Synthesis and characterization of new square planar heteroleptic cationic complexes [Ni(ii) β-oxodithioester-dppe]+; Their use as a catalyst for Chan-Lam coupling

Article abstract of DOI:10.1039/d0nj01139h

Novel heteroleptic [Ni(ii) β-oxodithioester-dppe]+PF6- complexes (β-oxodithioester = methyl-3-hydroxy-3-benzyl-2-propenedithioate L1 1, methyl-3-hydroxy-3-(p-methoxyphenyl)-2-propenedithioate L2 2, methyl-3-hydroxy-3-(naphthyl)-2-propenedithioate L3 3, methyl-3-hydroxy-3-(p-chlorophenyl)-2-propenedithioate L4 4, methyl-3-hydroxy-3-(p-bromophenyl)-2-propenedithioate L5 5 and methyl-3-hydroxy-3-(p-cyanophenyl)-2-propenedithioate L6 6) have been synthesized and characterized by elemental (C, H, N) analysis, ESI-MS, IR, UV-visible, 1H, 13C{1H}, 31P{1H} and 19F{1H} NMR spectroscopy. The distorted square planar structures of the isomorphous cationic complexes 2, 3, 4 and 5 have been determined by X-ray crystallography. The catalytic activities of 1-6 were investigated for the Chan-Lam coupling reaction involving arylboronic acids and amines to afford N-arylated products in good to excellent yields under mild conditions with 1 mol% catalyst loading. This catalytic protocol offers significant functional group tolerance, and is endowed with a broad substrate scope. This journal is

Full text of DOI:10.1039/d0nj01139h

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Synthesis and characterization of new square planar heteroleptic cationic
complexes [Ni(II) β-oxodithioester-dppe]+; their use as catalyst for Chan−Lam
coupling
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Kavita Kumaria, Saurabh Kumara, Krishna Nand Singha, Michael G. B. Drewb and Nanhai
Singha*
aDepartment of Chemistry, Institute of Science, Banaras Hindu University, Varanasi 221005,
India.
bDepartment of Chemistry, University of Reading, Whiteknights, Reading RG6 6AD, UK .
Abstract

Novel heteroleptic [Ni(II) β-oxodithioester-dppe]+ PF6 complexes (β-oxodithioester = methyl-3-
hydroxy-3-benzyl-2-propenedithioate
L1
1,
methyl-3-hydroxy-3-(p-methoxyphenyl)-2-
propenedithioate L2 2, methyl-3-hydroxy-3-(naphthyl)-2-propenedithioate L3 3, methyl-3-
hydroxy-3-(p-chlorophenyl)-2-propenedithioate L4 4, methyl-3-hydroxy-3-(p-bromophenyl)-2-
propenedithioate L5 5 and methyl-3-hydroxy-3-(p-cyanophenyl)-2-propenedithioate L6 6) have
been synthesized and characterized by elemental (C, H, N) analysis, ESI-MS, IR, UV-visible, 1H,
31
19
13C{1H}, P{1H} and F{1H} NMR spectroscopy. The distorted square planar structures of the
isomorphous cationic complexes 2, 3, 4 and 5 have been determined by X-ray crystallography.
The catalytic activities of 16 were investigated for Chan–Lam coupling reaction involving
arylboronic acids and amines to afford N-arylated products in good to excellent yields under mild
conditions with 1 mol % catalyst loading. This catalytic protocol offers significant functional
group tolerance, and is endowed with broad substrate scope.
INTRODUCTION
The construction of carbon–nitrogen bonds by transition‐metal‐catalysis represents an
important area of research and has witnessed a spectacular advancement over the years.
Significant progress has been made in the construction of carbon–nitrogen bond through Chan−
Lam coupling for N−arylation of arylboronic acids with amines and other nucleophiles.1 Most of
the explored cross-coupling strategies for carbon–nitrogen bond formation employed Cu/Pd
metal catalyst including Ullmann,2 Goldberg,3 and Buchwald-Hartwig,4 coupling reactions, yet
the use of Ni salts is somewhat scanty.5
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Recently various metal complexes have been synthesized and used for Chan−Lam
coupling by Schaper et al.6 and Phukan et al.7 using Cu(II) complexes having DMAP and
pyridyliminoarylsulfonato ligands. Similar transformations have also been achieved using
different nickel/palladium/copper catalysts, although the majority of work is centered around the
use of copper salts in the presence of bipy/TMEDA/N−Heterocyclic carbenes (NHCs) ligands.8,9
Nickel-based catalysts are also employed in C−C bond forming reactions and extended for C−N
bond formation.10 Recently Ni mixed ligand complexes [Ni(DHASICy)CpCl] and
[Ni(DHASIiPr)CpCl] have been used in the Chan−Lam coupling by Ishizuka and co-workers.11
Generally the use of nickel catalysts require high catalyst loading. It has been observed that the
NHC-Ni complex in the presence of a co-ligand, 4,4’-dimethyl-2,2-bipyridine(dmbpy) enhanced
catalytic activity. Thus, there stands enough scope to synthesize new and useful preformed nickel
complexes to be explored for their catalytic activity.
