Fluxional Pd(II) NHC complexes - Synthesis, structure elucidation and catalytic studies

Article abstract of DOI:10.1016/j.jorganchem.2016.05.002

Four catalytically relevant Pd(II) complexes involving N-heterocyclic carbenes (NHCs) and bidentate N- and P-donor ligands were synthesized and characterized. The structures and conformations of the complexes were elucidated on the basis of combination of

Full text of DOI:10.1016/j.jorganchem.2016.05.002

Accepted Manuscript
Fluxional Pd(II) NHC complexes – Synthesis, structure elucidation and catalytic
studies
Miroslav Dangalov, Malinka Stoyanova, Petar Petrov, Martin Putala, Nikolay G.
Vassilev
PII:
S0022-328X(16)30177-2
10.1016/j.jorganchem.2016.05.002
JOM 19491
DOI:
Reference:
To appear in: Journal of Organometallic Chemistry
Received Date: 5 February 2016
Revised Date: 14 April 2016
Accepted Date: 2 May 2016
Please cite this article as: M. Dangalov, M. Stoyanova, P. Petrov, M. Putala, N.G. Vassilev, Fluxional
Pd(II) NHC complexes – Synthesis, structure elucidation and catalytic studies, Journal of Organometallic
Chemistry (2016), doi: 10.1016/j.jorganchem.2016.05.002.
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ACCEPTED MANUSCRIPT
Who is who? (combined DNMR and DFT approach)
P
P
Br
Br
anti,( )
syn,( )

ACCEPTED MANUSCRIPT
Fluxional Pd(II) NHC Complexes - Synthesis, Structure Elucidation
and Catalytic Studies
a
a
b
c
Miroslav Dangalov , Malinka Stoyanova , Petar Petrov , Martin Putala and Nikolay G.
Vassilev a,*
a Institute of Organic Chemistry with Center of Phytochemistry, 9, Acad. G. Bonchev Str., 1113 Sofia, Bulgaria
b Department of Organic Chemistry, Faculty of Chemistry and Pharmacy, Sofia University St. Kliment Ohridsky, 1,
James Bourchier Blvd., 1164 Sofia, Bulgaria
c Department of Organic Chemistry, Faculty of Natural Sciences, Comenius University in Bratislava, Mlynska dolina,
Ilkovičova 6, 84215 Bratislava, Slovakia
ABSTRACT: Four catalytically relevant Pd(II) complexes involving N-heterocyclic carbenes (NHCs) and bidentate
N- and P-donor ligands were synthesized and characterized. The structures and conformations of the complexes were
elucidated on the basis of combination of dynamic NMR and DFT studies. Conformational studies in respect to
hindered rotation around C-Ndonor and Pd-CNHC bonds were performed resulting in surprisingly good agreement
between the calculated and the experimental results. The results from dynamic NMR and DFT studies confirm
hindered rotation around the C-N bond in 1,3-disubstituted imidazole complexes. The fluxional behavior of P-donor
ligands includes exchange between left-handed and right-handed phosphine propellers. The catalytic studies of 1,3-
disubstituted 4,5-fused imidazole complexes produced excellent activities in Suzuki–Miyaura Reaction.
Keywords: Palladium(II), NHC complexes, dynamic NMR, DFT calculations, catalytic studies
1. Introduction
N-Heterocyclic carbenes (NHC) are state of the art ligands in organometallic chemistry [1-6] and catalysis [7-10]. The
nitrogen atoms in the heterocycle offer possibilities for tuning the ligand structure - through changes in the N
substituents, the steric demands and electronic properties of the ligand can be modified to provide complexes with
enhanced catalytic performances [11-14]. Also, various functional groups can be introduced, resulting in complexes
with wider applications [15, 16]. The introduction of a suitable donor group can lead to versatile structures in ditopic
complexes or enhanced catalytic performance of complexes with hemilabile ligands [17-22]. Potentially antibacterial
compounds have also been synthesized by the introduction of a biologically active function [23-25]. In addition,
complexes of bifunctional ligands can be immobilized or their solubilities altered by suitable functionalization to
afford recoverable catalysts [26-30].
During the last decade, numerous applications of N-heterocyclic carbenes (NHCs) as ligands in all areas of transition
metal catalysis have been found [7, 31-33]. NHCs are strong, neutral σ-donor ligands which form very stable bonds
with the majority of transition metals [7, 33]. NHC complexes also possess greater thermal stability than their
phosphane analogues, which benefits the catalyst stability. The most successful NHC cores are derived from
imidazolium and 4,5-dihydroimidazolium salts, that have bulky substituents at both nitrogen atoms [31, 34]. The
steric and electronic properties NHCs can be tuned independently, because the N-substituents, are not directly
connected to the carbene carbon atom and their influence on the electronic density of this atom is small [35, 36]. The
heterocyclic core determines the electronic properties of the carbene [37] and fusing an additional aromatic ring
provides further possibilities for fine tuning of the electronic properties of the NHCs [38].
* Corresponding author. Tel.: +359 2 9606172; fax: +359 2 8700225
E-mail: niki@orgchm.bas.bg (N. G. Vassilev)
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Recently 4-amino-3-nitro substituted 1,8-naphthalimides as potential photoactive sensors and starting compounds for
further transformations to fluorescent sensors have been reported [39]. The application of 1,8-naphthalimide
derivatives as the photoactive units for design of optical chemosensors for metal cations and protons with different
mechanisms of analyte binding signal transduction and different receptors was recently reviewed [40]. In an ongoing
investigation on catalysis we synthesized carbene complexes based on the fluorescent naphthalimide core
connected/fused to an imidazolium salt. Since the fluxional behavior of a molecule may have a dramatic impact on the
relaxation pathways from its respective excited states, it was important to study the dynamics of these newly
synthesized compounds in details. In this study we introduce the 1,8-naphthalimides as an N substituent and as a fused
aromatics to the NHC to form catalytically relevant Pd(II) complexes with additional bidentate N- and P-donor
ligands to the metal.
Herein, we report the synthesis of novel Pd N-heterocyclic carbene complexes. Two of them, 1 and 2, (Fig. 1) are 1,3-
disubstituted imidazole NHC complexes (1,3-disubstituted), while the others two are the corresponding 1,3-
disubstituted 4,5-fused imidazole NHC complexes (4,5-fused), 3 and 4. Conformational exchanges occurred in
1
solution at rates that were intermediate on the NMR time scale. The H NMR signals of complexes 1, 2 and 4 were
broad at room temperature and therefore, it was necessary to study their NMR spectra at lower temperatures. The
NMR spectra of complex 3 were recorded at room temperature due to the presence of the single preferred conformer.
The possible conformers, exchange routes and the origin of the observed exchanged were studied by combination of
dynamic NMR and DFT calculations.
The assignment of VT NMR spectra of studied complexes is a challenging task that required combination of dynamic
NMR study and DFT calculation. Dynamic NMR study using 2D EXSY spectra provides information about the
exchange routes and the corresponding rate constants can be calculated directly from the volume integrals. The DFT
calculations of GS structures provide information about thermodynamic stability of possible conformers. Calculating
the theoretical populations and comparing them with the experimental one allows the conformers assignment. If given
NMR chemical shifts are sensitive to the exchange, comparison of DFT calculated and the experimental values can
confirm the assignment of conformers. The comparison of experimental and DFT calculated barriers can reveal the
exchange mechanism. This integrated approach, which combines methods of dynamic NMR spectroscopy and
computational chemistry was successfully applied recently for studying the structure and exchange mechanism of
ortho-diphenylphosphinobenzenecarboxamide ligands[41] and atropisomers of 2,2′-diaryl-1,1′-binaphthalenes
containing three stereogenic axes[42].
Figure 1. Complexes 1-4 (o-tol = ortho-tolyl)
2. Results and Discussion
Synthesis of complexes
The first step of synthesis of the desired 1,3-disubstituted Pd(II) NHC complexes 1 and 2 was preparation of
imidazolium salt NHC.HBr, which was synthesized from commercial 4-bromo-1,8-naphthalic anhydride (Scheme 1).
6-Bromo substituted naphthalimide II was prepared by reaction of 2,6-diisopropylaniline and 4-bromo-1,8-naphthalic
anhydride in refluxing acetic acid according the literature [43]. The naphthalimide II reacts with imidazole in the
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presence of CuI, proline-based ligand and Cs2CO3 in DMF to obtain compound III [44], which was quaternized with
3,3-dimethylallyl bromide in ethyl acetate to yield the corresponding imidazolium bromide salt (NHC.HBr).
Scheme 1. Synthesis of imidazolium bromide salt NHC.HBr, precursor of complexes 1 and 2 (R = 2,6-
diisopropylphenyl, ligand = (S)-(N-benzylpyrrolidin-2-yl)-2-methylimidazole).
The desired Pd(II) NHC complexes were synthesized in good yields using a well-established procedure (Scheme 2),
via generation of carbene in situ from the relevant imidazolium salt by a weak base in the presence of corresponding
dimeric palladacycles [45, 46].
O
R1
N
O
O
N
N
N
N
R1
R2
N
R
Br
Br
O
K2CO3 CH3CN
K2CO3 CH3CN
Ac
Ac
O
O
Cl
Cl
Pd
Pd
2
2
N
N
P
P
o-tol
o-tol
o-tol
o-tol
O
R1
O
R1
N
N
O
O
O
O
N
N
N
N
N
N
N
N
R1
R2
R1
R2
N
R
N
R
Pd Br
P
Pd Br
P
Me2N Pd Br
Me2N Pd Br
O
O
o-tol
o-tol
o-tol
o-tol
1
2
3
4
Scheme 2. Synthesis of Pd(II) NHC complexes (R = 2,6-diisopropylphenyl, R1 = n-butyl, R2 = 4-methylbenzyl, o-tol =
ortho-tolyl).
