N-donor 2-(Sulfonamido)benzamide ligands, their palladium(II) coordination species and C–C coupling catalysis efficiencies

Article abstract of DOI:10.1016/j.molstruc.2019.07.054

A series of synthetically accessible ligands based on new 2-(R-sulfonamido)benzamide have been prepared (R = methyl for H₃M; R = 4-toly for H₃T and T₂CN; R = 2,4,6-triisopropylphenyl for H₃iP and HiPCN). The R-substituents were selected to vary in sizes. Allowing ligand H₃iP and palladium acetate to stand in solvent leads to self-assembly of the well-defined solvent- and stoichiometry-controlled tetranuclear or hexanuclear coordination macromolecules Pd₄(iP)₂ and (PdHiP)₆, which were analysed by X-ray crystallography. It was observed that palladium active species for Suzuki coupling catalysis could be stabilized by these simple and synthetically assessable N-donor ligands as revealed by turnover frequencies reaching 5500 h^?1. Electronic features of these N-donors appear to be more important than the steric properties.

Full text of DOI:10.1016/j.molstruc.2019.07.054

Journal of Molecular Structure 1197 (2019) 336e344
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: http://www.elsevier.com/locate/molstruc
N-donor 2-(Sulfonamido)benzamide ligands, their palladium(II)
coordination species and CeC coupling catalysis efficiencies
,
b
b
a
Hammed Olawale Oloyede a , Helmar Gorls , Joseph Anthony Orighomisan Woods ,
€
Winfried Plass b **, Abiodun Omokehinde Eseola b
a Inorganic Chemistry Unit, Department of Chemistry, University of Ibadan, Ibadan, Nigeria
,
, c, *
b
€
Institut Fü;r Anorganische und Analytische Chemie, Friedrich-Schiller-Universitat Jena, Humboldtstraße 8, 07743 Jena, Germany
c Materials Chemistry Group, Department of Chemical Sciences, Redeemer's University Ede, Osun State, Nigeria
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of synthetically accessible ligands based on new 2-(R-sulfonamido)benzamide have been pre-
pared (R ¼ methyl for H3M; R ¼ 4-toly for H3T and T2CN; R ¼ 2,4,6-triisopropylphenyl for H3iP and
HiPCN). The R-substituents were selected to vary in sizes. Allowing ligand H3iP and palladium acetate to
stand in solvent leads to self-assembly of the well-defined solvent- and stoichiometry-controlled tet-
ranuclear or hexanuclear coordination macromolecules Pd4(iP)2 and (PdHiP)6, which were analysed by X-
ray crystallography. It was observed that palladium active species for Suzuki coupling catalysis could be
stabilized by these simple and synthetically assessable N-donor ligands as revealed by turnover fre-
quencies reaching 5500 hꢀ1. Electronic features of these N-donors appear to be more important than the
steric properties.
Received 5 June 2019
Received in revised form
2 July 2019
Accepted 12 July 2019
Available online 17 July 2019
Keywords:
N-Donor ligands
Palladium
CeC coupling
Homogeneous catalysis
Catalyst design
© 2019 Elsevier B.V. All rights reserved.
1. Introduction
because of their simplicity and substrate availability [18,19].
Different ligand designs ranging from monodentate through
In the last few decades, many transition metal materials have
been explored for their roles as catalyst in carbon-carbon (CeC)
synthetic protocols [1e7]. However, the catalytic utility and
versatility of palladium species in CeC coupling is unequaled
[8e10]. Consequently, molecular scientists concerned with natural
products total synthesis, drug designs, supramolecular organic or
organometallic chemistry and syntheses of smart materials and
fine chemicals have continued to benefit from the use of palladium-
mediated catalytic interventions [11e14], which has tremendously
eased synthetic organic manipulations [15e17]. Among the
commonly utilized palladium-catalyzed coupling methodologies
such as Suzuki-Miyaura, Hiyama, Kumada, Stille, Buchwald-
Hartwig, Sonogashira, Heck, Negishi, etc., Suzuki-Miyaura and
Heck coupling techniques enjoy more widespread patronage
bidentate to polydentate have been studied as an organic backbone
for active palladium centres [20e22]. Numerous highly active
palladium compounds have been patented and even commercial-
ized with trademarks [23e26]. These are mostly organometallic
palladium complexes incorporating only one phosphine or N-het-
erocyclic carbene donor arm as the only strong base while the
complementary co-ligands are usually of various weaker and easily
detachable donor systems such as organometallic allylic and
cyclometallated amine or halide fragments (Scheme 1, top)
[26e28]. Thus, there are reasons to anticipate that the active
transient species generated during catalysis are of monodentate
mono-ligand compositions in nature [29e32] while coordinatively
saturated palladium complexes tend to yield poor catalyst perfor-
mances [33,34]. Furthermore, catalyst generation is also routinely
achieved via in situ build-up from ligand and palladium salt or from
precatalyst decomposition (Scheme 1, bottom).
However, in addition to their potential air and moisture sensi-
tivity problems, the currently highly active phosphine or organo-
metallic palladium precatalysts are usually expensive and
synthetically inaccessible [28]. Therefore, development of inex-
pensive, simpler and more stable N-donor precatalysts could be
* Corresponding author. Institut für Anorganische und Analytische Chemie,
€
Friedrich-Schiller-Universitat Jena, Humboldtstr. 8, D-07743 Jena, Germany.;
** Corresponding author. Institut für Anorganische und Analytische Chemie,
€
Friedrich-Schiller-Universitat Jena, Humboldtstr. 8, D-07743 Jena, Germany.
E-mail addresses: sekr.plass@uni-jena.de (W. Plass), biodun.eseola@uni-jena.de,
bioduneseola@hotmail.com (A.O. Eseola).
https://doi.org/10.1016/j.molstruc.2019.07.054
0022-2860/© 2019 Elsevier B.V. All rights reserved.

H.O. Oloyede et al. / Journal of Molecular Structure 1197 (2019) 336e344
337
Scheme 1. (Top) Few examples of highly active and commercially available pre-catalysts [23e25,38,39] and (bottom) active catalyst formation from precatalysts decomposition or
in situ complexation build-up.
considered necessary [35]. Furthermore, based on the conviction
that hemilabile ligands could also fulfill the requirements for
generating monodentate mono-ligand active species, motivation
arose to design new 2-(sulfonamido)benzamide chelates derived
from 2-aminobenzamide (H4BA) and sulfonyl chloride reagents
(Scheme 2). Since ligand rigidity and bulkiness is often associated
with desirable catalyst efficiencies [36,37], systematic variation of
substituent bulks was introduced around the sulfonamide group.
Presented herein are the results for the study of the influence of
electronic and structural variations of new N-donor ligands on
palladium-catalyzed CeC cross coupling efficiencies.
excluded either by column chromatography on silica gel or
recrystallization. IR spectra were measured with a Bruker Equinox
FT-IR spectrometer equipped with a diamond ATR unit. Elemental
analyses were carried out on Leco CHNS-932 and El Vario III
elemental analysers. Mass spectrometry analyses were conducted
on a Bruker MAT SSQ 710 spectrometer. 1H and 13C NMR spectra
were collected on a Bruker AVANCE 400 MHz spectrometer using
deuterated solvents.
