Selenated NHC-Pd(II) catalyzed Suzuki-Miyaura coupling of ferrocene substituted β-chloro-cinnamaldehydes, acrylonitriles and malononitriles for the synthesis of novel ferrocene derivatives and their solvatochromic studies

Article abstract of DOI:10.1016/j.jorganchem.2021.121752

Suzuki-Miyaura coupling reaction between ferrocenyl/phenyl derivatives of (2-formyl-1-chlorovinyl)ferrocene, 3-chloro-3-ferrocenylacrylonitrile and (3-chloro-3-ferrocenylallylidene)malononitrile and arylboronic acid in the catalytic presence of a selenated NHC-Pd(II) full pincer complex was accomplished. Significantly, the couplings take place in water under normal atmospheric conditions, in contrast to many earlier reported Pd-catalysed reactions requiring inert atmosphere conditions. Solvatochromic studies of new ferrocene compounds revealed some interesting changes. Aggregation studies showed an increase of the absorbance with decrease of water content in the water/DMSO solvent mixture.

Full text of DOI:10.1016/j.jorganchem.2021.121752

Journal of Organometallic Chemistry 940 (2021) 121752
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Selenated NHC-Pd(II) catalyzed Suzuki-Miyaura coupling of ferrocene
substituted β-chloro-cinnamaldehydes, acrylonitriles and
malononitriles for the synthesis of novel ferrocene derivatives and
their solvatochromic studies
Vijesh Tomar a, Yachana Upadhyaya, Avinash K. Srivastavaa, Meena Nemiwala,∗
,
Raj K. Joshia,∗, Pradeep Mathurb,∗
a Department of Chemistry, Malaviya National Institute of Technology, Jaipur-302017, Rajasthan, India
b Department of Chemistry, Indian Institute of Technology Bombay, Powai 400076, Maharastra, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Suzuki-Miyaura coupling reaction between ferrocenyl/phenyl derivatives of (2-formyl-1-chlorovinyl)
ferrocene, 3-chloro-3-ferrocenylacrylonitrile and (3-chloro-3-ferrocenylallylidene)malononitrile and aryl-
boronic acid in the catalytic presence of a selenated NHC-Pd(II) full pincer complex was accomplished.
Significantly, the couplings take place in water under normal atmospheric conditions, in contrast to many
earlier reported Pd-catalysed reactions requiring inert atmosphere conditions. Solvatochromic studies of
new ferrocene compounds revealed some interesting changes. Aggregation studies showed an increase of
the absorbance with decrease of water content in the water/DMSO solvent mixture.
Received 30 December 2020
Revised 12 February 2021
Accepted 16 February 2021
Available online 13 March 2021
Keywords:
Suzuki-Miyura
NHC
© 2021 Elsevier B.V. All rights reserved.
Pd-full pincer complex
Ferrocene
Solvatochromism
1. Introduction
erably increases the stability of the complex under ambient condi-
tions. The N-heterocyclic carbene (NHC) based chalcogenated pin-
Cross coupling reactions have been the subject of an abundant
and fascinating history since the beginning of 19th century. In the
domain of C-C cross coupling reaction, however, the Pd based cat-
alyst continue to dominate. Several interesting transformations like
Suzuki-Miyaura and Mizoroki-Heck couplings are the important for
the laboratory and commercial synthesis [1,2]. Although, the Pd
based catalysts are well established for various catalytic applica-
tions, a majority of these catalysts require inert atmosphere and
moisture free conditions [3–5]. The issues of stability and catalytic
activities can be fine-tuned by selection of appropriate ligands.
Since, the initial reports of Shaw [6] and Noltes [7], pincer ligands
have attracted considerable attention in the last five decades as
candidates in the design of catalyst. In the last two decades, several
reviews have focused on the Pd-pincer complexes [8–20]. More re-
cently, an advancement in the pincer and bidentate ligands has
been observed which includes the use of chalcogens as one of the
donor site [21–30]. Introduction of chalcogen (a soft donor) consid-
cer ligands show improved stability, generally require low catalyst
loading, can function under ambient conditions, and importantly,
provide a combination of hard and soft donor sites [21,22]. The
ferrocene molecule continues to be much interest due to its elec-
trochemistry and incorporation in bioinorganic, polymer, medici-
nal, agrochemical and various others systems [31–35]. Ferrocene
substituted molecules have found to be used in molecular recog-
nition and sensing [33].
Compounds showing solvatochromic properties have ex-
cellent applications as sensors. Organometallic complexes,
[FeIII(CN)5imidazol]Na3 [36] and [CuII(acac)(tmen)]ClO4 [37] are
the well-known solavtochromic dyes used as scales of solvent
polarity. These complexes show positive solvatochromism, while
others such as Mo(CO)4(bipy)3 [38] and Fe(phen)2(CN)2 [39] show
negative solvatochromism which are the basis of Ek and EMLCT
polarity scales. Although there are few reports of dyes based on
ferrocene substituted organometallic compounds, those reporting
the solvatochromism and non linear optical (NLO) properties of
such molecules are rare [40]. Recently, Palanisami and co-workers
have reported a ferrocene conjugated π-acceptor malononitrile
dimer with interesting electrochemical, optical and nonlinear
optical properties [40]. The (2-formyl-1-chlorovinyl)ferrocene is
∗
Corresponding authors.
E-mail addresses: meena.chy@mnit.ac.in (M. Nemiwal), rkjoshi.chy@mnit.ac.in
(R.K. Joshi), mathur@iitb.ac.in (P. Mathur).
https://doi.org/10.1016/j.jorganchem.2021.121752
0022-328X/© 2021 Elsevier B.V. All rights reserved.

