Structural and theoretical studies of mono and di-insertion of symmetric alkynes into the Pd-C σ bond of cyclopalladated secondary (tert-butyl and ethyl) benzylamines

Article abstract of DOI:10.1016/j.jorganchem.2013.11.030

The reactivity of the dinuclear cyclopalladated complexes derived from secondary benzylamines, [Pd₂{(C,N)-C₆H₄CH ₂NH(R)}₂(μ-X)₂] [X = Br, R = t-Bu (1a); X = Cl, R = t-Bu (1b); X = Cl, R = Et (1c)] is reported. 1a reacted with dimethyl acetylenedicarboxylate (DMAD) to yield the mono-inserted complex [Pd ₂{(C,N)-C(CO₂Me)C(CO₂Me)C₆H ₄CH₂NH(t-Bu)}₂(μ-Br)₂] (2a). 1a, 1b and 1c reacted with (R′)CC(R′) (R′ = CO₂Me, Ph) to give [Pd{(C,N) C(R′)C(R′)C(R′)C(R′)C ₆H₄CH₂NH(R)}X] [X = Br, R = t-Bu, R′ = CO₂Me (3a); X = Cl, R = t-Bu, R′ = Ph (2b); X = Cl, R = Et, R′ = Ph (2c)] through a double insertion of the alkyne into the Pd-C σ bond. 2c also reacts with Ag(CF₃SO₃) and pyridine to give mononuclear cationic complex [Pd{(C,N)-C(Ph)C(Ph)C(Ph)C(Ph)}C ₆H₄CH₂NH(Et)(py)]CF₃SO₃ (3c). The crystal structures of di-inserted complexes 2b, 2c and 3c have been determined by X-ray diffraction studies. Their molecular structures showed that the conformation of the CC double bonds within the butadienyl group attached to the aromatic ring was trans-cis. Density functional theory (DFT) calculations also indicated that this arrangement is more stable than other possible conformations.