2.2. Synthesis of ligands and the palladium species Pd4(iP)2 and
(PdHiP)6
2. Experimental section
2.2.1. 2-(methylsulfonamido)benzamide (H3M)
To a solution of 2-aminobezamide, (2.00 g, 14.7 mmol) in a
mixture of water (5 mL) and pyridine (15 mL) was added dropwise
2.1. General information
over
a period of 30 min, methanesulfonyl chloride, (4.5 mL,
All starting materials for synthesis as well as substrates for the
catalytic experiments were obtained commercially as reagent and
used without further purification. Microwave assisted procedures
were conducted using Biotage Initiator 2.5 Microwave Reactor for
ligand preparations. Impurities in all organic syntheses were
58.7 mmol) while stirring inside an ice bath. After 2 h, the solid was
filtered and washed with methanol to give H3M as a light yellow
crystalline solid. Yield (2.52 g, 80%). M.p. ¼160e161 ꢁC. Selected IR
data (ATR, cmꢀ1): v 3444 (m, NH), 3181 (m), 2960 (m, methyl), 1666
(s, amide), 1617 (s, C]C), 1498 (s), 1435 (s), 1382 (s), 1319 (vs), 1270
Scheme 2. Synthetic scheme and structures for the bidentate chelating amine ligands subjected to in situ as well as palladium precatalyst studies.

338
H.O. Oloyede et al. / Journal of Molecular Structure 1197 (2019) 336e344
(s), 1149 (vs), 780 (vs). 1H NMR (400 MHz, DMSO‑d6): dppm 11.68 (s,
1H, NH), 8.41 (s, 1H, NH), 7.90 (d, J ¼ 7.7 Hz, 2H, Ph), 7.56 (t,
J ¼ 4.1 Hz, 2H, Ph), 7.16 (m, J ¼ 8.2, 5.0, 3.5 Hz, 1H, Ph), 3.13 (s, 3H,
117. Anal.: calc. for C22H30N2O3S C, 65.64; H, 7.51; N, 6.96; S, 7.96%.
Found: C, 65.40; H, 7.52; N, 6.86; S, 7.82%.
Ligand HiPCN was eluted after H3iP as off-white powder. Yield
(1.23 g, 68%). M.p. ¼146e147 ꢁC. Selected IR data (ATR, cmꢀ1): v
3223 (m, NH), 2961 (s, i-Pr), 2234 (m, nitrile), 1599 (s, C]C), 1489
(s), 1427 (m), 1364 (m), 1162 (vs), 901 (s), 759 (vs). 1H NMR
methyl). 13C NMR (101 MHz, DMSO‑d6):
d 175.95, 144.95, 138.22,
134.29, 127.72, 124.25, 123.51, 21.82 (methyl). MS (EI) m/z 214 (Mþ,
100%): 197, 184. Anal.: calc. for C8H10N2O3S C, 44.85; H, 4.70; N,
13.08; S, 14.97%. Found: C, 44.95; H, 4.64; N, 13.00; S, 15.04%.
(400 MHz, DMSO‑d6): d 12.31 (s,1H, NH), 8.36 (s, 1H, Ph), 7.86 (s,1H,
Ph), 7.82 (d, J ¼ 7.9 Hz, 1H, Ph), 7.42 (t, J ¼ 7.7 Hz, 1H, Ph), 7.29 (d,
J ¼ 8.3 Hz,1H, Ph), 7.24 (s, 2H, Ph), 7.06 (t, J ¼ 7.5 Hz,1H, Ph), 4.17 (m,
J ¼ 13.1, 6.5 Hz, 2H, i-Pr), 2.90 (m, J ¼ 13.7, 6.8 Hz, 1H, i-Pr), 1.17 (m,
2.2.2. 2-(4-methylphenylsulfonamido)benzamide (H3T)
2-aminobenzamide (1.00 g, 7.4 mmol) was added to toluene-
sulfonyl chloride (2.80 g, 14.7 mmol) in pyridine (15 mL). The re-
action mixture was stirred for 15 min before it was microwaved for
4 min at 120 ꢁC. Excess pyridine was removed by rotary evapora-
tion. Methanol was added and the precipitates was filtered and
washed with methanol which affords H3T as a white crystalline
solid. Yield (1.47 g, 70%). M.p. ¼ 250e251 ꢁC. Selected IR data (ATR,
cmꢀ1): v 3468 (m, NH), 3362 (m), 2960 (m, methyl), 1653 (m,
amide), 1608 (m, C]C), 1493 (m), 1317 (m) 1153 (vs), 939 (s), 759
(s). 1H NMR (400 MHz, DMSO‑d6): dppm 12.19 (s, 1H, NH), 8.33 (s, 1H,
NH), 7.86 (s, 1H, NH), 7.78 (d, J ¼ 7.9 Hz, 1H, Ph), 7.66 (d, J ¼ 7.7 Hz,
2H, Ph), 7.52 (d, J ¼ 8.3 Hz,1H, Ph), 7.46 (t, J ¼ 7.7 Hz,1H, Ph), 7.34 (d,
18H, methyl). 13C NMR (101 MHz, d6- DMSO):
d 171.24, 153.43,
150.39, 140.02, 132.99, 129.51, 124.43, 122.77, 118.79, 118.00, 49.06
(alkyl), 33.72 (alkyl), 29.64 (alkyl), 24.97 (alkyl), 23.75 (alkyl). MS
(EI) m/z 403 (Mþ, 10%): 383, 368, 267, 251, 203, 187, 136, 119. Anal.
calc. for C22H28N2O2S C, 68.72; H, 7.34; N, 7.29; S, 8.34%. Found: C,
68.71; H, 7.36; N, 6.75; S, 7.87%.
2.2.5. Pd4(iP)2 and (PdHiP)6
A mixture of H3iP (10 mg, 0.025 mmol) and two equivalent of
palladium(II) acetate (10 mg, 0.05 mmol) were stirred in acetoni-
trile for 3 h. The clear orange solution was allowed to stand at room
temperature under slow evaporation and the tetranuclear complex
Pd4(iP)2 was obtained as orange crystals suitable for x-ray mea-
surement after standing overnight. Yield (0.02 g, 64%)
M.p. ¼ 282e283 ꢁC. Selected IR data (ATR cmꢀ1): v 2962 (m), 2322
(m), 1678 (s), 1532 (s), 1465 (vs), 1412 (vs), 1286 (s), 1190 (vs), 1129
(vs), 832 (vs). Anal. Calc. for C54H69N9O10Pd4S2.(H2O) C, 42.90; H,
4.73; N, 8.34; S, 4.24 Found: C, 43.04; H, 4.72; N, 8.01; S, 4.09.
Hexanuclear greenish-yellow crystals of the palladium species
(PdHiP)6 suitable for x-ray analyses were also isolated from a so-
lution of H3iP (10 mg, 0.025 mmol) and one equivalent of palla-
dium(II) acetate (6 mg, 0.025 mmol) in acetonitrile, which was
layered with diethyl ether and allowed to stand at room tempera-
ture for 3 weeks under slow evaporation. NMR analyses of both
palladium species were considered not useful since there are non-
equivalent corresponding protons from multiple ligands, which
leads to complicated spectra.
J ¼ 7.9 Hz, 2H, Ph), 7.09 (t, J ¼ 7.5 Hz,1H, Ph), 2.32 (s, 3H, methyl). 13
C
NMR (101 MHz, DMSO‑d6):
d 171.14, 144.23, 139.71, 136.50, 133.32,
130.32, 129.41, 127.22, 123.46, 119.40, 21.41 (methyl). MS (EI) m/z
290 (Mþ, 100%): 273, 209, 180, 155, 110, 91. Anal.: calc. for
C
14H14N2O3S C, 57.92; H, 4.86; N, 9.65; S, 11.04%. Found: C, 57. 47; H,
4.77; N, 9.10; S, 11.35%.