Conformations and Exchange Mechanisms of Complexes 1-4 (Fluxional Behavior and Solution Structure of
complexes 1-4)
The structures of the newly synthesized complexes 1-4 were confirmed by 1D and 2D NMR spectra. Conformational
exchanges occurred in solution at rates that were intermediate on the NMR time scale. For complexes 1, 2 and 4 the
signals were broad at room temperature and therefore, it was necessary to measure NMR spectra at lower
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temperatures. However, the spectra of complex 3 were recorded at room temperature due to the presence of a single
preferred conformer.
Four conformers are predictable for 1,3-disubstituted Pd(II) NHC complexes 1 and 2 (Scheme 3): two conformers due
1
to rotation around the C-N bond and two conformers due to rotation around C-Pd bond. The H, 13C and 31P NMR
spectra of complex 2 showed the expected four conformers, while the 1H and 13C NMR spectra of complex 1 showed
only two conformers. Therefore it can be concluded that restricted rotation around only one of the two possible bonds
occurs, while in complex 2 the inversion of phosphine helicity is responsible for additional conformers.
O
N
O
O
N
O
DG
Pd
Br
Br
Pd
DG
N
N
N
N
N
Pd
DG
Pd
=
o-tol
tol-o
P
Pd
O
N
O
O
N
O
Br
DG
Pd
N
Pd
DG
N
N
N
Br
Scheme 3. Possible exchanges in complexes 1 and 2 by rotation around C-N and C-Pd bonds.
The decrease of observed number of conformers in 4,5-fused Pd(II) NHC complexes 3 and 4 (one and two,
respectively) compared to 1,3-disubstituted Pd(II) NHC complexes 1 and 2 (two and four, respectively) can be
explained by the restricted rotation around C-N bond (Figure 2). Further this conclusion was confirmed by
comparison of experimental and DFT calculated rotational barriers around C-N and C-Pd bonds.
Figure 2. Comparison of 31P NMR spectra of complexes 2 (a) and 4 (b) in CDCl3 at 233 K. Only in the lower
spectrum signals due to rotation around C-N bond are observed.
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In Scheme 4 the potential diastereomers of complex 2 as viewed down the C-Pd-P bonds are presented. The
diastereomers are related horizontally by rotation around C-N amine bond and vertically by inversion of phosphine
helicity. The top conformers are right-handed twist (ꢀ) propellers and bottom conformers are left-handed twist (Λ)
propellers. Similar inversion of phosphine helicity is observed in the 4,5-fused Pd(II) NHC complex 4.
In order to assign the signals of conformers in NMR spectra we performed DFT and NMR shift calculations for all
possible conformers of the complexes. The study of exchange processes between the conformers was performed
1
experimentally by complete line shape analysis (CLSA) of H NMR spectra of complex 1, by 31P EXSY spectra of
complexes 2 and 4 and by DFT calculations of the rotation around the C-N and C-Pd bonds of complexes 1 and 2. The
1
ratio of isomers was determined by signal integration in H NMR spectra of complex 1 and 31P VT NMR spectra of
complexes 2 and 4 (Table 1). DFT calculated populations fit perfectly to the experimental populations of the
conformers in complexes 2 and 4, while the calculated populations in complexes 1 and 3 only predict the preferred
conformer.
P
P
Br
Br
anti,( )
syn,( )
P
P
Br
Br
anti,( )
syn,( )
Scheme 4. Potential diastereomers of complex 2 as viewed down the C-Pd-P bond. Diastereomers are related
horizontally by rotation around C-N amine bond and vertically by inversion of phosphine helicity.
Table 1. Comparison of experimental and calculated populations of the conformers.
Conformer ꢀG difference (kcal) a Calc. populations (%) a Exp. populations (%) b
1-anti
0
99.7
0.3
47
31
17
5
52.4
47.6
47
1-syn
2.5
0
2-anti,(ꢀ)
2-anti,(Λ)
2-syn,(Λ)
2-syn,(ꢀ)
3-anti
0.2
0.4
0.9
0
30
13
9
90
10
33
67
100
n.o.
33
3-syn
1.3
0.4
0
4-(ꢀ)
4-(Λ)
67
a Calculated by the DFT method at B3LYP/ECP (LanL2DZ for Pd and 6-31G* for other atoms) level of theory at 223
K for complex 1, at 213 K for complex 2 and at 243 K for complex 4.
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b Calculated by integration of experimental 1H NMR spectrum at 223 K for complex 1, by integration of 31P NMR
spectrum at 213 K for complex 2 and at 243 K for complex 4. n.o.: not observed
1
The assignment of the signals in H NMR spectra to particular conformer was confirmed by NMR shift calculations.
1
The experimental and calculated H chemical shifts of syn- and anti- conformers of complex 1 for naphthalimide
protons 4-H, 5-H and 7-H (for proton numbering see Supp. Info), which are most sensitive to exchange, are presented
1
in Table 2 and a very good agreement between the calculated and observed H chemical shifts was found. Selective
1
experimental and calculated H chemical shifts of possible conformers of complex 3 are also given in the Table 2 in
order to estimate the errors in NMR shift prediction at the chosen level of theory. The attempt to confirm the
assignment of the conformers of complexes 2 and 4 by NMR shift calculations was obstructed by the very small
1
difference in either H (Table 2) or 31P (see exp. part) chemical shifts of conformers. The difference in conformers
chemical shifts were of order of expected errors in chemical shift prediction, which prevents additional confirmation
1
of conformers assignment. The assignment of the signals in H NMR spectrum of complex 4 in aromatic region of
phosphine moiety was accomplished using 31P-1H HMBC correlation (Fig. 3).
Figure 3. 31P-1H HMBC spectrum for complex 4 in CDCl3 at 233 K, the correlation involves aromatic protons in
phosphine moiety.
Table 2. Selected experimental and calculated 1H chemical shifts using B3LYP/ECP (LanL2DZ for Pd and 6-31G(d)
for other atoms) geometries in ppm. a
Conformer
1-H
2-H
3-H
4-H
5-H
7-H
8-H
9-H
Exp./calc. Exp./calc. Exp./calc. Exp./calc.
Exp./calc.
Exp./calc.
Exp./calc. Exp./calc.
1-anti
9.33/9.35 10.11/10.07 8.30/8.19
7.98/7.75 9.17/9.07
1-syn
8.95/8.91 7.54/7.53
8.26/9.05 8.76/9.64
8.62/8.82 7.95/8.39
8.52/8.82 7.69/7.77
8.61/8.92 8.70/9.35
10.22/10.05 8.27/8.12 9.13/9.15
2-anti,(Λ)
2-syn,(Λ)
2-syn,(ꢀ)
2-anti,(ꢀ)
3-anti
3-syn
4-(ꢀ)
4-(Λ)
8.64/8.92 7.94/8.20 8.68/8.97
n.o./8.92 n.o./8.28 n.o./8.96
8.59/8.90 7.98/8.21 8.70/8.93
8.56/8.87
n.o./8.61
8.70/8.93
8.68/8.87
8.53/8.99 7.93/8.27 8.66/8.93
a
1
Experimental H NMR chemical shifts are measured at -50°C for complexes 1 and 2, -40°C for complex 4, while for
complex 3 the reported values are at room temperature. The PCM//B3LYP/ECP (LanL2DZ for Pd and 6-31G(d) for other
atoms) calculated 1H NMR chemical shifts use TMS as a reference system. n.o.: not observed
Further refinements of the assignment were based on the observed exchange peaks in the 31P EXSY spectra of
complex 2. Exchange peaks in the 31P EXSY spectrum of 2 (Fig. 4) are observed only between anti and syn
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conformers, and between (Λ) (left-handed twist) and (ꢀ) (right-handed twist) conformers, as well. This is in agreement
with the assignment of the conformers.
Figure 4. 31P EXSY spectrum of complex 2 in CDCl3 at 243 K using mixing time of 0.1 s.
It is well known that in metal complexes from the second and the third transition series, the values of vicinal coupling
constants depend strongly on the geometry and 2J(31P-M-Ltrans) > 2J(31P-M-Lcis) [47]. For the directly bound σ carbon,
the same geometric dependence of 2J(P,C) is observed, for example for organometallic chiral complexes of palladium
containing the chelate Duphos, 2J(P,C)trans = ca. 101, 2J(P,C)cis = ca. 5 Hz [48]. Therefore our experimental values for
2J(Ccarbene-Pd-P) (144.5 Hz for major conformer of complex 2 and 142.0 Hz for both conformers of complex 4) prove
the P-donor ligand's trans orientation in respect to the carbene atom.
Analysis of the variable temperature 1D 1H NMR spectra of Pd complex 1 and DFT calculations of Pd complex 1
The dynamic NMR study of Pd complex 1 was carried out in CDCl3 in the temperature range from 223 K to 328 K.
The low temperature 1H NMR spectrum of 1 exhibits two resonances for each nonequivalent proton. These resonances
correspond to two conformers with of 1.0 : 1.1 integral ratio at 223 K. The Complete Line Shape Analysis (CLSA) of
1
the aromatic protons in the range from 7.5 to 9.5 ppm was performed. The H NMR measured and fitted signals of
aromatic protons of complex 1 in CDCl3 at different temperatures and the corresponding rate constants are presented
in Fig. 5. The NOESY spectrum of complex 1 in CDCl3 at 278 K using mixing time of 1.0 s is presented on Fig. 2S
and the five exchanging pairs are clearly seen. The difference between the chemical shift of exchanging sites are in the
range between 0.1 and 1.4 ppm. They coalesce at different temperatures, thus effectively increasing the temperature
range in which the lineshape is most sensitive to the rate constant changes. Therefore it is not surprising to achieve a
very good linear dependence of the rate constants in Eyring plots, as evidenced by correlation coefficients ranging
from 0.9980 to 0.9985 (Fig. 3S, 13 rate constants in temperature range of 105 K). The activation parameters ∆S≠, ∆H≠
and ∆G≠ at T = 298.2 K are summarized in Table 3.
