Novelmeta-benzothiazole and benzimidazole functionalised POCOP-Ni(ii) pincer complexes as efficient catalysts in the production of diarylketones

Article abstract of DOI:10.1039/d1nj01348c

The synthesis of four novel non-symmetric Ni(ii)-POCOP pincer complexesmeta-functionalized with either benzothiazole or benzimidazole at the central aryl ring is described. All complexes were fully characterised in solution by various analytical techniques and the molecular structures in the solid state of complexes1b,2aand2bwere unequivocally determined by single crystal X-ray diffraction analysis. In addition, the Ni(ii)-POCOP pincer complexes were efficiently used as catalysts in the synthesis of diarylketones by cross-coupling reactions of functionalized benzaldehydes and boronic acid derivatives under relatively mild conditions. An important aspect of this transformation is the dependence on the steric properties of the donor groups (OPR₂) of the pincer ligands, the more active compounds having the phosphinitos bearing isopropyl groups (1aand2a) than those containingtert-butyl substituents (1band2b).

Full text of DOI:10.1039/d1nj01348c

View Article Online
View Journal
NJC
New Journal of Chemistry
Accepted Manuscript
A journal for new directions in chemistry
This article can be cited before page numbers have been issued, to do this please use: A. A. Castillo-
García, G. Lucero, L. Lomas-Romero, S. Hernandez-Ortega, R. A. Toscano and D. Morales-Morales, New
J. Chem., 2021, DOI: 10.1039/D1NJ01348C.
Volume 42
Number
March 2018
Pages 3963-4776
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
6
21
NJC
New Journal of Chemistry
rsc.li/njc
A journal for new directions in chemistry
Accepted Manuscripts are published online shortly after acceptance,
before technical editing, formatting and proof reading. Using this free
service, authors can make their results available to the community, in
citable form, before we publish the edited article. We will replace this
Accepted Manuscript with the edited and formatted Advance Article as
soon as it is available.
You can find more information about Accepted Manuscripts in the
Information for Authors.
Please note that technical editing may introduce minor changes to the
text and/or graphics, which may alter content. The journal’s standard
Terms & Conditions and the Ethical guidelines still apply. In no event
shall the Royal Society of Chemistry be held responsible for any errors
or omissions in this Accepted Manuscript or any consequences arising
from the use of any information it contains.
ISSN 1144-2546
PAPER
Chechia Hu, Tzu-Jen Lin et al.
Yellowish and blue luminescent graphene oxide quantum dots
prepared via a microwave-assisted hydrothermal route using
H2O2 and KMnO4 as oxidizing agents
rsc.li/njc

Page 1 of 26
New Journal of Chemistry
1
2
3
4
5
6
7
8
9
View Article Online
DOI: 10.1039/D1NJ01348C
Novel meta-Benzothiazole and Benzimidazole Functionalised POCOP-
Ni(II) Pincer Complexes as Efficient Catalysts in the Production of
Diarylketones.
a
b,
b
Antonio A. Castillo-García, Lucero González-Sebastián, * Leticia Lomas-Romero,
a
a
a,
Simon Hernandez-Ortega, Ruben A. Toscano and David Morales-Morales *
a
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Instituto de Química, Universidad Nacional Autónoma de México, Circuito Exterior,
Ciudad Universitaria, Ciudad de México, C.P. 04510, México. Departamento de
b
Química, Universidad Autónoma Metropolitana-Iztapalapa, Av. San Rafael Atlixco No.
86, Ciudad de México, C.P. 09340, México.
1
*Corresponding author. Tel.: +52 55 56224514; fax: +52 55 56162217.
E-mail address: damor@unam.mx (D. Morales-Morales)
ABSTRACT
The synthesis of four novel non-symmetric Ni(II)-POCOP pincer complexes meta-
functionalized with either benzothiazole or benzimidazole at the central aryl ring is
described. All complexes were fully characterised in solution by various analytical
techniques and the molecular structures in the solid state of complexes 1b, 2a and 2b
were unequivocally determined by single crystal X-ray diffraction analysis. In addition,
the Ni(II)-POCOP pincer complexes were efficiently used as catalysts in the synthesis of
diarylketones by cross-coupling reactions of functionalized benzaldehydes and boronic
acid derivatives under relative mild conditions. An important aspect of this
transformation is the dependence on the steric properties of the donor groups (OPR )
2
of the pincer ligands, being more active the compounds having the phosphinitos
bearing isopropyl groups (1a and 2a) than those containing tert-butyl substituents (1b
and 2b).

New Journal of Chemistry
Page 2 of 26
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
View Article Online
DOI: 10.1039/D1NJ01348C
1
. Introduction
Pincer compounds represent an important facet of contemporary organometallic
[1]
chemistry and homogenous catalysis. Conferring thermal stability whilst permitting a
broad range of metal-based reactivity. In particular, the application of mer-tridentate
pincer ligands in different fields of science and catalysis has had a huge impact.[1b,2] The
predictable and modular composition of pincer ligands enables the tunning of the
steric and electronic properties of their metal derivatives through changes in the
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
constituent donor groups (phosphines PR
2
, amines NR , thioethers SR, selenoethers
2
SeR and N-heterocyclic carbenes or a pair of donor groups among these
functionalities), their substituents (R) or the backbone configuration itself.[1b,3] As a
result, these adaptions have been extensively studied. However, despite much is
already known about the chemistry of the most emblematic symmetric phosphine-
based pincers with central pyridine or aryl donors,[4] the design of non-symmetric
pincer architectures is still a highly developing topic, since these species can combine
the properties of their symmetrical counterparts and disclose unique reactivities and
non-typical features.[1c] In this sense, even though the non-symmetric pincer
complexes are less common, mainly due to the difficulties in their preparation, in the
last decade there has been a significant progress in this research field providing several
examples of how the C2v symmetry of aryl or pyridine-linked pincer ligand systems can
be broken, generally, through one of the three ways shown in Figure 1.[1c,5]
The meta-substitution
at the central aromatic core
G
Variations of linkers by changing
E
M
X
(L )
2 m
their length and nature
n(L1)
D1
(L1 ≠L2 and/or n m)
≠
D2
Changes in donor groups (D1 ≠ D2)
Figure1. Modifiablesitesonapincerframeworktoproducenon-symmetricpincercompounds.
The substitution on the main pincer backbone plays a more interesting role than the
simple modification of the electronic character on the pincers, leading to the
possibility of functionalization of the aromatic ring of the main framework with the
introduction of potential molecular recognition sites or anchoring the metal pincer
2

Page 3 of 26
New Journal of Chemistry
1
2
3
4
5
6
7
8
9
complex to supporting materials, dendrimers, polymers, etc.[6] On the other hand,
View Article Online
DOI: 10.1039/D1NJ01348C
within of the large family of phosphine-based pincer ligands, POCOP pincer ligands and
their complexes are of special interest due to their relatively easy synthesis, turning
them perfect templates to yield non-symmetric systems. In this respect, our group has
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
been involved in the development of symmetric and non-symmetric functionalised
POCOP pincer complexes and their application as colorimetric sensors of anions (CN-,
-
-
[7]
[8]
OH , F )[A] and catalysts [B, C] (Chart 1).
Preceding
work
OH
O
N
9
X
H
O
O
O
O
O
O
O
O
R P
2
Ni PR2 R2P
M
PR2
R P Pd PR2
R2P
Ni PR2
2
Cl
Cl
Cl
Cl
M=Ni, Pd, Pt
X= N, S
i
t
[A]
[B]
[C]
R= Pr, Bu
This
work
Chart 1
On the other side, diarylketone frameworks are an important motif in a wide array of
[9]
pharmaceutical, organic materials, natural products and fine chemicals. To date, the
Friedel-Crafts reaction of substituted aromatic rings,[10] the cross-coupling reactions of
boronic acid with either acyl chlorides or carboxylic anhydrides catalysed by
palladium,[11] the Houben-Hoesch reaction of nitriles,[12] the acylation of
organometallics with acyl electrophiles catalysed by transition metals and the nickel
and palladium-catalysed Negishi cross-coupling of amides, among other procedures,[13]
are some of the methods more used for the synthesis of diarylketones and their
derivatives. However, these reactions still suffer some drawbacks, such as the highly
basic or acidic conditions, use of expensive substrates, incompatibility with many
functional groups and need for further functionalization steps that are time-
consuming. Thus, the search of new routes to produce diarylketones through less
expensive and practical procedures, using easily available substrates, is a challenging
task for researches of worldwide. In this context, a very promising approach is the
3