2.2.3. N-(2-cyanophenyl)-4-methyl-N-tosylbenzenesulfonamide
(T2CN)
2-(4-methylphenylsulfonamido)benzamide,
H3T
(0.50 g,
1.7 mmol) was added to p-toluenesulfonyl chloride (1.00 g,
5.2 mmol) in pyridine (10 mL). The mixture was refluxed for 5 h at
110 ꢁC and then concentrated by rotary evaporation. Methanol was
added to the concentrate which affords T2CN as a white crystalline
solid. Yield (0.45 g, 60%). M.p. ¼193e194 ꢁC. Selected IR data (ATR,
cmꢀ1): v 2960 (m, methyl), 2229 (m, nitrile) 1596 (s, C]C), 1446 (s)
1361 (vs), 1166 (vs), 1085 (s), 912 (vs), 860 (s), 660 (vs). 1H NMR
(400 MHz, DMSO‑d6): dppm 8.00 (d, J ¼ 7.5 Hz, 1H, Ph), 7.80 (t,
J ¼ 7.7 Hz, 1H, Ph), 7.78e7.74 (m, 1H, Ph), 7.71 (d, J ¼ 7.9 Hz, 4H, Ph),
7.49 (d, J ¼ 7.9 Hz, 4H, Ph), 7.14 (d, J ¼ 7.9 Hz, 1H, Ph), 2.46 (s, 6H,
2.3. Catalysis experiments
2.3.1. Suzuki-Miyaura
methyl) 13C NMR (101 MHz, d6- DMSO):
d
146.53, 135.21, 133.20,
In a typical Suzuki-Miyaura coupling reaction, (4-bromophenyl)
methanol (0.19 g, 1.0 mmol), (4-acetylphenyl)boronic acid (0.23 g,
1.2 mmol), K3PO4 (0.26 g, 1.4 mmol), Pd(AcO)2 (0.2 mol % relative to
the aryl bromide) and a given ligand (0.7 mol %) were weighed into
a 10 mL round-bottom flask equipped with magnetic stirrer bar.
These were then refluxed for the desired reaction time using 3:1
ethanol/water mixture (4 mL) as reaction media. In the case of
preformed palladium(II) complex, 0.05 mol % equivalent relative to
the aryl bromide was used. After the desired reflux duration, an
aliquot of the reaction mixture was transferred into a clean conical
flask and the solvents was largely removed under vacuum. The
residue was then collected in deuterated DMSO and its 1H NMR
analysed. The yields were evaluated by comparing integration
values for NMR signal of the methylene eCH2- protons of (4-
131.98, 130.54, 128.99, 115.97, 21.69 (methyl). MS (EI) m/z 426 (Mþ,
47%): 209, 155, 91. Anal.: calc. for C21H18N2O4S2 C, 59.14; H, 4.25; N,
6.57; S, 15.03%. Found: C, 59.59; H, 4.23; N, 6.63; S, 15.26%.
2.2.4. 2-(2,4,6-triisopropylphenylsulfonamido)benzamide (H3iP)
and N-(2-cyanophenyl)-2,4,6-triisopropylbenzenesulfonamide
(HiPCN)
A mixture of 2- aminobenzamide (0.30 g, 2.2 mmol) and 2, 4, 6-
triiso-propylbezenesulfonyl chloride (2.00 g, 6.6 mmol) in 15 mL
pyridine was refluxed overnight at 120 ꢁC. Pyridine was removed
under reduced pressure while the residue was purified on silica gel
column with THF/n-hexane (3:7). H3iP was obtained as off-white
crystalline solid. Yield (0.13 g, 9%). M.p. ¼ 217e218 ꢁC. Selected IR
data (ATR, cmꢀ1): v 3436 (m, NH), 3183 (m), 2958 (m, methyl), 1673
(s, amide), 1622 (m, C]C), 1601 (m, C]C), 1493 (m), 1423 (m), 1333
(m), 1266 (m), 1150 (vs), 921 (s), 752 (vs). 1H NMR (400 MHz,
DMSO‑d6): dppm 10.43 (s, 1H, NH), 7.84 (d, J ¼ 7.6 Hz, 1H, Ph), 7.64 (t,
J ¼ 7.8 Hz, 1H, Ph), 7.42 (t, J ¼ 7.4 Hz, 1H, Ph), 7.22 (s, 2H, Ph), 7.12 (d,
J ¼ 8.1 Hz, 1H, Ph), 3.83 (dd, J ¼ 12.9, 6.4 Hz, 2H, i-Pr), 2.92 (dt,
J ¼ 13.6, 6.8 Hz, 1H, i-Pr), 1.20 (d, J ¼ 6.8 Hz, 6H, methyl), 1.09 (d,
bromophenyl)methanol at
sponding biphenyl products at
d
z 4.4 ppm with that of the corre-
z 4.7 ppm [31]. The various
d
biphenyl products have been characterized in our previous studies
[20,31,34].
2.3.2. Heck-mizoroki
In a typical Heck coupling experiment, (4-bromophenyl)meth-
anol (0.19 g, 1.0 mmol), styrene (0.17 mL, 1.5 mmol), potassium
carbonate (0.17 g, 1.5 mmol) and precatalyst Pd4(iP)2 (0.8 mg,
0.05 mol % relative to the aryl bromide) were weighed into a 10 mL
J ¼ 6.6 Hz, 12H, methyl). 13C NMR (101 MHz, d6- DMSO):
d 153.11,
150.35, 134.53, 127.98, 124.21, 33.73 (alkyl), 29.70 (alkyl), 25.00
(alkyl), 22.76 (alkyl). MS (EI) m/z 385 (Mþ, 20%): 343, 267, 251, 202,

H.O. Oloyede et al. / Journal of Molecular Structure 1197 (2019) 336e344
339
round-bottom flask equipped with magnetic stirrer bar. Using 3:1
DMF/water mixture (4 mL) as media, the mixture was then refluxed
at a given temperature and for the desired duration. An aliquot of
the reaction mixture was taken directly into NMR tube while
deuterated DMSO was added for 1H NMR measurement. The
determination of yields was achieved by comparing the methoxy
solvent molecules. The size of the voids are 576 and 770 Å3/unit
cell, respectively. Their contribution to the structure factors was
secured by back-Fourier transformation using the SQUEEZE routine
of the program PLATON [44] resulting in 152 and 207 electrons/unit
cell, respectively. The crystal of H3M was a non-merohedral twin.
The twin law was determined by PLATON [44] to (ꢀ0.002
0.000e0.998) (0.000e1.000 0.000) (ꢀ1.002 0.000 0.002). The
contribution of the main component were refined to 0.615(1).