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Metal dithioester ligand complexes have been extensively utilized for many catalytic
transformations such as hydrosilylation, oxygen activation, ethylene oligomerization,
enantioselective Diels Alder, asymmetric epoxidation, and Click transformed triazolyl
glycoconjugates.12 Generally monodentate/chelating N/O/C donor ligand metal complexes have
so far been used in Chan−Lam coupling. As far as we are aware, despite synthetic versatility and
practical utility, the use of molecularly defined metal coordination complexes particularly with
O, S− donor chelating ligands have not previously been investigated in Chan–Lam coupling
reaction involving arylboronic acids and amines for the N-arylated products. Therefore we
consider it important to explore this chemistry. With this approach, herein we report the
synthesis and crystal structures of novel structurally characterized heteroleptic [Ni(II) β-

oxodithioester-dppe]+ PF6
complexes 16 derived from β-oxodithioester and
bis(diphenylphosphinoethane), dppe ligands and applied them as catalyst in Chan−Lam coupling
for C−N bond formation to access variety of N-substituted aniline derivatives. The promising
catalytic activity observed for this system and the possible existence of rare Ni∙∙∙H−C anagostic
interactions in the crystal structures of complexes 2, 3, 4 and 5 have been described in this
contribution. We were motivated for undertaking this work due to the following considerations:
(i) Both small and hard O and large, more polarizable and soft S donor atoms of the β-
oxodithioester groups may show preferential bonding with the Ni(II) on the border of hard and
soft Lewis acids. This difference in their characteristics may considerably affect the stability and
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polarity of the Ni−O/Ni−S bond hence catalytic activity of the complexes; (ii) The changes to
substituents on the dithioester group may change the properties of the ligands. It is therefore
critical to make methodical changes to the ligand environment to compare the catalytic activities
and structural characteristics of the complexes, accordingly phenyl, p-methoxyphenyl, 2-
naphthyl, p-chlorophenyl, p-bromophenyl and p-cyanophenyl substituents have been introduced
in the ligand framework. These ligands may render enhanced electron delocalization over the
six-membered chelate ring formed about the metal centre; (iii) The use of preformed transition
metal coordination complexes is to be preferred to metal salts due to the conformational rigidity
provided by the chelating β-oxodithioester and dppe which are good σ-donor and π-acid ligands
and the substituents on the dithioester group may serve to protect the metal from attack by
species/solvents during the course of reaction. Also the preformed complexes may protect the
catalyst from oxidation/reduction and stabilize the desired oxidation state of the metal thus
overall accelerating activity. The steric factors of the phosphine ligands are important in
determining the stereochemistry and structure of the complexes as well as their selective
catalytic activity; the catalytic activity of particularly square planar Ni(II) phosphine complexes
are well documented.13 The use of chelating ligands may prevent or minimize the use of an
additional base as a ligand to facilitate the catalyst performance; (iv) The donor atoms on the
substituents may facilitate the formation of intriguing metal assisted as well as other non-
covalent bonding interactions thereby generating of supramolecular structures with useful
properties; and (v) The complexes featuring rare M∙∙∙H−C anagostic interactions are relevant in
many catalytic processes.14
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Results and discussion
Synthesis and characterization
The potassium salts of the β-oxodithioester ligands KL1-KL6 were synthesized adopting the
previously reported method.12(i),15 The air and moisture stable heteroleptic [Ni(II) β-

oxodithioester-dppe]+ PF6 complexes 16 were isolated in good yields by adding methanolic
solution of NiCl2.6H2O and KL1-KL6 simultaneously to a dichloromethane solution of dppe
with the further addition of solid NH4PF6 in an equimolar ratio (Scheme 1). Complexes were
1
characterized by elemental analysis, spectroscopy (IR, UV-Vis, H, 13C{1H}, 31P{1H} and
19F{1H} NMR), ESI-MS and the solid state structures of 2, 3, 4 and 5 have been elucidated by
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single crystal X-ray diffraction. The homogeneity of the bulk samples of 2−5 was confirmed by
comparing the observed PXRD patterns with the respective simulated powder patterns observed
from the single crystal data. The experimental and simulated PXRD patterns are in agreement
indicating the phase purity of the bulk samples (Figure S1). A close look at the isomorphous
crystal structures of the complexes 2, 3, 4 and 5 revealed the possibility of unusual C–H∙∙∙Ni
anagostic interactions in all four structures. The pre-formed complexes 1−6 were examined as
catalyst for C−N cross coupling of arylboronic acids and amines for the synthesis of a variety of
secondary aryl amines via the Chan−Lam coupling reaction.
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H
O
1. Hexane, NaH
2. DMF, TTC
O
S
0 °C, N2 atm., 10h
Ar
CH3
Ar
S
L1-L6
Ar = Phenyl
CH3
(L1)
4-Methoxyphenyl (L2)
2-Naphthyl (L3)
4-Chlorophenyl (L4)
4-Bromophenyl (L5)
4-Cyanophenyl
(L6)
PF6
K2CO3, Acetone
Reflux 60-70 °C
4-5 h
Ar
O
P
P
O K
S
dppe, NiCl2
Ni
MeOH, -KCl
NH4PF6, 6h,
r.t.
S
Ar
S
CH3
S
H3C
KL1-KL6
1 6
-
Scheme 1. Synthetic methodology for the synthesis of potassium salts of the ligands KL1-KL6
and their corresponding complexes 1-6, (where TTC is dimethyltrithiocabonate).
Spectroscopic Studies
In the IR spectra, complexes 1–6 display bands at 1508−1602, 1465−1504 and 1029−1103 cm-1
for the νC=O, νC=C and νC–S vibrations, respectively, diagnostic of coordinated β-oxodithioester
ligand.
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In the 1H NMR spectra, a single resonance signal at δ 15.03−15.18 ppm of the –OH proton in the
ligands HL1−HL6 is absent in complexes 1−6 due to deprotonation of the ligand. The vinylic
proton resonances for the ligands (δ 6.88−7.10 ppm) and their corresponding complexes (δ
6.57−7.12 ppm) remain almost unchanged. The anticipated downfield shift for the ortho-proton
of the phenyl ring of the dppe ligand participating in the rare Ni∙∙∙H−C intramolecular anagostic
interactions as revealed by X-ray crystallography (vide infra) could not unambiguously
authenticate that these interactions remained in solution because of the occurrence of the
aromatic signals of the β-oxodithioester ligands in the same region. In the 13C{1H} NMR spectra,
resonance for the C−OH carbon in the free ligands and complexes are observed in the range of δ
167.58−169.63 and δ 160.81−177.73 ppm, respectively. The vinylic carbon of the ligands lying
in the range δ 107.20−108.34 ppm is slightly downfield shifted and appear in the range of δ
109.33−110.54 ppm in the complexes. A noticeable upfield shift in the C−S carbon at  177.08–
199.86 ppm in the complexes in comparison to the range observed in free ligands at 
215.75−217.44 ppm is indicative of metal–sulfur coordination. The 31P{1H} NMR spectra of 1−6
display two doublets in the range of   and 61.1561.73 ppm due to proximity of
O/S donor atoms of the dithioester ligands to the phosphorous centres. Also, a septet present
at  -- ppm in the 31P{1H} NMR spectra and a doublet present at  --
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
 ppm in the 19F{1H} NMR spectra is due to the PF6 anion in all complexes. The resulting
NMR spectra of 16 are depicted in Supporting Information, Figure S2.
Additionally, all the complexes display molecular ion peaks due to [M-PF6]+ in high-
resolution MS (Figures S3-S8).
Crystal structures
The crystal structures of 2, 3, 4 and 5 have been determined and the selected bond lengths and
bond angles are listed in Table 1. All four structures are isomorphous. ORTEP diagrams of the
complex cationic part of 2–5 with displacement ellipsoids at 50% probability are shown in
Figures 1-4. Though we could not grow single crystals of 1 and 6, by analogy they can be
assumed to have similar structure.