New Journal of Chemistry
Page 4 of 26
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
View Article Online
DOI: 10.1039/D1NJ01348C
synthesis of diarylketones by coupling reactions of aldehydes and arylboronic acids,
which has been well documented with the assistance of homogeneous catalysts of
palladium,[14] cobalt,[15] rhodium,[16] copper,[17] platinum,[18] ruthenium[19] and nickel[20]
(
Table 1). This process is particularly attractive because of the organoboron reagents
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
are stable to air and moisture and have a good functional group tolerance, while the
aldehydes are inexpensive and highly available. Then, the generation of diarylketones
through more economical and cleaner processes by the use of stable compounds able
to catalyse the coupling of aldehydes and arylboronic acids, without the requirement
of any extra additive, using low catalyst loading under mild reaction conditions
remains a topic of current relevance. In this context, the catalyst stability is a major
concern, which enforces the usage of high catalyst loading (more than 5 mol%) in
many reactions. And taking into account that, the pincer complexes have been widely
used as catalysts in diverse coupling reactions[1b,2] offering excellent activities, largely,
due to their high thermal stability, the assessment of pincer complexes as catalysts in
the coupling of aldehydes and arylboronic acids to give diarylketones is relevant and
pertinent. To the best of our knowledge, the synthesis of substituted benzophenones
from aldehydes and arylboronic acids efficiently catalysed by Ni(II) pincer complexes
has not been explored ever before.
Table 1. Comparison of Ni(II)-POCOP pincer complex, 1a, with other catalytic systems
in the arylation of aldehydes with arylboronic acids to produce diaryl ketones.
a
Arylation of both aliphatic and aromatic aldehydes. NA= not applicable.
Entry
[M] (mol%)
Ligand (mol%)
Xantphos (15 mo%)
tmphen (15 mo%)
Reaction conditions
Ref.
[17]
[15]
KF, Toluene, 24 h, 120 oC
1
2
Cu(OTf)
2
(10 mol%)
CoCl
2
(10 mol%)
Cs
2
CO , MeCN/Toluene 3:1, 12
3
o
h, 80 C
, Toluene, 24 h, 120 oC
3
4
Pd
2
(dba)
3
(2.5 mol %) NA
Cs
2
CO
3
[14a]
[14b]
Pd(PPh
3
)
4
(2 mol %)
2-chloro-1,3-dimethyl
3
K PO
4
, Dioxane, 16 h, 90 oC
imidazolidinium (1.2 eq)
Thioether-imidazolinium CsF, Dioxane, 3 h, 80 oC
chloride (0.5-1.5 mol%),
5
6
[Pd(allyl)Cl]
0.5 - 1.5 mol%)
RuHCl(CO)(PPh
5 mol%)
2
[14c]
[19a]
(
3
)
3
]
NA
Cs
2
CO
3
, H O, Toluene, 13 h,
2
o
(
110 C.
4

Page 5 of 26
New Journal of Chemistry
1
2
3
4
5
6
7
8
9
a[Ru(CO)
View Article Online
DOI: 10.1039/D1NJ01348C
7
8
9
3
Cl
2
]
t-Bu
3
P•HBF
4
(10 mo%)
K
3
PO
4
, t-BuCOMe (2 eq), H
2
O,
[19b]
o
(
2.5 mol%)
Toluene, 24 h, 100 C
[Rh(CH
2
CH
2
)Cl]
2
P(t-Bu)
3
(3 mol%)
K
2
CO3, Dioxane/Acetone 4:1, 4-
[16]
o
(
a
1.5 mol%)
8 h, 80 C
Acetone, DMSO, 12h, 120 C
o
[Ni(PPh
3
)
4
]
dcype (6 mol%)
NA
[20]
(5 mol%)
Ni(II)-POCOP, 1a,
1 mol%)
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
10
Cs
2
CO
3
, Toluene/Acetone 4:1,
This
o
(
8 h, 80 C
work
Thus, motivated by the potential applications of functionalised POCOP-based pincers
and the construction of non-symmetric pincer complexes by meta-substitution at the
central aromatic core of the pincer, and as an extension to our related work with
POCOP pincer ligands, we became interested in developing the chemistry of
functionalized POCOP-based pincers with heterocyclic scaffolds. Specifically,
benzimidazole and benzothiazole are important precursors due to their potential
biological and pharmaceutical properties including anticancer, antimicrobial,
antifungal, anticonvulsant, anti-inflammatory and antiviral activities.[21] Hence, the
incorporation of biologically relevant fragments into the pincer backbone could be the
start of a new type of potentially important bioorganometallic compounds with
potential catalytic and biological applications. Furthermore, the inclusion of these
heterocycles could lead to the coordination to a second transition metal such as Cu(II),
Ag(I), Au(I), Pt(II), etc. to generate bimetallic complexes.[22] Thus, herein, we describe
the synthesis and full characterization of a series of non-symmetric nickel pincer
complexes based on meta-benzothiazole and meta-benzimidazole resorcinol
derivatives and their catalytic evaluation in the synthesis of diarylketones from
substituted benzaldehydes and phenylboronic acid.
2
. Results and discussion.
2
.1. Proligand synthesis.
The proligands P1 and P2 were prepared using an adapted procedure previously
reported from commercially available 2,4-dihidroxybenzaldehyde, 2-aminothiophenol
(
P1) and 1,2-phenylendiamine (P2) outlined in Scheme 1. P1 was synthetized in one
step and isolated as a light-yellow solid with a yield of 62%, meanwhile P2 was
obtained in 77 % yield over two steps as a bright-white powder after its purification by
1
13
1
flash chromatography. These compounds were further characterized by H and C{ H}
5

New Journal of Chemistry
Page 6 of 26
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
View Article Online
DOI: 10.1039/D1NJ01348C
NMR and mass spectroscopy and structurally confirmed by direct comparison of
previously reported data (full details are provided in the experimental section).[23]
N
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
S
X= SH
EtOH, 4 h, reflux
HO
OH
P1 (62%)
O
NH2
X
H
+
HO
OH
1
2
) NaHSO , EtOH,
3
N
2
h, r.t.
X= SH, NH2
o
) DMF, 4 h, 70 C
N
H
X= NH2
HO
OH
P2 (77%)
Scheme 1. Synthesis of proligands P1 and P2
2
.2. Ni-POCOP pincer complexes synthesis.
With the proligands in hand, the synthesis of nickel derivatives was targeted (Scheme
2). Using an adapted literature procedure[7b,8b,24], the non-symmetric nickel POCOP-
i
t
pincer complexes were prepared by the meta-benzothiazole (1a; R= Pr, 1b; R= Bu)
i
t
and meta-benzimidazole (2a; R= Pr, 2b; R= Bu) aryl backbone substitution and the
products were obtained as analytically pure materials in moderate isolated yields (48-
6
2%). POCOP-pincer ligands L1 (benzothiazole) and L2 (benzimidazole) were obtained
through a procedure that involved the reaction of the proligands P1 and P2 with a
o
base (Et
3
N or DMAP) in THF at 40 C for 1h. This was followed by treatment with the
corresponding chlorophosphine at reflux temperature for 4h under nitrogen
3
1
1
atmosphere. P{ H} NMR analysis of the ligands exhibited two singlets consistent with
the non-symmetric nature of the pincer ligands[8a] L1a:  146.6(P ) and 150.0(P ) ppm,
1
2
1
2
1
2
1
L1b:  146.5(P ) and 153.5(P ) ppm, L2a:  146.1(P ) and 154.3(P ) ppm, L2b: 147.2(P )
2
and 155.0(P ) ppm. These chemical shifts are similar to those reported for their non-
symmetric POCOP free ligands analogous, and in general, as we have observed before,
2
the signals at lower field correspond to the phosphorus nuclei (P ) adjacent to the
substituent at the 4 position, this assignation was established by direct comparison of
their symmetric POCOP ligand counterparts.[8] Then, compounds L1a, L1b, L2a, L2b
6

Page 7 of 26
New Journal of Chemistry
1
2
3
4
5
6
7
8
9
View Article Online
DOI: 10.1039/D1NJ01348C
were used in situ without further purification for their direct metalation with NiCl
2
in
refluxing toluene generating four air-stable non-symmetric Ni–POCOP pincer
complexes.
N
O
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
N
N
O
X
1
) Base, THF,
40 °C, 1 h
NiCl , toluene,
reflux, 24 h
2
X
X
O
2
) ClPR2,
R P
2
Ni
Cl
PR2
O
-HCl
HO
OH
reflux, 4h
1
2
P R
P R
2
2
P1: X= S
P2: X= NH
i
t
i
(
L1): X= S; a) R= Pr, b) R= Bu
(1): X= S; 1a) R= Pr (62%)
X= S; 1b) R= Bu (52%)
(2): X= NH; 2a) R= Pr (56%)
i
t
t
(L2): X= NH; a) R= Pr, b) R= Bu
i
t
X= NH; 2b) R= Bu (48%)
Scheme 2. Synthesis of non-symmetric Ni(II)-POCOP pincer complexes: 1a, 1b, 2a and 2b.
Ni(II)-POCOP pincer complexes were characterised in solution, observing typical AB
patterns of 31P{ H} resonances, displaying diagnostic trans-phosphinito couplings
1
1
2
2
1
2
2
centred at δ 192.6 (d, P )/187.5(d, P ) ( JP-P= 332 Hz), δ 197.5(d, P )/189.8(d, P ) ( JP-P
=
1
2
2
1
2
2
3
03 Hz), δ 193.6(d, P )/187.5(d, P ) ( JP-P= 338 Hz), 196.2(d, P )/190.0(d, P ) ( JP-P= 303
Hz) for 1a, 1b, 2a, 2b respectively. As can be noticed, the phosphorus resonances in
the nickel complexes are shifted to higher frequencies, ca. 50 ppm than those of the
free pincer ligands (vide supra) due to the coordination to the metal center, thus
1
confirming the formation of the desired non-symmetric pincer complexes. H and
13
1
C{ H} NMR spectra also provide further structural information. In all the cases, the C-
H bond activation by the metalation process was evidenced by the disappearance of
the ortho-protons resonances (R
) of the complexes in the 1H
2
POCaryl-CHaryl-CarylOPR
2
1
3
1
NMR spectra. Coordination of the pincer was also affirmed by C{ H} NMR displaying
signals of the metallated C-Ni carbon as apparent triplets due to their coupling with,
inequivalent, mutually trans-phosphorous nuclei at δ 124.8 (at, 2JC-P= 19.4, 20.6 Hz) for
1
a, 125.4 (at, 2JC-P= 19.8, 22.1 Hz,) for 1b, 124.2 (at, 2JC-P= 22.5, 22.8 Hz) for 2a, and
24.5 (at, 2JC-P= 22.3, 22.5 Hz) for 2b. The FT-IR spectra of all complexes exhibit key
1
-
1
-1
-1
bands at ca. 1575 –1597cm , ca. 1238 -1257 cm and ca. 443-470 cm assigned to v(P-
), v(C=N), and v(C-Ni), respectively. In the IR spectra of 2a and 2b, the v(N-H) band is
0
-
1
observed at ca. 3400 cm . Mass spectra also confirmed the formation of the
+
complexes. The resulting spectra exhibited the molecular ion [M] at 568, 624, 551 and
6
07 m/z for complexes 1a, 1b, 2a and 2c respectively. Results obtained from elemental
7