V. Tomar, Y. Upadhyay, A.K. Srivastava et al.
Journal of Organometallic Chemistry 940 (2021) 121752
a common molecule of ferrocene but the chemical reactivity of
this compound is rarely discussed in the available literature. The
transformation of (2-formyl-1-chlorovinyl)ferrocene to respective
β-ketoacetals and bis-dithianes have been reported by our group
in recent past [41,42].
In this manuscript, we wish to report a series of ferrocene
conjugated aldehyde, nitrile and malononitrile molecules which
have been synthesized by using a full pincer NHC chalcogenated
Pd(II) complex. The presented Pd(II) complex was earlier used for
Suzuki-Miyaura coupling of arylbromides [22], however, its use for
arylchloride is not reported. In the present report, the complex is
shown to be exceptionally efficient to couple the chloro-derivatives
of phenyl/ferrocenyl substituted β-chlorocinnamaldehydes, β-
chloroacrylonitrile and 3-chloroallylidinemalononitriles with vari-
ous arylboronic acids. All obtained ferrocene molecules are new
and we also report on their solvatochromic properties.
Scheme 1. Synthesis of tridentate selenated NHC ligand and Pd(II) complex.
(a) Diphenyl diselenide, NaBH4, reflux, EtOH, 15 min., N2 atm.; (b) Add 1-
(2-chloroethyl)-1H-benzoimidazole, reflux; (c) Add N-benzyl-2-chloroacetamide,
Toluene, N2 atm, reflux, 8 h; (d) Add (CH3CN)2PdCl2, DMF, N2 atm., 90 min.
Catalytic screening of Pd(II) complex for Suzuki-Miyaura reac-
tion: In the very first reaction, aqueous solution of 0.5 mmol of
(2-formyl-1- chlorovinyl)ferrocene, 2 equiv of base (K2CO3), phenyl
boronic acid (0.8 mmol) and full pincer NHC-Pd (II) complex (0.1
mmol) were refluxed with continuous monitoring of the reaction
on TLC. After 3 h, a complete consumption of reactant along with
the significant formation of the desire C-C coupled product was
observed (Scheme 3).
2. Results and Discussion
Synthesis of full pincer selenated NHC-Pd(II) Complex (1):
Full pincer selenated NHC ligand and its NHC-Pd(II) complex
(Scheme 1) were synthesized by the earlier reported known pro-
cedures [22].
The reaction was reinvestigated in the absence of NHC-Pd(II)
catalyst but no chemical transformation was observed (Table 1,
Entry 1). Then, the reaction was optimized in search of the best
suitable parameters for maximum transformation (Table 1). Ini-
tially, the amount of NHC-Pd(II) catalyst was optimized: 0.004
mmol of the catalyst produces only 13% coupling product (Table 1,
entry 2), however, yield was significantly improved to 91% with
the subsequent increase of the catalyst amount from 0.008 to
Synthesis of 3-chloro-3-ferrocenylacrylonitrile (3) and (3-
chloro-3-ferrocenylallylidene) malononitrile (4): Compounds
3
and 4 were synthesized by the thermal reaction of (2-formyl-1-
chlorovinyl)ferrocene (2) and CH3CN and CH2(CN)2 respectively
(Scheme 2).
Table 1
Optimisation of various reaction parameters.
S. No.
Pd (II) Cat. (mmol)
K2CO3 (mmol)
Temp [°C]
Time [min.]
Solvent
Yielda
%
1
–
2
110
110
110
110
110
110
110
110
110
110
110
110
50
180
180
180
180
180
180
180
180
180
180
180
180
180
180
180
180
180
30
H2O
Nd
13
37
57
74
91
90
Nd
64
Nd
76
Nd
40
60
73
91
90
20
36
54
65
76
91
90
91
90
34
Nd
71
2
0.004b
0.008b
0.010
0.016
0.020
0.030
0.020
0.020
0.020
0.020
0.020
0.020
0.020
0.020
0.020
0.020
0.020
0.020
0.020
0.020
0.020
0.020
0.020
0.020
0.020
0.020
0.020
0.020
2
H2O
3
2
H2O
4
2
H2O
5
2
H2O
6
2
H2O
7
2
H2O
8
Cs2CO3
H2O
9
K3PO4
H2O
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
KOH
H2O
DABCO
H2O
TEA
2
H2O
H2O
2
70
H2O
2
90
H2O
2
110
120
110
110
110
110
110
110
110
110
110
110
110
110
H2O
2
H2O
2
H2O
2
60
H2O
2
90
H2O
2
120
150
180
200
180
180
180
180
180
H2O
2
H2O
2
H2O
2
H2O
2
H2O
2
Toluene
1,4 dioxane
DMF
DMA
2
2
2
a
Isolated Yields,
b
Reactions performed at gram scale, (2-formyl-1-chlorovinyl) ferrocene (1 mmol), phenylboronic acid (1.6
mmol), nd (not detected).
2