Crystallographic data as well as structure solution and refinement
details are summarized in Table 1. XP (SIEMENS Analytical X-ray
Instruments, Inc.1994) [45] was used for structure representations.
eOCH3 protons of 4-methoxystyrene at
d z 3.74 ppm with that of
the corresponding Heck product at z 3.76 ppm. The produced
d
Heck coupling product (4-styrylphenyl)methanol was isolated,
purified and characterized: M.P ¼ 173 ꢁC. Selected IR data (ATR,
cmꢀ1): v 3290 (m), 3052 (w), 3022 (w), 2860 (w, methylene CH)
1593 (m, C]C), 1576 (m), 1507 (m), 1488 (w), 1446 (s), 998 (s), 970
(s), 802 (s), 687 (s). 1H NMR (400 MHz, DMSO‑d6) dppm 7.59 (dd,
J ¼ 12.4, 7.7 Hz, 4H), 7.32 (m, 7H), 5.22 (s, 1H), 4.51 (s, 2H). 13C NMR
(101 MHz, DMSO‑d6) dppm 142.59, 137.58, 135.94, 129.16, 128.77,
128.27, 127.99, 127.26, 126.86, 126.71, 63.16. EI MS: 210 (Mþ, 100%):
193 (Mþ ꢀ OH), 178 ((Mþ ꢀ CH2OH), 165, 152, 31 (CH2OH), 27. Anal.
calc. for C15H14O, C, 85.60; H, 6.71% found: C, 85.11; H, 6.65%.
3. Results and discussion
3.1. Synthesis and characterization
Elemental analysis and spectroscopic data gave good agreement
with the identities of the series of synthesized ligands H3M ꢀ
HiPCN. In all cases of syntheses, between 2 and 4 equivalents of the
sulfonyl chloride reagents were deployed. However, reactions at
low temperatures and/or shorter reaction times as for both H3M
and H3T yielded only mono-sulfonyl condensation products as the
main products (Scheme 2). Attempting prolonged reflux at high
temperature enabled condensation of a second sulfonyl chloride
reagent on the same aromatic NH2 function and/or an unexpected
reduction of the amide NH2 group to nitrile, which produced T2CN
and HiPN (Scheme 2) as the predominant products. Under this
condition, the amide NH2 function reacts with the excess sulphonyl
chloride by dehydration of the amide as illustrated in Scheme 3
[46,47]. Perhaps this may mark another new aspect of sulfonyl
chloride utility as well as novel pathway to the conversion of pri-
mary amide to nitrile due to its operational simplicity. Several ef-
forts were made under various reaction conditions to obtain
palladium(II) complexes from the isolated N-donors ligands.
2.4. Structure determinations
The intensity data for the compounds were collected on a
Nonius KappaCCD diffractometer using graphite-monochromated
Mo-Ka radiation. Data were corrected for Lorentz and polarization
effects; absorption was taken into account on a semi-empirical
basis using multiple-scans [40e43]. The structures were solved
by direct methods (SHELXS) and refined by full-matrix least
squares techniques against Fo2 (SHELXL-97 and SHELXL-2014) [43].
The hydrogen atoms bonded to the amine-groups of H3M and
(PdHiP)6 were located by difference Fourier synthesis and refined
isotropically. All other hydrogen atoms were included at calculated
positions with fixed thermal parameters. All non-hydrogen, non-
disordered atoms were refined anisotropically [43]. The crystal of
(PdHiP)6 and Pd4(iP)2 contain large voids, filled with disordered
Table 1
Crystal and structural refinement data for ligands H3M and T2CN as well as palladium complexes (PdHiP)6 and Pd4(iP)2.
Compound
H3M
T2CN
(PdHiP)6
Pd4(iP)2
formula
fw (g∙molꢀ1
ꢁC
crystal system
space group
a/Å
C8H10N2O3S
214.24
20(2)
monoclinic
P 21/n
19.733(4)
5.2950(11)
19.791(4)
90
116.84(3)
90
1845.1(6)
8
1.542
3.33
C21H18N2O4S2
426.49
C156H204N24O18Pd6S6*
3534.18[*]
C56H69N10O10Pd4S2*
1531.93[*]
ꢀ140(2)
)
ꢀ140(2)
ꢀ140(2)
triclinic
triclinic
triclinic
ꢀ
P ı
ꢀ
P ı
ꢀ
P ı
7.4591(4)
8.1714(4)
16.7248(9)
85.057(3)
86.259(3)
74.408(3)
977.29(9)
2
16.5121(4)
17.8664(4)
18.6882(5)
110.329(1)
108.604(1)
100.765(1)
4616.8(2)
1
10.7928(3)
18.2590(4)
20.7825(5)
112.833(1)
100.598(1)
92.204(1)
3682.84(16)
2
b/Å
c/Å
ꢁ
ꢁ
a
/
b
/
ꢁ
/
g
V/Å3
Z
r
(g∙cmꢀ3
(cmꢀ1
)
1.449
3.04
1.271[*]
0.7[*]
1.381[*]
10.7[*]
m
)
measured data
data with I > 2
unique data (Rint
wR2 (all data, on F2)a
24108
4171
4223/0.0350
0.1070
0.0397
9349
3781
4404/0.0377
0.1640
0.0616
55920
15740
20818/0.0539
0.1383
0.0574
40584
14329
16656/0.0291
0.0938
0.0415
s
(I)
)
R1 (I > 2
s
(I))a)
Sb
1.104
1.137
1.086
1.055
Res. dens./e∙Åꢀ3
absorpt method
absorpt corr Tmin
CCDC No.
1.228/-0.442
multi-scan
0.6793/0.7456
1878808
0.748/-0.656
multi-scan
0.5925/0.7456
1878809
1.040/-0.641
multi-scan
0.5527/0.7455
1878810
2.375/-1.470
multi-scan
0.6399/0.7456
1878811
/
max
*
The derived parameters do not contain the contribution of the disordered solvent.
a
Definition of the R indices: R1 ¼ (SrjFoj-jFcjr)/SjFoj; wR2j¼ {S[w(F2o-Fc2)2]/S[w(Fo2)2]}1/2 with wꢀ1
¼
s
2(F2o) þ (aP)2þbP; P ¼ [2Fc2 þ Max(F2O]/3.
b
s ¼ {S[w(F2o-Fc2)2]/(NoeNp)}1/2
.

340
H.O. Oloyede et al. / Journal of Molecular Structure 1197 (2019) 336e344
bond lengths around the coordination centre for the structures of
(PdHiP)6 and Pd4(iP)2 are collected in the Supplementary Infor-
mation Table S2 and they are within expected values [49]. The
PdeO bonds are generally in the range from 2.041 Å to 2.071 Å
while the PdeN bonds generally range from 1.942 to 2.025 Å, which
suggests that the nitrogen donor atoms are stronger donors than
the oxygen donor atoms.
The assembly of six units of square planar palladium centres
into the hexanuclear macromolecular (PdHiP)6 can be considered
as networking between the palladium ion of one complex unit and
the amide carbonyl oxygen of another complex unit. On the other
hand, the structure of Pd4(iP)2 consist of two ligands and four
palladium centres. Each palladium centre is different from one
another. In general, the hemilability of the studied ligands could be
implied from the consistently longer PdeN bond lengths for the
anilinyl N-donor than for the amide N-donor. Furthermore, the
incorporation of coordinated acetonitrile suggests that the palla-
dium complexes would easily generate coordinatively non-
saturated active catalyst centres, which presents hope of forming
desirable monodentate mono-ligand active catalyst species. These
structural features also suggest how the ligands may possibly
assemble during in situ ‘Pd(AcO)2 þ ligand’ catalysis situations. For
comparative reasons, Pd4(iP)2 has been tested as precatalyst in CeC
coupling reactions.
Scheme 3. Probable mechanism for sulfonyl chloride-mediated dehydration of the
amide function to form the nitrile product.