New Journal of Chemistry
Page 8 of 26
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
View Article Online
DOI: 10.1039/D1NJ01348C
analysis of all compounds are also in agreement with the proposed structural
formulations.
In addition, the molecular structures of complexes 1b, 2a and 2b were determined
using single crystal X-ray diffraction analyses, fully confirming the structural
formulations inferred from NMR spectroscopy and mass spectrometry. In all cases,
crystals of the complexes suitable for their analysis were obtained by slow diffusion of
methanol into saturated dichloromethane solutions of the complexes at room
temperature (Figure 2).
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Nickel pincer complexes crystallised in the monoclinic (1b, 2a) and triclinic (2b)
systems exhibiting the adoption of distorted square planar metal coordination
geometries. The coordination sphere in all complexes is constituted by one chloride
and the corresponding pincer ligand, bonded in a tridentate manner through the two
1
2
phosphorus atoms (P , P ) and a sigma C-Ni bond with one carbon atom from the aryl
backbone forming two five-membered metallocycles. The main distortion arises
primarily from the bite angle of the POCOP ligand that results in a tightening of all C–
o
o
Ni–P and P–Ni–P angles (ca.82 and ca.164 , respectively), whereas the C-Ni-Cl angles
are fairly linear between 175-179o.
The Ni-C bond distances in all compounds are very similar ca.1.882 Å, while the Ni-Cl
bonds distances are ca. 2.195Å (average), which are in agreement with other reported
POCOP nickel complexes.[25] Also, complex 2a displays an intramolecular hydrogen
interaction N7-H---O2 providing a six-membered ring.
t
i
t
1
b, [NiCl{C
6
H
2
-3-C
7
H
4
NS-2,6-(OP Bu
2
)
2
}]
2a, [NiCl{C
6
H
2
-3-C
7
H
5
N
2
-2,6-(OPPr
2
)
2
}]
6 2 7 5 2 2 2 3
2b, [NiCl{C H -3-C H N -2,6-(OP Bu ) }]•CH OH
Figure 2. Solid-state structures of 1b, 2a and 2b (thermal ellipsoids drawn at 30 %
probability). Selected bond lengths (Å): 1b Ni1-C2, 1.889(3), Ni1-P2 2.1685(11), Ni1-P1
.1763(11), Ni1-Cl1 2.2051(10); 2a Ni2-C2 1.883(2), Ni2-P1 2.1461(6), Ni2-P2
2
8

Page 9 of 26
New Journal of Chemistry
1
2
3
4
5
6
7
8
9
View Article Online
DOI: 10.1039/D1NJ01348C
2
.1480(7), Ni2-Cl1 2.1820(7); 2b Ni1-C2 1.885(2), Ni1-P1 2.1862(6), Ni1-P2 2.1929(6),
o
Ni1-Cl1 2.1971(6). Selected angles ( ): 1b C2-Ni1-P2 82.11(10), C2-Ni1-P1 82.19(11), P2-
Ni1-P1 164.31(4), C2-Ni1-Cl1 179.43(11), P2-Ni1-Cl1 98.16(4), P1-Ni1-Cl1 97.53(4); 2a
C2-Ni2-P1 82.53(7), C2)-Ni2-P2 82.62(7), P1-Ni2-P2 164.41(3), C2-Ni2-Cl1 175.63(7),
P1-Ni2-Cl1 99.11(3), P2-Ni2-Cl1 96.04(3); 2b C2-Ni1-P1 82.59(7), C2-Ni1-P2 82.20(7),
P1-Ni1-P2 164.48(3), C2-Ni1-Cl1 178.44(7), P1-Ni1-Cl1 95.97(2), P2-Ni1-Cl1 99.20(2).
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
0
Noteworthy, the fact that the twisting is minimum (= 0.06-2.93 ) in the metallacyles
formed in the nickel 5,5-POCOP complexes (1b, 2a and 2b), however the torsion in the
metallacycle adjacent to the benzothiazole or benzimidazole groups is slightly larger
than the other, probably, due to the steric effect of the substituent. Furthermore, the
meta-substituents in the complexes 1b and 2a are slightly twisted out of the central
aryl moiety plane, as indicated by the dihedral angle between the corresponding
o
o
o
o
planes: 1b 6.0 /6.0 for C5-C4-C7-N1/C3-C4-C6-S and 2b 8.2 /11.4 for C5-C4-C8-
N9/C3-C4-C8-N7), while the benzimidazole-substituent in the complex 2b is twisted
o
out by more than 35 (as measured by the C5-C4-C23-N1 and C3-C4-C23-N2 dihedrals
o
o
of 36.4 and 41.5 respectively).
Table 2. Crystallographic data for 1b, 2a and 2b
Compound
1b
2a
2b
Formula
C
29
H42ClNNiO
2
P
2
S
C
25 2 2
H35ClN NiO P
2
29 2 2 2 4
C H43ClN NiO P , CH O
Formula weight
Crystal system
Space group
a (Å)
624.79
Monoclinic
P21/c
551.65
639.79
Triclinic
P-1
Monoclinic
P21/c
16.901(3)
11.935(2)
15.493(3)
90
17.1985(11)
15.1991(9)
10.8855(6)
90
7.9426(2)
b (Å)
12.3331(3)
17.1446(4)
75.000(1)
83.451(1)
84.215(1)
1607.17(7)
2
c (Å)
α (°)
β (°)
98.920(4)
90
104.680(2)
90

(°)
V (Å3)
Z
3087.4(10)
4
2752.6(3)
4

calc (g/cm3)
F(000)
T (K)
1.344
1.331
1.322
1320
1160
680
298
301
150
Crystal size / colour / shape
0.486 x 0.220 x 0.080 mm3
yellow / prism
2.16 to 27.10
/
0.339 x 0.220 x 0.048 mm3
yellow / hexanal-plate
2.35 to 29.23
/
0.397 x 0.183 x 0.091 mm3

range (°)
2.350 to 25.275
13892
No. of rflns collected
28923
68831
No. of indep rflns (Rint ) (%)
6803 [R(int) = 10.5]
7454 [R(int) = 4.6]
5794 [R(int) = 6.37]
Completeness to theta= 25.242o
99.9
99.9
99.3
(
%)
2
2
2
Refinement method
Full-matrix least-squares on F
6803 / 0 / 346
1.044
Full-matrix least-squares on F
7454 / 0 / 309
1.024
Full-matrix least-squares on F
5794 / 0 / 371
0.949
Data/restraints/parameters
2
Goodness-of-fit on F
9

New Journal of Chemistry
Page 10 of 26
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
View Article Online
= 6.64 DOI: 10.1039/D1NJ01348C
Final R índices
I>2 (I)] (%)
R indices (all data) (%)
R = 5.87, R
R = 9.85, R
w
w
= 11.03
= 12.66
R = 4.23, R
w
= 8.85
R = 3.45, R
R = 5.55, R
w
w
[
R = 7.68, R
w
= 10.37
= 7.34
2.3. Catalytic activity
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
The catalytic activity of the synthesised complexes was evaluated in the synthesis of
diarylketones by coupling of arylboronic acids and benzaldehyde derivatives. We
started the investigation evaluating the activity of all the nickel complexes (1a, 1b, 2a
and 2b) in the cross-coupling reaction of phenylboronic acid and benzaldehyde
(selected as a model reaction), using Cs
2
CO as base in either THF/acetone or
3
toluene/acetone (Table 3). Among the screened complexes, 1a and 2a were, by far,
the most efficient catalysts affording the benzophenone product in 98.5 and 96.3 %
yields (Table 3, entries 1 and 5). By comparing the effect of the benzothiazole and
benzimidazole substituents was observed that those do not have a significant
influence in the coupling efficiency, but the yields are strongly related with the steric
properties of the phosphine (entries 1, 3, 5 and 7). In this context, complexes bearing
phosphinitos with isopropyl groups are better catalysts than those with tert-butyl
substituents. Furthermore, a comparison between 1a and its related symmetric Ni-
i
POCOP pincer complex [NiCl{C
6
H
3
(OP Pr
2
)
2
}], under the optimized reaction conditions,
was made, resulting 1a (98.5 % yield) better catalyst than its symmetric analogous
25.8 % yield) (Table 3, entries 1 and 14). These outcomes disclose the unique
(
reactivity of the non-symmetric pincer complexes, however the true role of
benzothiazole and benzimidazole substituents on the aryl ring is still unclear. However
this behaviour may be related to electronic effects exerted by the heterocycle at the
meta-position overall enhancing the reactivity of this species, although we cannot rule
out potential steric effects or even discard the potential non innocent nature of the
heterocycle during the catalytic reactions. All these hypotheses will require further
theoretical and experimental (mechanistic) studies that will in turn allow us to shed
further light on the real role of the meta-substituent. On the other hand, the efficiency
of the reaction was found strongly dependent of the solvent nature, being the
toluene/acetone mixture the most suitable giving better conversions than the
THF/acetone system (Table 3, entries 1, 3, 5, 7, 11).
10