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Figure 5. Measured (left) and calculated (right) 1H NMR spectra of the aromatic protons in complex 1 in CDCl3 at
different temperatures and the corresponding rate constants.
Br
Br
Pd
Pd
O
N
O
N
N
=
anti-GS
syn-GS
N
N
Br
N
Pd
Pd
Br
N
anti-TS (C-N)
syn-TS (C-N)
O
N
O
O
N
O
Br
N
Pd
Pd
Br
N
syn-TS (Pd-C)
anti-TS (Pd-C)
Figure 6. The calculated ground state (GS) and transition state (TS) conformers of complex 1.
In order to find out which are the preferred stable conformers and to model the possible transition structures, DFT
calculations of Pd complex 1 were carried out. Two ground state (GS) structures and two sets of transition state (TS)
structures were localized computationally (Fig. 6). The anti-GS (Br atom is anti in respect to naphthalimide) is
energetically preferred compared to syn-GS. Therefore, the assignment of the major conformer as anti-GS and minor
as syn-GS can be made, which is in agreement with the results from NMR shift calculations for imidazole protons 4-
H, 5-H and 7-H, presented in Table 2.
For the rotation around C-N bond two TS were located: anti-TS (Pd atom is anti in respect to naphthalimide) and syn-
TS. The anti-TS is lower in energy than the syn-TS. For the rotation around C-Pd bond two TS were located, as well:
anti-TS (Br atom is anti in respect to naphthalimide) and syn-TS (Br atom is syn in respect to naphthalimide). The
anti-TS is lower in energy than the syn-TS.
The calculated rotational barriers for rotation around C-N and Pd-C bond are summarized in Table 3. There is a good
agreement between the experimental free energy and the calculated one for the C-N rotation. Therefore the observed
conformers are due to the restricted rotation around C-N bond, which is in agreement with the experimental
observations (Fig. 2).
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Table 3. Standard activation parameters for the rotational barriers of complex 1.
ꢀH≠
ꢀS≠
ꢀG≠
ꢀG≠eff
Method
(kcal mol-1) (cal K-1 mol-1) (kcal mol-1) (kcal mol-1)
Pd-C rotation: a
syn-TS (Pd-C) - anti-GS
anti-TS (Pd-C) - anti-GS
N-C rotation: a
23.2
23.0
-2.7
-4.2
24.0
24.3
23.7
syn-TS (C-N) - anti-GS
anti-TS (C-N) - anti-GS
17.4
14.5
-8.3
-8.6
19.8
17.1
17.1
NMR experiment major to minor 15.4 ± 0.3
1.6 ± 1.0
14.97 ± 0.13
Pd-C rotation: a
syn-TS (Pd-C) - syn-GS
anti-TS (Pd-C) - syn-GS
N-C rotation: a
20.9
20.8
-1.0
-2.4
21.2
21.5
20.9
syn-TS (C-N) - syn-GS
anti-TS (C-N) - syn-GS
15.1
12.3
-6.6
-6.9
17.1
14.3
14.3
NMR experiment minor to major 15.2 ± 0.4
0.6 ± 1.0
15.05 ± 0.14
a ZPE, thermal and entropy corrections are calculated at PCM//B3LYP/ECP (LanL2DZ for Pd and 6-31G* for other
atoms) level of theory for 298 K.
Analysis of the variable temperature 2D 31P EXSY NMR spectra of Pd complex 2 and DFT calculations of complex 2
The dynamic NMR study of Pd complex 2 was carried out in CDCl3 by measuring NMR spectra in the temperature
1
range of 213 K to 328 K. The low temperature H and 31P NMR spectra of 1 exhibit four resonances for every
nonequivalent nucleus. The 31P NMR resonances at 31.57, 31.28, 28.53 and 27.29 ppm correspond to four conformers
with integral ratio 1.0 : 0.44 : 0.30 : 1.56 at 213 K. In Fig. 3 the 31P EXSY spectrum of 2 in CDCl3 at 243 K using
mixing time of 0.1 s is presented. The assignment of the conformers is based on the very good agreement between
experimental and calculated populations of the conformers of complex 2 (Table 1) and by observation of exchange
peaks in the 31P EXSY spectrum of 2 (Fig. 3) only between anti and syn conformers, and only between (Λ) (left-
handed twist) and (ꢀ) (right-handed twist) conformers, as well.
The peak volume integration of 31P EXSY spectra of complex 2 in CDCl3 in the temperature region between 223 K
and 253 K was carried out and the calculated rate constants are presented in Table 4S. The activation parameters of
the studied exchanges of complex 2 are summarized in Table 5S. The Eyring plots demonstrate a very good linear
dependence of the rate constants, as evidenced by high correlation coefficients ranging from 0.9986 to 0.9999 (Fig.
5S, 7 rate constants in temperature range of 30 K).
The starting geometries for DFT studies of the four conformers of complex 2 were prepared starting from X-ray data
of Pd2(µ-OAc)2{o-CH2C6H4P(o-Tol)2}2 structure [49]. Similarly to complex 1 two GS of 2 were studied
computationally (Fig. 7). The anti-GS(∆) (Br atom is anti in respect to naphthalimide) is energetically preferred
compared to syn-GS(∆). For the rotation around C-N bond two TS were located: anti-TS (Pd atom is anti in respect to
naphthalimide) and syn-TS (Pd atom is syn in respect to naphthalimide). The anti-TS is lower in energy than the syn-
TS. For the rotation about C-Pd bond two TS were located, as well: anti-TS (Br atom is anti in respect to
naphthalimide) and syn-TS (Br atom is syn in respect to naphthalimide). The anti-TS is lower in energy than the syn-
TS.
The experimental and theoretical activation parameters for the rotational barriers of complex 2 are summarized in
Table 4. Similar to complex 1, it is clearly seen that the C-N restricted rotation is the process, which we observe in
NMR spectra. There is a good agreement between the experimental free energy and the calculated one for the C-N
rotation.
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Molecular propellers and gears as artificial molecular rotors were reviewed recently [50]. Mislow and co-workers
performed the first detailed investigation of correlated rotation in aryl propeller systems [51]. For three phenyl
propellers four ring-flip mechanisms are possible. The mechanism of correlated rotations in phosphorus analogues of
triarylmethanes were studied using iterative analysis of exchange-broadened NMR band shapes by Binsch and co-
workers [52]. The lowest energy process for P-C bond rotation in P(o-tol)3 complexes involves rotation of one ring
through the plane perpendicular to the M-P-ipso-C plane with correlated rotation of the other two rings through the
corresponding M-P-ipso-C planes [53, 54]. This two-ring-flip mechanism [55, 56] leads to complete interchange of
the o-tolyl rings. The mechanism and dynamic stereochemistry of Pd{2-CH2C6H4P(o-tol)2} propeller has not been
studied yet. The bridging bonding reduces the flexibility of 2-CH2C6H4 ring and it is difficult to predict which will be
the preferred mechanism of interconversion without detailed DFT study of all possible ring-flip mechanisms. Such
study can only be performed using enormous computer resources on a much smaller model complex and is out of the
scope of this investigation.
Figure 7. The calculated ground state (GS) and transition state (TS) conformers of complex 2. All TS in figure are
(∆) (right-handed twist) propeller structures.
Table 4. Standard activation parameters for the rotational barriers of complex 2.
ꢀH≠
ꢀS≠
ꢀG≠
ꢀG≠eff
Method
(kcal mol-1) (cal K-1 mol-1) (kcal mol-1) (kcal mol-1)
Pd-C rotation: a
syn-TS (Pd-C) - anti-GS
anti-TS (Pd-C) - anti-GS
N-C rotation: a
23.1
18.5
-6.6
-2.3
25.1
19.2
19.2
syn-TS (C-N) - anti-GS
anti-TS (C-N) - anti-GS
NMR experiment anti,(ꢀ) to syn,(ꢀ)
Pd-C rotation: a
20.2
14.8
-3.0
-5.1
21.1
16.4
16.4
13.9 ± 0.6
-4.8 ± 2.9
15.36 ± 0.07
syn-TS (Pd-C) - syn-GS
anti-TS (Pd-C) - syn-GS
N-C rotation: a
21.8
17.3
-7.7
-3.4
24.1
18.3
18.3
syn-TS (C-N) - syn-GS
anti-TS (C-N) - syn-GS
18.9
13.6
-4.0
-6.2
20.1
15.4
15.4
NMR experiment syn,(ꢀ) to anti,(ꢀ)
12.2 ± 0.6
-9.3 ± 2.6
14.99 ± 0.07
a
ZPE, thermal and entropy corrections are calculated at PCM//B3LYP/ECP (LanL2DZ for Pd and 6-31G* for other
atoms) level of theory for 298 K. All GS and TS in table are (∆) (right-handed twist) propeller structures.
10

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Analysis of the variable temperature 2D 31P EXSY NMR spectra of Pd complex 4
The dynamic NMR study of Pd complex 4 was carried out in CDCl3 in the temperature range from 233 K to 323 K.
1
The low temperature H and 31P NMR spectra of 1 exhibit two resonances for every nonequivalent nucleus. The 31P
NMR resonances at 29.70 and 28.78 ppm correspond to two conformers with 1.0 : 1.59 integral ratio at 233 K
(Similar integral ratio is observed between anti,(Λ) and anti,(ꢀ) conformers of complex 2). In the Fig. 7S the 31P
EXSY spectrum of complex 4 in CDCl3 at 233 K using mixing time of 1.3 s is presented.
The peak volume integration of 31P EXSY spectra of complex 4 in CDCl3 in the temperature region between 233 K
and 283 K was carried out and the calculated rate constants are presented in Table 5S. The activation parameters of
the studied exchanges of complex 4 are summarized in Table 7S. The Eyring plots demonstrate a very good linear
dependence of the rate constants, as evidenced by very high correlation coefficients (higher than 0.9999, Fig. 8S, 7
rate constants in temperature range of 50 K).