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Table 1. Bond lengths (Å) and bond angles (o) in complexes 2–5
5
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Bond Lengths (Å)
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2
3
4
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Ni1-O11
Ni1-S15
Ni1-P1
1.866(2)
2.1476(9)
2.1573(9)
2.2017(9)
1.282(4)
1.403(5)
1.382(5)
1.699(4)
1.750(4)
1.8703(19)
2.1443(8)
2.1542(8)
2.1943(8)
1.274(3)
1.385(4)
1.384(4)
1.687(3)
1.751(3)
1.866(4)
2.1531(15)
2.1557(14)
2.2065(15)
1.293(6)
1.395(8)
1.391(8)
1.681(6)
1.756(5)
1.871(2)
2.1483(9)
2.1569(10)
2.2024(9)
1.283(4)
1.393(5)
1.381(5)
1.684(4)
1.754(3)
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Ni1-P4
O11-C12
C12-C13
C13-C14
C14-S15
C14-S16
Bond Angles (o)
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5
P1-Ni1-P4
84.29(4)
98.43(8)
88.80(4)
171.82(4)
171.56(8)
88.80(8)
133.1(2)
125.1(3)
126.4(3)
128.5(3)
108.26(13)
117.2(2)
84.02(3)
98.54(6)
88.20(3)
171.07(3)
172.24(6)
89.54(6)
131.80(19)
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126.5(3)
128.3(2)
108.26(11)
117.33(17)
84.01(5)
98.44(12)
88.37(6)
171.04(6)
171.59(12)
89.58(12)
133.0(4)
124.4(5)
127.5(5)
128.1(4)
108.6(2)
118.0(3)
83.91(4)
98.40(8)
88.39(4)
170.98(4)
171.65(7)
89.68(8)
132.4(2)
125.4(3)
126.9(3)
128.3(3)
108.48(13)
117.6(2)
O11-Ni1-S15
P1-Ni1-S15
P4-Ni1-S15
P1-Ni1-O11
P4-Ni1-O11
C12-O11-Ni1
C13-C12-O11
C14-C13-C12
S15-C14-C13
Ni1-S15-C14
S15-C14-S16
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Figure 1. ORTEP diagram of the cation of 2 with ellipsoids given at the 50% probability level.
−
H atoms and the PF6 anion have been omitted for clarity.
Figure 2. ORTEP diagram of the cation of 3 with ellipsoids given at the 50% probability level.
−
H atoms and the PF6 anion have been omitted for clarity.
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Figure 3. ORTEP diagram of the cation of 4 with ellipsoids given at the 50% probability level.
−
H atoms and the PF6 anion have been omitted for clarity.
Figure 4. ORTEP diagram of the cation of 5 with ellipsoids given at the 50% probability level.
−
H atoms and the PF6 anion have been omitted for clarity.
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In complexes 2, 3, 4 and 5, the Ni atom lie at the centre of a distorted square plane
formed by P,P− and O,S− chelating dppe and β-oxodithioester ligands respectively, thus creating
five- and six-membered chelate rings. The distortion is due to large and small bite angles O11–
Ni1–S15 and P1–Ni1–P4 falling in the ranges 98.40(8)–98.54(6)° and 83.91(4)−84.29(4)°
respectively, substantially deviating from the 90° for ideal square planar geometry. The P1–Ni1–
S15 and P4–Ni–O11 angles are both much closer to 90o. The Ni1–S15 distances are in the range
2.1443(8)–2.1573(9) Å and Ni1–O11 distances in the range 1.865(3)–1.871(2) Å. The Ni1–P1
and Ni1–P4 distances in 2–5 range from 2.1542(8)–2.1573(9) and 2.1943(8)–2.2024(9) Å
respectively, thus Ni1–P4 distances are slightly longer than Ni1–P1 distances in all four
structures which could be due to trans effect of O compared to S and/or the geometrical
constraints imposed by the β-oxodithioester as coligands. The four atoms in the equatorial planes
show slight tetrahedral distortions with r.m.s. values of 0.079, 0.075, 0.087, 0.086 Å, but the
metal atoms remain close to the plane with deviations of 0.001(1), 0.003(1), 0.003(1), 0.003(1) Å
for 2-5 respectively. The C12–C13/C13–C14 distances at 1.385(4)−1.405(5)/1.381(5)–1.391(8)
Å in these complexes are intermediate between single and double bond lengths. In all the
structures, the C14–S15 distances at 1.681(6)–1.699(4) Å are significantly shorter than the C14–
S16 distances at 1.750(4)–1.756(5) Å but both are intermediate between the carbon-sulphur
single and double bond lengths.16
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The six-membered chelate rings about the metal centres are approximately planar in all
four structures with r.m.s. deviations of 0.011, 0.028, 0.006, 0.009 Å respectively. The five-
membered rings are puckered as expected. The plane of the Ni1, P1, P4 atoms intersects the
plane of the six-membered ring at angles of 5.97(10), 6.54(8), 6.62(15) and 6.53(10)o. The
substituents on the five- and six-membered rings are somewhat twisted away from co-planarity
with the rings.
The possibility of Ni⋯H–C intramolecular anagostic or preagostic interactions14 formed
between the metal atom and ortho protons of the phenyl groups of dppe ligand was investigated.
As shown in figure 5, the ortho-phenyl hydrogen atoms H42 and H52 form contacts in 2 with
the Ni atom of 3.00, 3.04 Å and ∠Ni⋯H−C angles of 117, 110o which are within the expected
range for such interactions. Values in 3, 4 and 5 are very similar (Figure S9). However it should
be noted that the two aforementioned hydrogen atoms are positioned on the same side of the
equatorial plane with an H∙∙∙Ni∙∙∙H angle of 69o. This positioning ensures that neither hydrogen
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2
3
4
5
6
7
8
9
atom is in an axial position relative to the equatorial plane as is usually found in anagostic or
preagostic interactions14. Indeed H52 and H42 are observed to be only 2.65 Å from O11 and 3.21
Å from S15 respectively which may indicate some electrostatic interaction. It must be concluded
that it is not clear whether the Ni∙∙∙H interactions found in this structure represent any significant
interactions. The complexes featuring such type of interactions are important because of their
possible implications in many catalytic reactions in C–H bond activation.14(b),17
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
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40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 5. Intramolecular Ni∙∙∙H−C anagostic interactions in 2.
In all the four complexes, polymeric chain like structures are generated due to involvement of
−
PF6 anion in the formation of C−H···F non-conventional hydrogen bonding interactions given
in Figure 6 for 2 and Figures S10, S11 and S12 for 3, 4 and 5. The C−H···F distances (Å) of 2−5
have been included in the Supporting Information (Table S13).
Figure 6. Noncovalent C−H∙∙∙F interactions in 2.