V. Tomar, Y. Upadhyay, A.K. Srivastava et al.
Journal of Organometallic Chemistry 940 (2021) 121752
Scheme 2. Synthesis of 3-chloro-3-ferrocenylacrylonitrile (3) and (3-chloro-3-ferrocenylallylidene)malononitrile (4) from (2-Formyl-1-chlorovinyl)ferrocene (2)
dimethylformamide (no transformations) contrasting results were
observed.
3. Substrate Scope
Furthermore, to generalize the catalytic applicability of the
NHC-Pd(II) complex towards the range of arylboronic acids and
Scheme 3. NHC-Pd(II) mediated Suzuki-Miyaura C-C cross coupling reaction
various functionalized phenyl/ferrocenyl-chlorovinyl derivatives, a
vast substrate scope has been investigated. The coupling reactions
of 2 with various functionalized phenyl boronic acids lead to the
formation of desired coupling products 2a-2h.
Scheme 4. Plausible mechanism for the catalytic reaction.
0.02 mmol (Table 1, Entry 3-7). No substantial improvement in
the yield was observed on further increment of catalyst loading
(0.04 mmol). Hence, 0.02 mmol of catalyst was found to be the
ideal amount for the best transformation. Various bases were in-
vestigated to scale up the yield of transformations; 2 mmol of
K2CO3 gave 91% yield, while K3PO4 and DABCO produced the 64
and 76 % yield respectively, whereas, Cs2CO3, KOH and TEA does
not work for the present coupling reaction. To check the effect
of temperature on present coupling reaction, reactions at 50 to
120°C temperatures were investigated (Table 1, Entry 13-17) and
it was found that yield of the desired product was improved with
gradually increasing the temperature, maximum transformation of
91% was obtained at 110°C, while further increasing the reac-
tion temperature did not affect the product yield. Similar trend
was observed in the optimization of time duration of the reac-
tion; below to average yield (up to 36%) of the desired prod-
uct was obtained in initial 60 min, whereas, it improved up to
65% in next 60 minutes and stabilized at 91% in 180 minutes
(Table 1, Entry 18-23). During the solvent optimisation studies, it
was observed that whereas yield with toluene was also compa-
rable to the best yields when aqueous medium was used, and
with polar solvents, dioxane (34% yield), DMA (71% yield) and
Conditions: (2-formyl-1-chlorovinyl)ferrocene (1mmol), Boronic
acid (1.6 mmol), Catalyst (0.02 mmol), K2CO3 (2 mmol), Temp.
110°C, Time 180 min.
The best yield was obtained through the reaction between
the model substrate 2 and phenyl boronic acid (2a, 91%). Re-
actions of p-flourophenylboronic acid was found equally efficient
and produced 2b in excellent amount (87%). While, the reac-
tion with p-methylphenylboronic produced 2c with the slightly
reduced transformation (78%). The overview related to the ef-
3