However, only ligand H3iP formed well-defined complexation
products Pd4(iP)2 and (PdHiP)6, which respectively assembled as
tetranuclear and hexanuclear complexes from the same starting
materials, but in the presence of slight solvent media variation
(Scheme 4). It is noteworthy that one of the ligands in Pd4(iP)2 was
covalently modified by probable incorporation of acetonitrile
moiety (CH3C]N) at the amide oxygen. Furthermore, a strange
appearance of a bridging NO2 group was also observed in the
structure of Pd4(iP)2, which is uncommon. However, in the course
of our studies of palladium structures, this surprise appearance of
coordinated NO2 group has been encountered a number of times in
different styles (see Supplementary Information Fig. S1) and
attempt to explain its origin has been reported by Raithby and
Fairlamb [48].
3.3. Determining suitable reaction parameters for Suzuki-Miyaura
3.2. Structural characterization
CeC coupling
Single crystals of H3M, T2CN and Pd4(iP)2 suitable for X-ray
measurement were obtained by slow solvent evaporation from
their acetonitrile solution. Single crystals of (PdHiP)6 were obtained
by slow diffusion of diethylether into a previously stirred acetoni-
trile solution of ligand H3iP and Pd(AcO)2. Data for their structural
refinement and processing parameters are collected in Table 1 and
their crystal structures are presented in Fig. 1 e 3. Compounds H3M
In order to determine reaction settings under which the various
ligands would be compared, ligands H3M and H3T were used as
representatives of the ligand series to test for suitable reaction
time, base additive, boronic acid loading and Pd(AcO)2: ligand ratio.
The typical coupling reaction consisted of (4-bromophenyl)meth-
anol and (4-acetylphenyl)boronic acid and the decision to use (4-
bromophenyl)methanol arose from the need to use 1H NMR
signal of its methylene (-CH2-) function for yield determination
[31]. The results of the various parameters tested are summarized
in Table 2.
ꢀ
and T2CN crystallize in the monoclinic P21/n and triclinic Pı space
groups respectively (Fig. 1). Complexes (PdHiP)6 and Pd4(iP)2 both
ꢀ
crystallize in the triclinic Pı space group (Figs. 2 and 3). Selected
Scheme 4. Isolated palladium complexes Pd4(iP)2 and (PdHiP)6. Shaded parts of complex Pd4(iP)2 respectively indicate covalently incorporated acetonitrile on the ligand H3iP and
NO2 moiety coordinatively bridging between two Pd centres.

H.O. Oloyede et al. / Journal of Molecular Structure 1197 (2019) 336e344
341
Fig. 1. X-ray structure of ligands H3M (top) and T2CN (bottom). Protons and solvent
molecules have been omitted for clarity.
Fig. 2. X-ray structure of complex Pd4(iP)2. The bonds in the triisopropylphenyl sub-
stituents are displayed as dashes to improve clarity. Protons and solvent molecules
have also been omitted for clarity and ellipsoids are drawn at the 20% probability level.
Fig. 3. X-ray structure of complex (PdHiP)6 showing (a) the complete molecule where
the bonds of the triisopropylphenyl substituents are displayed as dashes for clarity and
(b) the molecule where all substituents sulfonyl fragments have been omitted for
clarity. Protons and solvent molecules have been omitted for clarity and ellipsoids are
drawn at the 20% probability leve.
At oil bath temperature of 100 ꢁC and 10 min reflux in the
presence of K2CO3 (1 mmol), Pd(AcO)2 (0.2 mol %) and in 4 mL of
3:1 EtOH/H2O mixture, changing the amount of ligand H3T from
0.4 mol % through 0.7 mol % to 1.0 mol % produced marginal yield
increase from 16% through 24%e29% respectively. Thus, further
reactions were continued with 0.7 mol % ligand. Conducting the
same reaction with ligand H3M at 10 min and 30 min respectively
yielded 38% and 40% of the coupling product. Therefore, necessity
for longer reflux times was not supported and the results indicate
that the generated active species are probably short-lived under the
reflux condition.
K3PO4 was increased to 1.2 mmol the yield increased to 74% even
under reflux time of 5 min, which further suggests that the original
10 min is probably much more than the effective duration of the
catalyst's life under the reflux situation.
3.4. Comparing ligand frameworks in relation to catalysis outcomes
Continuing with 0.7 mol % of H3M at 10 min reflux and keeping
other parameters constant, the test of various base additives
revealed that K3PO4 is favoured in the coupling reaction
(yield ¼ 57% with 1.0 mmol K3PO4). Furthermore, as the amount of
Eventually, the optimized catalytic reaction setting consisting of
4 mL of 3:1 EtOH/H2O, 1.2 mmol K3PO4, 0.7 mol % ligand þ0.2 mol %
Pd(AcO)2, 1 mmol 4-bromophenylmethanol, 1.2 mmol 4-

342
H.O. Oloyede et al. / Journal of Molecular Structure 1197 (2019) 336e344
Table 2
Optimization of reaction parameters for Suzuki-Miyaura couplinga.
Ligand (mol %)b
Time (min)
Base (mmol)
Yield (%)
H3T (0.4)
H3T (0.7)
H3T (1.0)
H3M (0.7)
H3M (0.7)
H3M (0.7)
H3M (0.7)
H3M (0.7)
H3M (0.7)
H3M (0.7)
10
10
10
10
30
10
10
10
10
5
K2CO3 (1.0)
K2CO3 (1.0)
K2CO3 (1.0)
K2CO3 (1.0)
K2CO3 (1.0)
Na2CO3 (1.0)
Et3N (1.0)
KOH (1.0)
K3PO4 (1.0)
K3PO4 (1.2)
16
24
29
38
40
41
21
29
57
74
a
Reaction conditions: (4-acetylphenyl)boronic acid (1.2 mmol); (4-
relative to (4-
bromophenyl)methanol (1 mmol); Pd(AcO)2 (0.2 mol
%
Fig. 4. In situ catalytic performance of ligand H3M at 50 ꢁC at varying times.
bromophenyl)methanol); ligand amount (0.4e1.0 mol % relative to); solvent 3:1
EtOH/H2O (4 mL); base (1.0e1.2 mmol); oil bath temperature set at 100 ꢁC; Yield
was determined by 1H NMR and reported to the nearest whole number.
h
ꢀ1) > triisopropylphenyl for H3iP (TOF ¼ 3780 hꢀ1) > tolyl for H3T
b
The amount of ligand in mol
% is relative to (4-bromophenyl)methanol
(TOF ¼ 3300 hꢀ1). Consequently, the role of electronic character of
the N-donors overrides the influence of steric features of the sub-
stituents around the N-donor atom. Furthermore, similar N-sup-
ported palladium complexes require higher catalyst loadings and
hours of reflux to attain high catalyst yields [50e52].
(1 mmol).
acetylphenylboronic acid, oil bath temperature of 100 ꢁC and 5 min’
reflux duration was applied in the presence of differing N-donor
ligand frameworks. The results for the in situ catalyst generation
experiments are presented in Table 3, which generally shows that
changing the ligands has some influence on the activity of the
palladium active centres.
For the purpose of comparison, the precatalyst Pd4(iP)2 at
0.05 mol % loading was also subjected to same catalytic condition as
for the ligands and it could be concluded that preformed complexes
possess advantage over the in situ approach; i.e. TOF ¼ 4500 hꢀ1 for
Pd4(iP)2 compared to TOF ¼ 3780 hꢀ1 for H3iP. In calculating the
TOF values, the tetranuclear nature of Pd4(iP)2 was taken into
consideration, which is why 0.05 mol % (i.e. 0.2 mol % ÷ 4) of the
complex was deployed.