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7
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9
−
The interaction energies between the PF6 anion and various hydrogen atoms in complex 2 have
been calculated via single point DFT. The molecules with symmetry elements x,y,z; 1+x,y,z; 1-
x, -1/2+y, ½+z ; x,3/2-y, z-1/2 which all form hydrogen bonds to the anions have been used as
starting models and their energies compared with the sum of the energies of the cation + anion
calculated separately and interaction energies of -26.75, -55.49, -33.72, -53.429 kcalmol-1
obtained showing the importance of the ionic interactions of which the C−H∙∙∙F interactions
listed in Table S13 are likely to be a minor component.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
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29
30
31
32
33
34
35
36
37
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40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Furthermore, stacking interactions are found between benzene and six-membered metal-chelate
rings of nickel as shown in Figure 7 for 2 having distance 3.77 Å and Figures S14-S16 for 3−5
having distances 3.76, 3.76, 3.74 Å respectively. However the energy of interaction between two
molecules so connected proved to be unfavourable at 26.75 kcalmol-1. Clearly it is the presence
of the anion and the C−H∙∙∙F hydrogen bonds that is the dominant force in the mode of packing.
Figure 7. Stacking interaction between benzene and metal-chelate ring in 2.
Absorption spectra
The UV-Vis absorption spectra (Figure 8) of Ni(II) complexes 1−6 were recorded in
dichloromethane. 1−6 display virtually similar absorption bands near 285 nm ( = 4.00−5.11 x
104 M-1 cm-1), 335 nm ( = 2.24−4.00 x 104 M-1 cm-1) and 410 nm ( = 1.32−2.75 x 104 M-1 cm-
1). The first two absorptions at higher energies can be assigned to ligand centered (ILCT)
whereas the band at 410 nm is due to metal centered π-π transition. Additionally, in 1, 2 and 4
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weak broad absorption bands are observed near 650 nm ( = 0.08−0.51 x 102 M-1 cm-1) arising
due to d-d transitions18 consistent with the square planar geometry about the metal centre.
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
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29
30
31
32
33
34
35
36
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40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Figure 8. UV-Vis absorption spectra in CH2Cl2
solution showing (a) intraligand and ligand to metal charge transfer for 1−6 (C = 1 x 10−5 M) and
(b) d-d transition for 1, 2 and 4 (C = 1 x 10−2 M).
Catalytic activity of the pre-formed Ni(II) complexes 1−6 in N-arylation
Considering the importance of cross coupling reactions and C−N bond formation for the
synthesis of versatile motifs that constitute the core structure of various natural products,
materials, dyes, agrochemicals and pharmaceuticals, the well defined heteroleptic Ni(II) β-
oxodithioester-phosphine complexes were screened for C−N cross coupling using arylboronic
acid and amine. A model reaction employing phenylboronic acid (7a) and p-toluidine (8a) was
screened thoroughly by varying different parameters such as catalyst, base, solvent and
temperature; and the findings are given in Table 2.
The initial reaction conditions involved the use of phenylboronic acid (1 mmol) and p-toluidine
(1.2 mmol) in presence of DBU (1 equiv.) and catalyst 1 (4 mol %) in CH3CN (1 mL) at 60 °C
for 10 h (Entry 1), which gave rise to the product 4-methyl-N-phenylaniline (9a) in 81% yield.
All the nickel complexes 1−6 invariably provided the product 9a in considerable yields (Entries
1−6), however catalyst 2 was concluded to be the best choice to afford the maximum yield of the
product (Entry 2). Thus electron donating −OMe group on the phenyl ring favour the catalytic
reaction in comparison to the electron withdrawing −Cl, −Br and −CN groups on the phenyl
rings. Complex 6 with −CN substituent showed lowest catalytic conversion efficiency (Entry 6).
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Table 2. Optimization of Reaction Conditionsa
H
N
5
6
7
8
conditions
OH
OH
H2N
CH3
B
+
CH3
9
7a
Catalyst
8a
9a
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Entry
mol%
Base
Solvent
Temp. (oC) Time (h)
Yield(%)b
1
2
1
4
4
4
4
4
4
4
4
4
4
4
4
DBU
DBU
DBU
DBU
DBU
DBU
DBU
–
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
MeOH
60
60
60
60
60
60
60
60
60
60
60
60
10
10
10
10
10
10
10
10
10
10
10
10
81
85
82
75
78
65
23
nr
2
3
3
4
4
5
5
6
6
7
NiCl2.6H2O
8
1
2
2
2
2
9
KOH
NaOH
24
22
12
17
10
11
12
K2CO3
DBU
13
14
15
2
2
2
4
4
4
DBU
DBU
DBU
DMF
DMSO
THF
60
60
60
10
10
10
38
40
27
16
17
18
19
20
21
22
23
24
25
26
27
28
2
2
2
2
2
2
2
2
2
2
2
2
2
4
3
2
1
0
1
1
1
1
1
1
1
1
DBU
DBU
DBU
DBU
DBU
DBU
DBU
DBU
DBU
DBU
DBU
DBU
DBU
Toluene
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
60
60
60
60
60
60
60
60
60
60
60
r.t.
50
10
10
10
10
10
2
15
86
88
88
Trace
13
4
29
6
58
8
79
12
14
10
10
88
86
24
79
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29
2
1
DBU
CH3CN
70
10
88
a)
b)
Using 7a (1.0 mmol), 8a (1.2 mmol), base (1 equiv.) and solvent (1 mL) in open vessel. Isolated yield after column
chromatography. nr, no reaction.
7
8
9
Nickel(II) chloride hexahydrate (NiCl2.6H2O) also afforded the product, albeit with lower yield
than those of Ni(II) complexes 1−6 (Entry 7). When reaction was performed in the absence of
base, no product formation was observed (Entry 8). Different bases viz. KOH, NaOH and K2CO3
were also examined, which resulted in very low product yields (Entries 9-11). The organic non
nucleophilic base (N-bases) was found to be the best for reaction conditions showing much effect
on the coupling. In contrast to other bases, the high pKa value and strong basic nature of N-bases
might be the responsible factor for efficient coupling.19 Maintaining other parameters intact
(Entry 2), the effect of different solvents viz. MeOH, DMF, DMSO, THF and toluene were then
examined, which failed to provide the product in appreciable yields (Entries 12-16). The catalyst
loading was also examined (Entries 17-19), which disclosed 1 mol % of the catalyst 2 for
maximum conversion. Notably, only trace amount of product was observed, when reaction was
carried out in the absence of any catalyst (Entry 20). The room temperature reaction provided
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
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56
57
58
59
60
o
poor product yield (Entry 21), whereas the reaction at 50 C reduced the product yield to 79%
(Entry 22). A further increase in the reaction temperature, however, could not further enhance
the product yield (Entry 23). On optimizing the time-period keeping other parameters intact we
found that the maximum conversion was obtained in 10 h (Entries 19, 21-26). Further increase in
the time period (Entries 25-26) did not cause any significant change in the final yield. Thus, the
optimum conditions comprised of catalyst 2 (1 mol %) and DBU (1 equiv.) as base in acetonitrile
at 60 °C (Entry19).
