arenes with N-substituted
formamides [16]. For this reaction different yields have been obtained using varying amounts
of tetrabutylammonium iodide (TBAI) as catalyst, tertbutylhydroperoxide (TBHP) as oxidant
and Zn(II) salts as additives.
The intermolecular transamidation reaction is widely reported [17-19]. An iron-based
catalytic system for transamidation has been developed for the transamidation of primary
carboxamides (Scheme 1A) [17]. In this account, the intermolecular transamidation of urea
and thiourea was also carried out [17]. A MnO2-catalyzed one-pot method for the formylation
of amine and transamidation of primary and secondary amides has been reported (Scheme
1B) [18]. A nickel catalyst has been used in a two-step approach leading to the
transamidation of secondary amides (Scheme 1C) [19].

O
R2
O
Fe(OH)3@Fe3O4
R2
HN
p-xylene, reflux, 10 h
R1
N
R1
NH2
R3
R3
(A)
O
R
O
NH2
R
R
H2N
N
R
H
MnO2 cat (10 mol %
neat, 150 oC, 12h
(B)
O
O
Br
HN
Ni(cod)2 SlPr
Toluene, 14 h
N
N
O
O
R
R
R
(C)
Scheme 1: A. Fe(OH)3@Fe3O4-catalyzed transamidation of primary carboxamides [17]. B.
MnO2-catalyzed formylation of amine and transamidation of primary and secondary amides
[18]. C. Nickel-catalyzed transamidation of secondary amides [19].
A novel L-proline-catalyzed transamidation process has also been used to catalyze
transamidation reactions of benzylic, aromatic, aliphatic, propargylic, and heteroaromatic
amines [20]. Catalytic amounts of H2SO4–SiO2 have also been used for the transamidation of
carboxamides with amines [21].
In this work, a gold(I)-mediated [22-35] intramolecular transamidation of thiourea derivatives
yielded benzamides via dethiocyanation of thiourea derivatives. To our knowledge,
intramolecular transamidation reaction has not been reported in the literature. The compounds
have been characterized using IR and NMR spectroscopy as well as GC-MS and
microanalysis. The single crystal XRD of compounds, 3-(1,3-benzothiazol-2-yl)-1-(3-bromo
benzoyl)thiourea (5), 3-(1,3-benzothiazol-2-yl)-1-(3-methoxybenzoyl)thiourea (6), N-
(benzothiazol-2-yl)benzamide (10), N-(benzothiazol-2-yl)-3-chlorobenzamide (11), N-

(benzothiazol-2-yl)-4-nitrobenzamide (12), N-(benzothiazol-2-yl)-3-bromobenzamide (14)
have been discussed.
2. Experimental
2.1 Materials and reagents
Analytical grade reagents and solvents for synthesis, such as 2-aminobenzothiazole, 4-
chorobenzoyl chloride, 3-chorobenzoyl chloride, 4-bromobenzoyl chloride, 3-
bromobenzoyl chloride, 4-methoxybenzoyl chloride, 3-methoxybenzoyl chloride, 4-
nitrobenzoyl chloride, 3-nitrobenzoyl chloride and benzoyl chloride, were obtained
from Sigma Aldrich (USA) whilst acetone was obtained from Merck Chemicals (SA).
The chemicals were used as received (i.e. without further purification).
2.2 Instrumentation and methods
The 1H NMR and 13C NMR spectra were recorded on a Bruker Avance AV 400 MHz
1
13
spectrometer operating at 400 MHz for H and 100 MHz for C using DMSO-d6 as
solvent and tetramethylsilane as internal standard. Chemical shifts are expressed in
ppm. FT–IR spectra were recorded on a Bruker Platinum ATR Spectrophotometer
Tensor 27. Elemental analyses were performed using a Vario Elementar Microcube
ELIII. Melting points were obtained using a Stuart Lasec SMP30. Masses were
determined using an Agilent 7890A GC System connected to a 5975C VL-MSC with
electron impact as the ionization mode and detection by a triple-Axis detector. The GC
was fitted with a 30 m x 0.25 mm x 0.25 µm DB-5 capillary column. Helium was used
as carrier gas at a flow rate of 1.63 mL.min−1 with an average velocity of 30.16 cm s−1
and a pressure of 63.73 kPa.
2.3 General method for the synthesis of thiourea derivatives
2-Aminobenzothiazole (0.04 mol, 5.326 g) was added to the respective benzoyl
isothiocyanate derivatives (0.04 mol) in acetone (80 mL) and heated under reflux for 6
h. The mother liquor was allowed to stand overnight in a fume hood.
3-(1,3-Benzothiazol-2-yl)-1-(benzoyl)thiourea (1)
The product obtained was filtered and recrystallized from DMSO:toluene (1:1) as a
1
yellow solid. Melting point = 161–163 °C. Yield = 75.0% H NMR ( DMSO-d6,
400MHz, ppm): 8.14 (d, 2H,
J = 7.6 Hz)), 8.0 (d, 1H, J = 7.6 Hz), 7.8 (d, 1H, J = 8.0