In general, the methyl-substituted H3M ligand performed better
than the triisopropylphenyl- and tolyl-substituted ligands. There-
fore, it may be concluded that N-donor active palladium centres are
better stabilized by ligand H3M, which may can be attributed to
stronger N-donor strength enabled by the methyl fragment on the
sulfonyl S-atom. Comparing ligands H3M, H3T and H3iP, the ligands
varied only at the S-atom with the substituents of methyl, tolyl and
triisopropyl respectively. It is therefore noteworthy that the
observed trend appears to follow the þI contribution from these
Table 4
Substrate scope by Pd4(iP)2 as precatalyst.a.
Substrates
Yield(%)
84
TOF (hꢀ1
5290
)
substituents;
i.e.
methyl
for
H3M
(TOF ¼ 4500
Table 3
70
92
4000
5520
Catalytic performance for the series of ligands investigateda.3
80
74
4800
4440
Catalyst system
Yield (%)
TOF (hꢀ1
)
Pd(AcO)2
39
74
55
53
63
59
75
2340
4500
3300
3180
3780
3540
4500
H3M þ Pd(AcO)2
H3T þ Pd(AcO)2
T2CN þ Pd(AcO)2
H3iP þ Pd(AcO)2
HiPCN þ Pd(AcO)2
19
56
1140
3360
b
Pd4(iP)2
a
Reaction conditions: (4-Acetylphenyl)boronic acid (1.2 mmol), (4-
bromophenyl)methanol (1 mmol), solvent: EtOH/H2O (3 mL þ 1 mL), Base (K3PO4,
1.2 mmol), time (5 min reflux), temperature (100 ꢁC), ligand amount (0.7 mol %
a
relative to (4-bromophenyl)methanol), Pd(AcO)2 (0.2 mol
%
relative to (4-
Reaction conditions: Solvent: EtOH/H2O (3 mL þ 1 mL), Base (K3PO4, 1.2 mmol),
time (5 min reflux), temperature of oil bath (100 ꢁC), Pd4(iP)2 (0.05 mol%) (4-
acetylphenyl)boronic acid (1.2 mmol), (4-bromophenyl)methanol (1 mmol), Yield
was determined by 1H NMR and reported to the nearest whole number.
bromophenyl)methanol); Yield was determined by 1H NMR and reported to the
nearest whole number.
b
Pd4(iP)2 (0.05 mol % relative to (4-bromophenyl)methanol).

H.O. Oloyede et al. / Journal of Molecular Structure 1197 (2019) 336e344
343
In order to investigate the observed early termination of catalyst
activities during the reflux experiments, the determined reaction
conditions except for reaction temperature of 50 ꢁC was applied for
ligand H3M, and yields were determined as a function of time.
Interestingly, the catalyst generated in situ at ambient temperature
proved to be living as illustrated in Fig. 4.
In an attempt to elucidate the substrate profile of the precatalyst
Pd4(iP)2 at 0.05 mol % loading, the catalytic activity of the complex
was investigated towards other substrates according to the already
established reaction settings above. The results are presented in
Table 4. One important observation is that the pre-catalyst gener-
ally displayed favourable catalytic activity towards various aryl
halides and arylboronic acids within the 5 min’ reaction duration.
However, presence of carboxy group ortho to the bromo atom
proved to hinder the coupling reaction.
H3iP and HiPCN. The complexation experiments revealed that the
ligands potentially possess variable coordination possibilities as
well as possible accompanying ligand and/solvent oxidative re-
activities. Defined solvent-controlled tetranuclear and hexanuclear
coordination products Pd4(iP)2 and (PdHiP)6 were self-assembled
by allowing palladium acetate and ligand H3iP to stand in solvent.
Single crystal analyses confirmed the structures of ligands H3M and
T2CN as well as for the complexes Pd4(iP)2 and (PdHiP)6.
Testing the N-donors as support ligands in palladium-catalyzed
Suzuki coupling revealed high performances either by in situ
‘Pd(AcO)2 þ ligand’ approach or by deployment of the precatalyst.
That such simple and synthetically assessable N-donor ligands
could couple aryl bromides and arylboronic acids with turn over
frequencies attaining 5500 hꢀ1 within 5 min of reflux enables the
conclusion that palladium active species could also be stabilized by
N-donor ligand frameworks. It was also concluded that, under
similar reaction conditions, preformed coordination precatalyst
Pd4(iP)2 offered better catalytic benefit relative to the correspond-
ing in situ catalyst generation. Heck coupling activities by Pd4(iP)2
were also observed. While the active species formed during the
Suzuki coupling showed stability at ambient temperatures in
ethanol/water media, catalyst activity in the Heck coupling only
produced high yields at high temperatures. In general, the overall
catalytic results present motivation for further study of N-donor-
stabilized palladium catalysts and optimism that affordable and
efficient phosphine-free catalysts can be attained.
3.5. Heck CeC coupling performance in the presence of Pd4(iP)4
Test for the Heck coupling potential was carried using the pre-
formed complex Pd4(iP)2 in the coupling of (4-bromophenyl)
methanol and styrene. Due to the volatile nature of styrene (S),
1.5 mmol was used. The catalysis outcomes are summarized in
Table 5. While varying reaction media and base additives under 60-
min reflux and oil bath temperature set to 100 ꢁC, the catalytic
yields remained low in the range of 8%e31%. However, if higher
temperatures would be explored, only the DMF/H2O (3:1) provides
the possibility despite its lower yield at 100 ꢁC than for acetonitrile/
water, ethanol/water or only water. Thus, exploring 140 ꢁC in DMF/
H2O (3:1), a yield of 8% at 100 ꢁC relative to the 73% recorded at
140 ꢁC indicated the preference for high temperature catalyst pro-
ductivity by Pd4(iP)4. Furthermore, there is a gradual increase in
yields when reflux durations of 1 and 3 h are compared, which
suggests that, in the Heck case, the catalyst species formed in DMF/
H2O and at the operational temperatures remained active.
Acknowledgements
HOO is grateful to the Government of the Federal Republic of
Nigeria for financial support through TETfund research grants
(TETfund AST&D year 2012 intervention) and to Adeyemi College of
Education, Ondo, Nigeria for granting study leave. AOE is thankful
to Alexander von Humboldt Foundation for granting post-doctoral
scholarship. The DFG grants (PL 155/11, PL 155/12 and PL155/13) are
thankfully acknowledged.
4. Conclusion
2-Aminobenzamide was condensed with the sulfonyl chloride
reagents (methylsulfonyl chloride, p-toluenesulfonyl chloride or
2,4,6-triisopropylbenzenesulfonyl chloride), which yielded well
characterized, simple, N-donor ligand derivatives H3M, H3T, T2CN,
Appendix A. Supplementary data
Supplementary data to this article can be found online at
https://doi.org/10.1016/j.molstruc.2019.07.054.
References
Table 5
a
Heck coupling reaction by the precatalyst Pd4(iP)2
.
[1] P.S. Hanley, M.S. Ober, A.L. Krasovskiy, G.T. Whiteker, W.J. Kruper, Nickel- and
palladium-catalyzed coupling of aryl fluorosulfonates with aryl boronic acids
enabled by sulfuryl fluoride, ACS Catal. 5 (2015) 5041e5046.
[2] Y.-S. Feng, X.-Y. Lin, J. Hao, H.-J. Xu, PdeCo bimetallic nanoparticles supported
on graphene as a highly active catalyst for SuzukieMiyaura and Sonogashira
cross-coupling reactions, Tetrahedron 70 (2014) 5249e5253.