V. Tomar, Y. Upadhyay, A.K. Srivastava et al.
Journal of Organometallic Chemistry 940 (2021) 121752
fect of functional groups showed the reaction was favorable with
the electron withdrawing groups. As p-bromo (2d, 84%) and p-
phenyl (2e, 81%) boronic acids were producing substantially bet-
ter transformation compared to o-methylphenyl boronic acid (2f,
72%). Exceptionally, the reaction with napthalene boronic acid
showed significantly reduced yield of 77% (2g). While a reaction
with isobutylboronic acid took a considerably longer time (48 h)
to produce reasonable yield (2h, 68%) of the desired coupling
product.
Results of coupling between 3 and phenylboronic acids are
summarized below.
Conditions: (3-chloro-3-ferrocenylallylidene)malononitrile (1
mmol), Boronic acid (1.6 mmol), Catalyst (0.02 mmol), K2CO3 (2
mmol), Temp. 110°C, Time 180 min.
Various boronic acids were further subjected to the reactions
with 4, but, no change in the trend of reactivity was observed,
the electron withdrawing groups were found to be more favor-
able for the reaction. Four different products from the reaction of
phenyl boronic acid, p-flouro, p-bromo, and p-phenyl showed sig-
nificant transformation of 88% (4a), 86% (4b), 81% (4d) and 79%
(4e). Reaction with p-methyl phenyl boronic acid and o-methyl
phenyl boronic acid was found to be a bit sluggish to produce the
76% (4c) and 72% (4g) yield of their respective products. A 76%
(4f) transformation was also recorded with bulkier napthylboronic
acid.
Conditions: 3-Chloro-3-ferrocenylacrylonitrile (1 mmol), Boronic
acid (1.6 mmol), Pd (II) Catalyst (0.02 mmol), K2CO3 (2 mmol),
Temp. 110°C, Time 180 min.
A similar trend of the reactions were obtained with compound
3, i.e. increased products yield with the electron withdrawing
functionalities. The phenylboronic acid, p-flouro phenylboronic p-
phenyl-phenylboronic acid efficiently coupled with 3 and produce
the good yield of 3a (89%), 3b (86%) and 3d (80%) respectively.
While 75% (3c) and 71% (3e) yields were obtained with the cou-
pling of p-methyl and o-methylboronic acids, however, a marginal
decrease in yield of 3f (77%,) was obtained when bulky napthyl-
boronic was used.
Lastly the scope of present coupling reaction with 3-chloro-3-
phenylacrylaldehyde (5) was investigated. However, a similar reac-
tion which is the only report [43] shows the use of Pd(PPh3)2Cl2
and Cs2CO3, but catalyst loading was very high and general scope
of the reaction was not studied. Hence, to add some diversity in
the substrate scope, p-methoxy, p-nitro and p-flouro derivatives
Substrate scope of the reaction was further extended to another
important 4(3-chloro-3-ferrocenylallylidene)malononitrile (4).
4