13
Hz), 7.66 (t, 1H,
J = 7.6 Hz), 7.56 (t, 2H), 7.47 (m, 1H), 7.34 (m, 1H). C NMR
(DMSO-d6, 100MHz, ppm): 169.0 (C=S), 166.0 (C=O), 159.1, 133.0, 128.9, 128.6,
128.3, 127.3, 126.1, 123.7, 121.8, 120.3. IR (νmax, cm−1): 3327 (N−H), 3055 (N−H),
1673 (C=O), 1595 (C=C), 1436 (C−N). Anal. Calcd for C15H11N3OS2: C, 57.49; H,
3.54; N, 13.41; S, 20.46. Found: C, 57.38; H, 3.46; N, 13.55; S, 20.33. LRMS (m/z
,
M+): Found for C15H11N3OS2 = 313.25, Expected mass = 313.40.
3-(1,3-Benzothiazol-2-yl)-1-(4-chlorobenzoyl)thiourea (2)
The product obtained was filtered and recrystallized from DMSO:toluene (1:1) as a
1
yellow solid. Melting point = 206–207 °C. Yield = 85.9%. H NMR (DMSO-d6,
400MHz, ppm): 14.17 (br, 1H, N−H), 12.31 (br, 1H, N−H), 8.03 (m, 3H), 7.81 (m,
13
1H), 7.62 (m, 2H), 7.51 (m, 1H), 7.39 (m, 1H). C NMR (DMSO-d6, 100MHz, ppm):
131.7, 131.0, 126.60, 124.5. IR (νmax, cm−1): 3379 (N−H), 3229 (N−H), 1676 (C=O),
1595 (C=C), 1538 (C=C), 1486 (C−N), 1475 (C−N). Anal. Calcd for C15H10ClN3OS2:
C, 51.79; H, 2.90; Cl, 10.19; N, 12.08, S, 18.44. Found: C, 51.65; H, 3.01; Cl, 10.25,
N, 12.16; S, 18.52. LRMS (m/z, M+): Found for C15H10ClN3OS2 = 347.95, Expected
mass = 347.84.
3-(1,3-Benzothiazol-2-yl)-1-(3-chlorobenzoyl)thiourea (3)
The product obtained was filtered and recrystallized from DMSO:toluene (1:1) as a
yellow solid. Melting point = 140–142 °C. Yield = 76.4%.1H NMR (DMSO-d6,
400MHz, ppm): 12.29 (br, 1H, N–H), 8.20 (s, 1H), 8.06 (m, 2H), 7.93 (d, 1H,
J
= 8
Hz), 7.80 (t, 1H,
J = 8.4, 8.8 Hz), 7.73 (t, 1H, J = 8.0, 8.4 Hz), 7.59 (m, 1H), 7.51 (m,
13
1H). C NMR (DMSO-d6, 100MHz, ppm): Aromatic carbon signals (133.4, 133.1,
133.0, 130.5, 128.6, 128.1, 127.6, 127, 126.6, 124.2, 124.5, 123.8, 122.0, 121.8). IR
(νmax, cm−1): 3296 (N−H), 3058 (N−H), 1670 (C=O), 1596 (C=C), 1544 (C=C), 1457
(C−N), 1432 (C−N). Anal. Calcd for C15H 10ClN3OS2: C, 51.79; H, 2.90; N, 12.08; S,
18.44. Found: C, 51.73; H, 2.84; N, 12.12; S, 18.49. LRMS (m/z, M+): Found for
C15H10ClN3OS2 = 347.70 Expected mass = 347.84.
3-(1,3-Benzothiazol-2-yl)-1-(4-bromobenzoyl)thiourea (4)
The product obtained was filtered and recrystallized from DMSO:toluene (1:1) as a
1
yellow solid. Melting point = 230–232 °C. Yield = 75.0%. H NMR (DMSO-d6,
400MHz, ppm): 14.17 (br, 1H, N−H), 12.31 (br, 1H, N−H), 8.06 (d, 1H,
J = 8.0 Hz),

7.93 (d, 2H,
J
= 8.0 Hz), 7.78 (m, 3H,
J
= 8.0 Hz), 7.50 (t, 1H,
J = 8.0 Hz), 7.39 (t, 1H,
13
J
= 7.6 Hz). C NMR (DMSO-d6, 100MHz, ppm): 131.5, 130.9, 126.6, 124.5, 122.0.
IR (νmax, cm−1): 3060 (N−H), 3018 (N−H), 1676 (C=O), 1561 (C=C), 1499 (C−N),
1475 (C−N). Anal. Calcd for C15H10BrN3OS2: C, 45.92; H, 2.57; N, 10.71; S, 16.35.
Found: C, 46.03; H, 2.65; N, 10.68; S, 16.42. LRMS (m/z, M+): Found for
C15H10BrN3OS2 = 392.10, Expected mass = 392.29.
3-(1,3-Benzothiazol-2-yl)-1-(3-bromobenzoyl)thiourea (5)
The product obtained was filtered and recrystallized from DMSO:toluene (1:1) as a
1
yellow solid. Melting point = 152–153 °C. Yield = 80.0% H NMR (DMSO-d6,
400MHz, ppm): 8.34 (s, 1H) 8.13 (d, 1H,
8.0 Hz), 7.80 (d, 1H, = 7.6 Hz), 7.54 (t, 1H,
7.37 (t, 1H, = 8.0 Hz) C NMR (DMSO-d6, 100MHz, ppm): aromatic resonances
J
= 8.0 Hz), 8.01 (m, 1H), 7.87 (d, 1H,
J =
J
J
= 7.6, 8.0 Hz), 7.48 (t, 1H, = 8.0 Hz),
J
13
J
(135.6, 130.9, 127.5, 126.6, 123.64, 121.8). IR (νmax, cm−1): 3232 (N−H), 3155 (N−H),
1694 (C=S), 1665 (C=O), 1599 (C=C), 1509 (C=C), 1475 (C–N), 1456 (C–N). Anal.
Calcd for C15H10BrN3OS2: C, 45.92; H, 2.57; N, 10.71; S, 16.35. Found: C, 45.88; H,
2.57; N, 10.65; S, 16.43. LRMS (m/z, M+): Found for C15H10BrN3OS2 = 392.40,
Expected mass = 392.29.
3-(1,3-Benzothiazol-2-yl)-1-(4-methoxybenzoyl)thiourea (6)
The product obtained was filtered and recrystallized from DMSO:toluene (1:1) as a
yellow solid. Melting point = 192–193 °C. Yield = 73.0%.1H NMR (DMSO-d6,
400MHz, ppm): 12.06 (s, 1H, N–H), 8.06 (m, 3H), 7.83 (d, 1H,
J = 8.0 Hz), 7.51(t,
1H, = 7.2 Hz), 7.40 (t, 2H, = 7.2, 7.6 Hz), 7.11( d, 2H, = 8.0 Hz), 3.87 (s, 3H).
J
J
J
13C NMR (DMSO-d6, 100MHz, ppm): 163.6 (C=O), 131.3, 126.6, 124.2, 121.9, 113.9,
55.5. IR (νmax, cm−1): 3303 (N−H), 3054 (N−H), 2961 (C−H), 2928 (C−H), 1675
(N−H), 1594 (C=C), 1533 (C=C), 1499 (C–N), 1476 (C–N), 1437 (C−N). Anal. Calcd
for C16H13N3O2S2: C, 55.96; H, 3.82; N, 12.24; S, 18.67. Found: C, 56.02; H, 3.86; N,
12.31; S, 18.74. LRMS (m/z, M+): Found for C16H13N3O2S2 = 343.30, Expected mass
= 343.42.
3-(1,3-Benzothiazol-2-yl)-1-(3-methoxybenzoyl)thiourea (7)
The product obtained was filtered and recrystallized from DMSO:toluene (1:1) as a
yellow solid. Melting point = 117–119 °C. Yield = 78.5%.1H NMR (DMSO-d6,

