Stable ferrocenyl-NHC Pd(II) complexes: Evidence of C-H ?H/π interaction and M-O bonding in solution

Article abstract of DOI:10.1016/j.jorganchem.2017.07.038

New air stable palladium(II)-NHC complexes where carbene ligand is substituted with a bulky ferrocenylmethyl and pyranylmethyl groups viz. PdI(Phpy){FcCH₂-C₃H₂N₂-Me} (3), PdI₂{FcCH₂-C₃H₂N₂-C₆H₁₁O} (4) and PdI₂{FcCH₂-NHC}(L) (5–10) (NHC = C₃H₂N₂-Me or C₆H₁₁O; L = pyridine, imidazole and thiazole) are reported. The presence of C-H?H/π interactions has been confirmed for complex 3 by NOE interaction and multinuclear NMR experiments. In addition, for this complex, a quantum chemical analysis was performed using PM3 semi-empirical calculations to find the possible conformers. The conformation with minimal energy confirms the NMR interpretation for complex 3. The M-O bond in complex 4 was ruptured by the reaction of an extra pyridine ligand to afford PdI₂{FcCH₂-C₃H₂N₂-C₆H₁₁O}(py) (5) which was synthetized differently by reacting NHC ligand, Pd(OAc)₂ and pyridine. Molecular structure of complex 5 was determined by X-ray diffraction. The catalytic activity of these complexes was checked in Suzuki-Miyaura reaction. Complex 5 exhibits excellent conversions and selectivities (up to 99%).

Full text of DOI:10.1016/j.jorganchem.2017.07.038

Accepted Manuscript
Stable ferrocenyl-NHC Pd(II) complexes: Evidence of C-H ⋯H/π interaction and M-O
bonding in solution
Ramón Azpiroz, Pankaj Sharma, F. Javier Pérez-Flores, René Gutierrez, Georgina
Espinosa-Pérez, Francisco Lara-Ochoa
PII:
S0022-328X(17)30474-6
10.1016/j.jorganchem.2017.07.038
JOM 20052
DOI:
Reference:
To appear in: Journal of Organometallic Chemistry
Received Date: 5 June 2017
Revised Date: 25 July 2017
Accepted Date: 31 July 2017
Please cite this article as: Ramó. Azpiroz, P. Sharma, F. Javier Pérez-Flores, René. Gutierrez, G.
Espinosa-Pérez, F. Lara-Ochoa, Stable ferrocenyl-NHC Pd(II) complexes: Evidence of C-H ⋯H/π
interaction and M-O bonding in solution, Journal of Organometallic Chemistry (2017), doi: 10.1016/
j.jorganchem.2017.07.038.
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ACCEPTED MANUSCRIPT
Ramón Azpiroz, Pankaj Sharma, F.
Javier Pérez-Flores, René
Gutiérrez, Georgina Espinosa-Pérez
and Francisco Lara-Ochoa
Stable Ferrocenyl-NHC Pd(II)
Complexes: Evidence of C-H
·
··H/π Interaction and M-O
Bonding in Solution

ACCEPTED MANUSCRIPT
Stable Ferrocenyl-NHC Pd(II) Complexes: Evidence of C-H
···H/π Interaction and M-O Bonding in Solution
,
a
, a
a
b
Ramón Azpiroz,* Pankaj Sharma,* F. Javier Pérez-Flores, René Gutierrez,
a
a
Georgina Espinosa-Pérez and Francisco Lara-Ochoa
a
Instituto de Química, Universidad Nacional Autónoma de México, Ciudad Univesitaria, Circuito Exterior, Coyoacán 04510, Ciudad de
México.
Laboratorio de Síntesis de Complejos, Facultad de Ciéncias Químicas, Universidad Autónoma de Puebla, A. P. 1067, 72001, Puebla,
b
Pue., México.
*
Corresponding autor: E-mail: rayazp2@gmail.com (R. Azpiroz) and pankajshar@unam.mx (P. Sharma).
Abstract
New air stable palladium(II)-NHC complexes where carbene ligand is substituted with a bulky ferrocenylmethyl and
pyranylmethyl groups viz. PdI (Phpy){FcCH -C H N -Me} (3) PdI {FcCH -C H N -C H O} (4), and PdI {FcCH -
2
2
3
2
2
2
2
3
2
2
6
11
2
2
NHC}(L) (5-10) (NHC = CH H N -Me or C H O; L = pyridine, imidazole and thiazole) are reported. The presence of C-
3
2
2
6
11
H···H/π interactions has been confirmed for complex 3 by NOE interaction and multinuclear NMR experiments. In
addition, for this complex, a quantum chemical analysis was performed using PM3 semi-empirical calculations to find the
possible conformers. The conformation with minimal energy confirms the NMR interpretation for complex 3. The M-O
bond in complex 4 was ruptured by the reaction of an extra pyridine ligand to afford PdI {FcCH -C H N -C H O}(py)
2
2
3
2
2
6
11
2
(5) which was synthetized differently by reacting NHC ligand, Pd(OAc) and pyridine. Molecular structure of complex 5
was determined by X-ray difraction. The catalytic activity of these complexes was checked in Suzuki-Miyaura reaction.
Complex 5 exhibits excellent conversions and selectivities (up to 99%).
Keywords: Ferrocenyl-NHC Ligands • Pd complexes •Hemilabile interactions.
1
. Introduction
N-heterocyclic carbenes (NHCs) are known to be stronger σ-donors than phosphines and usually form
1
strong bonds with the majority of transition metals. These carbenes have attracted greater interests due to
their structural diversity, wide applications and their anticancer properties since Arduengo and co-workers
2
isolated the first NHC in free form. In particular, NHC-palladium complexes play a very important role in
organometallic chemistry and homogeneous catalysis due their easy access, stability and high activity
3
,4
specially in C-C or C-X (X = N, S, O, etc.) cross-coupling reactions. Recently, a large number of
mononuclear Pd-NHCs with trans geometry such as Pd-NHC-pyridine ligands known as Pd-PEPPSI
5
6
7
complexes, Pd-NHC with allyl ligands, cyclometalated Pd-NHC and Pd-(NHC) complexes have been
2
8
reported and used as potential catalysts. Other complexes containing bidentate bis-NHC ligands and a few
complexes of NHC ligands with hemilabile functional group have also been described in the literature.
9
,10
Despite the advantages that NHCs offer as ligands in palladium complexes, modification of substituents
particularly at the N-atoms with different steric and electronic properties still remains a major challenge.
Therefore, the synthesis of new Pd-NHCs with high σ-donor influence and bulky substituents seem to be a
good strategy to improve the catalytic activity and selectivity. An elegant alternative is the functionalization of
NHCs linked with ferrocenyl group, which is sterically a bulky group with particular/special requirements due
to cylindrical shape and electronically, its donor capacity stabilizes and increases the electronic properties of
1
1
12
the NHCs. Ferrocenyl-linked-NHC ligands where metallocene is bonded directly to imidazole moiety or
13
14
linked by alkylene fragments or by another spacer are known. Particularly, NHC species substituted with
ferrocenyl groups (I), ferrocenyl fragments functionalized with other groups (II) and ferrocene diamino
carbenes (III) has been described (Figure 1). However, except with the only report of Tang´s group.
1
5
16
1
7
18
ferrocenyl NHC species of type IV substituted with heterocyclic fragment on imidazolyl ring are still
unknown. This class of ligands are of great interest due to the conformational freedom that can stimulate
hemilabile or labile interactions which are necessary to promote the catalytic transformations.