It is worth to note that all studied exchange barriers are in the short range between 14.0 and 15.4 kcal/mol (Tables 3,
4, 5S and 7S) thus making the assignment of NMR spectra difficult without combination of dynamic NMR study and
DFT calculation. The applied integrated approach, which combines methods of dynamic NMR spectroscopy and
1
computational chemistry, was successful in estimation the stability of conformers, in prediction of H NMR chemical
shifts and in the estimation of rotational barriers. The applied computational approach use moderate basis sets and the
B3LYP functional, which is objected to criticism because this functional do not describe pure dispersion interactions
[57]. We managed to solve the problems of assignment of conformers and reveal the exchange mechanism at the
possible reasonable computational cost.
On the other hand the fact that the studied barriers are of the same order (14.0 ÷ 15.4 kcal/mol) may be connected with
the same origin of the studied restricted fluxional motions. Similar steric factors may influence these fluxional
motions. In 1,3-nonsubstituted Pd-NHC complexes DFT calculations predict energy barriers around the Pd−NHC
bond of 3.0 and 4.9 kcal/mol [58]. In bis Pd-NHC complexes with unsymmetrical 1,3-substituents the energy barrier
around Pd−NHC bond of 17.7 kcal/mol was estimated using the coalescent method [59]. The rotational barriers of
mesityl rings around C-N bonds in Ru-NHC complexes were estimated to be in the range of 14.5 ÷ 15.5 kcal/mol
depending of solvent [60]. At the same time the rotational barrier around the C–N bond in simple N,N-dimethylaniline
has been calculated to be 5.1 kcal/mol [61]. The resonance contribution can be neglected for C-N rotation in 1,3-
disubstituted Pd(II) NHC complexes 1 and 2 since the two aromatic systems (naphthalimide and NHC) are not
coplanar. Therefore the steric hindrance that occurs between the Pd ligands and 1- and 3- substituents in NHC are
mainly responsible for the increased barriers of studied restricted fluxional motions.
Catalytic activity of complexes 3 and 4
The catalytic activity of complex 3 and 4 was studied in Suzuki-Miyaura reactions, using 4-bromoanisole and
phenylboronic acid as model reagents, due to its fertility for preparation of wide range of unsymmetrical biaryls, low
toxicity and usage of mild conditions, compared to other cross-coupling reactions. The reaction is tolerant of a wide
range of functional groups, and the nature of the initial precatalyst, solvent and base are crucial for excellent yields.
Preliminary experiments were performed with complexes 3 and 4, using low catalyst loading (0.1 mol %, Scheme 5).
Complex 3 exhibited higher activity: the yield obtained by this precatalyst was 35 % vs. 27 % for the phosphorus
counterpart 4.
Scheme 5.
11

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Complex 3 was chosen for optimization of the reaction conditions. Reactions were performed in 0.1 mmol scale. The
yields were determined using 1H NMR spectra with ferrocene as an internal standard. Solvent screening was examined
with potassium carbonate as base and representative results are summarized in Table 5. The highest yields were
obtained with dimethoxyethane/water mixture (5:1) and toluene under inert atmosphere in both cases, therefore both
of them were used for base screening.
Table 5. Solvent screening in Suzuki-Miyaura reaction.a
Entry
1
Solvent
Water
Conditions Yield (%)
argon
argon
argon
argon
argon
argon
argon
argon
air
6
8
2
DME
3
DME-H2O, 5:1
Dioxane
72
7
4
5
Dioxane-H2O, 5:1
CH3CN
42
19
10
7
6
7
CH3CN-H2O, 5:1
Isopropyl alcohol
Ethanol
8
9
7
10
11
12
Ethanol
argon
argon
argon
29
82
9
toluene
THF
a
Reaction conditions: 4-bromoanisole (0.1 mmol), phenylboronic acid (1.2 equiv.), K2CO3 (3 equiv.), complex 3
(0.033 mol%), solvent (0.6 mL), 12 h.
Due to importance of the base in Suzuki-Miyaura reaction, screening was performed using the most frequently
reported in the literature bases (Table 6). The best results were obtained in dimethoxyethane/water mixture with
potassium phosphate as base, besides toluene with potassium carbonate.
Table 6. Base screening in Suzuki-Miyaura reaction. a
Entry
Solvent
Base
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
Cs2CO3
CsF
K3PO4
Ba(OH)2
K3PO4
K3PO4
Yield (%)
1
2
3
4
5
6
7
8
9
DME-H2O, 5:1
Toluene
7
83
7
27
7
7
4
85
5
66
66
Toluene-H2O, 5:1
Еthylene glycol
DME-H2O, 5:1 b
DME-H2O, 5:1
DME-H2O, 5:1
DME-H2O, 5:1
DME-H2O, 5:1
Toluene
10
11
Toluene-H2O, 7:1
a
Reaction conditions: 4-bromoanisole (0.1 mmol), phenylboronic acid (1.2 equiv.), K2CO3 (3 equiv.), complex 3
(0.033 mol%), solvent (0.6 mL), reflux, 12 h, under argon.
b with complex 4;
12

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After reaction conditions optimization, the catalytic activity of both carbene complexes was compared once more.
Toluene was preferred as a solvent, because of its higher boiling point and less irritating properties. In this case,
preparative experiments in 1 mmol scale of 4-bromoanisole were performed and the quantity of catalyst was increased
to 0.066 mol %, the amount of phenylboronic acid was slightly increased to 1.5 equiv, and the reaction was performed
under inert atmosphere by refluxing for 12 h. Both catalysts showed high activity, yielding 4-methoxybiphenyl in 95
% isolated after flash chromatography (cyclohexane : dichloromethane = 24 : 1).
3. Conclusion
In conclusion, we have synthesized four new NHC complexes involving bidentate N- and P-donor ligands.
Conformational studies in respect of hindered rotation around C-N bond, Pd-C and phosphine helicity were
performed. The conformations of the newly prepared complexes were elucidated on the base of NMR and DFT
studies. In solution of 1,3-disubstituted complex 1 two conformers were revealed and proved to originate from
restricted rotation around C-N bond, while for 1,3-disubstituted complex 2 four conformers resulting from the
restricted rotation around C-N bond and phosphine helicity reversal were observed. In the case of 4,5-fused complex 3
only one conformer was detected, while for 4,5-fused complex 4 two conformers resulting from phosphine helicity
reversal were observed. The palladium complexes 3 and 4 were evaluated as catalysts in Suzuki–Miyaura Reaction
and exhibited excellent catalytic activity.
4. Experimental section
4.1. General
All reagents purchased from commercial suppliers were used without any further purification. 6-bromo-2-(2,6-
diisopropylphenyl)-1H-benzo[de]isoquinoline-1,3(2H)-dione, (S)-1-((1-Benzylpyrrolidin-2-yl)methyl)-2-methyl-1H-
imidazole, 10-dibutylbenzo[de]imidazo[4,5-g]isoquinoline-4,6(5H,10H)-dione and trans-di(ꢁ-acetato)-bis[o-(di-o-
tolylphosphino)benzyl]dipalladium(II) were synthesized using published procedures [43, 44, 62, 63]. All of the
reactions were performed under inert atmosphere using standard Schlenk techniques. The NMR spectra were recorded
1
on a Bruker Avance II+ 600 (600.13 for H NMR, 150.92 MHz for 13C NMR and 242.92 MHz for 31P NMR)
1
spectrometer with TMS (85% H3PO4 for 31P) as internal standard for chemical shifts (δ, ppm). H and 13C NMR data
are reported as follows: chemical shift, multiplicity (s = singlet, d = doublet, t = triplet, q = quartet, br = broad, m =
1
multiplet), coupling constants J (Hz), integration and identification. The assignment of the H and 13C NMR spectra
was made on the basis of DEPT, COSY, HSQC, HMBC and NOESY experiments. Flash chromatography was
performed on Silica Gel 60 (0.040–0.063 nm). Elemental analyses were performed using Vario EL3 CHNS(O) and
Microanalytical service Laboratory of the Institute of Organic Chemistry, Bulgarian Academy of Science.
4.2. Dynamic NMR measurements
VT 1H NMR spectra of complex 1 were recorded on a Bruker II+ 600 instrument (BBO probe) at 600.13 MHz in steps
1
of 10 K between 223 and 323 K in CDCl3. VT 1H and 31P{1H} (power-gated decoupling of H) spectra of complex 2
were recorded at 600.13 MHz and 242.94 MHz in steps of 5 K between 213 and 323 K in CDCl3, for complex 4
between 233 and 323 K. Temperature calibration was done with B-VT 3000 unit (it was checked and calibrated with
methanol and ethylene glycol reference samples). 1H NMR spectra were acquired using a spectral width of 10 kHz, an
acquisition time of 3.4 s and 32 scans, zerofilled to 64k datapoints (0.15 Hz per point) and processed without
apodization.
The Complete Line Shape Analysis of exchange broadened spectra of complex 1 was performed by the dnmr module
of topspin suite of programs. The chemical shifts and populations were obtained by lorenzian fit at lower temperatures
and extrapolated to higher temperatures. The signal of TMS was used as a reference and the following equation was
used to estimate the T2 values of the exchanging signals: T2 = 1/[π(Wref + ꢀW)], where ꢀW = W0 - Wref, ꢀW is the
difference between the halfwidth of the reference signal, Wref, and the observed signal in the absence of exchange, W0
[64]. In the fitting procedure, all parameters were allowed to change and the overlap of more than 95% was achieved.
The rate constant of the process major to minor conformers was fitted, while the other was recalculated using the
populations ratio.
1
VT H EXSY NMR spectra of compounds 1–4 were recorded on a Bruker II+ 600 instrument (BBO probe). The
spectra were acquired using a spectral width of 1.2 kHz, 2048 x 256 complex time domain datapoints, with 2 scans in
13

ACCEPTED MANUSCRIPT
about 45 min. The spectra were zerofilled to 4096 x 4096 datapoints and processed with a shifted square sine bell
apodization in both dimensions.