400MHz, ppm): 12.89 (br, 1H, N–H), 12.21 (br, 1H, N–H), 8.04 (dd, 1H,
J
= 8.0 Hz),
7.80 (t, 1H,
J
= 8.0 Hz), 7.73 (s, 1H), 7.57 (m, 1H), 7.48 (t, 2H, J = 8.0 Hz), 7.36 (m,
13
1H), 7.23 (t, 1H,
J = 8.0 Hz), 3.86 (s, 3H). C NMR (DMSO-d6, 100MHz, ppm):
159.50 (C=O), 159.0, 129.8, 129.7, 126.6, 126.2, 124.5, 123.7, 121.5, 120.7, 119.4,
113.4, 112.9, 55.4. IR (νmax, cm−1): 3313 (N−H), 3070 (N−H), 2075 (C−H), 1650
(C=O), 1596 (C=C), 1582 (C=C), 1515 (C=C), 1464 (C−N), 1429 (C−N). Anal. Calcd
for C16H13N3O2S2: C, 55.96; H, 3.82; N, 12.24; S, 18.67. Found: C, 55.91; H, 3.88; N,
12.30; S, 18.75. LRMS (m/z, M+): Found for C16H13N3O2S2 = 343.36, Expected mass
= 343.42.
3-(1,3-Benzothiazoyl-2-yl)-1-(4-nitrobenzoyl)thiourea (8)
The product obtained was filtered and recrystallized from DMSO:toluene (1:1) as a
1
yellow solid. Melting point = 226–228 °C. Yield = 75.6% H NMR (DMSO-d6,
400MHz, ppm): 12.44 (br ,1H, N-H), 9.14 (br, 1H, N–H), 8.36 ( d, 2H,
J = 8.0 Hz),
8.29 (d, 2H, = 8.0 Hz), 8.20 (d, 1H, = 8.0 Hz), 8,10 (m, 2H), 7.79 (m, 1H, (11)),
J
J
7.71 (m, 1H), 7.52 (m, 1H), 7.41 (m, 1H), 7.25 (m, 1H). 13C NMR (DMSO-d6,
100MHz, ppm): 166.5, 148.8, 140.0, 129.9, 128.7, 114.9. IR (νmax, cm−1): 3351 (N−H),
3075 (N−H), 2073, 1679 (C=O), 1595 (C=C), 1510 (C=C), 1462 (C−N). Anal. Calcd
for C15H10N4O3S2: C, 50.27; H, 2.81; N, 15.63; S, 17.89. Found: C, 50.31; H, 2.84; N,
15.57; S, 17.86. LRMS (m/z, M+): Found for C15H10N4O3S2 = 358.28, Expected mass
= 358.39.
3-(1,3-Benzothiazol-2-yl)-1-(3-nitrobenzoyl)thiourea (9)
The product obtained was filtered and recrystallized from DMSO:toluene (1:1) as a
yellow solid. Melting point = 215–216 °C. Yield = 77.3%.1H NMR (DMSO-d6,
400MHz, ppm): 14.03 (br, 1H, N–H), 12.60 (br, 1H, N–H), 8.81 (s, 1H), 8.50 (d, 1H,
J
= 8.0 Hz), 8.39 (d, 1H,
J
= 7.6 Hz), 8.06 (d, 1H,
J
= 7.6 Hz) 7.86 (dd, 2H, J = 8 Hz),
13
7.52 (t, 1H, = 7.6 Hz), 7.41 (t, 1H,
J
J = 7.6 Hz). C NMR (DMSO-d6, 100MHz,
ppm): aromatic carbon signals (147.4, 135.2, 130.3, 124.7, 123,7). IR (νmax, cm−1)
:3460 (N−H), 3088 (N−H), 1692 (C=S), 1670 (C=O), 1567 (C=C), 1516 (C=C), 1482
(C–N), 1410 (C–N). Anal. Calcd for C15H10N4O3S2: C, 50.27; H, 2.81; N, 15.63; S,
17.89. Found: C, 50.35; H, 2.74; N, 15.69; S, 17.94. LRMS (m/z, M+): Found for
C15H10N4O3S = 358.80, Expected mass = 358.39.

2.4 General method for the synthesis of benzamides
The thiourea compound 0.08 mmol) was dissolved in 10 mL of THF, and then
dimethylsulfoxide gold(I) chloride (0.08 mmol, 20 mg) or
(
chloro(tetrahydrothiophene)gold(I) (0.08 mmol, 26 mg) was added in the absence of
light and stirred under nitrogen at 60°C for 4 h. The reaction mixture was filtered and
allowed to stand overnight.
N-(Benzothiazol-2-yl)benzamide (10)
The solid product found was filtered, washed with dry methanol and dried under
1
vacuum to obtain a yellow solid. Melting point: 115–117 °C Yield: 47.0%. H NMR
(DMSO-d6, 400MHz, ppm): 8.35 (s, 1H, N–H), 8.14 (d, 1H,
= 8.0 Hz), 7.88 (d, 1H, = 7.6 Hz), 7.81 (d, 1H, = 7.6 Hz), 7.69 (m, 2H,
Hz), 7.55 (t, 1H, = 7.2, 7.6 Hz), 7.49 (t, 1H, = 7.2, 8.0 Hz), 7.36 (t, 1H, = 7.6 Hz).
J
= 7.6 Hz), 8.04 (d, 1H,
J
J
J
J
= 8.0
J
J
J
13C NMR (DMSO-d6, 100MHz, ppm): 136.1, 131.5, 127.9, 126.9, 124.3, 122.3. IR
(νmax, cm−1): 3273 (N−H), 3059 (C−H, aromatic), 1693 (C=O), 1599 (C=C), 1549
(C=C), 1456 (C−N, amide), 1442 (C−N, thiazole). Elemental analysis for
C14H10N2OS: Calculated: Found: C: 66.12, H: 3.96, N: 11.02, S: 12.61. Found: C:
65.98, H: 4.05, N: 11.10, S: 12.55 (%) LRMS (m/z, M+) for C14H10N2OS: Found:
254.42 Expected: 254.31
N-(Benzothiazol-2-yl)-4-chlorobenzamide (11)
The solid product found was filtered, washed with dry methanol and dried under
vacuum to obtain a yellow solid. Melting point: 205–206 °C Yield: 19.0%. (IR νmax
,
cm-1): 3286 (N–H, amide), 3034 (C–H, aromatic), 1697 (C=O), 1592 (C=C, aromatic),
1454 (C–N, amide), 1437 (C–N, thiazole), 721 (C–Cl). Elemental analysis for
C14H9N2OSCl: Calculated: C: 58.2, H: 3.14, N: 9.70, S: 11.10 (%) Found: C: 42.69, H:
2.49, N: 11.72, S: 17.21 (%) LRMS (m/z, M+) for C14H9N2OSCl: Found: 288.90
Expected: 288.76
N-(Benzothiazol-2-yl)-3-chlorobenzamide (12)
The solid product found was filtered, washed with dry methanol and dried under
1
vacuum to obtain a yellow solid. Melting point: 155–156 °C. Yield: 52.4% H NMR
(DMSO-d6, 400MHz, ppm): 8.19 (s, 1 H, N–H), 8.08 (d, 1H), 8.02 (d, 1H), 7.79 (d,
1H), 7.73 (d, 1H), 7.61 (t, 1H), 7.48 (t, 1H), 7.36 (t, 1H). 13C NMR (DMSO-d6,