Page 11 of 26
New Journal of Chemistry
1
2
3
4
5
6
7
8
9
View Article Online
DOI: 10.1039/D1NJ01348C
Table 3. Cross-coupling reaction of phenylboric acid and benzaldehyde
a
catalysed by nickel complexes 1a, 1b, 2a and 2b.
OH
O
O
[
Ni] (1 mol%)
B
+
H
HO
Cs CO , Solvent, 8h
2
3
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
o
T( C) Yield (%)b
Entry
[Ni]
Solvent (4:1)
1
2
3
4
5
6
7
8
9
10
1
1
1
1
1a
1b
2a
2b
1a
1a
1a
Toluene/acetone
THF/acetone
Toluene/acetone
THF/acetone
Toluene/acetone
THF/acetone
Toluene/acetone
THF/acetone
Toluene/acetone R.T.
THF/acetone
Toluene/acetone
THF/acetone
80
65
80
65
80
65
80
65
98.5
75.8
67.6
33.5
96.3
70.8
78.3
39.5
ND
R.T.
50
50
80
80
ND
1
2
3*
4**
43.3
39.5
52.6
25.8
Toluene/acetone
}] Toluene/acetone
i
[NiCl{C
6
H
3
(OP Pr
2
)
2
a
Reaction conditions: phenylboronic acid (1.0 mmol), benzaldehyde (1.2 mmol), [Ni] (1 mol%),
CO (3.0 mmol) for 8 h. Yields were determined by CG-MS/ H NMR and
are the average of two independent runs. ND = Not detected. R.T.= Room
b
1
solvent (3.0 mL), Cs
2
3
temperature.*Reaction carried out at 4h (entry 13). **Reaction catalysed by the symmetric
i
pincer complex [NiCl{C
6
H
3
(OP Pr
2
)
2
}].
As is well known, cross-coupling reactions are strongly related on the base used, thus,
several bases were tested under the optimized reaction conditions using the best-
found catalyst, 1a (Table 3). The results obtained revealed that Cs
2
CO
3
affords the best
yield (Table 4, entry 6), nevertheless other bases such as SrCO
good results (Table 4, entries 3 and 4).
3
and Li
2
CO
3
also showed
Table 4. Cross-coupling reaction of phenylboric acid and
benzaldehyde catalysed by nickel complexes 1a using differnt bases.
a
OH
O
O
[
Ni]:1a (1 mol%)
B
H
+
HO
Toluene/acetone 4:1
o
Base, 8h, 80 C
Entry
Base
Yield (%)b
1
2
K
Na
2
CO
CO
3
77.7
45.0
2
3
11

New Journal of Chemistry
Page 12 of 26
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
View Article Online
DOI: 10.1039/D1NJ01348C
3
4
5
6
SrCO
Li CO
DMAP
Cs CO
3
93.6
97.2
50.0
98.5
2
3
2
3
a
Reaction conditions: phenylboronic acid (1.0 mmol), benzaldehyde (1.2 mmol), [Ni] (1 mol%),
b
1
toluene/acetone 4:1 (3.0 mL), base (3.0 mmol) for 8 h. Yields were determined by CG-MS/ H
NMR and are the average of two independent runs.
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
In order to explore the effectiveness of complex 1a, the coupling reaction was also
performed under the above reaction conditions with different catalyst loadings (Table
5
). When 1 mol % of 1a was used, benzophenone was obtained in ca. 98% yield after 8
h (entry 3). Reducing the amount of catalyst to 0.1 and 0.5 mol% (entries 1 and 2) the
reaction produced low to moderate yields of the ketone in 8 h. Consequently, the
catalyst loading of 1 mol % was used for further studies.
Table 5. Effect of catalyst 1a loading.a
OH
O
O
[Ni]:1a
B
+
HO
H
Toluene/acetone 4:1
o
Cs CO , 8h, 80 C
2
3
Entry
mol % of 1a
Yield (%)b
TOF (h-1)
1
2
3
0.1
0.5
1
43.2
66.2
98.5
54
16.6
12.3
a
Reaction conditions: phenylboronic acid (1.0 mmol), benzaldehyde (1.2 mmol), [Ni] (0.1-1
b
mol%), toluene/acetone (3.0 mL), Cs
MS/ H NMR and are the average of two independent runs.
2
CO (3.0 mmol) for 8 h. Yields were determined by CG-
3
1
Encouraged by these results, we turned our attention to extend the scope of this
reaction to a series of substituted benzaldehydes to examine their electronic and steric
effects (Table 6). Interestingly, variation of the electronic nature of the aromatic ring
had little impact on the reaction efficiency and as a result, neutral 3a along with
electron-withdrawing and electron-donating substituents at para-positions provided
the desired ketone products in moderate to excellent yields (3d, 3e, 3g-3i). On the
other hand, meta-substituted benzaldehydes (entries 3c, 3f) coupled slightly less
effectively than the corresponding para-substituted derivatives (3e, 3g). Di-substituted
aldehydes are readily tolerated, and the desired product was obtained in good yields
(
3k).
12

Page 13 of 26
New Journal of Chemistry
1
2
3
4
5
6
7
8
9
View Article Online
DOI: 10.1039/D1NJ01348C
Table 6. Cross-coupling reactions of substituted aldehydes and
a
phenylboronic acid catalysed by complex 1a.
O
OH
[Ni]:1a (1 mol%)
O
H
+
B
Toluene/acetone 4:1
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
R
HO
R
o
Cs CO , 8h, 80 C
2
3
1
2
3
O
O
O
Cl
N
b
c
b
c
b
c
3
a: ( 98.5%, 91%)
3b: ( 63.1%, 60%)
3c: ( 90.5%, 82.6)
O
O
O
F
Cl
b
c
b
c
b
c
3
d: ( 87.3%, 84%)
3e: ( 94.0%, 91%)
3f: ( 83.5%, 78.3%)
O
O
O
O
NC
b
c
b
c
b
c
3
g: ( 89.0%, 87.1%)
3h: ( 98.0%, 89.7)
3i: ( 91.9%, 87%)
O
O N
2
O
NC
NO2
b
c
b
c
3
j: ( 81.7%, 74%)
3k: ( 85.3%, 80.2%)
a
Reaction conditions: phenylboronic acid (1.0 mmol), benzaldehyde derivatives (1.2 mmol),
b
[Ni] (1-0.1 mol%), toluene/acetone (3.0 mL), Cs
2
CO (3.0 mmol) for 8 h. Yields determined by
3
1
c
CG-MS/ H NMR and are the average of two independent runs. Isolated Yields.
In addition, the scope of boronic acids was then investigated using benzaldehyde and
4
-methoxybenzaldehyde as coupling partners, Table 7. These results indicate that
hetero-aryl boronic acids, such as 3l and 3m, proceeded well and the desire coupling
products were obtained, albeit the yields decreased to 64 %, which may be owing to
the fact that heteroatom in the hetero-aryl boronic acid may deactivate the transition
metal. On the other hand, we tried to extend this strategy on aliphatic aldehydes also.
However, the results were not encouraging on these substrates.
13

New Journal of Chemistry
Page 14 of 26
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
View Article Online
DOI: 10.1039/D1NJ01348C
Table 7. Cross-coupling reactions of boronic acids with either
benzaldehyde or 4-methoxybenzaldehyde catalysed by complex 1a.
a
O
O
OH
B
[
Ni]: 1a (1 mol%)
Ar
H
+
R
R
HO
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
Ar
Toluene/acetone 4:1
Cs CO , 8h, 80 C
o
1
2
2
3
3
O
O
O
S
O
S
O
b
c
b
c
b
c
3
l: ( 64.0%, 56.8%) 3m: ( 66.0%, 61%) 3n: ( 67.0%, 64%)
O
O
O
O
O
3p: ( 88.0%, 83%)
Reaction conditions: boronic acid derivatives (1.0 mmol), benzaldehyde derivatives (1.2
b
c
b
c
3
o: ( 68.0%. 60%)
a
b
mmol), [Ni] (1 mol%), toluene/acetone (3.0 mL), Cs
2
CO (3.0 mmol) for 8 h. Yields determined
3
1
c
by CG-MS/ H NMR and are the average of two independent runs. Isolated Yields.
It is worth noting that controlled experiments showed that in the absence of catalyst
or base, no coupling reaction occurs. Furthermore, when the reactions were
conducted in the absence of acetone, only traces of diarylketone were formed and
reduction of benzaldehyde derivatives were also detected, which indicate that during
the catalysis a nickel hydride species is likely produced, therefore the use of a hydride
acceptor such as acetone was crucial to perform this reaction.
Finally, a mechanistic proposal for the synthesis of diarylketones catalysed by the Ni-
POCOP complex (1a) is illustrated in the Scheme 3. This mechanism could involve a
transmetalation step to yield (I), followed by the insertion of the aldehyde into the
aryl-nickel bond furnished an alkoxo-nickel species (II). At this stage, two competitive
mechanisms may be envisioned. The first one, include a -hydrogen-elimination to
release diarylketone (Heck-type mechanism) and a nickel hydride species (III). The
later, reacted with acetone to afford and alkoxo-nickel (IV) complex, which is suitable
for transmetalation with the boron reagent. In the second, the protonation of the
alkoxo-nickel intermediate (II) with either water or boronic acid can led to the carbinol
compound and the release of an active hydroxo-nickel species [Ni-X], followed by the
deprotonation of carbinol and the consecutive regeneration of the alkoxo-nickel (II). At
14