1
VT 31P EXSY spectra (power-gated decoupling of H) of complex 2 were recorded on a BBO probe in steps of 5 K
between 223 and 253 K, for complex 4 between 233 and 283 K. The spectra were acquired using a spectral width of
4.8 kHz, 2048 x 256 complex time domain data points, mixing times in the range of 0.075 to 1.0 s and 2 scans in
about 45 min. Linear prediction (32 coefficients and 256 points) in F1 was applied. The spectra were zerofilled to
4096 x 4096 data points and processed with a shifted square sine bell apodization in both dimensions. The populations
were obtained by integration of 1D 31P signals and the exchange rates were calculated by program EXSYCalc [65]
from diagonal- and crosspeak integrals.
2
E = ES2 + EkT
The errors Etot, quoted in Tables 3, 4, 2S, 5S and 7S are calculated according to the expression:
, where
tot
ES is the statistical error based on scattering of the data in the Eyring plot while EkT is computed using error
propagation equations as derived by Binsch [66] and Heinzer and Oth [67], in which errors due to both the calculated
rate constants and the measured temperature are taken into account. The absolute error in temperature is assumed to be
not more than ±0.5 K. The relative errors in
k are estimated to be not more than ±10% at all temperatures according
the precision of the volume integration of peaks. The errors analysis was performed using a self-made computer
program using the cited equations.
4.3. DFT calculations
Geometry optimizations were performed by using the density functional theory [68-70] as implemented in
GAUSSIAN 09 [71] and the B3LYP functional [72, 73]. As for the basis sets, we used 6-31G(d) for C, H, P and Br
[73]. For Pd, the basis set LANL2DZ was adopted [74], whose core parts were represented by effective core potentials
(ECP). Solvent was included implicitly to the optimizations via the SMD [75] model with the built in parameters for
solvent CHCl3. After locating the first GS structure, the next one was found by scanning the torsional profile for the
rotation (incrementing the dihedral angle about C-N or Pd-C bond in 10 degrees step). The next minimum on the
torsional profile was fully optimized in order to locate the next GS structure. The maximum in the reaction coordinate
calculations was optimized by fixing the dihedral angle of rotation and subsequent full geometry optimization of the
TS structure using the Berny algorithm. All critical points (GS and TS structures) were characterized by performing
vibrational analysis, and ZPV energies were also evaluated. The thermal and entropy corrections to the Gibbs free
energy at 298.15 K were calculated for all minima using unscaled vibrational frequencies obtained at the same level.
1
The H NMR chemical shifts of complexes in chloroform environment (SMD) were calculated using the B3LYP
functional with the 6-31+G(d,p) basis set for C, H, P and Br [73]. For Pd, we used LANL2DZ basis set [74], whose
core parts were represented by effective core potentials (ECP).
4.4. 2-[2,6-di(propan-2-yl)phenyl]-6-(1H-imidazol-1-yl)-1H-benzo[de]isoquinoline-1,3(2H)-dione (III): 6-bromo-
2-(2,6-diisopropylphenyl)-1H-benzo[de]isoquinoline-1,3(2
H)-dione (II) (2.00 g, 4.5 mmol), CuI (0.044 g, 0.23 mmol,
5 mol %), ( )-1-((1-Benzylpyrrolidin-2-yl)methyl)-2-methyl-1H-imidazole (0.116 g, 0.45 mmol 10 mol%), imidazole
S
(0.31 g, 4.5 mmol) and Cs2CO3 (2.93 g, 9 mmol) were dissolved in dry DMF (50 mL), degassed and the reaction
mixture was heated to 100 °C for 24 hours. The reaction mixture was then poured into water and extracted with
CHCl3. The combined organic layers were washed with water, dried with Na2SO4 and evaporated. The desired product
was isolated by flash chromatography (EtOAc : hexanes = 4 : 1) to give 1.81 g (95% yield) of III as a white solid;
m.p. 140-142°C. 1H NMR (600 MHz, CDCl3): δ = 1.189 (d,
2H, (CH3)2CH), 7.374 (d,
7.524 (t, = 7.7 Hz, 1H, H4-phenyl), 7.853 (d,
J
= 6.8 Hz, 12H, (CH3)2CH), 2.757 (septet,
= 7.7 Hz, 2H, H3, 5-phenyl), 7.432 (bs, 1H, H-imidazole), 7.491 (bs, 1H, H-imidazole),
= 7.6 Hz, 1H, H5-naphthyl), 7.925 (dd, = 8.5, 7.5 Hz, 1H, H8-
= 8.6 Hz, 1H, H7-naphthyl), 8.184 (bs, 1H, NCHN-imidazole), 8.803(d, = 7.4 Hz, 1H, H9-
= 7.6 Hz, 1H, H4-naphthyl). 13C NMR (151 MHz, CDCl3): δ = 24.00 (CH(CH3)2), 29.23
J = 6.8 Hz,
J
J
J
J
naphthyl), 8.164 (d,
naphthyl), 8.791 (d,
J
J
J
(CH(CH3)2), 121.73 (Ar-4C), 123.26 (Ar-4C), 123.45 (Ar-4C), 124.17 (Ar), 124.49 (Ar), 127.68 (Ar-4C), 128.74 (Ar),
128.83 (Ar), 129.35 (NCHN), 129.74 (Ar-4C), 129.79 (Ar), 130.36 (Ar-4C), 131.56 (Ar), 132.81 (Ar), 137.91 (Ar-4C),
138.85 (Ar-4C), 145.56 (Ar-4C), 163.20 (4C-carbonyl), 163.70 (4C-carbonyl). C27H25N3O2 (423.51): calcd. C 76.57, H
5.95, N 9.92, found: C 76.69, H 6.01, N 9.98.
4.5. 1-[2-(2,6-Isopropylphenyl)-1,3-dioxo-2,3-dihydro-1H-benzo[de]isoquinolin-6-yl]-3-(3-methylbut-2-en-1-yl)-
1H-imidazol-3-ium bromide, (NHC.HBr, precursor of 1 and 2): Compound III (0.105 g, 0.133 mmol) was
dissolved in minimal amount of ethyl acetate and 2,2-dimethylallylbromide (0.04 mL) was added to the resulting
14

ACCEPTED MANUSCRIPT
solution. The reaction mixture was stirred at room temperature overnight, then all volatiles were evaporated in vacuo
.
1
The solid residue was recrystallized from isopropyl alcohol. Yield: 80% m.p. 199-201°C. H NMR (600 MHz,
CDCl3): δ = 1.153 (d, J = 6.8 Hz, 12H, (CH3)2CH), 1.946 (s, 3H, CH3-butenyl), 1.988 (s, 3H, CH3-butenyl), 2.708
(septet, J = 6.8 Hz, 2H, (CH3)2CH), 5.444 (d, J = 7.4 Hz, 2H, H1-butenyl), 5.768 (t, J = 7.4 Hz, 1H, H2-butenyl),
7.337 (d, J = 7.8 Hz, 2H, H3, 5-phenyl), 7.493 (t, J = 7.8 Hz, 1H, H4-phenyl), 7.632 (bs, 1H, H-imidazole), 7.727 (bs,
1H, H-imidazole), 8.016 (dd, J = 8.4, 7.3 Hz, 1H, H8-naphthyl), 8.307 (dd, J = 0.8, 8.4 Hz, 1H, H7-naphthyl), 8.362
(d, J = 7.7 Hz, 1H, H5-naphthyl), 8.777 (d, J = 7.7 Hz, 1H, H4-naphthyl), 8.795 (dd, J = 0.8, 7.3 Hz, 1H, H9-
naphthyl), 10.451 (bs, 1H, NCHN-imidazole). 13C NMR (151 MHz, CDCl3): δ = 18.54 ((CH3)-butenyl), 23.92
((CH3)2CH), 23.95 ((CH3)2CH), 25.81 ((CH3)-butenyl), 29.17 ((CH3)2CH), 50.08 (C1-butenyl), 118.02 (C2-butenyl),
123.30 (Ar-4C), 123.52 (CH-imidazole), 124.15 (CH-imidazole), 124.81 (Ar-4C), 124.83 (C3,5-phenyl), 125.34 (Ar-
4C), 126.00 (C7-naphthyl), 126.54 (Ar-4C), 128.08 (C4-phenyl), 129.56 (Ar-4C), 129.82 (C5-naphthyl), 129.88 (C7-
naphthyl), 130.07 (Ar-4C), 131.18 (C4-naphthyl), 133.23 (C9-naphthyl), 135.28 (Ar-4C), 138.54 (NCHN-imidazole),
145.51 (Ar-4C), 162.72 (4C-carbonyl), 163.27 (4C-carbonyl). C32H34BrN3O2 (572.54): calcd. C 67.13, H 5.99, N 7.34,
found: C 67.22, H 6.07, N 7.39.