100MHz, ppm): 133.93, 133.07, 131.11, 128.57, 127.52, 126.81, 124.35, 122.30. (IR
νmax, cm-1): 3106 (C–H, aromatic), 1670 (C=O), 1596 (C=C, aromatic), 1456 (C–N),
720 (C–Cl) Elemental analysis for C14H9N2OSCl: Calculated: C: 58.23, H: 3.14, N:
9.70, S: 11.10 (%) Found: C: 51.60, H: 2.60, N: 10.02, S: 12.45 (%) LRMS (m/z, M+)
for C14H9N2OSCl: Found for: 289.00, Expected = 288.76.
N-(Benzothiazol-2-yl)-4-bromobenzamide (13)
The solid product found was filtered, washed with dry methanol and dried under
1
vacuum to obtain a yellow solid. Melting point: 230–232 °C. Yield: 17.1% H NMR
(DMSO-d6, 400MHz, ppm): aromatic protons (8.00, 7.76, 7.74, 7.47, 7.34). 13C NMR
(DMSO-d6, 100MHz, ppm): 132.24, 130.73, 127.38, 126.94, 124.51, 122.23. (IR νmax
,
cm-1): 3424 (N–H), 1674 (C=O), 1594 (C=C, aromatic), 1447 (C–N, thiazole), 693
(C–Br). Elemental analysis for C14H9N2OSBr: Calculated: C: 50.47, H: 2.72, N: 8.41,
S: 9.62 (%) Found: C: 49.14, H: 2.51, N: 8.28, S: 9.42 (%) LRMS (m/z, M+) for
C14H9N2OSBr: Found: 333.90, Expected = 333.21.
N-(Benzothiazol-2-yl)-3-bromobenzamide (14)
The solid product found was filtered, washed with dry methanol and dried under
1
vacuum to obtain a yellow solid. Melting point: 194–196 °C. Yield: 42.0%. H NMR
(DMSO-d6, 400MHz, ppm): 8.35 (s, 1H, N-H), 8.12 (d, 1H,
= 8.4 Hz), 7.86 (d, 1H, = 8.4 Hz), 7.79 (d, 1H, = 8.4 Hz), 7.55 (t, 1H,
Hz), 7.49 (t, 1H,
= 7.6, 6.8 Hz), 7.36 (t, 1H, 7.6, 6.8 Hz). IR (νmax, cm−1): 3066
J
= 8.0 Hz), 8.02 (d, 1H,
J
J
J
J
= 7.6, 8.4
J
(C−H, aromatic), 1677 (C=O), 1600 (C=C, aromatic), 1453 (C−N), 1425 (C−N), 669
(C–Br). Elemental analysis for C14H9BrN2OS: Calculated: C: 50.46, H: 2.72, N: 8.41,
S: 9.62 (%) Found: C: 50.65, H: 2.63, N: 8.57, S: 9.73 (%) LRMS (m/z, M+): Found
for C14H9BrN2OS: 333.10, Expected: 333.20.
N-(Benzothiazol-2-yl)-4-methoxybenzamide (15)
The solid product found was filtered, washed with dry methanol and dried under
1
vacuum to obtain a yellow solid. Melting point: 193–195 °C. Yield: 21.3% H NMR
(DMSO-d6, 400MHz, ppm): 14.41, 12.09, aromatic protons (8.24, 8.22, 8.07, 7.83,
7.53, 7.50, 7.42, 7.39, 7.23, 7.14, 7.10, 6.98). (IR νmax, cm-1): 3304 (N-H), 1672
(C=O), 1598 (C=C, aromatic), 1468 (C–N, amide), 1246 (C–O, ether). Elemental
analysis for C15H12N2O2S: Calculated: C: 63.36, H: 4.25, N: 9.85, S: 11.28 (%) Found:

C: 51.07, H: 3.80, N: 11.55, S: 17.52 (%) LRMS (m/z, M+): Found for C15H12N2O2S=
284.15, Expected = 284.33.
N-(Benzothiazol-2-yl)-3-methoxybenzamide (16)
The solid product found was filtered, washed with dry methanol and dried under
1
vacuum to obtain a yellow solid. Melting point: 170–176 °C. Yield: 38.0%. H NMR
(DMSO-d6, 400MHz, ppm): 11.58 (s, 1H, N−H), 8.02 (t, 1H,
J = 7.2 Hz), 7.77 (m, 1H,
J
= 6.8, 7.6 Hz), 7.73 (s, 1H), 7.54−7.47 (m, 1H), 7.37 (m, 1H), 7.21 (m, 1H). IR (νmax
,
cm−1): 3458 (N−H), 3290 (N−H), 2863 (C-H, methoxy), 1686 (C=O), 1578 (C=C),
1448 (C−N, amide), 1426 (C−N, thiazole), 1237 (C-O, ether). Elemental analysis for
C15H12N2O2S: Calculated: C: 63.36, H: 4.25, N: 9.85, S: 11.28 (%) Found: C: 63.41,
H: 4.33, N: 9.93, S: 11.32 (%) LRMS (m/z, M+) for C15H12N2O2S: Found: 284.20,
Expected: 284.33.
N-(Benzothiazol-2-yl)-4-nitrobenzamide (17)
The solid product found was filtered, washed with dry methanol and dried under
1
vacuum to obtain a yellow solid. Melting point: 295–296 °C. Yield: 42.0% H NMR
(DMSO-d6, 400MHz, ppm): 8.39 (q, 4H,
J
= 6.8, 8.8 Hz), 8.05 (d, 1H,
J = 8.0 Hz),
7.81 (d, 1H, = 8.0 Hz), 7.50 (d, 1H,
J
J
= 7.6, 8.0 Hz), 7.37 (t, 1H, = 7.6 Hz). IR
J
(νmax, cm−1): 3117 (N−H), 3038 (C−H), 1686 (C=O), 1599 (C=C), 1522 (N–O), 1461
(C−N, amide), 1441 (C−N, thiazole), 1330 (N–O), 1272 (C–N, nitro). Elemental
analysis for C14H9N3O3S: Calculated: C, 56.18; H, 3.03; N, 14.04; S, 10.71 (%)
Found: C, 56.05; H, 3.01; N, 13.96; S, 10.52 (%) LRMS (m/z, M+) for C14H9N3O3S:
Found: 299.70, Expected mass: 299.50
.
N-(Benzothiazol-2-yl)-3-nitrobenzamide (18)
The solid product found was filtered, washed with dry methanol and dried under
1
vacuum to obtain a yellow solid. Melting point: 231–234 °C. Yield: 17.6% H NMR
(DMSO-d6, 400MHz, ppm): 12.93 (N–H), aromatic protons (8.58, 8.21, 7.26, 7.25,
13
6.18, 6.17). C NMR (DMSO-d6, 100MHz, ppm): 168.97, 166.49, 148.27, 136.09,
135.11, 130.60, 127.58, 126.98, 126.41, 126.01, 124.48, 124.03, 122.66, 115.51. (IR
νmax, cm-1): 3125 (br, N-H), 1676 (C=O), 1600 (C=C, aromatic), 1525 (N-O), 1349 (N-
O, nitro), Elemental analysis for C14H9N3O3S: Calculated: C: 56.18, H: 3.03, N: 14.04,

S: 10.71 (%) Found: C: 55.50, H: 3.07, N: 13.91, S: 10.99 (%) LRMS (m/z, M+) for
C14H9N3O3S: Found: 299.00, Expected = 299.31.
2.5
X-ray diffraction analysis of
Bruker Kappa Apex II diffractometer with monochromated Mo Kα radiation (
X-ray crystallography
5, 6, 10, 11, 12 and 14 were performed at 200 K using a
λ
=
0.71073 Å). APEXII [36], was used for data collection and SAINT [36], for cell
refinement and data reduction. Data were corrected for absorption effects using the
numerical method implemented in SADABS [36]. The structures were solved by dual-
space methods using SHELXT–2014/7 [37], and refined by least-squares procedures
using SHELXL-2014/7 [38], with SHELXLE [39], as a graphical interface. All non-
hydrogen atoms were refined anisotropically. Carbon-bound H atoms were placed in
calculated positions (C–H 0.95 Å for aromatic carbon atoms and C–H 0.99 Å for
methylene groups) and were included in the refinement in the riding model
approximation, with Uiso (H) set to 1.2Ueq (C). The H atoms of the methyl groups were
allowed to rotate with a fixed angle around the C–C bond to best fit the experimental
electron density (HFIX 137 in the SHELXL program [38]), with Uiso (H) set to 1.5Ueq
(C). The H atoms of the hydroxyl groups were allowed to rotate with a fixed angle
around the C–O bonds to best fit the experimental electron density (HFIX 147 in the
SHELXL program [38]), with Uiso(H) set to 1.5Ueq(O). Nitrogen-bound H atoms were
located on a difference Fourier map and refined freely.
2.6 Computational Details
All calculations were performed using the GAUSSIAN program16 (version 03) [40].
The crystal structure was used as an initial molecular geometry for compound
1 was
drawn using GAUSSVIEW 6 software. The computations were carried out using
GAUSSIAN 16 whilst the output files were visualized via GAUSSVIEW 6 software.
The reaction coordinate for the formation of benzamide was computed at the
B3LYP/6-311+G(d,p) level for all atoms except gold (LANL2TZ with
pseudopotential). Empirical Dispersion=GD3BJ, and SCRF in THF. The predicted
vibrational spectra for transition states gave one imaginary frequency whilst
intermediates gave no imaginary frequency proving that the optimized geometry is
located at the lowest point on the potential energy surface

3.
Results and Discussion
3.1 Spectroscopic characterization of 3-(1,3-benzothiazol-2-yl)-1-(benzoyl)thiourea
derivatives
The IR spectra showed bands between 3460 and 3054 cm-1 for the N–H stretch, bands for the
C=O stretch occurred between 1694 and 1668 cm–1 whilst bands for the C=N stretch were
observed between 1596 and 1585 cm–1 and the aromatic C=C were observed between 1591
and 1549 cm–1 [41]. The 1H NMR and 1H–1H COSY spectra gave signals between 14.17 and
11.23 ppm for a proton of an amide whilst aromatic protons occurred between 8.14 and 7.23
ppm. The 13C NMR spectrum gave signals between 169.0 and 163.6 ppm, for the C=S, while
the C=O signal occurred between 166.0 and 159.5 ppm. Signals between 147.4 and 114.7
ppm were observed for aromatic carbons. Table 1 gives the list of synthesized thiourea
derivatives and their corresponding benzamides.
Table 1
List of the synthesized thiourea derivatives and their corresponding
benzamides
Number
Reactant
Yield%
75.0
Number
Products
Yield%
47.0
H
S
N
O
N
1
10
N
O
N
S
S
N
H
H
H
S
N
H
N
S
85.9
19.0
2
11
N
O
N
O
N
Cl
Cl
Cl
Cl
S
H
H
S
H
N
76.4
75.0
52.4
17.1
3
4
12
13
N
O
N
N
S
S
N
H
O
H
S
H
N
N
N
N
S
Br
N
Br
Br
S
O
H
O
Br
H
S
H
N
S
80.0
73.0
42.0
21.3
5
6
14
15
N
N
N
S
N
O
H
O
H
H
S
N
N
S
N
N
N
H3CO
H3CO
O
S
O
H