ACCEPTED MANUSCRIPT
Figure 1. Representative ferrocenyl-substituted-NHC salts reported in the literature
.
In view of versatility of Pd-NHC complexes in organometallic and catalytic transformations herein, we
describe the synthesis of new functionalized NHC ligands to access stable Pd(II) species bearing hemilabile
group on the side chain and their catalytic activity in Suzuki-Miyaura cross coupling reaction.
2
. Results and Discussion
2
.1. Synthesis of imidazolium salts.
19,20
1
-substituted imidazoles (1a-1b) were prepared according to the literature procedure,
which were
reacted with N-trimethylaminomethyl ferrocenium iodide in dry CH CN to obtain their corresponding
3
21
22
ferrocenyl-NHC salts (2a-2b) (Scheme 1). FcCH -C H N -Me}I (2a) has been reported by Bildstein et all,
2
3
3
2
however {FcCH -C H N -C H O}I (2b) is unknown in the literature. The compound 2b was fully
2
3
3
2
6
11
1
characterized by multinuclear NMR and mass spectroscopy (see supporting information). In general, the H
NMR spectrum of 2a-b in CDCl at room temperature showed characteristic resonances of N-CH-N proton
3
23
approx at δ 9.9 ppm. A signal at ~δ 5.3 ppm corresponds to methylene protons and three signals for
13
1
cyclopentadienyl ring of ferrocenyl group at ~ δ 4.0-4.5 ppm were observed. C{ H} NMR spectra is in
agreement with the proposed structures.
Scheme 1. Synthesis of imidazolium salts (2a-b).
2
.2. Preparation and characterization of new Pd-NHC complexes.
These new complexes were synthesized by reacting 2a and 2b with palladium (II) acetate using an extra
nitrogenated ligand such as 2-phenylpyridine (3), pyridine (5, 6), imidazole (7, 8), and thiazole (9, 10) in the
absence of a strong base in dry CH CN. Interestingly, when 2-phenylpyridine was used as an extra ligand, an
3
air stable PdI(Phpy){FcCH
was formed as result of C-H bond activation of 2-phenylpyridine. Unfortunately, reaction of FcCH
C H N -C H O}I (2b) with Pd(OAc) and 2-phenylpyridine did not lead give the desired complex which may
2 3 2 2
-C H N -Me} (3) complex was obtained (Scheme 2). This square planar complex
3
2
-
3
3
2
6
11
2
be due to the electronic and steric differences in the structures of 2a and 2b.

ACCEPTED MANUSCRIPT
2 2 3 2 2
Scheme 2. Synthesis of PdI (Phpy){FcCH -C H N -Me} (3).
NMR spectroscopy data of 3 clearly indicated the ortho metalation of 2-phenylpyridine with palladium
13
atom. In the C NMR spectra, the most significant signal appearing at δ 154.0 ppm corresponds to Pd-C7
carbon. The signal associated to Pd-CNHC was observed at δ 171.5 ppm which is in accordance with other Pd-
7
NHC complexes reported in the literature. Interestingly, the A -B symmetry of ferrocene disappears,
2
2
displaying four signals corresponding to four protons of Fc at δ 4.46, 4.17, 4.09, and 4.08 ppm (Figure 2). This
1
13
chemical shifts were unambiguously stablished from H, C NMR spectra and supported by bidimensional
1
1
1
13
H- H COSY and H- C HMBC experiments. It is worth mentioning that complex 3 shows a remarkable
upfield shift ∆δH = 0.42 ppm for H proton of ferrocenyl group as compared to symmetric H2/5 protons of
2
corresponding ligand precursor 2a. Additionally, two doublets at δ 5.34 and 5.27 ppm (JH-H = 14.5 Hz) belong
1
3
1
1
to the diastereotopic methylene protons of Fc-CH group. C{ H} NMR spectra is in agreement with H
2
NMR, observing four chemical shifts at δ 70.0, 69.8, 68.9, and 68.5 ppm for corresponding ferrocene carbons.
2
4
25
26
An interaction with halogen atom, palladium, and C-H···H/π could be a possible reason for the restricted
rotation of cyclopentadienyl ring. However, observation of strong upfield shift of H2 proton of
cyclopentadienyl ring in the NMR spectra, suggests the presence of C-H···H/π interactions in comparison to
26
C-H···X (X= I , Pd), where downfield shift would be expected as reported earlier. In order to confirm the C-
1
1
1
H···H/π interactions, H- H NOESY and H-Sel NOE experiments were realized (Figure 2c and 2d) and NOE
interactions were observed between H proton of phenylpyridine with methylene of Fc-CH moiety, H of
8
2
2
ferrocenyl and methyl proton. Moreover, NOE interactions confirm that pyridine ligand is trans to carbene
and aromatic rings of 2-phenylpyridine are in a plane perpendicular to imidazole moiety.
1
13
1
1
1
Figure 2. Asymmetry of substituted cyclopentadienyl ring showed in (a) H NMR, (b) C NMR, (c) H- H NOESY and (d) H-Sel
NOE spectrum of complex 3 in CDCl3.
In order to validate this conformation, a quantum chemical analysis was performed for complex 3. PM3
semi-empirical calculations were used to find these conformers, where their electron density maps of H , Pd
8