[3] J. Magano, J.R. Dunetz, Large-scale applications of transition metal-catalyzed
couplings for the synthesis of pharmaceuticals, Chem. Rev. 111 (2011)
2177e2250.
[4] L.-Y. Xu, C.-Y. Liu, S.-Y. Liu, Z.-G. Ren, D.J. Young, J.-P. Lang, Suzuki-Miyaura
cross-coupling reaction of aryl chlorides with aryl boronic acids catalyzed by a
palladium dichloride adduct of N-diphenylphosphanyl-2-aminopyridine,
Tetrahedron 73 (2017) 3125e3132.
Solvent
Base
Temp.(oC)
Time (min)
Yield (%)
H2O
K2CO3
K2CO3
K2CO3
K3PO4
NaOH
KOH
K2CO3
K2CO3
K2CO3
K3PO4
K3PO4
100
100
100
100
100
100
100
140
140
140
140
60
60
60
60
60
60
60
60
180
60
180
9
CH3CN/H2O (1:1)
EtOH/H2O (1:1)
EtOH/H2O (1:1)
EtOH/H2O (1:1)
EtOH/H2O (1:1)
DMF/H2O (3:1)
DMF/H2O (3:1)
DMF/H2O (3:1)
DMF/H2O (3:1)
DMF/H2O (3:1)
18
22
31
27
27
8
73
84
46
48
[5] P.-A. Payard, L.A. Perego, I. Ciofini, L. Grimaud, Taming nickel-catalyzed
suzuki-miyaura coupling:
a mechanistic focus on boron-to-nickel trans-
metalation, ACS Catal. 8 (2018) 4812e4823.
[6] T. Akiyama, T. Taniguchi, N. Saito, R. Doi, T. Honma, Y. Tamenori, Y. Ohki,
N. Takahashi, H. Fujioka, Y. Sato, M. Arisawa, Ligand-free SuzukieMiyaura
coupling using ruthenium(0) nanoparticles and a continuously irradiating
microwave system, Green Chem. 19 (2017) 3357e3369.
[7] A.K. Steib, O.M. Kuzmina, S. Fernandez, D. Flubacher, P. Knochel, Efficient
chromium(II)-catalyzed cross-coupling reactions between Csp
2 centers,
J. Am. Chem. Soc. 135 (2013) 15346e15349.
a
Reaction conditions: Solvent (4 mL), Base (1.5 mmol), time (60, 180 min reflux),
Pd4(iP)2 pre-catalyst (0.05 mol%), styrene, (1.5 mmol), (4-bromophenyl)methanol,
(1 mmol). Yield was determined by 1H NMR and reported to the nearest whole
number.
[8] J.-J. Ning, J.-F. Wang, Z.-G. Ren, D.J. Young, J.-P. Lang, Versatile palladium(II)-
catalyzed SuzukieMiyaura coupling in ethanol with
ligand, Tetrahedron 71 (2015) 4000e4006.
a novel, stabilizing
[9] X. Yang, G. Xu, W. Tang, Efficient synthesis of chiral biaryls via asymmetric

344
H.O. Oloyede et al. / Journal of Molecular Structure 1197 (2019) 336e344
Suzuki-Miyaura cross-coupling of ortho-bromo aryl triflates, Tetrahedron 72
(2016) 5178e5183.
[10] A. Mahanta, M. Mondal, A.J. Thakur, U. Bora, An improved SuzukieMiyaura
cross-coupling reaction with the aid of in situ generated PdNPs, Tetrahe-
dron Lett. 57 (2016) 3091e3095.
[11] B. Cornelio, M. Laronze-Cochard, M. Ceruso, M. Ferraroni, G.A. Rance, F. Carta,
A.N. Khlobystov, A. Fontana, C.T. Supuran, J. Sapi, 4-Arylbenzenesulfonamides
as human carbonic anhydrase inhibitors (hCAIs), J. Med. Chem. 59 (2016)
721e732.
characteristics and in situ generation of Pd active species towards CC coupling
using series of 2-(1H-imidazol-2-yl)phenols, J. Mol. Catal. A Chem. 387 (2014)
112e122.
[32] T.E. Pickett, F.X. Roca, C.J. Richards, Synthesis of monodentate ferrocenyl-
phosphines and their application to the palladium-catalyzed Suzuki reaction
of aryl chlorides, J. Org. Chem. 68 (2003) 2592e2599.
[33] A. Ratnam, M. Bala, R. Kumar, U.P. Singh, K. Ghosh, Design and syntheses of a
new family of palladium complexes derived from tridentate ligands and their
application as catalysts for Suzuki-Miyaura cross-coupling reactions,
J. Organomet. Chem. 856 (2018) 41e49.
[12] E. Broumidis, P.A. Koutentis, A one-pot, two-step synthesis of 3-deazacanthin-
4-ones via sequential Pd-catalyzed Suzuki-Miyaura and Cu-catalyzed Buch-
wald-Hartwig reactions, Tetrahedron Lett. 58 (2017) 2661e2664.
€
[34] A.O. Eseola, H. Gorls, J.A.O. Woods, W. Plass, Cyclometallation, steric and
electronic tendencies in
a series of Pd(II) complex pre-catalysts bearing
ꢁ
[13] S. Vichier-Guerre, L. Dugue, S. Pochet, A convenient synthesis of 4(5)-(hetero)
imidazoleephenol ligands and effects on SuzukieMiyaura catalytic effi-
ciencies, J. Mol. Catal. A Chem. 406 (2015) 224e237.
aryl-1H-imidazoles via microwave-assisted SuzukieMiyaura cross-coupling
reaction, Tetrahedron Lett. 55 (2014) 6347e6350.
[14] M.M. Heravi, E. Hashemi, Recent applications of the Suzuki reaction in total
synthesis, Tetrahedron 68 (2012) 9145e9178.
[15] N. Miyaura, A. Suzuki, Palladium-catalyzed cross-coupling reactions of orga-
noboron compounds, Chem. Rev. 95 (1995) 2457e2483.
[16] E.-i. Negishi, T. Takahashi, K. Akiyoshi, Palladium-catalyzed or -promoted
reductive carbon-carbon coupling. Effects of phosphines and carbon ligands,
J. Organomet. Chem. 334 (1987) 181e194.
[17] A. Suzuki, Cross-coupling reactions of organoboranes: an easy way to
construct C-C bonds (Nobel Lecture), Angew. Chem. Int. Ed. 50 (2011)
6722e6737.
[18] K.W. Quasdorf, A. Antoft-Finch, P. Liu, A.L. Silberstein, A. Komaromi,
T. Blackburn, S.D. Ramgren, K.N. Houk, V. Snieckus, N.K. Garg, Suzuki-Miyaura
cross-coupling of aryl carbamates and sulfamates, J. Am. Chem. Soc. 133
(2011) 6352e6363.
[35] M. Waheed, N. Ahmed, Coumarin based novel ligands in the SuzukieMiyaura
and MizorokieHeck cross-couplings under aqueous medium, Tetrahedron
Lett. 57 (2016) 3785e3789.
_
€
ꢂ
ꢁ
[36] M. Kaloglu, D. Semeril, E. Brenner, D. Matt, I. Ozdemir, L. Toupet, The influence
of imidazolylidene ligands with bulky resorcinarenyl substituents on catalysts
for-suzuki-miyaura coupling, Eur. J. Inorg. Chem. 2016 (2016) 1115e1120.