H3CO
H
S
N
H3CO
H
N
S
78.5
38.0
7
16
N
O
N
S
N
O
H
H
S
N
O
N
75.6
77.3
42.0
17.0
8
9
17
18
N
O
O2
N
N
N
S
O2
N
S
N
H
H
O2
O2
N
H
S
O
N
N
S
S
N
N
N
O
H
H
3.2 Crystal structures of 3-(1,3-benzothiazol-2-yl)-1-(benzoyl)thiourea derivatives
Compounds 5 and 6 were recrystallized from DMSO:Toluene (1:1) and obtained as yellow
crystals. The crystallographic data, selected bond lengths and bond angles for the crystal
structures of compounds 5 and 6 are provided in Tables 2 and 3. The ORTEP diagrams for
compounds 5 and 6 are presented in Figures 1 and 2. Compound 5 crystallized in the
orthorhombic space group Pbca. Compound 6 crystallized in the triclinic space group P-1.
The O1–C1 bond distances in compound
respectively. The S2–C22 bond distances for compounds
1.751(1), respectively, which confirm the C=S bond of a thione [42] whilst the N1–C2
bond distances in compounds and are 1.391(2) and 1.389(8), respectively, are
5
and
6
are 1.220 (2) and 1.418 (9)
5
and are 1.745(2) and
6
5
6
consistent with C–N bond of an amide with significant double bond character.
Table 2 Crystallographic data and structure refinement summary for compounds 5 and 6.
Property
Formula
CCDC Number
Formula Weight
Crystal System
Space group
a [Ǻ]
5
C15H10BrN3OS2
1872966
392.28
6
C16H13N3O2S2
1872967
344.42
Orthorhombic
Pbca
Triclinic
P-1
13.4779(7)
11.7371(5)
19.2452(10)
90
5.8481(5)
11.6099(11)
11.7178(10)
90.784(4)
90.059(3)
101.936(3)
b [Ǻ]
c [Ǻ]
α [°]
β [°]
90
γ [°]
90

V [Ǻ^3]
3044.4(3)
8
778.31(12)
2
Z
D(calc) [g/cm^3]
Mu(MoKa) [ /mm ]
F(000)
1.712
2.978
1.470
0.355
1568
358
Crystal Size [mm]
Temperature (K)
Radiation [Å] Mo Ka
θ Min-Max [°]
0.36 x 0.40 x 0.43
200
0.10 x 0.17 x 0.64
200
0.71073
0.71073
2.5, 28.4
1.7, 28.4
Dataset
-17: 16 ; -15: 15 ; -25: 20
22448, 3759, 0.024
3052
-7: 4 ; -15: 15 ; -15: 15
12421, 3776, 0.024
3526
Tot., Uniq. Data, R(int)
Observed data [I > 2.0
sigma(I)]
Nref, Npar
3759, 207
0.0235, 0.0610, 1.04
0.00, 0.00
3776, 210
0.1036, 0.2738, 1.12
0.00, 0.00
R, wR2, S
Max. and Av. Shift/Error
Min. and Max. Resd. Dens.
[e/Å^3]
-0.40, 0.35
-0.60, 1.27
Table 3
Selected bond lengths (Å) and bond angles (˚) for compounds 5 and 6.
Bond lengths
5
6
O1-C1
S2-C22
N1-C2
N2-C3
N3-C21
S1-C2
1.220(2)
1.745(2)
1.391(2)
1.384(2)
1.382(2)
1.650(2)
1.746(2)
1.379(2)
O1-C1
S2-C22
N1-C2
N2-C3
N3-C21
S1-C3
1.418(1)
1.751(1)
1.389(1)
1.331(1)
1.385(1)
1.671(1)
1.762(1)
1.231(1)
S2-C3
S2-C4
N1-C1
O2-C2
N2-C2
1.340(2)
1.896(2)
N1-C3
1.377(1)
1.346(1)
Br1-C13
O1-C14
Bond angles
5
6
O1-C1-N1
C1-N1-C2
S1-C2-N1
S1-C2-N2
S2-C3-N2
S2-C3-N3
N2-C3-N3
122.6(2)
127.8(2)
120.0(1)
125.2(1)
125.4(1)
117.4(1)
117.3(2)
109.9(1)
121.3(2)
O2-C2-N1
C2-N1-C3
S1-C3-N1
S1-C3-N2
S2-C4-N2
S2-C4-N3
N2-C4-N3
C1-O1-C14
C4-S2-C22
120.6(6)
128.6(5)
119.5(1)
125.0(1)
124.5(1)
117.1(1)
118.4(1)
118.8(1)
87.5(1)
C3-N3-C21
O1-C1-C11

Br1
C26
C25
C13
O1
C21
N3
C12
C24
C14
C11
C3
C1
N2
C23
N1
C22
C15
C16
C2
S2
S1
Figure 1
An ORTEP view of compound 3-(1,3-benzothiazol-2-yl)-1-(3-bromobenzoyl)
thiourea (5) showing 50% probability displacement ellipsoids and the atom labelling
S1
S2
C16
C23
C22
C3
C15
N1
N2
C4
C1
C2
C14
C24
C11
N3
O1
C21
C25
C12
O2
C13
C26
Figure 2
An
ORTEP
view
of
compound
3-(1,3-benzothiazol-2-yl)-1-(3-
methoxybenzoyl)thiourea (6) showing 50% probability displacement ellipsoids and the atom
labelling.
The bond angles of O1-C1-N1 in compound
C2-N1 in compound
is 120.6(2), confirming that the carbon atom involved is sp2
hybridized. The bond angle of C1-N1-C2 is 127.8(2) in compound . The bond angle
is 128.6(5) confirming the sp2 hybridization of the
5 is 122.6(2) whilst the bond angle of O2-
6
5
in C2-N1-C3 in compound
nitrogen atom.
6
3.3 Dethiocyanation reaction of benzoyl thiourea derivatives
The treatment of 3-(1,3-benzothiazol-2-yl)-1-(4-benzoyl) thiourea derivatives with gold(I)-
complexes led to the dethiocyanation of 3-(1,3-benzothiazol-2-yl)-1-(4-benzoyl) thiourea

derivatives to give benzamides (Scheme 2). The reaction is thought to be initiated by the
coordination of sulfur to gold(I). A suspected electron redistribution converts the gold(I) to
give gold(I) thiocyanate which is a by-product whilst the thiocyanate is lost from the ligand
in the process (Scheme 3).
S
N
H
C
C
H
N
O
R
S
N
THF, no light
N2, 60oC , 4 h
Au(DMSO)Cl
or Au(tht)Cl
O
C
N
H
R
S
N
R= H, 4-NO2, 3-Br, 3-OMe,
3-NO3, 4-OMe, 4-Br, 3-Cl, 4-Cl
Scheme 2
Scheme for the synthesis of benzamide derivatives.
3.3.1 Spectroscopic characterization of benzamides
The IR spectra showed bands for the N–H stretch of an amide between 3117 and 3066 cm–1,
bands for the C=O stretch were observed between 1686 and 1677cm–1 and the C–N stretch
were observed between 1599 and 1578 cm–1. Whilst the aromatic C=C stretch was observed
1
between 1555 and 1522 cm-1. The H NMR spectrum gave signals between 8.39 and 7.21
13
ppm for aromatic protons. The C NMR spectrum gave signals between 130.4 and 124.1
ppm for aromatic carbons.