Page 15 of 26
New Journal of Chemistry
1
2
3
4
5
6
7
8
9
View Article Online
DOI: 10.1039/D1NJ01348C
this stage, we believe that the base plays a key role in the catalytic cycle to regenerate
the active alkoxo- and hydroxo-nickel species.
The presence of water in the reaction mechanism is proposed taking into account that
boronic acids are prone to dehydratation, resulting in the formation of boroxine and
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
water.26 Furthermore, transmetallation of organoboron compounds to alkoxo or
hydroxo complexes of palladium,[27] rhodium[16,28] or ruthenium[29] have been
described, allowing regeneration of the aryl-metal species. However, the scope and
mechanism of this catalytic reaction with Ni-POCOP complexes are still under
investigation in our laboratory and the mechanistic proposal is base on some
experimental results and literature reports.
Ar-B(OH)2
[Ni] O
O
H
IV
Transmetalation
ROB(OH)2
Ar-B(OH)2
X
ROB(OH)2
[
Ni]
H
[Ni]
[Ni] Ar
III
Transmetalation
I
b
-hydrogen
elimination
Insertion
O
O
Ar1
Ar1
H
Ar Ar1
H
Ar
[Ni] O
II
X = Cl or OH
R = iPr or H
H O
or Ar-B(OH)2
2
[Ni] X
Ar1
OH
Base
Ar
[Ni]
H
[
Ni] O
Ar Ar1 [Ni]
X
O
II
Ar Ar1
Base
H O
2
OH
Ar1
+ [Ni] OH
Ar
Scheme 3. Mechanistic proposal for the synthesis of diarylketones catalysed by the Ni-
POCOP complex.
15

New Journal of Chemistry
Page 16 of 26
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
View Article Online
DOI: 10.1039/D1NJ01348C
3
. Conclusions
A series of new non-symmetric Ni(II)-POCOP pincer complexes have been synthetized
in a facile manner in moderate to good yields (48-62%), where the main pincer
backbone is meta-functionalized with heterocyclic scaffolds (benzothiazole or
benzimidazole). All complexes were fully characterised and proved to be air, water and
thermally stable. In addition, single crystal X-ray diffraction studies of complexes 1b,
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
2
a and 2b unequivocally confirmed the tridentate coordination of the pincer ligands
producing distorted square planar geometries around the Ni(II) center. The catalytic
activity of these complexes was explored in the cross-coupling reactions of
functionalized benzaldehydes and boronic acid derivatives to produce diarylketones in
good to excellent yields, being the best catalysts those nickel complexes with less
i
steric hindered donor groups i.e. R= Pr. Noteworthy the fact that the benzothiazole
and benzimidazole substituents doesn’t seem to play any significant influence on the
catalytic activity of the complexes.
This study represents the first synthesis of substituted benzophenones from aldehydes
and arylboronic acids catalysed by Ni(II) pincer complexes. The successful use of these
Ni(II) species suggest their potential in other transformations, and thus efforts to
further explore their catalytic activity in other cross coupling reactions in currently
under development in our laboratories, as well as the exploration of the potential
biological activities of these species. These results will be disclosed in due time.
4. Experimental Section
4
.1. General considerations
Unless otherwise noted, all experiments were carried out in nitrogen atmosphere.
Solvents were purchased from Aldrich and dried under standard procedures. Solvents
0
0
were dried (THF: Na /benzophenone, toluene: Na ) and distilled under inert
atmosphere. CH Cl was dried over CaH2. All other chemicals and filter aids were
2
2
reagent grade and were used as received. Column chromatography was performed on
silica gel (Merck, 230-700 mesh). Melting points were determined on a MEL-TEMP II in
an open capillary tube. Elemental analyses were performed in a Thermo Scientific
Flash 2000 elemental analyser. NMR experiments were recorded at 300 K on Bruker
Avance 300 MHz and Varian Unity Inova 500 MHz spectrometers using TMS or residual
16

Page 17 of 26
New Journal of Chemistry
1
2
3
4
5
6
7
8
9
View Article Online
DOI: 10.1039/D1NJ01348C
proton solvents as internal standard; and H
3
PO as external standard. The deuterated
4
solvent used was CDCl
3
and DMSO-d
6
; chemical shifts (d) are quoted in ppm and
1
coupling constants in Hz.; to indicate the multiplicity of the signals of H NMR spectra,
the following abbreviations have been used: (s) singlet, (d) doublet, (t) triplet, (at)
apparent triplet, (m) multiplet, (dd) double doublet. Catalysis products were quantified
with a GC-MS Agilent 6890N chromatograph equipped with a 30 m DB-1MS Agilent
capillary column, coupled to an Agilent Technologies 5973 Mass Spectrometer
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
equipped with an Inert Mass Selective Detector and H NMR. Mass spectra were
recorded on Jeol The AccuTOF JMS-T100LC and The MStationJMS-700 spectrometers,
+
+
using DART and FAB , respectively, as ionization techniques. Reagents for ligands
preparation as well as reagents for POCOP ligands synthesis and solvents were
purchased from Sigma-Aldrich. Flash chromatography was carried out using Silica gel
6
0, (Merck 230-400 mesh). Anhydrous NiCl
2
was prepared by heating NiCl
2
·6H O
2
(Sigma-Aldrich) at 120 °C for several hours. Ligands P1 (4-(benzo[d]thiazol-2-
yl)benzene-1,3-diol) and P2 (4-(1H-benzo[d]imidazol-2-yl)benzene-1,3-diol) were
prepared according to literature procedures using materials without further
purification. Synthesis of POCOP-Ni(II) complexes was performed under N atmosphere
2
using standard Schlenk techniques. POCOP ligands were used in situ to lead the
formation of respective nickel pincer complexes.
4.2. Synthesis of Proligands P1 and P2.
4
.2.1. Synthesis of (4-(benzothiazol-2-yl)benzene-1,3-diol) (P1).
Ligand P1 was obtained by reaction of 2,4-dihidroxybenzaldehyde (1.000 g, 7.24 mmol)
and 2-aminothiophenol (0.776 mL, 7.24 mmol) in EtOH (25 mL) under reflux for 4 h.
After heating, the reaction mixture was allowed to cool to room temperature, then
concentrated in vacuo and purified by flash chromatography using silica gel and
EtOAc/Hexanes (1:3) as eluent. The final product was isolated in 62% yield as a light-
1
yellow solid (m.p.> 250 °C). H NMR (300 MHz, DMSO-d
6
): (δ) 11.80 (s, 1H, OH), 10.23
(
s, 1H, OH), 8.06 (d, 3JH-H= 9 Hz, 1HBzt), 7.96 (d, 3JH-H= 9 Hz, 1HBzt), 7.91 (d, 3JH-H= 9 Hz,
aryl), 7.48 (t, 3JH-H= 9 Hz, 1HBzt), 7.36 (t, 3JH-H= 9 Hz, 1HBzt), 6.52 (s, 1Haryl), 6.50 (d, 3JH-
H
1
13
1
H
= 9 Hz, 1Haryl). C{ H} NMR (75.5 MHz, DMSO-d
6
): (δ) 167.0 (Bzt), 162.5 (aryl), 158.0
(Aryl), 152.5 (Bzt), 133.5 (Bzt), 131.0 (aryl), 127.5 (Bzt), 125.0 (Bzt), 123.0 (Bzt), 122.0
17

New Journal of Chemistry
Page 18 of 26
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
+
Vie+w Article Online
(
Bzt), 111.0 (Aryl), 109.0 (Aryl), 103.0 (Aryl). MS m/z DART : found, 244.0 [(M+H)]
DOI: 10.1039/D1NJ01348C
-
1
(100%), calc. for C13
H
9
NO S: 243.28. FT-IR (KBr, cm ): 3437, 1615, 1457, 1217, 956,
2
756, 459.
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
4
.2.2. Synthesis of (4-(1H-benzoimidazol-2-yl)benzene-1,3-diol) (P2).
A mixture of 2,4-dihidroxybenzaldehyde (1.000 g, 7.24 mmol) and an equivalent of
NaHSO (0.760 g, 7.24 mmol) was dissolved in EtOH (25 ml) and stirred at room
3
temperature for 2h. Then, a solution of 1,2-phenylendiamine (0.782 g, 7.24 mmol) in
DMF (10 ml) was added to the mixture and refluxed for 4 h. Finally, the reaction
mixture was poured in cold water to precipitate a white powder. Ligand P2 was
purified by flash chromatography (EtOAc/Hexanes, 1:3) and isolated in 77% yield as a
1
bright-white powder (m.p.> 250 °C). H NMR (300 MHz, DMSO-d
6
): (δ) 13.12 (s, 1H,
NH) 12.95 (s, 1H, OH), 10.00 (s, 1H, OH), 7.86 (d, 3JH-H= 9 Hz, 1Haryl), 7.57 (dd, 3JH-H= 9
Hz, 4JH-H= 3 Hz, 2HBim) 7.24(dd, 3JH-H= 9 Hz, 4JH-H= 3 Hz, 2HBim,), 6.46 (dd, 3JH-H= 9 Hz, 4JH-
1
3
1
H
= 3 Hz, 1Haryl,), 6.41 (s, 1Haryl). C{ H} NMR (75.5 MHz, DMSO-d
6
): (δ) 161.1 (Aryl),
1
60.2 (Aryl), 152.8 (Bim), 141.4(Bim), 133.5 (Bim), 127.9 (Aryl), 122.9 (Bim), 117.9
+
(
Bim), 111.62 (Bim), 108.0 (Aryl), 105.0 (Aryl), 103.0 (Aryl). MS m/z DART : found,
+
-1
2
1
27.0 [(M+H)] (100%), calc. for C13
H
11
N
2
O
2
: 226.24. FT-IR (KBr, cm ): 3550, 3340,
610, 1420, 1248, 828, 718, 518.
4.3. Synthesis of Ni-POCOP pincer complexes
.3.1. Synthesis of [NiCl{C -3-C
i
4
6
H
2
7
H
4
NS-2,6-(OP Pr
2
)
2
}] (1a).
A 50 ml Schlenk flask provided with a magnetic stirring bar was charged with 100.0 mg
0.411 mmol) of proligand P1 and dissolved in THF (20 mL). To this solution was added
(
DMAP (110.4 mg, 0.904 mmol) and the resulting reaction mixture was heated at 40 °C
for 1 h. Then, chlorodiisopropylphosphine (131.0 µL, 0.822 mmol) was aggregated
dropwise to the stirring solution and refluxed for further 4 h. The resulting solution
was filtrated and evaporated under reduced pressure and the residue redissolved in
toluene (20 mL) and then NiCl (53.03 mg, 0.411 mmol) was added. The resulting
2
suspension was then set to reflux for 24 h. Finally, the reaction mixture was
concentrated in vacuo, dissolved in dichloromethane (15 mL) and purified by flash
chromatography on silica gel using dichloromethane/hexanes (1:1) as eluent. Complex
18