ACCEPTED MANUSCRIPT
and I overlap the electron density map of H atom of cyclopentadienyl ring. Three conformers were selected
2
and their energies and potential energy surfaces were calculated using density functional methods.
2 8
The conformation with minimal energy shows an interaction between H and H with a distance of 2.610
Å. On the other hand, the optimized distance between H and Fc-CH and H-Me is 3.067 Å 3.345 Å
8
2
respectively (Conformer 1, Figure 3). Calculations of potential energy surface show that H2 of
cyclopentadienyl ring is surrounded by the aromatic electron density of 2-phenylpyridine. This can be the
1
reason that a strong upfield shift was observed for H proton in H NMR spectra and appearance of signals
2
1
1
arose from protons that are close to each other in space though they are not bonded directly, H- H NOESY
experiment.
Figure 3. a) Least energy conformer with optimized distances. b) Potential energy surface of conformer at minimum energy.
Similarly, a quantum chemical analysis was performed for two other conformers (Table 1). Conformer 2
shows an interaction between H and iodine and the calculated distance between these two atoms is 2.34 Å.
2
This conformer has a relative energy of 12.42 kcal/mol in comparison to conformer 1. Nonetheless, there is no
electron density overlapping between H and H , which is contrary to the observed NOE correlation.
2
8
Conformer 3 presents an interaction between H
2
and Pd metal and they are at a distance of 2.051 Å. However,
the relative energy of this conformer is very high (15.26 kcal/mol) with respect to the minimal energy
conformer.
a
Table 1. Energies and optimized distances calculated for conformers in study
Entry
Conformer
Energy
kcal/mol)
Distances (Å)
···I
(
H
2
···H
8
H
2
2
H ···Pd
1
2
3
1
2
3
0
2.610
5.656
4.079
4.247
2.343
3.493
6.345
3.654
2.059
12.42
15.76
a
The optimized energy and potential energy surfaces for three
conformers were calculated with DF/M06-2X/6-31G*.
In view of possible chelation of palladium by oxygen atom, 1-ferrocenylmethyl-3-methylpyranyl
imidazolium iodide ligand (2b), was reacted with Pd(OAc) in dry CH CN (Scheme 3). An air stable
2
3
2 2 3 2 2 6
PdI {FcCH -C H N -C H11O} 4, complex was formed in moderate yield (47%). On the other hand, when

ACCEPTED MANUSCRIPT
complex 4 was reacted with an extra nitrogen donor such as pyridine, a new yellow complex 5 is formed in
7
7% yield. This complex was synthesized by a different route also by the reaction of ligand 2b, Pd(OAc) and
2
o
pyridine at 80 C in a similar yield.
Scheme 3. Synthesis of complexes 4 and 5.
1
13
Interestingly, in 2D heteronuclear correlation H– C HSQC spectrum of complex 4 two resonances were
observed for two diastereotopic methylene protons linked to cyclopentadienyl ring of ferrocene and
tetrahydropyran frameworks (Figure 4a). Appearance of two resonances for ferrocenyl methylene protons (δ
5
.55 and 5.39 ppm) indicates the restricted rotation around the metal as a result of pyran ring coordination to
palladium atom. Also methylene protons attached to tetrahydropyran ring (δ 4.85 and 4.01) suggests the same.
3
These diastereotopic methylene protons correlate with corresponding Csp atoms at δ 50.0 and 55.1 ppm
respectively. Furthermore, molecular ion peak (m/z = 724) in the mass spectra of complex 4 confirm the
monomeric nature of the complex.
1
13
Figure 4. H- C HSQC in acetone-d
6
correlation spectrum showed (a) coordination of pyran fragment to palladium atom (4) and (b)
non coordination of pyran fragment (5).

ACCEPTED MANUSCRIPT
1
13
In H– C HSQC spectra of complex 5, a singlet appeared at δ 5.38 ppm can be assigned to the methylene
1
3
C-H protons linked to ferrocenyl group which correlates with a signal at δ 51.4 ppm in C NMR spectra
Figure 4b). However, methylene protons linked to pyran fragment displays two doublets at δ 4.79 and 4.01
(
13
ppm which are in correlation with the carbon atom that appeared at δ 56.6 ppm. In the C NMR spectra of
complex 5, CNHC appears at δ 143.0 ppm slightly shifted towards high field in comparison to C chemical
shift of complex 4 (δ 149.9 ppm), which is due to the coordination by oxygen atom. The H, C NMR and
heteronuclear correlation H– C HSQC reveal that the hemilabile Pd-O bond which was present in complex 4
disappears in complex 5, confirming a coordination of pyridine ligand.
NHC
13
1
1
13
Single crystals of 5 were obtained by the slow diffusion of hexane into a concentrated solution of the solid
in chloroform (Figure 5). The crystallographic independent unit of 5 displayed the pyridine ring disordered
over two positions for liberation effect. Both molecules show similar distances and angles. The metal center
presents a slightly distorted square planar geometry ({C(1)-Pd(1)-N(1), 178.4(5)° and I(1)-Pd(1)-I(2),
1
79.21(2)°}) with four coordination sites occupied by two iodine atoms, a carbene carbon atom and nitrogen
atom of pyridine ligand which is in trans position to the carbene ligand. The bond lengths and bond angles
27,28
are within the reported bond distances and angles respectively for others Pd-NHC complexes.
Figure 5. Molecular structure of 5 depicted with 50 % thermal ellipsoids. Hydrogens atoms have been omitted for clarity and of the
disordered pyridine only that at higher occupancy is shown. Selected distances (Å) and angles (°): Pd(1)-C(1), 1.971(6); Pd(1)-N(1),
.083(5); Pd(1)-I(1), 2.5953(6); Pd(I)-I(2), 2.6045(6); C(1)-N(2), 1.344(7); C(1)-N(3), 1.342(7); C(1)-Pd(1)-N(1), 178.4(5); I(1)-Pd(1)-
I(2), 179.21(2); N(2)-C(1)-N(3), 105.5(6); C(1)-N(2)-C(4), 125.2(5); N(2)-C(4)-C(5), 114.3(5); N(3)-C(15)-C(16), 115.1(3).
2
2
With the above results in hand, it was decided to synthesize a series of new square planar NHC-PdI -L
complex 6-10 derived from known Pd-PEPSI employing the ferrocenyl-NHC ligands (2a-b) and nitrogen
donors such as pyridine, imidazole and thiazole as shown in Scheme 4. These yellowish orange palladium
1
13
complexes are stable to moisture and air, which were characterized by mass spectrometry and H and
C
13
NMR spectra (see supporting information). In the C NMR spectra, the characteristic signal of carbene
carbon of Pd-CNHC bond is observed at ~ δ 143-145 ppm, which is comparable with other Pd-NHC PEPPSI
5
complexes reported in the literature.
Scheme 4. General synthesis of Pd-NHC complexes (5-10).