With the optimized reaction conditions in hand, the scope and versatility of the reaction was
examined and the results are summarized in Table 3. The influence of different substituent was
investigated thoroughly by varying the substitution pattern on both the reacting partners, which
afforded a diverse range of the products 9a-9o in good to excellent yields. A number of
substituent viz. CH3, Cl, F, OMe and NO2, were well tolerated during the course of reaction. The
reaction was also extended to a representative heteroaromatic amine viz. 2-aminopyridine to
afford the corresponding product 9h in excellent yield. Aliphatic amines such as n-hexylamine
also worked well to give the corresponding product 9i in good yield. This catalytic system
further can be expanded to different types of heterocycles. The catalytic product was confirmed
by 1H and 13C NMR studies (Figure S17). NMR data of arylated products are given in S18.
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Table 3. Substrate scope and versatility of the reaction[a,b]
5
6
7
8
9
OH
H
N
2
Catalyst
H2N
B
DBU (1 equiv.)
OH
+
R2
R2
CH3CN (1mL)
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
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60
R1
R1
9
8
7
H
N
H
H
N
N
Cl
9a
9b
9e
, 88%
, 85%
9c
, 72%
H
N
H
N
H
N
F
Cl
OMe
9f
, 74%
, 86%
9d
, 78%
H
N
H
H
N
NO2
N
N
9i
, 66%
9g
, 68%
9h
, 84%
NO2
H
N
H
N
H
N
MeO
F
9j
9k
, 72%
9l
, 76%
, 65%
H
N
H
N
H
N
Me
MeO
Cl
9m
, 84%
9n
, 76%
9o
, 71%
[a] Using 7 (1mmol), 8 (1.2 mmol), Catalyst 2 (1 mol %), DBU (1 equiv.), CH3CN (1 mL). [b] Isolated yields after
column chromatography.
The reusability of a catalyst considered important was explored with complex 2 for C–N
cross coupling of phenylboronic acid (7a) and p-toluidine (8a) under the optimized
reaction conditions. Three reactions were set up sequentially, in which each reaction was
catalyzed with recovered catalyst 2 from the previous reaction. The reaction crude was
extracted three times with 2-3 mL of methanol where the product was soluble in methanol
and decanted in another pot. The remaining solid product was catalyst which was reused
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in the next cycle for C–N cross coupling. The catalyst was reused two times, providing
the product 9a with no significant decrease in its yields (Table 4; entries 2 and 3). These
results demonstrate the stability of catalyst 2 under ambient conditions.
7
8
9
Table 4. Recyclability of catalyst 2 in N-arylation
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
H
N
2
catalyst
OH
OH
H2N
CH3
B
+
DBU, CH3CN
CH3
Yield(%)b
9a
8a
7a
Entrya
Catalyst (mol%)
Temp(oC)
Time(h)
10
1
2
3
1
60
60
60
88
85
81
_c
_d
10
10
a)
b)
Using 7a (1.0 mmol), 8a (1.2 mmol), DBU (1 equiv.), CH3CN (1 mL). Isolated yield after column chromatography.
c) Catalyst recovered from entry 1. d) Catalyst recovered from entry 2.
Conclusions
-
In summary, six novel heteroleptic [Ni(II) β–oxodithioester-dppe]+ PF6 complexes have been
synthesized and fully characterized. These molecularly defined preformed cationic complexes
1−6 have been applied in the Chan−Lam coupling reactions of a variety of arylboronic acids and
amines under mild conditions and they show excellent catalytic activity in the range 65%-85%
yield. The electronic properties of the substituents on the β–oxodithioester group showed
significant impact on the catalytic performance of the complex. The electron donating –OMe
group is beneficial in comparison to the electron withdrawing –Cl, –Br and –CN groups on the
phenyl ring. These are inexpensive complexes and can be readily prepared using easily
accessible materials in good yield. This study widens the scope of heteroleptic Ni(II) dithioester
complexes bearing phosphine ligands for their possible applications in N-arylation. A low
catalyst loading of 1 mol % resulted in isolation of a variety of secondary aryl amines. Thus, an
efficient and economical protocol has been established for N-arylation with broad substrate
scope. Catalyst 2 could be reused two times without significant loss of catalytic activity. In
addition we have observed less common Ni∙∙∙H−C anagostic or preagostic interactions in the
crystal structure investigation of complexes 2, 3, 4 and 5. The complexes featuring anagostic
interactions are of considerable importance in many catalytic reactions for C−H bond activation
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and stabilization of structures. To gain more insights into their catalytic activity and anagostic
interactions investigations on the heteroleptic metal dithioester-phosphine ligand complexes are
being carried in our group.
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Experimental
Materials and methods
All the experiments were performed in air at ambient conditions. The reagent grade
chemicals were procured as follows; acetophenone, p-methoxy acetophenone, p-
bromoacetophenone (SPECTROCHEM), 2-acetylnaphthalene, p-chloroacetophenone, p-
cyanoacetophenone (Avra) and all the aniline and phenylboronic acid derivatives
(SPECTROCHEM/ Avra) were used as received without further purification. The
solvents dichloromethane, methanol and hexane were distilled and purified by standard
procedures. Melting points of the complexes were measured in open capillaries using a
Gallenkamps apparatus and are uncorrected. The experimental details pertaining to
elemental analysis (C, H, N), recording of IR (KBr) and UV–Vis absorption spectra are
the same as described earlier.12(i),15 X-ray powder diffraction data (PXRD) were collected
using a Brüker D8 diffractometer with Cu Kα radiation (λ = 1.541836 Å) in the 2θ range
5–50°, with a scan speed and a step size of 1° and 0.02° min-1 respectively. The ESI-MS
spectra were obtained from Agilent Technologies 6545 Q-TOF LC/MS. Thin layer
chromatography (TLC) was performed on Merck 60 F254 silica gel, pre-coated on
aluminium plates. Visualization was performed with a 254 nm UV lamp and by staining
in I2 chamber. Crude products were purified by column chromatography using silica gel
100-200 mesh, SPECTROCHEM, using n-hexane and ethyl acetate as the eluent. NMR
(1H, 13C{1H}, 31P{1H}, 19F{1H}) spectra were recorded on a JEOL AL500 FT-NMR
spectrometer in CDCl3. Chemical shifts were reported in ppm using TMS as internal
1
13
31
standard for H and C NMR spectra and phosphoric acid for P and J values were
reported in Hz.