Page 19 of 26
New Journal of Chemistry
1
2
3
4
5
6
7
8
9
1
View Article Online
DOI: 10.1039/D1NJ01348C
1
a was isolated as a bright-yellow powder in 62% yield. H NMR (500 MHz, CDCl ): (δ)
3
8
.19 (d, 3JH-H= 9 Hz, 1Haryl), 8.01 (d, 3JH-H= 9 Hz, 1HBzt), 7.89 (d, 3JH-H= 9 Hz, 1HBzt,), 7.45
(d,3JH-H= 6 Hz, 1HBzt), 7.33 (t, 3JH-H= 6 Hz, 1HBzt,), 6.60 (d, 3JH-H= 9 Hz, 1Haryl,), 2.59 (m,
iPr, CH), 2.46 (m, 2HiPr, CH), 1.48 (td, 3JH-H= 9 Hz, 3JH-P= 6 Hz, 15HiPr, CH ), 1.37 (dd, 3JH-
): (δ) 169.5 (dd, 2JC-P= 7.2
Hz, 3JC-P= 13.0 Hz, Aryl), 164.6 (dd, 2JC-P= 6.7 Hz, 3JC-P= 14.2 Hz, Aryl), 162.9 (Bzt), 151.5
Bzt), 134.3 (Bzt), 128.1 (Aryl), 124.9 (Bzt), 124.8 (at, 2JC-P= 19.4, 20.6 Hz, Aryl), 123.2
(Bzt), 121.4 (Bzt), 120.0 (Bzt), 111.6 (d, 3JC-P= 11.9 Hz, Aryl) 105.8 (d, 3JC-P= 12.5 Hz,
2
H
3
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
= 9 Hz, 3JH-P= 6 Hz, 9HiPr, CH
). C{ H} NMR (126.6 MHz, CDCl
13
1
H
3
3
(
Aryl), 27.1(dd, JC-P= 28.4, 3JC-P= 17,) CH) 26.85 (dd, JC-P= 28.4, 3JC-P= 17), 16.5 (dd, 2JC-P
=
5.6, 4JC-P = 5.6 Hz, CH
), 16.0 (br, CH
), 15.7 (br, CH
). P{ H} NMR (201.6 MHz, CDCl
31
1
):
1
3
3
3
3
δ) 192.6 (d, P1, 2JP-P= 332 Hz), 187.5 (d, P2, 2JP-P= 332 Hz). MS m/z DART : found, 568.0
+
(
[
(M+H)]+ (30%), calc. for C25
34ClNNiO S: C, 52.80; H, 6.03; N, 2.46; S, 5.64. Found: C, 52.75; H, 6.08; N, 2.43;
H
34ClNNiO
P S, 568.70. Anal. Calcd. for 1a,
2
2
C
25
H
P
2 2
-
1
S, 5.61. FT-IR (KBr, cm ): 2921, 1596, 1241, 754, 460.
t
4
.3.2. Synthesis of [NiCl{C
6
H
2
-3-C
7
H
4
NS-2,6-(OP Bu
2
)
2
}] (1b).
An analogous procedure to that used for the synthesis of 1a was employed for the
preparation of 1b, using triethylamine (125.26 µL, 0.905 mmol) as base and di-
terbutylchlorophosphine (155.78 µl, 0.823 mmol). The product was isolated in 52%
yield as a yellow powder. X-Ray quality crystals were grown by slow diffusion of MeOH
1
(6 mL) into a saturated CH
CDCl
2
Cl
2
solution (2 mL) of compound 1b. H NMR (300 MHz,
): (δ) 8.12 (d, 3JH-H= 9 Hz, 1Haryl), 7.94 (d, 3JH-H= 6 Hz, 1HBzt), 7.81 (d, 3JH-H= 6 Hz,
Bzt), 7.37 (t, 3JH-H= 6 Hz, 1HBzt), 7.25 (t, 3JH-H= 6 Hz, 1HBzt), 6.51 (d, 3JH-H= 9 Hz, 1Haryl),
3
1
1
1
H
.47 (dd, 3JH-H= 15 Hz, 3JH-P= 24 Hz, 36HtBu, CH
). C{ H} NMR (75.5 MHz, CDCl ): (δ)
13
1
3
3
71.3 (dd, 2JC-P= 8 Hz, 3JC-P= 11 Hz, Aryl), 166.2 (dd, 2JC-P= 6 Hz, 3JC-P= 13 Hz, Aryl), 164.0
(Bzt), 152.6 (Bzt), 135.3 (Bzt), 128.9 (Aryl), 125.9 (Bzt), 125.4 (at, 2JC-P= 19.8, 22.1 Hz,
Aryl), 124.1 (Bzt), 122.4 (Bzt), 121.2 (Bzt), 112.3 (d, 3JC-P= 11.9 Hz, Aryl), 106.6 (d, 3JC-P
=
1
2.6 Hz, Aryl), 39.8-39,4 (m, CtBu), 28.3 (d, 3JC-P= 5 Hz, CH
3
), 28.0 (d, 3JC-P= 5 Hz, CH
).
3
3
1
1
): (δ) 197.5 (d, 2JP-P= 300 Hz, P1), 189.8 (d, 2JP-P= 300 Hz,
P{ H} NMR (121.6 MHz, CDCl
3
+
+
P2). MS m/z FAB : found, 624.0 [(M+H)] (60%), calc. for C29
H
42ClNNiO
2
P S: 624.81.
2
Anal. Calcd. for 1b, C29
H
42ClNNiO
2
P S: C, 55.75; H, 6.78; N, 2.24; S, 5.13. Found: C,
2
-
1
55.71; H, 6.98; N, 2.19; S, 5.03. FT-IR (KBr, cm ): 2921, 1574, 1429, 1238, 827, 538.
19

New Journal of Chemistry
Page 20 of 26
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
View Article Online
DOI: 10.1039/D1NJ01348C
i
4
.3.3. Synthesis of [NiCl{C
6
H
2
-3-C
7
H
5
N
2
-2,6-(OP Pr
2
)
2
}] (2a).
A 50 ml Schlenk flask provided with a magnetic stirring bar was charged with 100.0 mg
0.442 mmol) of proligand P2 and dissolved in THF (20 ml). To the resulting solution
(
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
DMAP (118.6, 0.973 mmol) was added and the mixture heated to 40°C for 1h. After
this time, chlorodiisopropylphosphine (140.1 µl, 0.884 mmol) was added dropwise
under stirring and further refluxed for 4h. The resulting solution was filtrated and
evaporated under reduced pressure and the residue redissolved in toluene (20 ml) and
then NiCl (57.27 mg, 0.442 mmol) added. The resulting suspension was set to reflux
2
for 24h. After the prescribed reaction time, the reaction mixture is concentrated in
vacuo and purified by flash chromatography using silica gel and
dichloromethane/hexanes (1:1) as eluent. The product was isolated in 56% yield as a
light-yellow powder. X-Ray quality crystals were grown by slow diffusion of MeOH (6
1
mL) into a saturated CH
2
Cl
2
solution (2 mL) of the pincer complex 2a. H NMR (300
MHz, CDCl
3
): (δ) 12.0 (s, NH), 8.40 (d, 3JH-H= 9 Hz, 1Haryl), 7.90 (m, 2HBim), 7.20 (m,
2
2
H
Bim), 6.50 (d, 3JH-H= 9 Hz, 1Haryl), 3.0 (m, 2HiPr, CH), 2.40 (m, 2HiPr, CH), 1.35 (tdd, 3JH-H
=
3.2, 13.5 Hz, 3JH-P= 7.1 Hz, 24HiPr, CH
). C{ H} NMR (75.5 MHz, CDCl
13
1
): (δ) 169.3 (dd,
3
3
2JC-P= 11.2 Hz, 3JC-P= 9.7 Hz, Aryl), 163.8 (dd, 2JC-P= 11.2 Hz, 3JC-P= 9.7 Hz, Aryl), 148.6
Bim), 136.8 (s, C8), 127.9 (Bim), 127.0 (Aryl), 124.8 (Bim), 124.2 (at, 2JC-P= 22.5, 22.8
(
Hz, Aryl), 122.0 (2C, Bim), 107.0 (d, 3JC-P= 10.5 Hz, Aryl), 106.3 (s, 3JC-P= 11.2 Hz, Aryl),
27.15 (dd, JC-P= 24 Hz, 3JC-P= 4 Hz, CHiPr), 26.9(dd, JC-P= 24 Hz, 3JC-P= 4.5 Hz, CHiPr), 16.45
dd, 2JC-P= 7.5, 4JC-P= 5.5 Hz, CH
), 16.0 (br, CH
), 15.6 (br, CH ). P{ H} NMR (121.6
31
1
(
3
3
3
MHz, CDCl
3
): (δ) 193.6 (d, 2JP-P= 338.0 Hz, P1), 187.5 (d, P2, 2JP-P= 338.0 Hz, P2). MS m/z
+
+
FAB : found, 551.0 [(M+H)] (100%), calc. for C25
H
35ClN
2
NiO
2
P : 551.6. Anal. Calcd. for
2
2
a, C25
H35ClN
2
NiO
2
P : C, 54.43; H, 6.40; N, 5.08. Found: C, 54.12; H, 6.28; N, 5.15. FT-IR
2
-
1
(KBr, cm ): 3389, 2920, 1583, 1257, 829, 656.
t
4
.3.4. Synthesis of [NiCl{C
A similar procedure to that of complex 2a was employed for the synthesis of complex
using triethylamine (134.68 µl, 0.973 mmol) as base and
6
H
2
-3-C
7
H
5
N
2
-2,6-(OP Bu
2
)
2
}], 2b.
1
b
chloroditertbutylphosphine (167.2 µl, 0.884 mmol). The product was isolated in 48%
yield as a yellow powder. X-Ray quality crystals were grown by slow diffusion of MeOH
20