[37] T.E. Barder, S.D. Walker, J.R. Martinelli, S.L. Buchwald, Catalysts for Suzuki-
Miyaura coupling processes: scope and studies of the effect of ligand struc-
ture, J. Am. Chem. Soc. 127 (2005) 4685e4696.
[38] D. Bulfield, S.M. Huber, Synthesis of polyflourinated biphenyls; pushing the
boundaries of suzukiemiyaura cross coupling with electron-poor substrates,
J. Org. Chem. 82 (2017) 13188e13203.
[39] A. Shen, C. Ni, Y.-C. Cao, H. Zhou, G.-H. Song, X.-F. Ye, Novel monoligated
imineePdeNHC
complexes:
extremely
active
pre-catalysts
for
SuzukieMiyaura coupling of aryl chlorides, Tetrahedron Lett. 55 (2014)
3278e3282.
[19] M. Busch, M.D. Wodrich, C. Corminboeuf, A generalized picture of CeC cross-
coupling, ACS Catal. 7 (2017) 5643e5653.
[40] B.V. Nonius, COLLECT, Data Collection Software, Netherlands, 1998.
[41] Z. Otwinowski, W. Minor, in: C.W. Carter, R.M. Sweet (Eds.), Macromolecular
Crystallography Part A: Processing of X-Ray Diffraction Data Collected in
Oscillation Mode, Academic Press, 1997.
€
[20] A.O. Eseola, D. Geibig, H. Gorls, W.-H. Sun, X. Hao, J.A.O. Woods, W. Plass,
Palladium(II) complexes bearing 2-(1H-imidazol/oxazol-2-yl)-pyridines,
J. Organomet. Chem. 754 (2014) 39e50.
[21] Q. Liu, X. Dong, J. Li, J. Xiao, Y. Dong, H. Liu, Recent advances on palladium
radical involved reactions, ACS Catal. 5 (2015) 6111e6137.
[42] Bruker-AXS inc., SADABS, Madison, WI, U.S.A., 2002.
[43] G.M. Sheldrick,
A short history of SHELX, Acta Crystallogr. A 64 (2008)
[22] S.-L. Mao, Y. Sun, G.-A. Yu, C. Zhao, Z.-J. Han, J. Yuan, X. Zhu, Q. Yang, S.-H. Liu,
A highly active catalytic system for Suzuki-Miyaura cross-coupling reactions
of aryl and heteroaryl chlorides in water, Org. Biomol. Chem. 10 (2012)
9410e9417.
112e122.
[44] A.L. Spek, PLATON SQUEEZE: a tool for the calculation of the disordered sol-
vent contribution to the calculated structure factors, Acta Crystallogr. C 71
(2015) 9e18.
[23] T.J. Colacot, Commercial development of palladium(0) catalysts for highly
selective cross-coupling reactions, Platin. Met. Rev. 56 (2012) 110e116.
[24] N.C. Bruno, M.T. Tudge, S.L. Buchwald, Design and preparation of new palla-
dium precatalysts for C-C and C-N cross-coupling reactions, Chem. Scr. 4
(2013) 916e920.
[25] O. Navarro, Y. Oonishi, R.A. Kelly, E.D. Stevens, O. Briel, S.P. Nolan, General and
efficient methodology for the SuzukieMiyaura reaction in technical grade 2-
propanol, J. Organomet. Chem. 689 (2004) 3722e3727.
[45] Siemens Analytical X-ray Instruments Inc, Siemens (1994), XP: Interactive
Molecular Graphics Program, Madison, Winscosin, USA, 1994.
[46] R. Brückner, M. Harmata, Organic Mechanisms: Reactions, Stereochemistry
and Synthesis, Springer, Berlin, 2010.
[47] S. Caron, Practical Synthetic Organic Chemistry: Reactions, Principles, and
ꢁ
Techniques/, in: Stephane Caron, Wiley; Chichester John Wiley [distributor],
Hoboken, N.J., 2011.
[48] S.E. Bajwa, T.E. Storr, L.E. Hatcher, T.J. Williams, C.G. Baumann, A.C. Whitwood,
D.R. Allan, S.J. Teat, P.R. Raithby, I.J.S. Fairlamb, On the appearance of nitrite
anion in [PdX(OAc)L2] and [Pd(X)(C^N)L] syntheses (X ¼ OAc or NO2): pho-
[26] A. Shen, Y.-C. Hu, T.-T. Liu, C. Ni, Y. Luo, Y.-C. Cao, Supporting ligand-assisted N
-heterocyclic carbene palladium complexes, Tetrahedron Lett. 57 (2016)
2055e2058.
tocrystallographic identification of metastable Pd(
Sci. 3 (2012) 1656e1661.
h
1-ONO)(C^N)PPh3, Chem.
[27] M. Charbonneau, G. Addoumieh, P. Oguadinma, A.R. Schmitzer, Support-free
palladiumeNHC catalyst for highly recyclable heterogeneous suzukiemiyaura
coupling in neat water, Organometallics 33 (2014) 6544e6549.
[28] B. Trettenbrein, M. Fessler, M. Ruggenthaler, S. Haringer, D. Oberhuber,
G. Czermak, P. Brüggeller, W. Oberhauser, First microwave-assisted synthesis
of an electron-rich phosphane and its coordination chemistry with plati-
num(II) and palladium(II), Inorg. Chim. Acta 375 (2011) 324e328.
[29] J.-Y. Lee, D. Ghosh, J.-Y. Lee, S.-S. Wu, C.-H. Hu, S.-D. Liu, H.M. Lee, Zwitterionic
palladium complexes: room-temperature suzukiemiyaura cross-coupling of
sterically hindered substrates in an aqueous medium, Organometallics 33
(2014) 6481e6492.
€
[49] K. Matos, L.L. de Oliveira, C. Favero, A.L. Monteiro, M. Horner, J.-F. Carpentier,
M.P. Gil, O.L. Casagrande, Palladium complexes based on tridentate pyrazolyl-
ligands: synthesis, structures and use in Suzuki cross-coupling reactions,
Inorg. Chim. Acta 362 (2009) 4396e4402.
€
[50] H.O. Oloyede, J.A.O. Woods, H. Gorls, W. Plass, A.O. Eseola, Flexible, N-sulfo-
nyl-substituted
aliphatic
amine
ligands
in
palladium-catalyzed
SuzukieMiyaura C C coupling: influence of substituents bulkiness and co-
ligand size, Polyhedron 159 (2019) 182e191.
[51] R. Fırıncı, Asymmetric palladacycle complexes with N,O-bidentate barbiturate
ligands: preparation, characterization and catalytic application in Suzuki-
Miyaura reaction, J. Mol. Struct. 1195 (2019) 246e251.
[52] P. Jerome, S.Y. Arafath, J. Haribabu, N.S.P. Bhuvanesh, R. Karvembu, Effect of 2-
bromopyridine ancillary ligand in the catalysis of Pd(II)-NNN pincer com-
plexes towards suzuki-miyaura cross-coupling reaction, Chemistry 4 (2019)
2237e2241.
[30] A.O. Eseola, W. Li, O.G. Adeyemi, N.O. Obi-Egbedi, J.A.O. Woods, Hemilability of
2-(1H-imidazol-2-yl)pyridine and 2-(oxazol-2-yl)pyridine ligands: imidazole
and oxazole ring Lewis basicity, Ni(II)/Pd(II) complex structures and spectra,
Polyhedron 29 (2010) 1891e1901.
€
[31] A.O. Eseola, O. Akogun, H. Gorls, O. Atolani, G.A. Kolawole, W. Plass, Ligand