Synthesis of ligands (HL1−HL6)
The ligands, methyl-3-hydroxy-3-benzyl-2-propenedithioate HL1, methyl-3-hydroxy-3-
(p-methoxyphenyl)-2-propenedithioate
HL2,
methyl-3-hydroxy-3-(2-naphthyl)-2-
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7
8
9
propenedithioate HL3, methyl-3-hydroxy-3-(p-chlorophenyl)-2-propenedithioate HL4,
methyl-3-hydroxy-3-(p-bromophenyl)-2-propenedithioate HL5 and methyl-3-hydroxy-3-
(p-cyanophenyl)-2-propenedithioate HL6 were synthesized according to literature
procedure.12(i),15 To a solution of NaH (0.6 g, 25 mmol) dissolved in DMF : n-hexane
mixture (4:1; 20 mL), was added slowly acetophenone (1.20 g, 10.0 mmol) (for HL1), p-
methoxyacetophenone (1.5 g, 10.0 mmol) (for HL2), 2-acetylnaphthalene (1.7 g, 10.0
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
mmol) (for HL3), p-chloroacetophenone (1.54 g, 10.0 mmol)
(for HL4), p-
bromoacetophenone (2.0 g, 10.0 mmol) (for HL5) and p-cyanoacetophenone (1.45 g, 10.0
mmol) (for HL6) in DMF (20 mL) separately. The reaction mixture was stirred for 1 h in
an ice bath under N2 atmosphere and a solution of dimethyltrithiocarbonate (TTC) (1.38
g, 10.0 mmol) was added slowly and the mixture was stirred for 10 h at room
temperature. Excess NaH was neutralized by addition of 0.1 M HCl (50 mL), and the
product was extracted three times with 50 mL portions of dichloromethane, washed with
brine solution and water, concentrated and dried over anhydrous Na2SO4. The product
thus obtained was purified by silica gel (100-200 mesh) chromatography using n-hexane
as the eluent to collect crystalline yellow solids and characterized by IR and NMR
spectroscopy (Ligand characterization data, see in S19).
Preparation of complexes 1-6
The potassium salts of the ligands KL1-KL6 required for the synthesis of complexes were
prepared according to the following method. Solid K2CO3 (0.21 g, 1.5 mmol) was added
separately to a stirred 10 mL acetone solution of the ligands HL1 (0.21 g, 1 mmol), HL2
(0.24 g, 1 mmol), HL3 (0.26 g, 1 mmol), HL4 (0.24 g, 1 mmol), HL5 (0.29 g, 1 mmol)
and HL6 (0.24 g, 1 mmol) and in each case the reaction mixture was stirred additionally
for 4-5 h under reflux condition. The solution was cooled at room temperature, filtered off
and dried on a vacuum evaporator to yield yellow to orange solids of the potassium salts
of the ligands KL1–KL6.
The heteroleptic Ni(II) β-oxodithioester-dppe complexes 1–6 were synthesized adopting
the following general procedure. To a stirred (10 mL) dichloromethane solution of dppe
(0.399 g, 1 mmol) was added gradually a 5 mL methanolic solution of NiCl2.6H2O (0.237
g, 1 mmol) and the resulting solution was stirred for 15 min. To this stirred solution was
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5
6
7
8
9
added slowly a (15 mL) methanol solution of KL1 (0.25 g, 1 mmol), KL2 (0.28 g, 1
mmol), KL3 (0.30 g, 1 mmol), KL4 (0.28 g, 1 mmol), KL5 (0.33 g, 1 mmol) and KL6
(0.27 g, 1 mmol) separately followed by addition of solid NH4PF6 (0.16 g, 1 mmol) at
room temperature. Reddish brown (brick red) precipitate was formed within a short while
and the reaction mixture was stirred additionally for 6 h (Scheme 1). The dark red solid
thus formed was filtered off, washed with methanol followed by diethyl ether. The single
crystals of complexes 2, 3, 4 and 5 were obtained by slow evaporation in dichloromethane
solution within 10-15 days. The crystal structures of 2, 3, 4 and 5 have been determined
and crystallographic data and structure refinement parameters are presented in Table 5.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Table 5. Crystallographic data and refinement parameters for complexes 2–5
Compound
Chemical formula
Formula weight
Crystal system
Space group
a (Å)
2
3
4
5
C37H35F6NiO2P3S2
841.39
C40H35F6NiOP3S2
861.42
C36H32ClF6NiOP3S2
845.80
C36H32BrF6NiOP3S2
890.26
monoclinic
P21/c
Monoclinic
P21/c
monoclinic
P21/c
Monoclinic
P21/c
10.9357(4)
12.1613(5)
28.0623(12)
98.9310(10)
3686.8(3)
4
11.1751(6)
12.1847(6)
28.1335(15)
100.960(6)
3760.9(3)
4
11.0392(6)
12.2336(6)
27.2764(15)
96.775(6)
3657.9(3)
4
10.9862(4)
12.1826(4)
27.6729(11)
98.034(4)
3667.4(2)
4
b (Å)
c (Å)
β(o)
V (Å3)
Z
ρcalc (g cm-3)
T (K)
1.516
1.521
1.536
1.612
100(2)
150(2)
150(2)
150(2)
μ(Mo Kα) (mm-1)
F(000)
0.834
0.818
0.910
1.924
1728
1768
1728
1800
Reflections collected
Independent reflns
53139
23604
19716
24131
9207
10822
10552
10557
Reflections with I >
2σ(I)
7110
8004
5558
6248
Final indices
[I > 2σ(I)] R1 , wR2
R1[a], wR2[b]
[all data]
GOF
0.0649, 0.1120
0.0908, 0.1242
1.068
0.0604, 0.1130
0.0886, 0.1252
1.069
0.0900, 0.1804
0.1729, 0.2155
0.994
0.0579, 0.1187
0.1134, 0.1383
0.921
a
b
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Max., min.
0.886, -0.771
0.575, -0.642
0.946, -0.432
0.950, -0.716
residual electron
density (e/ Å3)
6
7
aR1 = ∑ ǀǀFoǀ - ǀFcǀǀ/ ∑ǀFoǀ. bR2 = {[∑w(Fo2 – Fc2)/ ∑w(Fo ) ]}1/2, w= 1/[2(Fo ) + (xP)2], where P = (Fo2 + 2Fc2)/3.