3.3.2 Crystal structures of benzamides 10, 11, 12 and 14
Compounds 10, 11, 12 and 14 were recrystallized from methanol. The crystallographic data,
selected bond lengths and bond angles for the crystal structures of compounds 10, 11, 12 and
14 are provided in Tables 4 and 5. The ORTEP diagrams for compounds 10, 11, 12 and 14
are presented in Figures 3, 4, 5 and 6 respectively. Compound 10 crystallized in the
monoclinic space group P21/n. Compound 11 crystallized in the monoclinic space group
P21/c while compound 12 crystallized in the orthorhombic space group Pbcn. Compound 14
crystallized in the triclinic space group P-1.
Table 4
Crystallographic data and structure refinement summary for compounds 10, 11,
12 and 14
Property
10
C14H10N2OS
1872968
254.30
11
C14H9ClN2OS
1872971
288.74
12
C14H9N3O3S
1872969
299.30
14
C14H9BrN2OS
1872970
333.19
Formula
CCDC Number
Formula Weight
Crystal System
Space group
a [Ǻ]
Monoclinic
P21/n
Monoclinic
P21/c
Orthorhombic
Pbcn
Triclinic
P-1
5.9236(4)
16.7628(10)
11.8749(7)
90
15.1220(8)
13.7855(6)
6.0408(3)
90
29.023(4)
7.7882(10)
11.5676(17)
90
5.9083(3)
7.6853(4)
14.4978(8)
77.501(2)
78.463(3)
89.036(3)
629.47(6)
2
b [Ǻ
c [Ǻ
α [°]
β [°]
102.305(2)
90
90.215(2)
90
90
γ [°]
90
V [Ǻ^3]
1152.04(12)
4
1259.28(11)
4
2614.7(6)
8
Z
D(calc) [g/cm^3]
Mu(MoKa) [ /mm ]
F(000)
1.466
1.523
1.521
1.758
0.268
0.460
0.262
3.422
528
592
1232
332
Crystal Size [mm]
Temperature (K)
Radiation MoKa [Å]
θ Min-Max [°]
Dataset
0.34 x 0.40 x 0.74
200
0.08 x 0.17 x 0.47
200
0.15 x 0.30 x 0.51
273
0.03 x 0.17 x 0.50
200
0.71073
0.71073
2.0, 28.3
0.71073
2.7, 28.4
0.71073
2.7, 28.3
2.1, 28.3
-7: 7 ; -22: 20 ; -15: 14
10261, 2851, 0.012
-20: 20 ; -18: 16 ; -8: 8 -38: 38 ; -10: 6 ; -15: 15 -7: 7 ; -8: 10 ;-18: 19
Tot., Uniq. Data,
R(int)
11897, 3078, 0.019
29350, 3272, 0.025
11395, 3118, 0.029
Observed data [I >
2.0 sigma(I)]
Nref, Npar
2659
2535
2537
2603
2851, 167
0.0302, 0.0820, 1.05
0.00, 0.00
3078, 176
0.0316, 0.0818, 1.02
0.00, 0.00
3272, 194
0.0440, 0.1303, 1.09
0.00, 0.00
3118, 176
0.0283, 0.0710, 1.05
0.00, 0.00
R, wR2, S
Max. and Av.
Shift/Error
Min. and Max. Resd.
Dens. [e/Å^3]
-0.24, 0.38
-0.24, 0.34
-0.37, 0.34
0.42, 0.52

Table 5
Selected bond lengths (Å) and bond angles (°) for compounds for compounds
10, 12 and 14
Bond lengths (Å)
10
11
1.750(1)
1.738(1)
1.220(2)
1.395(2)
1.300(2)
1.379(2)
1.371(2)
Bond angles (°)
11
12
14
S1-C1
S1-C12
O1-C2
N1-C11
N1-C1
N2-C2
N2-C1
1.750(1)
1.741(1)
1.221(1)
1.397(1)
1.300(1)
1.375(1)
1.381(1)
1.737(2)
1.734(2)
1.213(2)
1.393(2)
1.296(2)
1.367(2)
1.375(2)
1.747(2)
1.741(2)
1.216(2)
1.391(3)
1.301(2)
1.370(2)
1.375(3)
10
12
14
C1-S1-C12
C1-N1-C11
C1-N2-C2
S1-C1-N1
S1-C1-N2
88.1(1)
109.7(1)
124.1(1)
117.2(1)
121.8(1)
87.8(1)
88.3(1)
109.8(2)
123.2(2)
116.9(1)
121.8(1)
87.9(1)
109.3(2
124.0(2)
117.5(2)
121.4(1)
109.5(1)
123.6(1)
117.5(1)
121.2(1)
O1
S1
C13
C22
C23
C12
C21
C2
N2
C14
C1
C11
C24
C26
C15
N1
C16
C25
Figure 3
An ORTEP view of
N-(benzothiazol-2-yl)benzamide (10) showing 50%
probability displacement ellipsoids and the atom labelling.

C13
O1
S1
C14
C12
C22
C2
C1
N2
C23
C24
C15
C21
C11
N1
C16
C26
Cl1
C25
Figure 4
An ORTEP view of N-(benzothiazol-2-yl)-3-chlorobenzamide (11)
showing 50% probability displacement ellipsoids and the atom labelling.
The bond distance of O1-C2 in compounds 10, 11, 12 and 14 are 1.221(1), 1.220(2),
1.213(2), and 1.216(1) respectively, which is consistent with a carbonyl whilst the S1–C1
bond distances were 1.750(1), 1.750(1), 1.737(2) and 1.747(2) Å respectively are consistent
with the C=S bond. The bond angle of C1-S1-C12 in compounds 10, 11, 12 and 14 are,
88.10(5), 87.8(1), 88,3(1), 87.9(1) (°) respectively whilst the bond angle of S1-C1-N1 in
compounds 10, 11, 12 and 14 are 117.2(1), 117.5(1), 116.9(1), and 117.5(2)(°) respectively.
O1
C13
S1
C14
C12
C22
C23
C1
N2
C2
O2
C21
C15
C24
C11
N3
C16
N1
C26
C25
O3
Figure 5
An ORTEP view of N-(benzothiazol-2-yl)-4-nitrobenzamide (12) showing
50% probability displacement ellipsoids and the atom labelling.
C16
N1
C25
C26
C11
C24
N2
C15
C1
C2
C23
C21
C14
C22
C12
Br1
C13
S1
O1