4.6.
bromide, (NHC.HBr, precursor of 3 and 4): Suspension of 5,10-dibutylbenzo[de]imidazo[4,5-
4,6(5 ,10 )-dione (1 g, 2.86 mmol) and 4-methylbenzyl bromide (7.54 ml, 20 equiv.) was stirred for 72 hours at
80 C. After coiling to room temperature, the reaction mixture was filtered and washed with diethyl ether. The residue
5,10-Dibutyl-8-(4-methylbenzyl)-4,6-dioxo-4,5,6,10-tetrahydrobenzo[de]imidazo[4,5-g]isoquinolin-8-ium
g
]isoquinoline-
H
H
°
was purified by column chromatography (gradient elution: first eluting with ethyl acetate, after that eluting with
1
mixture of DCM and methanol = 4.5 : 0.5). Yield 1.4 g (90%); m.p. 216-218 °C. H NMR (600 MHz, CDCl3): δ =
0.961 (t, J = 7.4 Hz, 3H, CH3-5-n-butyl), 1.025 (t, J = 7.4 Hz, 3H, CH3-10-n-butyl), 1.391-1.452 (m, 2H, 3-CH2-5-n-
butyl), 1.577-1.627 (m, 2H, 3-CH2-10-n-butyl), 1.658-1.709 (m, 2H, 2-CH2-5-n-butyl), 2.176-2.225 (m, 2H, 2-CH2-
10-n-butyl), 2.278 (s, 3H, CH3-(4-methylbenzyl)), 4.139-4.165 (m, 2H, 1-CH2-5-n-butyl), 5.167-5.192 (m, 2H, 1-
CH2-10-n-butyl), 6.015 (s, 2H, CH2-(4-methylbenzyl)), 7.166 (d, J = 8.0 Hz, 2H, H2, 6-4-methylbenzyl), 7.491 (d, J =
8.0 Hz, 2H, H3,5-4-methylbenzyl), 8.087 (dd, J = 7.5, 8.5 Hz, 1H, H2-naphthyl), 8.673 (dd, J = 0.8, 7.5 Hz, 1H, H1-
naphthyl), 8.778 (dd, J = 0.8, 7.5 Hz, 1H, H3-naphthyl), 8.793 (s, 1H, H7-naphthyl), 12.018 (s, 1H, NCHN). 13C-
NMR (151 MHz, CDCl3): δ = 13.67 (CH3-10-n-butyl), 13.81 (CH3-5-n-butyl), 19.77 (3-CH2-10-n-butyl), 20.34 (3-
CH2-5-n-butyl), 21.23 (CH3-(4-methylbenzyl)), 30.00 (2-CH2-5-n-butyl), 31.15 (2-CH2-10-n-butyl), 40.87 (1-CH2-5-
n-butyl), 50.99 (1-CH2-10-n-butyl), 51.99 (CH2-(4-methylbenzyl)), 117.21 (C7-naphthyl), 126.70 (C1-naphthyl),
128.44 (H3,5-4-methylbenzyl), 129.76 (C2-naphthyl), 130.31 (H3,5-4-methylbenzyl), 131.54 (C3-naphthyl), 144.61
(NCHN), 162.45 (4C4-carbonyl), 163.08 (4C6-carbonyl). C29H32BrN3O2 (534.49): calcd. C 65.17, H 6.03, N 7.86,
found: C 65.32, H 6.08, N 7.89.
General procedure for synthesis of complexes 1 and 3:
Complexes 1 and 3 were prepared according to the literature [45]. A Schlenk tube was charged with a
magnetic stir bar, PdCl2 (1.5 eq.), CH3CN (2 mL, HPLC grade) and N,N-dimethylbenzylamine (1.5 eq.). The mixture
was heated at reflux until a clear, dark orange solution was formed and PdCl2 was dissolved completely (in ~ 25 min).
Finely powdered K2CO3 (3.5 eq.) was added in one portion, and the mixture was stirred until the solution changed
color to bright canary yellow (in ~ 5 min). Relevant imidazolium salt, NHC.HBr, (1 eq.) was added in one portion,
and the heating at 50°C was continued for another 18 hours. After coiling to room temperature, the reaction mixtures
were filtered through a pad of Celite and washed with DCM. After evaporation of solvents, the products were purified
by column chromatography (acetone : cyclohexane = 0.5 : 4.5).
General procedure for synthesis of complexes 2 and 4:
Complexes 2 and 4 were prepared according to the literature [46]. A Schlenk tube was charged with a
magnetic stir bar, relevant imidazolium salt, NHC.HBr, (1 eq.), CH3CN (2 mL, HPLC grade), trans-di(ꢁ-acetato)-
bis[o-(di-o-tolylphosphino)benzyl]dipalladium(II) (0.75 equiv.) and finely powdered K2CO3 (2 equiv.), and the
mixture was stirred at 50°C for 18 hours. After coiling to room temperature, the reaction mixtures were filtered
through a pad of Celite and washed with DCM. After evaporation of solvents, the products were purified by column
chromatography (ethyl acetate : cyclohexane = 0.5 : 4.5).
4.7. Bromo{2-[(dimethylamino-κN)methyl]phenyl-κ
C1}}[1-[2-(2,6-isopropylphenyl)-1,3-dioxo-2,3-dihydro-1H-
benzo[de]isoquinolin-6-yl]-3-(3-methylbut-2-en-1-yl)-1,3-dihydro-2H-imidazol-2-ylidene]palladium (1). Yield
15

ACCEPTED MANUSCRIPT
0.18 g (92 %) of white solid with m.p. 120°C (decomposition): 1H-NMR (600 MHz, CDCl3, 223 K): two conformers
in 1.1 : 1.0 ratio; Major: δ = 1.072-1.156 (m, 12H, CH(CH3)2), 1.788 (s, 3H, a-(CH3)2-butenyl), 1.809 (s, 3H, b-
(CH3)2-butenyl), 2.570 (s, 3H, a-N(CH3)2-palladacycle), 2.676-2.755 (m, 2H, CH(CH3)2), 2.736 (s, 3H, N(CH3)2-
palladacycle), 3.706 (d, J = 14.3 Hz, 1H, a-N(CH3)2-CH2-palladacycle), 3.773 (d, J = 14.3 Hz, 1H, b-N(CH3)2-CH2-
palladacycle), 5.181-5.273 (m, 2H, a,b-H1-butenyl), 5.477-5.553 (m, 1H, H2-butenyl), 6.206 (d, J = 7.3 Hz, 1H, H3-
palladacycle), 6.632-6.656 (m, 1H, H4-palladacycle), 6.815-6.839 (m, 1H, H5-palladacycle), 6.882 (d, J = 7.0 Hz, 1H,
H6-palladacycle), 7.291-7.310 (m, 2H, imidazole), 7.354-7.399 (m, 2H, H3,5-phenyl), 7.524 (t, J = 7.8 Hz, 1H, H4-
phenyl), 7.804 (dd, J = 7.0, 8.4 Hz, 1H, H8-naphthyl), 7.994 (d, J = 7.8 Hz, 1H, H5-naphthyl), 8.294 (d, J = 8.4 Hz,
1H, H7-naphthyl), 8.516 (d, J = 7.8 Hz, 1H, H4-naphthyl), 8.639 (d, J = 7.0 Hz, 1H, H9-naphthyl); Minor: δ = 1.072-
1.156 (m, 6H, CH(CH3)2), 1.189 (d, J=7.0 Hz, 6H, CH(CH3)2), 1.799 (s, 3H, b-(CH3)2-butenyl), 1.808 (s, 3H, a-
(CH3)2-butenyl), 2.762 (s, 3H, N(CH3)2-palladacycle), 2.766-2.821 (m, 1H, a-CH(CH3)2), 2.831-2.902 (m, 1H, b-
CH(CH3)2), 2.855 (s, 3H, N(CH3)2-palladacycle), 3.792 (d, J = 14.3 Hz, 1H, a-N(CH3)2-CH2-palladacycle), 3.868 (d, J
= 14.3 Hz, 1H, b-N(CH3)2-CH2-palladacycle), 5.232 (dd, J = 7.3, 14.5 Hz, 1H, a-H1-butenyl), 5.392 (dd, J = 7.3, 14.5
Hz, 1H, b-H1-butenyl), 5.477-5.553 (m, 1H, H2-butenyl), 6.414 (d, J = 7.3 Hz, 1H, H3-palladacycle), 6.919-6.940 (m,
1H, H4-palladacycle), 7.041-7.080 (m, 2H, H5-palladacycle and H6-palladacycle), 7.291-7.310 (m, 1H, imidazole),
7.354-7.399 (m, 3H, H3,5-phenyl and imidazole), 7.524 (t, J = 7.8 Hz, 1H, H4-phenyl), 7.855 (dd, J = 7.0, 8.4 Hz, 1H,
H8-naphthyl), 8.307 (d, J = 8.4 Hz, 1H, H7-naphthyl), 8.705 (d, J = 7.0 Hz, 1H, H9-naphthyl), 8.767 (d, J = 7.8 Hz,
1H, H4-naphthyl), 9.179 (d, J = 7.8 Hz, 1H, H5-naphthyl). 13C NMR (151 MHz, CDCl3, 223 K); Major: δ = 18.62 (a-
(CH3)-butenyl), 24.28 (CH(CH3)2), 24.30 (CH(CH3)2), 26.32 (b-(CH3)-butenyl), 29.17 (CH(CH3)2), 49.86 (C1-
butenyl), 50.84 (N(CH3)2-palladacycle), 51.00 (N(CH3)2-palladacycle), 71.61 (N(CH3)2-CH2-palladacycle), 118.32
(C2-butenyl), 121.30 (imidazole), 122.36 (C6-palladacycle), 123.74 (C5-palladacycle), 124.20 (C3-phenyl), 124.25
(C5-phenyl),125.34 (C4-palladacycle), 126.81 (C5-naphthyl), 127.94 (C8-naphthyl), 130.02 (C4-phenyl), 131.00 (C7-
naphthyl), 131.16 (C4-naphthyl), 132.42 (C9-naphthyl), 135.50 (C3-palladacycle), 164.24 (4C3-carbonyl), 164.37
4
(4C1-carbonyl) 174.88 (bs, C-carbene); Minor: δ = 18.64 (a-(CH3)-butenyl), 24.38 (CH(CH3)2), 24.46 (CH(CH3)2),
26.35 (b-(CH3)2-butenyl), 28.94 (2C, s, CH(CH3)2), 50.08 (C1-butenyl), 51.19 (N(CH3)2-palladacycle), 51.38
(N(CH3)2-palladacycle), 71.74 (N(CH3)2-CH2-palladacycle), 118.44 (C2-butenyl), 123.03 (C6-palladacycle), 124.10
(imidazole), 124.36 (C5-palladacycle), 124.61 (C3-phenyl), 124.67 (C5-phenyl), 126.13 (C4-palladacycle), 127.89
(C4-naphthyl), 128.16 (C8-naphthyl), 129.20 (C7-naphthyl), 130.02 (C4-phenyl), 131.71 (C5-naphthyl), 132.93 (C9-
naphthyl), 135.70 (C3-palladacycle), 163.70 (4C3-carbonyl), 163.88 (4C1-carbonyl) 174.88 (4bs, 4C-carbene).