2 2
2
8
9
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Characterization
[Ni(L1)(dppe)] 1: (0.67 g, 83%). Mp: 229–233 °C. Anal. Calcd for C36H33NiF6OP3S2 (811.38): C
53.29, H 4.10%. Found: C 53.02, H 4.21%. IR (KBr, cm-1): 1508 (νC=O), 1465 (νC=C), 1103 (νC-
S). 1H NMR (500 MHz, CDCl3, δ (ppm)): 2.39 (s, 3H, –SCH3), 2.55–2.64 (m, 2H, –CH2–), 2.85–
2.92 (m, 2H, –CH2–), 7.05 (s, 1H, –CH=C–), 7.07–7.84 (m, 25H, Ar–H). C{1H} NMR (125
13
MHz, CDCl3, ppm): δ 16.99 (–SCH3), 23.32 (–CH2–), 28.78 (–CH2–), 109.87 (–CH=C–),
125.05–137.87 (Ar–C), 177.73 (–C=O), 186.67 (=C–S–). 31P{1H} NMR (202 MHz, CDCl3,
ppm): δ 56.29, 61.31 (Ph2P-CH2-CH2-PPh2), -143.71 (PF6). 19F NMR (470 MHz, CDCl3, ppm):
δ -72.40, -73.92 (PF6). UV-Vis. (CH2Cl2, λmax (nm), ε (M−1 cm−1)): 282 (5.11 × 104), 333 (4.00 ×
104), 402 (2.05 × 104), 663 (0.51 × 102). ESI-MS. (Calc., found, m/z): [M-PF6]+ 665.0807,
665.0808.
[Ni(L2)(dppe)] 2: (0.74 g, 88%). Mp: 242–246 °C. Anal. Calcd for C37H35NiF6O2P3S2 (841.39):
C 52.82, H 4.19%. Found: C 52.59, H 4.28%. IR (KBr, cm-1): 1602 (νC=O), 1494 (νC=C), 1029 (νC-
1
S). H NMR (500 MHz, CDCl3, ppm): δ 2.38 (s, 3H, –SCH3), 2.53-2.63 (m, 2H, -CH2-), 2.80-
2.90 (m, 2H, -CH2-), 3.78 (s, 3H, –OCH3), 6.57 (1H, s,–CH=C–), 7.04–7.84 (m, 24H, Ar–H).
13C{1H} NMR (125 MHz, CDCl3, ppm): δ 16.89 (–SCH3), 23.45 (–CH2–), 28.74 (–CH2–), 55.65
(–OCH3), 109.34 (–CH=C–), 113.95–133.76 (Ar–C), 163.11 (–C=O), 177.08 (=C–S–). P{1H}
31
19
NMR (202 MHz, CDCl3, ppm): δ 55.91, 61.15 (Ph2P-CH2-CH2-PPh2), -143.73 (PF6). F NMR
(470 MHz, CDCl3, ppm): δ -72.41, -73.94 (PF6). UV-Vis. (CH2Cl2, λmax (nm), ε (M−1 cm−1)): 296
(4.02 × 104), 338 (3.00 × 104), 410 (2.75 × 104), 661 (0.20 × 102). ESI-MS. (Calc., found, m/z):
[M-PF6]+ 695.0913, 695.0915.
[Ni(L3)(dppe)] 3: (0.74 g, 86%). Mp: 259–263 °C. Anal. Calcd for C40H35NiF6OP3S2 (861.42): C
55.77, H 4.10%. Found: C 55.58, H 4.16%. IR (KBr, cm-1): 1584 (νC=O), 1484 (νC=C), 1102 (νC-
1
S). H NMR (500 MHz, CDCl3, ppm): δ 2.41 (s, 3H, –SCH3), 2.55-2.66 (m, 2H, -CH2-), 2.87-
2.98 (m, 2H, -CH2-), 7.12 (1H, s,–CH=C–), 7.45–7.87 (m, 27H, Ar–H). 13C{1H} NMR (125
MHz, CDCl3, ppm): δ 17.24 (–SCH3), 23.85 (-CH2-), 28.42 (-CH2-), 110.54 (–CH=C–), 123.93–
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135.18 (Ar–C), 177.73 (–C=O), 199.86 (=C–S–). 31P{1H} NMR (202 MHz, CDCl3, ppm): δ
56.09, 61.56 (Ph2P-CH2-CH2-PPh2), -143.73 (PF6). 19F NMR (470 MHz, CDCl3, ppm): δ -
72.38, -73.91 (PF6). UV-Vis. (CH2Cl2, λmax (nm), ε (M−1 cm−1)): 280 (4.62 × 104), 337 (2.92 ×
104), 412 (2.41 × 104). ESI-MS. (Calc., found, m/z): [M-PF6]+ 715.0964, 715.0993.
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11
12
13
14
15
16
17
18
19
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23
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[Ni(L4)(dppe)] 4: (0.66 g, 78%). Mp: 248–252 °C. Anal. Calcd for C36H32ClNiF6OP3S2
(845.80): C 51.12, H 3.81%. Found: C 50.91, H 3.89%. IR (KBr, cm-1): 1589 (νC=O), 1504 (νC=C),
1099 (νC-S). 1H NMR (500 MHz, CDCl3, ppm): δ 2.41 (s, 3H, –SCH3), 2.57- 2.66 (m, 2H, -CH2-
13
), 2.84-2.92 (m, 2H, -CH2-), 6.99 (s, 1H, –CH=C–), 7.08–7.85 (m, 24H, ArH). C{1H} NMR
(125 MHz, CDCl3, ppm): δ 16.78 (–SCH3), 23.37 (-CH2-), 28.76 (-CH2-), 109.33 (–CH=C–),
124.75−138.17 (Ar-C), 175.74 (–C=O), 187.62 (=C–S–). 31P{1H} NMR (202 MHz, CDCl3,
ppm): δ 56.79, 61.46 (Ph2P-CH2-CH2-PPh2), -143.73 (PF6). 19F NMR (470 MHz, CDCl3, ppm):
δ -72.33, -73.85 (PF6). UV-Vis. (CH2Cl2, λmax (nm), ε (M−1 cm−1)): 283 (4.00 × 104), 330 (3.41 ×
104), 405 (1.58 × 104), 666 (0.08× 102). ESI-MS. (Calc., found, m/z): [M-PF6]+ 699.0417,
699.0441.