Full text of DOI:10.1016/j.jorganchem.2013.11.030

Journal of Organometallic Chemistry 752 (2014) 152e160
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Structural and theoretical studies of mono and di-insertion of
symmetric alkynes into the PdeC
s bond of cyclopalladated secondary
(tert-butyl and ethyl) benzylamines
,
a
b
a
Kazem Karami a , Mahboubeh Hosseini-Kharat , Corrado Rizzoli , Hossein Tavakol ,
*
Janusz Lipkowski c
a Department of Chemistry, Isfahan University of Technology, Isfahan 84156/83111, Iran
b Department of Chemistry, University of Parma, I-43124 Parma, Italy
c Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland
a r t i c l e i n f o
a b s t r a c t
Article history:
The reactivity of the dinuclear cyclopalladated complexes derived from secondary benzylamines,
Received 22 August 2013
Received in revised form
12 November 2013
[Pd2{(C,N)eC6H4CH2NH(R)}2(
m
-X)2] [X ¼ Br, R ¼ t-Bu (1a); X ¼ Cl, R ¼ t-Bu (1b); X ¼ Cl, R ¼ Et (1c)] is
reported. 1a reacted with dimethyl acetylenedicarboxylate (DMAD) to yield the mono-inserted complex
[Pd2{(C,N)eC(CO2Me)]C(CO2Me)C6H4CH2NH(t-Bu)}2(m
-Br)2] (2a). 1a, 1b and 1c reacted with (R0)
Accepted 16 November 2013
C^C(R0) (R0 ¼ CO2Me, Ph) to give [Pd{(C,N) C(R0)]C(R0)C(R0)]C(R0)C6H4CH2NH(R)}X] [X ¼ Br, R ¼ t-Bu,
R0 ¼ CO2Me (3a); X ¼ Cl, R ¼ t-Bu, R0 ¼ Ph (2b); X ¼ Cl, R ¼ Et, R0 ¼ Ph (2c)] through a double insertion of
Keywords:
the alkyne into the PdeC
s bond. 2c also reacts with Ag(CF3SO3) and pyridine to give mononuclear
Cyclopalladated complex
Insertion reaction
DMAD
Diphenylacetylene
Theoretical study
cationic complex [Pd{(C,N)eC(Ph)]C(Ph)C(Ph)]C(Ph)}C6H4CH2NH(Et)(py)]CF3SO3 (3c). The crystal
structures of di-inserted complexes 2b, 2c and 3c have been determined by X-ray diffraction studies.
Their molecular structures showed that the conformation of the C]C double bonds within the buta-
dienyl group attached to the aromatic ring was transecis. Density functional theory (DFT) calculations
also indicated that this arrangement is more stable than other possible conformations.
Ó 2013 Elsevier B.V. All rights reserved.
1. Introduction
alkyne, the stoichiometry of the reaction, the remaining ligands
bound to the palladium, etc [20e23]. In this context, the reaction
The insertion of alkynes into the PdeC bond of cyclopalladated
complexes has received great attention. In some cases the palla-
dation reaction and the insertion of the alkyne form part of a cat-
alytic cycle yielding interesting organic compounds [1e17]. Most
reactions of palladacycles with alkynes give stable complexes
because of intramolecular stabilization of the coordinated atom.
However, sometimes the resulting cyclopalladated complex is un-
stable and gives interesting organic products [18,19] or a non-
cyclopalladated aryl palladium complex forms a stable cyclo-
palladated derivative after the insertion of the alkyne [20].
between internal alkynes with electron-withdrawing substituents
and cyclometalladated compounds favors the production of mono-
inserted products, while internal alkynes with electron-donating
substituents promotes the synthesis of di-inserted products [24].
The mechanism of these insertion reactions show that mono-
inserted derivatives are difficult to prepare if the rate of the sec-
ond insertion is much greater than the first one [25].
Recently, a number of N-ligand derivatives have found practical
applications and the search for new, more useful and/or selective
species is still in progress [26]. N-containing palladacycles are the
most common palladacycles that undergo alkyne insertion because
these compounds are much more reactive than the corresponding
palladacycles where the heteroatom is phosphorus or sulfur [27].
Insertion of one, two or three molecules of the alkyne into the PdeC
bond of amine palladacycles has been reported [7,8,22e24,28e37].
Although the insertion reactions of alkynes into cyclopalladated pri-
mary amines are well-known [38], this is not so for secondaryamines.
The first study of the reactivity of a cyclopalladated secondary
amine with alkynes, was reported by Vicente et al. [30] in which
It is well known that the nature of the final product formed by
the insertion of alkynes depends on a wide variety of factors
including the nature of the metalated carbon, the electron-
withdrawing or -donating ability of the substituents on the
* Corresponding author. Tel.: þ98 3113913239; fax: þ98 3113912350.
E-mail addresses: karami@cc.iut.ac.ir (K. Karami), m.hosseinikharat@ch.iut.ac.ir
(M. Hosseini-Kharat).
0022-328X/$ e see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jorganchem.2013.11.030