C41H45BrN4O2Pd (810.18): calcd. C 60.63, H 5.58, N 6.90, found: C 60.79, H 5.62, N 6.94.
4.8.
({2-[Bis(2-methylphenyl)phosphanyl-κP]phenyl}methyl-κC)(bromo)[1-[2-(2,6-diisopropylphenyl)-1,3-
dioxo-2,3-dihydro-1H-benzo[de]isoquinolin-6-yl]-3-(3-methylbut-2-en-1-yl)-1,3-dihydro-2H-imidazol-2-
1
ylidene]palladium (2). Yield 0.16 g (90 %) of white solid with m.p. 120°C (decomposition): H-NMR (600MHz,
CDCl3, 223K): four conformers in 1.0 : 0.2 : 0.26 : 0.64 ratio; Major: δ = 1.033 (d, J = 6.5 Hz, 3H, CH(CH3)2), 1.162
(d, J = 6.5 Hz, 3H, CH(CH3)2), 1.244 (d, J = 6.5 Hz, 3H, CH(CH3)2), 1.281 (d, J = 6.5 Hz, 3H, CH(CH3)2), 1.651 (s,
3H, (CH3)2-butenyl), 1.684 (s, 3H, (CH3)2-butenyl), 1.868 (d, J = 13.0 Hz, 1H, a-CH2-Pd), 2.302 (s, 3H, CH3-o-tol-1),
2.543-2.594 (m, 1H, CH(CH3)2), 2.734 (s, 3H, CH3-o-tol-2), 2.705-2.777 (m, 1H, CH(CH3)2), 2.802 (d, J = 13.0 Hz,
1H, b-CH2-Pd), 4.835 (dd, J = 7.4, 14.0 Hz, 1H, a-H1-butenyl), 5.325 (dd, J = 7.4, 14.0 Hz, 1H, b-H1-butenyl), 5.434
(dd, J = 7.4, 7.4 Hz, 1H, H2-butenyl), 6.426-7.46 (m, 14H, 12H of o-tol-1, otol-2 and phosphapalladacycle and 2H of
imidazole), 7.383 (d, J = 7.9, 2H, H3,5-phenyl), 7.536 (t, J = 7.9 Hz, 1H, H4-phenyl), 8.016 (dd, J = 7.5, 8.5 Hz, 1H,
H8-naphthyl), 8.357 (d, J = 8.5 Hz, 1H, H7-naphthyl), 8.607 (d, J = 7.8 Hz, 1H, H4-naphthyl), 8.702 (d, J = 7.8 Hz,
1H, H5-naphthyl), 8.849 (d, J = 7.5 Hz, 1H, H9-naphthyl). 13C-NMR (251 MHz, CDCl3, 223K); Major: δ = 18.10
((CH3)2-butenyl), 22.97 (d, J=12.30 Hz, CH3-o-tol-2), 23.40 (d, J=10.80 Hz, CH3-o-tol-1), 23.89 (CH(CH3)2), 23.97
(CH(CH3)2), 24.04 (CH(CH3)2), 24.06 (CH(CH3)2), 24.29 (CH2-Pd), 25.91 ((CH3)2-butenyl), 28.84 (CH(CH3)2), 28.91
(CH(CH3)2), 49.09 (C1-butenyl), 118.69 (C2-butenyl), 124.2 (C3,5-phenyls), 128.17 (C8-naphthyl), 129.19 (C7-
naphthyl), 129.22 (C5-naphthyl), 129.76 (C4-phenyl), 131.48 (C4-naphthyl), 132.34 (C9-naphthyl), 163.12 (4C3-
2
4
carbonyl), 163.97 (4C1-carbonyl), 181.79 (d, JC-P-trans = 144.5 Hz, C-carbene). 31P{1H}-NMR (243 MHz, CDCl3,
223K); four conformers in 1.0 : 0.2 : 0.26 : 0.64 ratio; δ = 27.45, 28.64, 31.31, 31.58 ppm. C53H53BrN3O2PPd
(979.21): calcd. C 64.87, H 5.44, N, 4.28, found: C 65.02, H 5.52, N 4.31.
4.9. [5,10-Dibutyl-8-(4-methylbenzyl)-4,6-dioxo-5,6,8,10-tetrahydrobenzo[de]imidazo[4,5-g]isoquinolin-9(4H)-
ylidene](bromo){2-[(dimethylamino-κN)methyl]phenyl-κ
C1}palladium (3). Yield 0.14 g (80 %) of pale yellow
1
solid with m.p. 120°C (decomposition): H NMR (600 MHz, CDCl3): δ = 0.967 (t, J = 7.4 Hz, 3H, CH3-10-n-butyl),
1.075 (t, J = 7.4 Hz, 3H, CH3-5-n-butyl), 1.402-1.464 (m, 2H, 3-CH2-10-n-butyl), 1.622-1.679 (m, 2H, 2-CH2-5-n-
16

ACCEPTED MANUSCRIPT
butyl), 1.679-1.722 (m, 2H, 3-CH2-10-n-butyl), 2.017-2.091 (m, 1H, a-2-CH2-10-n-butyl), 2.254 (s, 3H, CH3-(4-
methylbenzyl)), 2.331-2.406 (m, 1H, b-2-CH2-10-n-butyl), 2.942 (s, 3H, a-N(CH3)2-palladacycle) 2.950 (s, 3H, b-
N(CH3)2-palladacycle), 3.914 (d, J = 14.1 Hz, 1H, a-N(CH3)2-CH2-palladacycle), 4.061 (d, J = 14.1 Hz, 1H, b-
N(CH3)2-CH2-palladacycle), 4.143-4.167 (m, 2H, 1-CH2-5-n-butyl), 5.297-5.342 (m, 1H, a-1-CH2-10-n-butyl),
5.4029-5.453 (m, 1H, a-1-CH2-10-n-butyl), 5.958 (d, J = 15.4 Hz, 1H, a-CH2-(4-methylbenzyl)), 5.972 (dd, J = 1.0,
7.5 Hz, 1H, H6-palladacycle), 6.215 (d, J = 15.4 Hz, 1H, b-CH2-(4-methylbenzyl)), 6.641 (ddd, J = 1.0, 7.4, 7.5 Hz,
1H, H5-palladacycle), 6.958 (ddd, J = 0.8, 7.4, 7.5 Hz, 1H, H4-palladacycle), 7.044 (dd, J = 0.8, 7.4 Hz, 1H, H3-
palladacycle), 7.075 (d, J = 8.0 Hz, 2H, H2,6-4-methylbenzyl), 7.447 (d, J = 8.0 Hz, 2H, H3,5-4-methylbenzyl), 7.937
(dd, J = 7.4, 8.3 Hz, 1H, H2-naphthyl), 8.559 (s, 1H, H7-naphthyl), 8.641 (dd, J = 1.0, 8.3 Hz, 1H, H1-naphthyl),
8.678 (dd, J = 1.0, 7.4 Hz, 1H, H3-naphthyl).13C NMR (151 MHz, CDCl3): δ = 13.73 (CH3-10-n-butyl), 13.86 (CH3-
5-n-butyl), 20.16 (2-CH2-5-n-butyl), 20.41 (3-CH2-5-n-butyl), 21.16 (CH3-(4-methylbenzyl)), 30.13 (3-CH2-10-n-
butyl), 30.74 (2-CH2-10-n-butyl), 40.60 (1-CH2-5-n-butyl), 50.88 (a-N(CH3)2-palladacycle), 51.41 (b-N(CH3)2-
palladacycle), 52.04 (1-CH2-10-n-butyl), 54.13 (CH2-(4-methylbenzyl)), 72.28 (N(CH3)2-CH2-palladacycle), 116.82
(C7-naphthyl), 122.60 (C3-palladacycle), 124.31 (C4-palladacycle), 125.74 (C5-palladacycle), 126.93 (C1-naphthyl),
127.92 (C3-naphthyl), 128.18 (C3,5-4-methylbenzyl), 129.67 (C3,5-4-methylbenzyl), 129.98 (C3-naphthyl), 135.49
(C6-palladacycle), 163.54 (4C6-carbonyl), 163.99 (4C4-carbonyl), 188.99 (4C, Pd-carbene). C38H43BrN4O2Pd (772.16):
calcd. C 58.96, H 5.60, N 7.24, found: C 59.04, H 5.66, N 7.27.