Page 21 of 26
New Journal of Chemistry
1
2
3
4
5
6
7
8
9
1
View Article Online
DOI: 10.1039/D1NJ01348C
(
6 ml) into a saturated CH
2.0(s, NH), 8.77 (d, 3JH-H= 9 Hz, 1Haryl), 7.85 (m, 2HBim), 7.50 (m, 2HBim), 6.8 (d, 3JH-H= 9
Hz, 1Haryl,), 1.58 (dd, 3JH-H= 15 Hz, 3JH-P= 24 Hz, 27HtBu, CH ), 1.42 (dd, 3JH-H= 9 Hz, 3JH-P= 6
): (δ) 170.0 (m, 2C, Aryl), 164.4 (dd, 2JC-P
Hz, 3JC-P= 13 Hz, Aryl), 148.9 (Bim), 128.3 (Bim), 127.9 (Bim), 127.18 (Bim), 124.5 (at,
2JC-P= 22.3, 22.5 Hz, Aryl), 124.3 (Bim), 121.3 (2C, Bim), 107.0 (d, 3JC-P= 11.3 Hz, Aryl),
2
Cl
2
solution (2 ml) of 2b. H NMR (300 MHz, CDCl
3
): (δ)
1
3
1
3
1
Hz, 9HtBu, CH
3
). C{ H} NMR (75.5 MHz, CDCl
3
=
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
6
06.1 (d, 3JC-P= 11.3 Hz, Aryl), 38.6-38.3 (m, CtBu), 27.1 (d, 3JC-P= 5 Hz, CH
), 26.9 (d, 3JC-P
=
1
3
3
1
1
): (δ) 196.2 (d, P1, 2JP-P= 302 Hz), 190.0 (d,
4.5 Hz, CH
3
). P{ H} NMR (121.6 MHz, CDCl
3
P2, 2JP-P= 302.8 Hz). MS m/z FAB : found, 607.0 [(M+H)] (100%), calc. for
+
+
C
4
6
29
H43ClN
2
NiO
2
P
2
: 607.7. Anal. Calcd. for 2b, C29
H
43ClN
2
NiO
2
P : C, 57.31; H, 7.13; N,
2
-
1
.61. Found: C, 57.19; H, 7.08; N, 4.71. FT-IR (KBr, cm ): 3389, 2920, 1583, 1257, 829,
56.
4.4. Catalytic experiments.
The reactions were performed in 10 mL reaction tubes equipped with J. Young valves
and an inner magnetic stirring bar containing a mixture of the corresponding Ni-cat.
(
0.01 mmol), phenylboronic acid (1 mmol), benzaldehyde derivative (1.2 mmol), base
3 mmol) and 3 mL of solvent (toluene/acetone or THF/acetone, 4:1). The reaction
(
o
o
mixture was stirred and heated in an oil bath at 80 C or 65 C for 8h. After the
prescrived reaction times the resulting mixtures were cooled to room temperature,
evaporated to dryness followed by extraction with CH
anhydrous Na SO
2
Cl
2
(3 X 3 mL) and dried with
1
2
4
, filtered through celite, and analysed by GC-MS and H NMR. The
crude products were purified by silica gel column chromatography using ethyl
acetate/hexanes as eluent.
4.5 Crystallographic details
Yellow prisms of complexes 1b (CCDC 2062553), 2a (CCDC 2062554) and 2b (CCDC
2
062552), were grown independently from CH
2
Cl
2
/CH OH solvent systems and
3
mounted on glass fibers, and then placed on a Bruker Smart Apex II diffractometer
with a Mo-target X-ray source (λ = 0.71073Å). Complex 1b and 2a were collected at
2
98 K and complex 2b at 150 K. The detector was placed at a distance of 5.0 cm from
the crystals, frames were collected with a scan width of 0.5 in ω and an exposure time
21

New Journal of Chemistry
Page 22 of 26
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
of 10 s/frame. Frames were integrated with the Bruker SAINT software package[3V0ie]w Article Online
DOI: 10.1039/D1NJ01348C
using a narrow-frame integration algorithm. Non-systematic absences and intensity
statistics were used in monoclinic P2(1)/c space group for 1b and 2a and triclinic space
group for 2b. The structures were solved using Patterson methods using SHELXS-
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
2
014/7 program.[31] The remaining atoms were located via a few cycles of least
squares refinements and difference Fourier maps. Hydrogen atoms were input at
calculated positions and allowed to ride on the atoms to which they are attached.
Thermal parameters were refined for hydrogen atoms on the phenyl groups using a
Ueq = 1.2 Å and a Ueq = 1.5 Å for methyl groups to precedent atom in all cases. For all
complexes, the final cycle of refinement was carried out on all non-zero data using
SHELXL-2014/7.[31] Absorption correction was applied using SADABS program.[32]
5
. Supplementary information
Supplementary data for compounds 1b (CCDC 2062553), 2a (CCDC 2062554) and 2b
(CCDC 2062552) was deposited at the Cambridge Crystallographic Data Centre. Copies
of this information are available free of charge on request from The Director, CCDC, 12
Union Road, Cambridge, CB2 1EZ, UK (Fax: +44-1223-336033; e-mail
deposit@ccdc.cam.ac.uk or www: http://www.ccdc.cam.ac.uk) quoting the deposition
numbers 2062552-2062554.
6. Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal
relationship that could have appeared to influence the work reported in this paper.
7
. Acknowledgments
We would like to thank Dr. Francisco Javier Pérez Flores, Q. Eréndira García Ríos, M.Sc.
Lucia del Carmen Márquez Alonso, M.Sc. Lucero Ríos Ruiz, M.Sc. Alejandra Núñez
Pineda (CCIQS), Q. María de la Paz Orta Pérez, Q. Roció Patiño-Maya and Ph.D. Nuria
Esturau Escofet for technical assistance. A. A. C-G. would like to thank CONACYT (No.
de becario: 583187) for Ph.D. scholarship. The financial support of this research by
PAPIIT-DGAPA-UNAM (PAPIIT IN210520) and CONACYT A1-S-33933 is gratefully
acknowledged.
22

Page 23 of 26
New Journal of Chemistry
1
2
3
4
5
6
7
8
9
View Article Online
DOI: 10.1039/D1NJ01348C
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
23

New Journal of Chemistry
Page 24 of 26
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
View Article Online
DOI: 10.1039/D1NJ01348C
References
[
1] (a) Pincer Compounds: Chemistry and Applications, ed. D. Morales-Morales,
Elsevier, 2018; (b) L. González-Sebastián and D. Morales-Morales, J. Organomet.
Chem., 2019, 893, 39-51; (c) M. Asay and D. Morales-Morales, Dalton Trans.,
2015, 44, 17432-17447; (d) Pincer and Pincer-Type Complexes: Applications in
Organic Synthesis and Catalysis, ed. K. J. Szabꢀ and O. F. Wendt, Wiley-VCH,
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
2
014; (e) M. E. van der Boom and D. Milstein, Chem. Rev., 2003, 103, 1759-1792;
(f) M. Albrecht and G. van Koten, Angew. Chem. Int. Ed., 2001, 40, 3750-3781.
[2] (a) The Privileged Pincer-Metal Platform: Coordination Chemistry & Applications,
in Topics in Organometallic Chemistry, ed. G. van Koten and R. A. Gossage,
Springer, 2016. b) H. Valdés, M. A. García-Eleno, D. Canseco-González, D.
Morales-Morales, ChemCatChem 2018, 10, 3136–3172. c) D. Morales-Morales
(
Ed.), Pincer Compounds Chemistry and Applications, Elsevier, The Netherlands,
2018.
[
3] (a) E. Peris and R. H. Crabtree, Chem. Soc. Rev., 2018, 47, 1959-1968; (b) H. P.
Dijkstra, M. Q. Slagt, A. McDonald, C. A. Kruithof, R. Kreiter, A. M. Mills, M. Lutz,
A. L. Spek, W. Klopper, G. P. M. v. Klink and G. van Koten, Eur. J. Inorg. Chem.
2003, 2003, 830-838; (c) D. Morales-Morales. M. Asay, Top. Organomet. Chem.,
2
016, 54, 239-268.
[
[
4] C. J. Moulton and B. L. Shaw, J. Chem. Soc., Dalton Trans., 1976, 1020-1024.
5] (a) Z. Wang, M. R. Eberhard, C. M. Jensen, S. Matsukawa and Y. Yamamoto, J.
Organomet. Chem., 2003, 681, 189-195; (b) E. Poverenov, M. Gandelman, L. J. W.
Shimon, H. Rozenberg, Y. Ben-David and D. Milstein, Organometallics, 2005, 24,
1
082-1090; (c) N. Á. Espinosa-Jalapa, S. Hernández-Ortega, D. Morales-Morales
and R. Le Lagadec, J. Organomet. Chem. 2012, 716, 103-109; (d) D. Sole, L.
Vallverdu, X. Solans and M. Font-Bardia, Chem. Commun., 2005, 2738-2740. e) H.
Valdés, E. Rufino-Felipe, G. van Koten, D. Morales-Morales. Eur. J. Inorg. Chem.
020, 4418–4424. f) R. Favela-Mendoza, E. Rufino-Felipe, H. Valdés, R. A.
Toscano, S. Hernandez-Ortega, D. Morales-Morales. Inorg. Chim. Acta 512, 2020,
19920.
2
1
[
6] (a) H. Valdés, L. González-Sebastián and D. Morales-Morales, J. Organomet.
Chem., 2017, 845, 229-257; (b) G. Guillena, G. Rodríguez, M. Albrecht and G. van
Koten, Chem. Eur. J., 2002, 8, 5368-5376; (c) G. Rodriguez, M. Albrecht, J.
Schoenmaker, A. Ford, M. Lutz, A. L. Spek and G. van Koten, J. Am. Chem. Soc.
2
002, 124, 5127.
[7] (a) M. K. Salomón-Flores, I. J. Bazany-Rodríguez, D. Martínez-Otero, M. A. García-
Eleno, J. J. Guerra-García, D. Morales-Morales and A. Dorazco-González, Dalton
Trans., 2017, 46, 4950-4959; (b) M. A. García-Eleno, E. Padilla-Mata, F.
Estudiante-Negrete, F. Pichal-Cerda, S. Hernández-Ortega, R. A. Toscano and D.
Morales-Morales, New J. Chem., 2015, 39, 3361-3365.
[8] (a) M. A. Solano-Prado, F. Estudiante-Negrete and D. Morales-Morales,
Polyhedron, 2010, 29, 592-600; (b) E. G. Morales-Espinoza, R. Coronel-García, H.
Valdés, R. Reyes-Martínez, J. M. German-Acacio, B. A. Aguilar-Castillo, R. A.
Toscano, N. Ortiz-Pastrana and D. Morales-Morales, J. Organomet. Chem., 2018,
867, 155-160.
24