Figure 6
An ORTEP view of N-(benzothiazol-2-yl)-3-bromobenzamide (14)
showing 50% probability displacement ellipsoids and the atom labelling.
3.4 Proposed Mechanism
Many gold(I)-catalyzed reactions proceed through an intrinsically similar mechanistic
route [43], which involves the activation of a π-system towards nucleophilic attack
[44-45]. Gold(I), being a soft Lewis acid and preferring orbital rather than charge
interactions, is selective towards these π-systems even in the presence of many other
functional groups [46-48].
The mechanism was explored at the B3LYP level using the LANL2TZ basis set for
Au and 6-311+G(d,p) for all other atoms, including GD3BJ empirical dispersion.
Solvent correction was included in separate calculations for p-xylene, water and THF
(as a comparison). The proposed mechanistic pathway (Scheme 3) begins with
formation of the gold(I) active species, (a). In this case, given the gold(I) starting
material is Au(tht)Cl or Au(DMSO)Cl, it is suspected that the gold(I) active species
has the form RS-AuCl, after the loss of tht (tetrahydrothiophene) or DMSO
(dimethylsulfoxide) because regardless of the starting material of gold used the same
product was obtained. The formation of a covalent Au-S bond in (a), which features π-
back donation from the sulfur atom, is the driving force facilitating the formation of
the tautomer observed (b) [49]. Figure 7 gives the reaction coordinate for formation of
benzamide computed at the B3LYP/6-311+G(d,p) level for all atoms except gold
(LANL2TZ with pseudopotential). Representative structures are also available in
Figure S1
.

Figure 7. The reaction coordinate for formation of benzamide computed at the B3LYP/6-
311+G(d,p) level for all atoms except gold (LANL2TZ with pseudopotential). Empirical
Dispersion=GD3BJ, and SCRF solvent THF.
The tautomerization is anticipated to be facile, and the 21 kcal/mol difference implies the
ratio of (a) to (b) at 300K will be about 97:3 in THF. The formation of the N-C bond and the
cyclic system in (c) via (tsi) is not possible on tautomer (a). Two transition states were
located breaking the first C-N bond, (tsii) connecting conformers (cii) and (dii) with
activation 21 kcal/mol, and (tsiii) connecting conformers (ciii) and (diii) with activation 24
kcal/mol. This leads to system (d). The second C-N bond was cleaved through (tsiv) to form
the benzamide and the isothiocyanatogold(I) species together as (e). Finally, tautomerization
was required to produce the benzamide product. An intramolecular transition state (tsv) was
located for this at high activation 34 kcal/mol, but it is conceivable that intramolecular proton
transfer could accomplish this with a much lower energy.
A reaction mechanism for the gold(I)-mediated cleavage of thiourea derivatives is proposed
to be initiated by attack of a gold(I) active species on the C=S π-system to form a covalent
Au-S bond. The latter species allows for intramolecular transamidation due to the close
proximity of the distal nitrogen to the carbonyl carbon, an observation which was made from

the crystal structures. To test the validity of this mechanism, further work must be done to
identify the side-products, which were initially removed by filtration, as well as inclusion of
thermodynamic, kinetic studies and crossover experiments. The reaction may become useful
in organic and organometallic synthesis fields, but this account presents the basic chemistry
that has been uncovered in this investigation.
Scheme 3
Proposed mechanism of gold(I)-mediated cleavage of thiourea derivatives.
Species (a) to (f) illustrate the mechanism subsequent to formation of the gold active species
up until production of the benzamide.
4. Conclusions

A series of benzamides have been synthesized by a reaction of 3-(1,3-benzothiazol-2-yl)-1-
(benzoyl)thiourea derivatives in the presence of gold(I). The compounds have been
characterized using IR, NMR, GC-MS and microanalysis. The single crystal XRD of 3-(1,3-
benzothiazol-2-yl)-1-(3-bromo
benzoyl)thiourea
(5),
3-(1,3-benzothiazol-2-yl)-1-(3-
methoxybenzoyl)thiourea (6), N-(benzothiazol-2-yl)benzamide (10), N-(benzothiazol-2-yl)-3-
chlorobenzamide (11), N-(benzothiazol-2-yl)-4-nitrobenzamide (12), N-(benzothiazol-2-yl)-
3-bromobenzamide (14) have been discussed. A mechanism for the novel intramolecular
transamidation reaction has been proposed to go through a 4-R,4-hydroxy-1,3-R′-diazetidine-
2-thione gold(I) chloride intermediate by computational chemistry calculations.
Supplementary Material
Supplementary material CCDC-1872966 for 5, CCDC-1872967 for 6, CCDC-1872968
for 10, CCDC-1872971 for 11, CCDC-1872969 for 12 and CCDC-1872970 for 14
contains the supplementary crystallographic data for this paper. These data can be
obtained free of charge at www.ccdc.cam.ac. uk/conts/retrieving.html
Acknowledgements
We thank MRC (SA) for the research funding (under MRC-SIR) and NRF (SA). F.
Odame thanks the National Research Foundation for awarding him a Postdoctoral
Fellowship. The authors would like to acknowledge the Center for High Performance
Computing (CHPC) for use of their computing cluster (project CHEM0864). We
would also like to thank Prof. Alex Brown from the University of Alberta (Canada)
and Prof. Israel Fernández López from Universidad Complutense de Madrid (Spain)
for their advice on computational chemistry.
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Highlights:
•
•
•
A novel intramolecular transamidation reaction is presented.
Gold(I) abstracts a thiocayanate moiety from thiourea derivatives.
A dethiocyanation mechanism is proposed.

South Campus
Chemistry Department
Tel. +27 (0)41 504 2074
Fax. +27 (0)504 1728
zenixole.tshentu@mandela.ac.za
10 April 2020
Journal of Organometallic Chemistry
Elsevier
Dear Editor
Re – Declaration of Interest
There are no interests to declare.
Yours sincerely,
Zenixole R. Tshentu
Director of School of Biomolecular and Chemical Sciences
Faculty of Science