ACCEPTED MANUSCRIPT
2
.3. Catalytic evaluation for Suzuki-Miyaura cross coupling reaction of Pd-NHC complexes.
Catalytic activity of complexes 5-10 were also evaluated in Suzuki-Miyaura cross coupling reaction. As a
preliminary test, 4-bromobenzaldehyde and phenylboronic acid were chosen as model substrates (Table 2).
The reaction was carried out in DMF at 100 °C for 19 h with 0.5 and 1 mol % of Pd-NHC catalysts using
2 3
Na CO as a base. Initially, the influence of the nitrogen donor ligand in the Pd-NHC catalysts (6, 8, and 10)
on the conversion of the final product was studied. All the NHC-Pd complexes were very active with >95%
yield. Complex 5 shows a little better activity for the model reaction in comparison to 8 and 10 (entry 1 vs 3
and 5). Catalysts 7 and 9 exhibited moderate activity in this reaction (entries 9 and 10). As decreased catalyst
loading (0.5 mol %) does not affect the yield of the final product (entries 2, 4 and 6), the generality of the
reaction was explored with 0.5 mol% of catalyst loading is used.
Table 2. Catalyst screening for the cross-coupling reaction of phenyl boronic
a
acid and 4-bromobenzaldehyde.
[
b]
Entry
Cat
6
% mol
Conv.
100
97
1
2
3
4
5
6
7
8
9
1
0.5
1
6
8
98
8
0.5
1
95
10
10
5
97
0.5
1
94
100
99
5
0.5
1
7
87
1
0
9
1
81
a
Reaction conditions: Aryl boronic acid (1.0 mmol), aryl bromide (1.0 mmol),
Na CO (2.0 mmol), DMF (5 mL), cat. (0.5 mol%) at 100 °C for 19 h.
Determined by GC-MS.
2
3
b
The substrate scope using 5 as catalyst was evaluated for various arylbromides and arylboronic acids with
different steric and electronic properties (Table 3). Conversions up to 99% of corresponding cross-coupling
products were obtained in the reaction. Reaction with ortho and para-substituted bromo benzene exhibited
moderate to excellent reactivity (entries 6-10). In the case of electron-rich substituents at p-position such as 4-
bromotoluene and 4-bromoanisole gave good conversions with 95 and 75% yields respectively (entries 7 and
1
1). Double cross-coupling reaction is obtained when 4,4-dibromobiphenyl was reacted with 2.4 equivalents
of phenylboronic acid afforded the desired compound with good conversion (88%, entry 6). It is noteworthy
that the reaction is influenced by the bulkiness of the substituents at the ortho positions on arylbromide. The
reaction with bromobenzene substituted with a –NO group was also considered, giving the expected product
2
in excellent conversion (entry 12). The use of an electron-rich boronic acid such as 4-methoxyphenylboronic
acid gave an excellent conversion (99%) in comparison with an electron-poor arylboronic acid such as 4-
carboxyphenyl boronic acid where the expected product is not formed (entries 2 and 3).

ACCEPTED MANUSCRIPT
a
Table 3. Substrate scope for Suzuki-Miyaura cross-coupling reactions.
[b]
Entry
ArBr
ArB(OH)
2
Product
Conv.
a
Reaction conditions: Arylboronic acid (1.0 mmol), arylbromide (1.0 mmol),
CO (2.0 mmol), DMF (5 mL), 5 (0.5 mol%) at 100 °C for 19 h.
Determined by GC-MS. nr = no reaction.
Na
2
3
b
c
The catalytic activity implies that the steric influence of ferrocenyl-linked-N-heterocyclic carbene ligands
2
9,30
play an important role for the reductive elimination of the final product in a catalytic cycle.
complexes inhibit the undesired homocoupling reactions of the substrates.
These
3
. Conclusions
In summary, the synthesis of air and moisture stable palladium(II)-NHC complexes where carbene ligand is
substituted with a bulky ferrocenylmethyl group and pyranylmethyl groups are reported. These new
complexes are of type of PdI (Phpy){FcCH -C H N -Me} (3) PdI {FcCH -C H N -C H O} (4), and
2
2
3
2
2
2
2
3
2
2
6
11
2 2
PdI {FcCH -NHC}(L) (5-10) (L= pyridine, imidazole and thiazole). Solution NMR spectra of 3 and 4 showed
an interesting diastereotopic shift of methylene group linked to NHC, an evidence for restricted rotation of
NHC ligand around the metal. Particularly, in complex 3 a strong upfield shift of cyclopentadienyl ring proton
and its NOE interactions with phenylpyridine proton suggest the presence of C-H···H/C-H---π interactions. In
order to confirm this conformation, a quantum chemical analysis was performed for this complex using PM3
semi-empirical calculations to find the possible conformers. The conformation with minimal energy confirms
the NMR interpretation regarding interaction between cyclopentadienyl ring proton and phenylpyridine
proton. The M-O bond in complex 4 was ruptured by the reaction of an extra pyridine ligand to afford
PdI {FcCH -C H N -C H O}(py) (5) which was synthetized by different method also from the reaction of
2
2
3
2
2
6
11
NHC ligand, Pd(OAc)
2
and pyridine. The molecular structure of this complex was determined by X-ray