4.10. ({2-[Bis(2-methylphenyl)phosphanyl-κP]phenyl}methyl-κC)(bromo)[5,10-dibutyl-8-(4-methylbenzyl)-4,6-
dioxo-5,6,8,10-tetrahydrobenzo[de]imidazo[4,5-g]isoquinolin-9(4H)-ylidene]palladium (4). Yield 70 mg (83 %)
of pale yellow solid with m.p. 120°C (decomposition): 1H-NMR (600 MHz, CDCl3, 233 K); two conformers in 1.59 :
1.0 ratio; Major: δ = 0.959 (t, 3H, CH3-5-n-butyl), 0.972 (t, 3H, CH3-10-n-butyl), 1.401-1.472 (m, 2H, 3-CH2-5-n-
butyl), 1.482-1.574 (m, 2H, 3-CH2-10-n-butyl), 1.648-1.715 (m, 2H, 2-CH2-5-n-butyl), 1.961-2.055 (m, 1H, a-2-CH2-
10-n-butyl), 2.138 (s, 3H, CH3-(4-methylbenzyl), 2.272-2.365 (m, 1H, b-2-CH2-10-n-butyl), 2.363 (d, J = 13.0 Hz,
1H, a-CH2-Pd), 2.645 (d, J = 13.0 Hz, 1H, b-CH2-Pd), 2.918 (s, 3H, CH3-o-tol-2), 2.924 (s, 3H, CH3-o-tol-1), 4.141-
4.1715 (m, 2H, 1-CH2-5-n-butyl), 5.112-5.181 (m, 1H, a-1-CH2-10-n-butyl), 5.284-5.337 (m, 1H, b-1-CH2-10-n-
butyl), 5.677 (d, J = 15.0 Hz, 1H, a-CH2-(4-methylbenzyl)), 5.993 (d, J = 15.0 Hz, 1H, b-CH2-(4-methylbenzyl)),
6.697 (d, J = 8.1 Hz, 2H, H3,5-4-methylbenzyl), 6.732-6.762 (m, 1H, Ar-phosphapalladacycle), 6.884-7.516 [(13H:
6.881-6.907 (m, 1H, o-tol-1), 6.986-6.994 (m, 1H, o-tol-2), 7.011-7.016 (m, 1H, Ar-phosphapalladacycle), 7.043-
7.064 (m, 1H, Ar-phosphapalladacycle), 7.183-7.205 (m, 1H, o-tol-2), 7.188-7.214 (m, 1H, Ar-phosphapalladacycle),
7.215 (d, J = 8.1 Hz, 2H, H2,6-4-methylbenzyl), 7.224-7.237 (m, 1H, o-tol-1), 7.241-7.264 (m, 1H, o-tol-2), 7.334-
7.381 (m, 1H, o-tol-2), 7.481-7.517 (m, 2H, o-tol-1)], 7.975 (dd, J = 8.5, 7.4 Hz, 1H, H2-naphthyl), 8.593 (dd, J = 0.9,
8.5 Hz, 1H, H1-naphthyl), 8.696 (dd, J = 0.9, 7.4 Hz, 1H, H3-naphthyl), 8.703(s, 1H, H7-naphthyl). Minor: δ = 0.82
(t, J = 7.3 Hz, 3H, CH3-10-n-butyl), 0.9511 (t, J = 7.3, 3H, CH3-5-n-butyl), 1.401-1.472 (m, 4H, 3-CH2-5-n-butyl and
3-CH2-10-n-butyl), 1.648-1.715 (m, 2H, 2-CH2-5-n-butyl), 1.789-1.867 (m, 1H, a-2-CH2-10-n-butyl), 2.158-2.227
(m, 1H, b-2-CH2-10-n-butyl), 2.291 (s, 3H, CH3-(4-methylbenzyl)), 2.583 (d, J = 13.0 Hz, 1H, a-CH2-Pd), 2.723 (s,
3H, CH3-o-tol-2), 2.796 (s, 3H, CH3-o-tol-1), 3.218 (d, J = 13.0 Hz, 1H, b-CH2-Pd), 4.141-4.1715 (m, 2H, 1-CH2-5-
n-butyl), 4.929-4.981 (m, 1H, a-1-CH2-10-n-butyl), 5.112-5.181 (m, 1H, b-1-CH2-10-n-butyl), 5.872 (d, J = 15.0 Hz,
1H, a-CH2-(4-methylbenzyl)), 6.324 (d, J = 15.0 Hz, 1H, b-CH2-(4-methylbenzyl)), 6.75-6.78 (m, 1H, Ar-
phosphapalladacycle), 6.884-7.516 [(16H: 6.935-6.951 (m, 1H, o-tol-1), 6.946-6.988 (m, 1H, Ar-
phosphapalladacycle), 6.997-7.012 (m, 1H, o-tol-2), 7.022-7.034 (m, 1H, Ar-phosphapalladacycle), 7.064 (d, J = 8.1
Hz, 2H, H3,5-4-methylbenzyl), 7.127-7.172 (m, 2H, o-tol-1), 7.184-7.214 (m, 1H, Ar-phosphapalladacycle), 7.187-
7.225 (m, 1H, o-tol-2), 7.266-7.278 (m, 1H, o-tol-2), 7.341-7.379 (m, 1H, o-tol-2), 7.428-7.433 (m, 2H, o-tol-1),
7.478 (d, J = 8.1 Hz, 2H, H2,6-4-methylbenzyl)], 7.931 (dd, J = 8.5, 7.4 Hz, 1H, H2-naphthyl), 8.528 (dd, J = 0.9, 8.5
Hz, 1H, H1-naphthyl), 8.662 (dd, J = 0.9, 7.4 Hz, 1H, H3-naphthyl), 8.684 (s, 1H, H7-naphthyl). 13C-NMR (151MHz,
CDCl3, 233 K); Major: δ = 14.27 (CH3-10-n-butyl-major), 14.30 (CH3-5-n-butyl), 20.54 (C3-CH2-10-n-butyl), 20.64
3
(C3-CH2-5-n-butyl), 21.46 (CH3-(4-methylbenzyl)), 22.64 (CH2-Pd-major), 23.12 (d, JC-P = 11.7 Hz, CH3-o-tol-2),
3
23.81 (d, JC-P = 9.0 Hz, CH3-o-tol-1), 30.21 (C2-CH2-5-n-butyl), 31.82 (C2-CH2-10-n-butyl), 40.87 (C1-CH2-5-n-
butyl), 52.10 (C1-CH2-10-n-butyl), 52.34 (CH2-(4-methylbenzyl)), 116.48 (C7-naphthyl), 125.80 (Ar-
2
3
phosphapalladacycle), 126.20 (d, JC-P = 4.0 Hz, o-tol-2), 126.74 (d, JC-P =18.0 Hz, Ar-phosphapalladacycle), 127.18
(C1-naphthyl), 128.36 (C2-naphthyl), 128.37 (C2,6-(4-methylbenzyl)), 129.48 (C3,5-(4-methylbenzyl)), 130.25 (C3-
naphthyl), 130.50 (o-tol-1), 130.80 (o-tol-2), 130.95 (Ar-phosphapalladacycle), 131.56 (d, JC-P = 7.7 Hz, o-tol-1),
131.79 (d, JC-P = 8.4 Hz, o-tol-2), 132.43 (Ar-phosphapalladacycle), 133.00 (o-tol-1), 133.14 (o-tol-2), ), 134.08 (d,
1JC-P = 49.0 Hz, ipso-P-Ar-phosphapalladacycle-major), 162.68 (4C6-carbonyl), 163.02 (4C6-carbonyl), 195.81 (d, 2JC-
17

ACCEPTED MANUSCRIPT
4
= 142.0 Hz, C-carbene). Minor: δ = 13.63 (CH3-10-n-butyl), 14.30 (CH3-5-n-butyl), 20.05 (C3-CH2-10-n-
P-trans
3
butyl), 20.64 (C3-CH2-5-n-butyl), 21.55 (CH3-(4-methylbenzyl)), 22.66 (CH2-Pd), 23.22 (d, JC-P = 11.7 Hz, CH3-o-
tol-2), 23.97 (d, 3JC-P = 9.0 Hz, CH3-o-tol-1), 30.19 (C2-CH2-5-n-butyl), 31.53 (C2-CH2-10-n-butyl), 40.89 (C1-CH2-
5-n-butyl), 51.45 (C1-CH2-10-n-butyl), 52.84 (CH2-(4-methylbenzyl)), 116.83 (C7-naphthyl), 125.80 (Ar-
2
3
phosphapalladacycle), 125.84 ( o-tol-1), 126.15 (d, JC-P = 4.0 Hz, o-tol-2), 127.17 (C1-naphthyl), 127.19 (d, JC-P
=
18.0 Hz, Ar-phosphapalladacycle), 128.13 (C2,6-(4-methylbenzyl)), 129.88 (C3,5-(4-methylbenzyl)), 130.23 (C3-
2
naphthyl), 130.42 (o-tol-1), 130.80 (o-tol-2), 130.86 (Ar-phosphapalladacycle), 131.31 (d, JC-P = 7.7 Hz, o-tol-1),
131.69 (d, 2JC-P = 8.4 Hz, o-tol-2), 132.14 (Ar-phosphapalladacycle), 132.98 (d, 2JC-P = 6.0 Hz, o-tol-1), 133.14 (o-tol-
2), 133.87 (d, 1JC-P = 49.0 Hz, ipso-P-Ar-phosphapalladacycle), 162.59 (4C6-carbonyl), 163.02 (4C6-carbonyl), 195.37
(d, 2JC-P-trans = 142.0 Hz, 4C-carbene). 31P{1H}-NMR (243 MHz, CDCl3, 233 K); two conformers in 1.59 : 1.0 ratio; δ =
28.65 (minor), 29.59 (major) ppm. C50H51BrN3O2PPd (941.19): calcd. C 63.67, H 5.45, N 4.45, found: C 63.82, H
5.53, N 4.46.
Appendix A. Supplementary data
Supplementary data related to this article (copies of the 1H, 13C and 31P NMR spectra of the new complexes, details of
dynamic NMR studies and DFT calculations) are provided.
Acknowledgement The financial support by the Bulgarian Science Fund (Projects UNA-17/2005, RNF01/0110 and
DRNF-02/13), the Sofia University Research Fund (143/05.2010) and COST action CM0802 ‘‘PhoSciNet” is
gratefully acknowledged.
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•
•
•
•
•
Four catalytically relevant Pd(II) NHC complexes involving bidentate N- and P-donor
ligands were synthesized and characterized
The structures and conformations of the complexes were elucidated on the basis of
combination of dynamic NMR and DFT studies
The results from dynamic NMR and DFT studies confirmed hindered rotation around
C-N bond in 1,3-disubstituted imidazole complexes
The fluxional behavior of P-donor ligands includes exchange between left-handed and
right-handed phosphine propellers
The palladium complexes 3 and 4 were evaluated as catalysts in Suzuki–Miyaura
Reaction and exhibited excellent catalytic activity.