V. Tomar, Y. Upadhyay, A.K. Srivastava et al.
Journal of Organometallic Chemistry 940 (2021) 121752
of chloro-3-phenylacrylaldehyde were synthesized and further re-
acted with arylboronic acids.
intermediate (4) reductively eliminate the desired cross coupled
product and again regenerate the active catalyst.
Solvatochromic Studies: Solvatochromic responses were studied
for four different compounds 2e, 3d, 4e and 5d. All of these
molecules were synthesized by the reaction of desired ferroce-
nated compound and the p-phenyl-phenylboronic acid. As it ap-
pears these molecules have extended conjugation and interesting
electron push and pull which may lead to get some interesting re-
sults. After the initial screening of the all four compounds in the
various solvents of different polarities interesting results has been
observed with compound 4e.
Emission spectra of compound 4e was also recorded and it
showed the emission in the range of 320 nm - 480 nm. The
effect of solvent polarity on emission spectra is also shown as
Fig. 1, a weak Solvatochromic colour was clearly observed upon
UV-radiation with increasing fluorescence intensity. Further, in UV-
Visible studies, compound 4e showed a positive solvatochromism
confirmed by red-shift with an increasing polarity of solvents
such as hexane (383nm) < ethyl acetate (387nm) < DMF (498
nm) < DMSO (501nm). However, slightly blue shifts were ob-
served in DMSO and DMF solvents, moreover, naked eye visible
colour change were also observed in different polar solvents. While
recording the fluorescence spectra a continuous decrease in the in-
tensity was observed with increasing the polarity of the solvent.
However, the compound 4e was showed some unprecedented peak
shifts and intensity drops in the case of chlorinated solvents (DCM
and CHCl3). The reasons for such unprecedented outcomes is yet
to explore. Further an aggregation studies were conducted in the
most favourable solvent DMSO (Fig. 2). Decreasing the quantity of
water in the DMSO, the absorbance increased continuously. There
was no increase in the absorbance up to the 40% mixture of DMSO
in water. A marginal increase in the absorbance was observed at
the 50% composition. Which further increased exponentially at 60%
composition. With further addition, a slight increase in the ab-
sorbance was recorded till 90% DMSO in water. Similarly, the flu-
orescence spectra of the same sample showed no increase in the
emission up to 60% DMSO in water. Data recorded at 70% and 80%
showed sudden increase in the emission spectra. At 90% DMSO and
water composition, an exponential rise in the emission was ob-
served. DMSO/H2O with the mixed solvents from 0% to 90% and
their fluorescence spectra has been shown in Fig. 2b.
Conditions: 3-chloro-3-phenylacrylaldehyde (1 mmol), Boronic
acid (1.6 mmol), Pd (II) Catalyst (0.02 mmol), K2CO3 (2 mmol),
Temp. 110°C, Time 180 min.
In comparison to ferrocene analogous, slightly reduced trans-
formations was obtained with the 3-chloro3-phenylaldehydes. P-
methoxyphenyl derivatives were found least active (5b, 64% yield)
while chloro-3-phenylacrylaldehyde showed the best transforma-
tion 75% of the desired coupling product 5a. With the marginal
change in the yield, p-nitro derivative yield 70% amount of
esired product (5c). Other two reactions of phenyl and p-flouro
derivatives with biphenyl boronic acid produces 73% and 71%
yields respectively of the desired Products (5d and 5e).
Mechanism: Based on the literature evidences [44–46], a plau-
sible reaction mechanism has been proposed and depicted as
Scheme 4. It is expected that the added Pd(II) complex 1 is itself
a active form of the catalyst in the reaction media and it under-
goes oxidative addition with the ferrocene reactant to produce an
intermediate (2). In the presence of base, intermediate (2) react
with boronic acids to produce an intermediate (3), which rearrange
via Cis-Trans isomerisation to produce an intermediate (4). Finally,
Fig. 1. Solvatochromic responses of compound 4e (a) UV-visible spectra of compound 4e in different solvents (2 mL, 7.5 × 10−5 M 1850μL DMSO, inset shows colour change
observed in different polar solvents) (b) Fluorescence spectral changes of 4e with various solvents (2 mL, 2.5 × 10−5 M 1850μL DMSO).
5

V. Tomar, Y. Upadhyay, A.K. Srivastava et al.
Journal of Organometallic Chemistry 940 (2021) 121752
Fig. 2. (a) Naked eye visible colour change and their absorption spectra (b) Vials irradiate under UV-light at 365nm containing compound 4e (7.5 × 10−5 M) in.
4. Conclusion
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