ACCEPTED MANUSCRIPT
crystallography. These new PdI {FcCH -NHC}(L) complexes were applied efficiently for the Suzuki-Miyaura
2
2
cross-coupling reaction. The complex 5 which contain pyridine ligand show better activity than other
complexes. Good catalytic activity was observed using aryl bromides substituted with electron-poor and
electron-rich groups.
4
. Experimental
4
.1. General Information.
All reactions and manipulations were carried out by using Schlenk-type techniques. Flash column
chromatography was performed on silica gel (70-230 mesh). Dimethylaminomethyl ferrocene, palladium (II)
acetate and nitrogen ligands were purchased from commercial sources and were used as received.
Trimethylaminomethyl ferrocene iodide and N-substituted imidazoles were synthetized according to the
1
8,31
1
literature.
Organic solvents were dried by standard procedures and distilled under nitrogen prior to use. H
1
3
1
and C{ H} spectra were recorded either on a Bruker 300 MHz or a Bruker Avance 500 MHz instruments.
1
13
1
Chemical shifts (expressed in parts per million) are referenced to residual solvent peaks ( H, C{ H}). All
chemical shifts (δ) are reported in ppm and coupling constants, J, are given in Hz to apparent peak
1
1
1
13
multiplications. Spectral assignments were achieved by combination of H- H COSY, and H- C
HSQC/HMBC experiments. Mass spectra were obtained using a JEOL JMS-SX102A instrument with m-
nitrobenzyl alcohol as the matrix (FAB+ mode), and a JEOL JMS-AX505-A (EI mode at 70 eV). Elemental
compositions were calculated within an uncertainty of 5 ppm by using the program installed in the computer
system. Conversions of all known organic products for Suzuki-Miyaura cross-coupling reaction were
determined by GC-MS analyses employing a Agilent Technologies 6890N coupled with JMS-GC/MS at 70
eV instruments employing a capillary column DB-1MS (0.25 mm x 0.25 mm x 30 m) and He as a carrier gas.
4
.2. General procedure for the synthesis of ferrocenylmethy-linked-NHC-ligands.
A solution of (ferrocenylmethyl)trimethylamonium iodide (2.56 g, 6.50 mmol) and the appropriate 1-
substituted imidazole derivative (7.00 mmol) in anhydrous MeCN (20 mL) at reflux for 24 h. After this
period, the cooled solution was poured into water (10 mL) and extracted with chloroform (4 x 25 mL). The
organic phase was washed with water (2 x 20 mL), dried with MgSO and evaporated to give orange oil.
4
Addition of diethyl ether (10 mL) precipitates the desired compound. The corresponding solid was collected
by filtration, washed with diethyl ether (10 mL) and dried at room temperature.
4
.3. Preparation of 1-ferrocenylmethyl-3-methyl imidazolium iodide (2a).
1
This compound was isolated as yellow solid. Yield (1.62 g, 61%). H NMR (300 MHz, CDCl , 298 K) δ
3
9
2
.90 (s, 1H, NCHN), 7.37 and 7.32 (both d, JH-H = 1.6, 2H, =CHN), 5.38 (s, 2H, Fc-CH ), 4.50 and 4.26 (both
1
3
1
d, JH-H = 2.0, 2H, H ), 4.27 (s, 5H, H ), 4.05 (s, 3H, Me). C{ H} NMR (75 MHz, CDCl , 298 K): δ 136.1
2-5
6
3
(
s, C1-im), 123.2 and 121.5 (both s, =CHN), 78.3 (s, C ), 69.9 and 69.7 (both s, C ), 68.2 (s, C ), 50.1 (s, Fc-
1 2-5 6
2
CH ), 37.1 (s, Me).
4
.4. Preparation of 1-ferrocenylmethyl-3-methylpyranyl imidazolium iodide (2b).
This compound was prepared according to the general procedure and it was isolated as orange oil. Yield
1
(
1.56 g, 49%). H NMR (300 MHz, CDCl , 298 K) δ 9.99 (s, 1H, NCHN), 7.38 and 7.17 (both s, =CHN), 5.35
3
(
s, 2H, Fc-CH ), 4.59 and 4.06 (both dt, J = 13.8, 7.5, 2H, N-CH ), 4.46 and 4.27 (both d, J = 1.9, 4H,
2
H-H
2
H-H
H
2-5), 4.26 (s, 5H, H
6
2
), 3.92 and 3.35 (both d, JH-H = 12.0, 2H, O-CH ), 3.70 (dd, JH-H = 12.0, 11.0, 1H, CHO),
1
3
1
1
1
5
1
.86, 1.67, 1.52 (all m, 6H, CH2). C{ H} NMR (75 MHz, CDCl , 298 K): δ 135.8 (s, NCHN), 123.3 and
20.6 (both s, =CHN), 78.5 (s, C ), 75.4 (s, CHO), 68.3 (s, O-CH ), 69.8 and 69.6 (both s, C ), 69.2 (s, C ),
4.3 (s, N-CH
3
1
2
2-5
6
+
2 2 2
), 50.0 (s, Fc-CH ), 28.3, 25.3, and 22.4 (all s, CH ). MS (DART) m/z: 365 [M-I] , 333, 199,
+
67. HRMS (DART) m/z calcd for C H N FeO [M-I] 365.1316, found 365.1299.
20
25
2
4
.5.Preparation of PdI(Phpy){FcCH -C H N -Me} (3).
2 3 2 2