[Ni(L5)(dppe)] 5: (0.72 g, 81%). Mp: 250–254 °C. Anal. Calcd for C36H32BrNiF6OP3S2
(890.26): C 48.57, H 3.62%. Found: C 48.44, H 3.76%. IR (KBr, cm-1): 1584 (νC=O), 1504 (νC=C),
1071 (νC-S). 1H NMR (500 MHz, CDCl3, ppm): δ 2.38 (s, 3H, –SCH3), 2.56-2.66 (m, 2H, -CH2-),
2.83-2.94 (m, 2H, -CH2-), 6.87 (s, 1H, –CH=C–), 7.00–7.83 (m, 24H, ArH). 13C{1H} NMR (125
MHz, CDCl3, ppm): δ 17.01 (–SCH3), 23.33 (-CH2-), 28.70 (-CH2-), 109.59 (–CH=C–), 125.03-
133.76 (Ar-C), 176.09 (–C=O), 186.13 (=C–S–). 31P{1H} NMR (202 MHz, CDCl3, ppm): δ
56.93, 61.52 (Ph2P-CH2-CH2-PPh2), -143.75 (PF6). 19F NMR (470 MHz, CDCl3, ppm): δ -72.37,
-73.89 (PF6). UV-Vis. (CH2Cl2, λmax (nm), ε (M−1 cm−1)): 287 (4.61 × 104), 336 (3.10 × 104), 405
(2.00 × 104). ESI-MS. (Calc., found, m/z): [M-PF6]+ 744.9888, 744.9903.
[Ni(L6)(dppe)] 6: (0.69 g, 83%). Mp: 202–206 °C. Anal. Calcd for C37H32NiF6OP3S2N (836.39):
C 53.13, H 3.86%. Found: C 52.97, H 3.98%. IR (KBr, cm-1): 1572 (νC=O), 1513 (νC=C), 1104 (νC-
1
S). H NMR (500 MHz, CDCl3, ppm): δ 2.42 (s, 3H, –SCH3), 2.61-2.68 (m, 2H, -CH2-), 2.88-
2.95 (m, 2H, -CH2-), 7.10 (s, 1H, –CH=C–), 7.11–7.85 (m, 24H, ArH). 13C{1H} NMR (125
MHz, CDCl3, ppm): δ 17.10 (–SCH3), 23.63 (-CH2-), 28.92 (-CH2-), 109.94 (–CH=C–), 127.86-
133.74 (Ar-C), 160.81 (–C=O), 181.57 (=C–S–). 31P{1H} NMR (202 MHz, CDCl3, ppm): δ
57.73, 61.73 (Ph2P-CH2-CH2-PPh2), -143.76 (PF6). 19F NMR (470 MHz, CDCl3, ppm): δ -72.30,
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-73.81 (PF6). UV-Vis. (CH2Cl2, λmax (nm), ε (M−1 cm−1)): 282 (4.07 × 104), 336 (2.24 × 104), 404
(1.32 × 104). ESI-MS. (Calc., found, m/z): [M-PF6]+ 690.0760, 690.0724.
7
8
General procedure for N-Arylation with arylboronic acids (9a-9o)
9
A mixture of arylboronic acid (7, 1.0 mmol), amine (8, 1.2 mmol), Ni-catalyst 2 (1 mol %), DBU
(1 equiv.) and CH3CN (1 mL) placed in a 10 mL borosilicate vial, was stirred under open
atmosphere at 60 °C for 10 h. On completion of the reaction (monitored through TLC), the
reaction mixture was worked-up using water-ethyl acetate. The organic phase was dried over
anhydrous Na2SO4, filtered and solvent was removed under reduced pressure to obtain the crude
product. The resulting crude product was finally purified by column chromatography using n–
hexane and ethyl acetate as eluent.
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X-ray crystal structure determination
Single crystals of 2, 3, 4 and 5 were obtained by slow evaporation of solutions of the
compound in CH2Cl2. Single crystal X-ray data for 2 was collected on a Bruker D8 Quest
SCM X-ray diffractometer at 100 K and 3, 4 and 5 on an Oxford X-calibur CCD
diffractometer at 150 K using Mo Kα radiation. Data reduction was carried out using the
CrysAlis program.20 The structures were solved by direct methods using SHELXS-9721
and refined on F2 by full matrix least-squares method using SHELXL2016-6.22
Nonhydrogen atoms were refined anisotropically and hydrogen atoms were geometrically
fixed with thermal parameters equivalent to 1.2 times that of the atom to which they were
bonded. Diagrams for the complexes were prepared using ORTEP,23 Mercury24 and
GaussView25 software. Crystal data for 2, 3, 4 and 5 have been deposited at the
Cambridge Crystallographic Data Centre with reference numbers CCDC 1966677,
1945464, 1945463 and 1945465.
Theoretical calculations
All calculations were carried out using the Gaussian 03 program.26 Structures were
optimized using the B3LYP density functional together with basis sets LANL2DZ for Ni,
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6-31+G* for S, P and O and 6-31G for the remaining atoms. Starting models were taken
from the crystal structures but with hydrogen atoms given theoretical positions.
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8
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Associated Content
Supporting Information
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Tables, figures and CIF files giving bond lengths and angles, secondary interaction figures and
distances calculated by DFT, NMR spectra and ESI-MS spectra.
Author Information
Corresponding Author
* E-mail: nsinghbhu@gmail.com, nsingh@bhu.ac.in
ORCID
K. Kumari 0000-0002-1468-7515
M. G. B. Drew 0000-0001-8687-3440
N. Singh 0000-0003-1578-5456
Notes
The authors declare no competing financial interest.
Acknowledgements
We gratefully acknowledge financial support from the Science and Engineering Research Board
(SERB), for the project: (SB/SI/IC-15/2014) and UGC, New Delhi for the award of BSR Faculty
Fellow (ref No. F.18-1(BSR) 30 Dec 2016) to NS and CSIR-SRF fellowship to KK, New Delhi.
We thank the Department of Chemistry, Institute of Science, Banaras Hindu University, UGC
CAS-II for infrastructural facilities. We also thank the University of Reading and the EPSRC
(UK) for funds for the diffractometer used for the data collections of structures 3–5.
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Table of Contents
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
Six new structurally characterized heteroleptic cationic [Ni(II) β-oxodithioester-dppe]+ PF6
complexes as efficient catalysts for Chan–Lam coupling reaction affording N-arylated products
with significant functional group tolerance and broad substrate scope.
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OH
B
NH2
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OH
R2
+
R1
Stable Catalyst,
Mild Reaction Conditions,
Broad Substrate Scope,
High yields,
Low Catalyst Loading
C-N
Cross-C
1 mol %
H
N
oupli
R2
n
g
R1
15 Examples
Yield up to 88 %
28