Page 25 of 26
New Journal of Chemistry
1
2
3
4
5
6
7
8
9
View Article Online
DOI: 10.1039/D1NJ01348C
[
9] a) N. Hsu, D. Cai, K. Damodaran, R. F. Gomez, J. G. Keck, E. Laborde, R. T. Lum, T.
J. Macke, G. Martin, S. R. Schow, R. J. Simon, H. O. Villar, M. M. Wick and P.
Beroza, J. Med. Chem., 2004, 47, 4875-4880. (b) K. M. Henry and C. A. Townsend,
J. Am. Chem. Soc., 2005, 127, 3300-3309. (c) M. Pecchio, P. N. Solís, J. L. López-
Pérez, Y. Vásquez, N. Rodríguez, D. Olmedo, M. Correa, A. San Feliciano and M. P.
Gupta, J. Nat. Prod., 2006, 69, 410-413. (d) Y. Deng, Y.-W. Chin, H. Chai, W. J.
Keller and A. D. Kinghorn, J. Nat. Prod., 2007, 70, 2049-2052. (e) H. S. Tae, J.
Hines, A. R. Schneekloth and C. M. Crews, Org. Lett., 2010, 12, 4308-4311. (f) T.
Itoh, T. Maemura, Y. Ohtsuka, Y. Ikari, H. Wildt, K. Hirai and H. Tomioka, Eur. J.
Org. Chem., 2004, 2004, 2991-3003. (g) D. D. Andjelkovic and V. V. Sheares,
Macromolecules, 2007, 40, 7148-7156. (H) W. Sharmoukh, K. C. Ko, C. Noh, J. Y.
Lee and S. U. Son, J. Org. Chem., 2010, 75, 6708-6711.
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
[10] A. Fürstner, D. Voigtländer, W. Schrader, D. Giebel and M. T. Reetz, Org. Lett.,
001, 3, 417-420.
11] (a) B. Xin, Y. Zhang and K. Cheng, J. Org. Chem., 2006, 71, 5725-5731; (b) R. N.
Prabhu and R. Ramesh, Tetrahedron Lett., 2017, 58, 405-409.
2
[
[
12] M. Yato, T. Ohwada and K. Shudo, J. Am. Chem. Soc., 1991, 113, 691-692.
[13] (a) S. Shi and M. Szostak, Org. Lett. 2016, 18, 5872-5875; (b) S. Shi and M.
Szostak, Chem. Eur. J., 2016, 22, 10420-10424.
14] (a) C. Qin, J. Chen, H. Wu, J. Cheng, Q. Zhang, B. Zuo, W. Su and J. Ding,
Tetrahedron Lett., 2008, 49, 1884-1888. (b) A. Pathak, C. S. Rajput, P. S. Bora and
S. Sharma, Tetrahedron Lett., 2013, 54, 2149-2150. (c) M. Kuriyama, R.
Shimazawa and R. Shirai, J. Org. Chem., 2008, 73, 1597-1600.
[
[
[
15] J. Karthikeyan, K. Parthasarathy and C.-H. Cheng, Chem. Commun., 2011, 47,
1
0461-10463.
16] (a) G. Mora, S. Darses and J.-P. Genet, Advanced Synthesis & Catalysis, 2007, 349,
1180-1184. (b) M. Pucheault, S. Darses and J.-P. Genet, J. Am. Chem. Soc., 2004,
1
26, 15356-15357.
17] H. Zheng, J. Ding, J. Chen, M. Liu, W. Gao and H. Wu, Synlett, 2011, 2011, 1626-
630.
[18] Liao, Y.-X.; Hu, Q.-S. J. Org. Chem. 2010, 75, 6986−6989.
[
1
[
19] (a) T. Fukuyama, H. Okamoto and I. Ryu, Chem. Lett., 2011, 40, 1453-1455. (b) H.
Li, Y. Xu, E. Shi, W. Wei, X. Suo and X. Wan, Chem. Commun., 2011, 47, 7880-
7
882.
[
20] C. Lei, D. Zhu, V. III. T. Tangcueco and J. S. Zhou, Org. Lett., 2019, 21, 5817-5822.
[21] (a) S. Aiello, G. Wells, E. L. Stone, H. Kadri, R. Bazzi, D. R. Bell, M. F. G. Stevens, C.
S. Matthews, T. D. Bradshaw and A. D. Westwell, J. Med. Chem., 2008, 51, 5135-
139; (b) P. J. Palmer, R. B. Trigg and J. V. Warrington, J. Med. Chem., 1971, 14,
48-251; (c) D. Loos, E. Sidoova and V. Sutoris, Molecules, 1999, 4, 81-93; (d) S.-J.
Choi, H. J. Park, S. K. Lee, S. W. Kim, G. Han and H.-Y. P. Choo, Bioorg. Med.
Chem., 2006, 14, 1229-1235; (e) A. P. Demchenko, K.-C. Tang and P.-T. Chou,
Chem. Soc. Rev., 2013, 42, 1379-1408; (f) J. J. Díaz-Mochón, G. Tourniaire and M.
Bradley, Chem. Soc. Rev., 2007, 36, 449-457.
5
2
[
22] (a) J. Stenger-Smith, I. Chakraborty and P. K. Mascharak, J. Inorg. Biochem.,
2018, 185, 80-85; (b) I. Chakraborty, M. Pinto, J. Stenger-Smith, J. Martinez-
Gonzalez and P. K. Mascharak, Polyhedron, 2019, 172, 1-7; (c) E. Rossi, A.
25

New Journal of Chemistry
Page 26 of 26
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
4
4
4
4
4
4
4
4
4
5
5
5
5
5
5
5
5
5
5
6
View Article Online
DOI: 10.1039/D1NJ01348C
Colombo, C. Dragonetti, D. Roberto, F. Demartin, M. Cocchi, P. Brulatti, V. Fattori
and J. A. G. Williams, Chem. Commun., 2012, 48, 3182-3184.
[
[
23] (a) A. Tavman and A. S. Birteksoz, Rev. Inorg. Chem., 2009, 29, 255-272; (b) S.
Murtaza, A. Abbas, K. Iftikhar, S. Shamim, M. S. Akhtar, Z. Razzaq, K. Naseem and
A. M. Elgorban, Med. Chem. Res., 2016, 25, 2860-2871; (c) V. S. Patil, V. S.
Padalkar, A. B. Tathe, V. D. Gupta and N. Sekar, J. Fluoresc., 2013, 23, 1019-1029.
24] D. Morales-Morales, R. Redon, C. Yung and C. M. Jensen, Chem. Commun., 2000,
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
619-1620.
[25] (a) A. B. Salah and D. Zargarian, Dalton Trans., 2011, 40, 8977-8985; (b) A. Salah,
M. Corpet, N. ul-Hassan Khan, D. Zargarian and D. M. Spasyuk, New J. Chem.,
2
015, 39, 6649-6658.
26] F.-X. Chen, A. Kina and T. Hayashi, Org. Lett., 2006, 8, 341-344.
[27] N. Miyaura and A. Suzuki, Chem. Rev., 1995, 95, 2457-2483.
[
[
28] T. Hayashi, M. Takahashi, Y. Takaya and M. Ogasawara, J. Am. Chem. Soc., 2002,
24, 5052-5058.
29] (a) F. Kakiuchi, S. Kan, K. Igi, N. Chatani and S. Murai, J. Am. Chem. Soc., 2003,
25, 1698-1699. (b) F. Kakiuchi, M. Usui, S. Ueno, N. Chatani and S. Murai, J. Am.
1
[
1
Chem. Soc., 2004, 126, 2706-2707
[
[
[
30] Bruker Programs: APEX3, SAINT, Bruker AXS Inc., Madison, Wisconsin, USA, 2018.
31] G. M. Sheldrick. Acta Crystallogr. C. Struct. Chem. 2015, C71, 3–8.
32] L. Krause; R. Herbst-Irmer; G. M. Sheldrick; D. J. Stalke. Appl. Crystallogr. 2015,
48, 3–10.
26