ACCEPTED MANUSCRIPT
A solution of palladium (II) acetate (41.4 mg, 0.185 mmol) in acetonitrile was treated with 1-
ferrocenylmethyl-3-methylimidazolium iodide (150 mg, 0.369 mmol) and 2-phenylpyridine (57 µL, 0.369
mmol). The solution was stirring at 80 °C for 18 h. After this period, the solvent was removed under reduce
pressure. The residue was purified by column chromatography over silica gel (70-230 mesh) with
1
dichlorometane to provide the title compound as an orange solid. Yield: 72 mg (58%). H NMR (500 MHz,
CDCl
3
, 298 K) δ 9.77 (d, JH-H = 5.6, 1H, H17), 7.80 (dd, JH-H = 8.0, 7.2, 1H, H15), 7.76 (d, JH-H = 8.0, 1H, H14),
7
.60 (d, JH-H = 7.8, 1H, H ), 7.22 (dd, J = 5.6, 7.2, 1H, H ), 7.12 (dd, J = 7.8, 7.7, 1H, H ), 6.93 (dd,
11
H-H
16
H-H
10
JH-H = 7.7, 7.5, 1H, H ), 6.92 and 6.86 (both d, J = 2.1, 2H, =CHN), 5.96 (dd, JH-H = 7.5, 1.0, 1H, H ), 5.34
9
H-H
8
and 5.27 (both d, JH-H = 14.5, 2H, Fc-CH
2
), 4.46 (m, 1H, H
5
), 4.17 and 4.09 (both m, 2H, H3-4), 4.12 (s, 5H,
1
3
1
H ), 4.08 (m, 1H, H ), 3.87 (s, 3H, Me). C{ H} NMR (75 MHz, CDCl , 298 K): δ 171.5 (s, CNHC-Pd), 164.2
6
2
3
(
s, C ), 157.4 (s, C ), 154.0 (s, C ), 146.7 (s, C ), 138.2 (s, C ), 136.7 (s, C ), 129.8 (s, C ), 124.3 (s, C ),
13
7
17
12
15
8
9
10
1
23.8 (s, C11), 122.8 (s, C16), 122.2 and 120.1 (both s, =CHN), 118.3 (s, C14), 81.2 (s, C
1
), 70.0 (s, C
5
), 69.8 (s,
C ), 68.9 and 68.5 (both s, C ), 68.8 (s, C ), 51.0 (s, Fc-CH ), 38.6 (s, Me). HRMS (FAB) m/z calcd for
2
3,4
6
2
C H N OFePdI [M]+ 666.9401, found 666.9399.
2
6
24
3
4
2 2 3 2 2 6
.6. Preparation of PdI {FcCH -C H N -C H11O} (4).
A solution of palladium (II) acetate (34.2 mg, 0.153 mmol) in acetonitrile was treated with 1-
ferrocenylmethyl-3-(tetrahydro-2H-pyran-2-ylmethyl)imidazolium iodide (150 mg, 0.305 mmol). The mixture
was stirring at 80 °C for 18 h. At the end of this period, the solvent was removed under reduce pressure. The
residue was purified by column chromatography over silica gel (70-230 mesh) with dichlorometane to provide
1
the title compound as yellow solid. Yield: 52 mg (47%). H NMR (300 MHz, CDCl , 298 K) δ 7.10 (br, 1H,
3
=
CHN), 6.74 (d, JH-H = 2.0, 1H, =CHN), 5.55 and 5.39 (both m, 2H, Fc-CH ), 4.85 and 4.01 (both m, 2H, N-
2
CH
2 6
), 4.47 and 4.23 (both d, JH-H = 2.0, 4H, H2-5), 4.32 (s, 5H, H ), 3.94 and 3.42 (both t, JH-H = 12.3, 2H, O-
13
1
CH ), 1.87, 1.54, and 1.31 (all m, CH ). C{ H} NMR (75 MHz, CDCl , 298 K): δ 149.9 (s, CNHC-Pd), 123.0
2
2
3
and 119.6 (both s, =CHN), 79.1 (s, C ), 76.1 (s, CHO), 68.9 and 67.8 (both s, C ), 67.9 (s, C ), 66.9 (s, O-
1
2-5
6
+
+
CH
2
), 55.1 (s, N-CH
2
2 2
), 50.0 (s, Fc-CH ), 28.1, 24.5, and 21.7 (all s, CH ). MS (FAB ) m/z: 724 [M] , 597,
4
69, 349. HRMS (FAB) m/z calcd for C H N OFePdI [M]+ 723.8362, found 723.8365.
20 24 2 2
4
.7. Preparation of PdI {FcCH -C H N -C H O}(py) (5).
2 2 3 2 2 6 11
A solution of palladium (II) acetate (34.2 mg, 0.153 mmol) in acetonitrile was treated with 1-
ferrocenylmethyl-3-(tetrahydro-2H-pyran-2-ylmethyl)imidazolium iodide (150 mg, 0.305 mmol) and pyridine
24 µL, 0.305 mmol). The mixture was stirring at 80 °C for 18 h. At the end, the solvent was removed under
(
reduce pressure and the residue was purified by column chromatography over silica gel (70-230 mesh) with
1
dichlorometane to provide the title compound as yellow solid. Yield: 92 mg (75%). H NMR (300 MHz,
CDCl , 298 K) δ 9.10 (d, J = 5.4, 2H, Ho-py), 7.76 (t, JH-H = 7.3, 1H, Hp-py), 7.36 (dd, JH-H = 7.3, 5.4, 2H, Hm-
3
H-H
py), 7.09 and 6.70 (both, JH-H = 1.0, 2H, =CHN), 5.38 (s, 2H, Fc-CH ), 4.79 and 4.01 (both d, J = 14.8, 2H,
2
H-H
N-CH
2 6
), 4.48 and 4.22 (both, JH-H =1.9, 4H, H2-5), 4.28 (s, 5H, H ), 4.12 (m, 1H, CHO), 3.94 and 3.44 (both d,
13
1
JH-H = 9.4, 2H, O-CH ), 1.85, 1.56, and 1.35 (all m, CH ). C{ H} NMR (75 MHz, CDCl , 298 K): δ 154.1 (s,
2
2
3
Co-py), 143.0 (s, CNHC-Pd), 137.6 (s, Cp-py), 124.5 (s, Cm-py), 123.7 and 120.3 (both s, =CHN), 80.5 (s, C ), 76.0
1
(
2
s, CHO), 70.3 and 68.9 (both s, C2-5), 69.0 (s, C
6
), 68.1 (s, O-CH
2
), 56.6 (s, N-CH
2 2
), 51.4 (s, Fc-CH ), 29.3,
+
+
5.8, and 23.0 (all s, CH ). MS (FAB ) m/z: 803 [M] , 724, 679, 597, 469, 349. HRMS (FAB) m/z calcd for
2
+
C H N OFePdI [M] 802.8784, found 802.8779.
2
5
29
3
2
4
.8. Preparation of PdI {FcCH -C H N -Me}(py) (6).
2 2 3 2 2
A solution of palladium (II) acetate (41.4 mg, 0.185 mmol) in acetonitrile was treated with 1-
ferrocenylmethyl-3-methylimidazolium iodide (150 mg, 0.369 mmol), and pyridine (29 µL, 0.369 mmol). The
mixture was stirring at 80 °C for 18 h. After this time, the solvent was removed under reduce pressure. The
residue was purified by column chromatography over silica gel (70-230 mesh) with dichlorometane to provide
1
the title compound as yellow solid. Yield: 85 mg (64%). H NMR (300 MHz, acetone-d
6
, 298 K) δ 9.08 (d, JH-
=
4.9, 2H, Ho-py), 7.97 (t, JH-H = 7.6, 1H, Hp-py), 7.55 (dd, JH-H = 7.6, 4.9, 2H, Hm-py), 7.23 and 7.03 (both d,
H
JH-H = 2.4, 2H, =CHN), 5.45 (s, 2H, Fc-CH ), 4.66 and 4.22 (both d, J = 1.9, 4H, H2-5), 4.30 (s, 5H, H6),
2
H-H
13
1
3
.93 (s, 3H, Me). C{ H} NMR (75 MHz, acetone-d
6
, 298 K): δ 153.6 (s, Co-py), 144.9 (s, CNHC-Pd), 138.3 (s,

ACCEPTED MANUSCRIPT
Cp-py), 124.6 (s, Cm-py), 123.6 and 120.9 (both s, CHN), 81.4 (s, C ), 70.4 and 68.5 (both s, C ), 68.8 (s, C ),
1
2-5
6
+
+
5
C
0.9 (s, Fc-CH ), 38.4 (s, Me). MS (FAB ) m/z: 719 [M] , 640, 512. HRMS (FAB) m/z calcd for
2
+
20
H
21
N
3
FePdI
2
[M] 718.8209, found 718.8212.
4
.9. Preparation of PdI {FcCH -C H N -C H O}(im) (7).
2
2
3
2
2
6
11
A solution of palladium (II) acetate (34.2 mg, 0.153 mmol) in acetonitrile was treated with 1-
ferrocenylmethyl-3-(tetrahydro-2H-pyran-2-ylmethyl)imidazolium iodide (150 mg, 0.305 mmol), and
imidazole (25 µL, 0.305 mmol). The mixture was stirring at 80 °C for 18 h. After this time, the solvent was
removed under reduce pressure. The residue was purified by column chromatography over silica gel (70-230
1
mesh) with dichlorometane to provide the title compound as yellow solid. Yield: 88 mg (71%). H NMR (300
MHz, CDCl
3
, 298 K) δ 8.26 (s, 1H, H1-im), 7.76 and 6.80 (both s, 1H, H3,4-im), 7.07 and 6.68 (both d, JH-H =
1
.8, 2H, =CHN), 5.34 (s, 2H, Fc-CH ), 4.77 and 3.92 (both d, J = 14.3, 2H, N-CH ), 4.45 and 4.20 (both d,
2
H-H
2
JH-H = 1.8, 4H, H ), 4.25 (s, 5H, H ), 4.06 (m, 1H, CHO), 3.92 and 3.42 (both t, J = 9.2, O-CH ), 3.70 (s,
2-5
6
H-H
2
13
1
3
2 3
H, Meim), 1.82, 1.56, and 1.30 (all m, 6H, CH ). C{ H} NMR (75 MHz, CDCl , 298 K): δ 143.5 (s, CNHC-
Pd), 142.9 (s, C1-im), 133.5 and 120.1 (both s, C3,4-im), 123.6 and 120.2 (both s, =CHN), 80.5 (s, C ), 75.9 (s,
1
CHO), 70.3 and 68.9 (both s, C ), 69.0 (s, C ), 68.10 (s, O-CH ), 56.2 (s, N-CH ), 51.0 (s, Fc-CH ), 34.1 (s,
2
-5
6
2
2
2
+
+
Meim), 29.2, 25.7, and 22.9 (all s, CH
2
). MS (FAB ) m/z: 806 [M] , 724, 679, 597, 469, 349. HRMS (FAB)
m/z calcd for C H N OFePdI [M]+ 805.8893, found 805.8907.
2
6
24
3
4
.10. Preparation of PdI {FcCH -C H N -Me}(im) (8).
2 2 3 2 2
A solution of palladium (II) acetate (41.4 mg, 0.185 mmol) in acetonitrile was treated with 1-
ferrocenylmethyl-3-methylimidazolium iodide (150 mg, 0.369 mmol), and imidazole (30 µL, 0.369 mmol).
The solution was stirring at 80 °C for 18 h. At the end of this period, the solvent was removed under reduced
pressure. The residue was purified by column chromatography over silica gel (70-230 mesh) with
1
dichlorometane to provide the title compound as orange solid. Yield: 77 mg (58%). H NMR (300 MHz,
acetone-d , 298 K) δ 8.17 (s, 1H, H1-im), 7.52 and 6.98 (both s, 3H, H3,4-im), 7.06 and 6.85 (both d, JH-H = 2.0,
6
2
H, =CHN), 5.23 (s, 2H, Fc-CH ), 4.49 and 4.08 (both d, J = 1.8, 4H,H ), 4.13 (s, 5H, H ), 3.74 (s, 3H,
2 H-H 2-5 6
1
3
1
Me), 3.72 (s, 3H, Meim). C{ H} NMR (75 MHz, acetone-d
6
, 298 K): δ 145.5 (s, CNHC-Pd), 143.0 (s, C1-im),
1
6
32.4 and 120.6 (both s, C3,4-im), 123.4 and 120.7 (both s, =CHN), 81.4 (s, C ), 70.3 and 68.4 (both s, C ),
1
2-5
+
+
8.7 (s, C ), 50.7 (s, Fc-CH ), 38.1 (s, Me), 33.4 (s, Me ). MS (FAB ) m/z: 722 [M] , 640, 512. HRMS
6
2
im
+
(
FAB) m/z calcd for C19
H
22
N
4
FePdI
2
[M] 721.8318, found 721.8329.
4
.11. Preparation of PdI
2
{FcCH -C
2
3
H
2
N
2
6
-C H11O}(tz) (9).
A solution of palladium (II) acetate (34.2 mg, 0.153 mmol) in acetonitrile was treated with 1-
ferrocenylmethyl-3-(tetrahydro-2H-pyran-2-ylmethyl)imidazolium iodide (150 mg, 0.305 mmol), and thiazole
22 µL, 0.305 mmol). The mixture was stirring 80 °C for 18 h. After, the solvent was removed under reduced
(
pressure and the residue was purified over silica gel (70-230 mesh) with dichlorometane to provide the title
1
compound as yellow solid. Yield: 73 mg (59%). H NMR (300 MHz, CDCl , 298 K) δ 9.64 (s, 1H, H1-tz), 8.64
3
(
2
(
d, JH-H = 3.5, 1H, H3-tz), 7.41 (d, JH-H = 3.5, 1H, H4-tz), 7.10 and 6.71 (both d, JH-H = 2.2, 2H, =CHN), 5.33 (s,
H, Fc-CH ), 4.77 and 3.92 (both d, JH-H = 14.8, 2H, N-CH ), 4.46 and 4.22 (both d, JH-H = 1.8, 4H, H2-5), 4.26
s, 5H, H ), 4.06 (m, 1H, CHO), 3.92 and 3.42 (both t, J = 9.1, O-CH ), 1.84, 1.57, and 1.27 (all m, 6H,
2
2
6
H-H
2
1
3
1
CH2). C{ H} NMR (75 MHz, CDCl , 298 K): δ 160.4 (s, C1-tz), 147.7 (s, C3-tz), 141.1 (s, CNHC-Pd), 123.7 (s,
3
C
4-tz), 120.4 and 118.6 (both s, =CHN), 80.3 (s, C
1 6
), 75.8 (s, CHO), 70.3 and 69.0 (both s, C2-5), 68.9 (s, C ),
+
6
8.10 (s, O-CH ), 56.4 (s, N-CH ), 51.3 (s, Fc-CH ), 29.2, 25.8, and 22.9 (all s, CH ). MS (FAB ) m/z: 724
2
2
2
2
+
+
[
M-tz] , 679, 597, 469, 349. HRMS (FAB) m/z calcd for C H N OFePdI [M-tz] 723.8362, found
20 24 2 2
7
23.8366.
4
.12. Preparation of PdI {FcCH -C H N -Me}(tz) (10).
2
2
3
2
2
A solution of palladium (II) acetate (41.4 mg, 0.185 mmol) in acetonitrile was treated with 1-
ferrocenylmethyl-3-methylimidazolium iodide (150 mg, 0.369 mmol), and tiazole (31 µL, 0.369 mmol). The
mixture was stirring at 80 °C for 18 h. After, the solvent was removed under reduced pressure and the residue

ACCEPTED MANUSCRIPT
was purified over silica gel (70-230 mesh) with dichlorometane to provide the title compound as orange solid.
1
Yield: 72 mg (54%). H NMR (300 MHz, acetone-d , 298 K) δ 9.73 (d, J = 1.5, 1H, H1-tz), 8.54 (d, JH-H
=
6
H-H
3
.5, 1H, H3-tz), 7.84 (dd, JH-H = 3.5, 1.5, 1H, H4-tz), 7.24 and 7.03 (both d, JH-H = 2.1, 2H, =CHN), 5.41 (s, 2H,
1
3
1
Fc-CH ), 4.64 and 4.22 (both d, J = 2.3, 4H, H ), 4.28 (s, 5H, H ), 3.91 (s, 3H, Me). C{ H} NMR (75
2
H-H
2-5
6
MHz, acetone-d , 298 K): δ 160.6 (s, C1-tz), 146.8 (s, C3-tz), 143.5 (s, CNHC-Pd), 123.7 and 121.1 (both s,
6
=
CHN), 119.8 (s, C4-tz), 81.3 (s, C
1
), 70.3 and 68.6 (both s, C2-5), 68.7 (s, C
6 2
), 50.8 (s, Fc-CH ), 38.3 (s, Me).
+
+
+
MS (FAB ) m/z 725 [M] , 640, 512. HRMS (FAB) m/z calcd for C H N FePdI [M-tz] 639.7787, found
1
5
16
2
2
6
39.7786.
.13. General procedure for the Suzuki-Miyaura cross-coupling reactions.
.0 mmol of halobenzene, 1.0 mmol of phenyl boronic acid, and the prescribed amount of catalyst (0.5%
4
1
mol) in 5 ml of DMF were introduced into a Schlenk tube in the open air. The tube was charged with a
magnetic stir bar and an equimolar amount of base (Na CO , 1.67 mmol), and sealed, then fully immersed in a
2
3
1
00 °C silicon oil bath. After the prescribed reaction time, the mixture was cooled to room temperature. Water
was added (20 mL). White suspension was extracted with dichloromethane (3x50 mL). The organic phase was
washed once again with water, separated and treated with anhydrous MgSO , filtered and analyzed by gas
4
chromatography (GC–MS). The results presented are the average of two runs.
4
.14. X-ray data.
Crystal data, data collection and refinement parameters for compounds 5 was collected on a Bruker Smart
APEX diffractometer equipped with an area detector and graphite monochromated Mo Kα radiation (0.71073
Å). Data reduction was carried out with the APEX2 software. The structure was solved by direct methods and
2
refined by full-matrix least-squares methods based on F using SHELXL-93 program. Non-hydrogen atoms
were refined anisotropically. H atoms were positioned geometrically and refined with isotropic displacement
parameters according the riding model. Distance and angle calculations were performed using the SHELXL-
9
1
3. Crystal data. [C25H29FeI2N3OPd], monoclinic, P 2 /n, a = 14.3896(15) Å, b = 12.1300(15) Å, c =
5.7051(17) Å, α = 90°, β = 91.119(2)°, γ = 90°, Z = 4, Mr = 803.56, V = 2740.7(5) Å3 , Dcalcd = 1.947 g
1
cm−3 , λ (Mo Kα) = 0.71073 Å, T = 298 K, µ = 3.460 mm−1 , 37923 reflections collected, the C atoms of
pyridine ring were found disordered over two positions with relative occupancies of 0.53/0.47 and N fixed,
7
991unique (Rint = 0.0570), 4476 observed, R1(Fo) = 0.0456 [I > 2σ(I)], wR2(Fo 2 ) = 0.0968 (all data).
4
.15. Computational details.
The semi-empirical PM3 method was used for structure optimization, energy calculation and
conformational energies for palladium compound. The parameters for those transition metals are based
exclusively on experimental information related to their structures. The optimized conformations were
calculated with DF/M06-2X/6-31G*- LANL2DZ. The package used in this part of the work was the
Spartan'16 Parallel Suite for Macintosh (Wavefunction, Irvine, CA, USA).
Acknowledgements
This work was supported by DGAPA-UNAM for postdoctoral fellowship (R. A.) and in the form of project
also (PAPIIT RN206615). We thank to Dr. Laura Rubio-Pérez for the valuable discussion. We also thank Luis
Velasco, M. Carmen García and R. Alfredo Toscano for the technical support.
References
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ACCEPTED MANUSCRIPT
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Highlights
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•
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New air stable palladium(II)-NHC complexes.
NHC ligand is substituted with a bulky ferrocenylmethyl and pyranylmethyl groups.
Confirmation of C-H···H/π interactions by multinuclear NMR and theoretical
studies.
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•
Rupturing of hemilabile coordination of pyrane group by other heterocyclic ligands.
Catalytic activity of these complexes was checked in Suzuki-Miyaura reaction.