K. Karami et al. / Journal of Organometallic Chemistry 752 (2014) 152e160
153
insertion of two molecules of alkynes occurred into the PdeC bond
2. Results and discussion
of the dimeric starting complex. In other attempts they tried to
obtain di-inserted derivatives from six-membered ortho-metalated
secondaryamine and 2-butyne, 3-hexyne, or diphenylacetylene, but
it was unsuccessful due to the formation of an unstable 10-
membered vinyl-palladated ring [34]. In this paper, regarding to the
2.1. Synthesis and spectroscopic characterization
We have previously described the formation of five-membered
acetato-bridged dinuclear palladacycles of general formula
fact that articles focusing on the reactivity of the PdeC
s
bond of
[Pd(benzylamine)(m-OAc)]2 from the reaction of the secondary
secondaryamine cyclopalladated complexes arenotso common and
also a few crystal structures of them have been reported in the
literature, we have used two symmetric alkynes, which expand a
five-membered secondary amine palladacycles 1ae1c to a seven
and nine-membered palladacycles by insertion of one and two
benzylamines PhCH2NH(Et) or PhCH2NH(t-Bu) with Pd(OAc)2 [39].
Treatment of acetato-bridged complexes with an excess of NaCl or
NaBr in methanol afforded the corresponding chloro- and bromo-
bridging dimers 1ae1c [39,40]. In order to prepare mono- and di-
inserted complexes, reactions of the 1ae1c with two symmetric
alkynes were studied. Under the reaction conditions, 1a and 1c
reacted with MeO2CC^CCO2Me (1:2 and 1:4 M ratio for mono and
di-insertion, respectively). Reaction of 1c with MeO2CC^CCO2Me
gave complicated mixtures that were not separable, but the reac-
tion of 1a afforded complexes 2a and 3a, resulting from the inser-
tion of one and two molecule of alkyne into the Pdearyl bond
(Scheme 1). Formation of 2a is remarkable considering that, mono-
inserted products are not common. We can relate the difference in
reactivity of 1a and 1c with MeO2CC^CCO2Me to the greater basic
character of complex 1a which lead to the more stable insertion
products [29]. In the IR spectra of 2a and 3a two bands in the range
3060e3250 cmꢀ1 were assigned to the NH stretching of the amino
groups. In addition, the IR spectra show two strong peaks at 1709,
1628 and four very strong peaks at 1725, 1713, 1690 and 1670 cmꢀ1
molecules of alkynes into the PdeC
s bonds. To the best of our
knowledge, the present work is the first reporting of the crystal
structures of the neutral complexes (2b and 2c) from di-insertion of
two molecules of alkyne (diphenylacetylene) into the PdeC bond of
cyclopalladated secondary amines. Furthermore, we report the
crystal structure of new cationic mononuclear organopalladium
complex (3c) which is formed by the reaction of neutral di-inserted
complex (2c) with the pyridine ligand. Theoretical studies using
density functional theory (DFT) calculations, have also been carried
out in order to investigate the influence of the nature of the sub-
stituents in the alkynes on the LUMOeHOMO energy gap of the di-
inserted products, and obtain molecular parameters and partial
atomic charges around the created nine-membered cycle so as to
compare relative energies of possible conformations of the C]C
double bonds within the butadienyl fragment of the di-inserted
complexes.
corresponding to
n(CO2) [29], suggesting that mono and di-
insertion products were obtained. In the 1H NMR spectra of 2a
Scheme 1. (i) MeO2CC^CCO2Me, acetone, room temperature, 6 h; (ii) alkyne, acetone, reflux, 3 h (complex 3a). Alkyne, dichloromethane, room temperature, 6 h (complex 2b and
2c).

154
K. Karami et al. / Journal of Organometallic Chemistry 752 (2014) 152e160
inserted complex, without isolation or observation of the mono-
inserted intermediate can occurs mainly. Kinetic studies have
shown that this is due to the fact that formation of the mono-
inserted complex is the rate-determining step [25]. As previously
mentioned in the introduction section, if the rate of the second
insertion is greater than the first one, the preparation of the mono-
inserted derivatives is difficult. Complexes 2b and 2c were obtained
at room temperature in good yields, and no evidence of the for-
mation of any other complex was detected by 1H or 13C{1H} NMR.
This finding suggests that the presence of the two phenyl rings on
the alkyne might introduce significant steric effects which may
hinder insertion of the second molecule of PhC^CPh. According to
mechanistic studies on alkyne insertions reported by Ryabov et al.
[25], a cis / trans isomerization of the olefinic fragment (of the
monoinsertion product) takes place during insertion of the second
molecule of the alkyne. In the 1H NMR spectra of 2b and 2c, simi-
larly to the cases for 2a and 3a, the methylene protons are also
nonequivalent and resonate at different places
(d 3.33 and
Fig. 1. Methoxy region of the 1H NMR spectra of mono-inserted complex 2a (a) and di-
inserted complex 3a (b).
3.63 ppm) and ( 2.33 and 4.57 ppm), respectively. In both com-
d
plexes, signals due to the phenyl protons of the alkyne and the four
aromatic protons of the benzyl moiety were overlapped with each
other and appeared at (6.81e7.51 ppm for 2b) and (6.55e7.83 ppm
for 2c). In the 13C{1H} NMR spectra of 2b and 2c, the resonances of
the four types of carbon nuclei of the butadienyl units (CaeCg)
and 3a, the NH protons and the tert-butyl protons appeared at
d 4.4
and 3.08 ppm as broad signals and at 1.35 and 1.46 ppm as sharp
d
singlets, respectively. Methylene protons in 2a and 3a appeared as
AB patterns, indicating that they are situated in different environ-
ments. But the most relevant features observed in the 1H NMR
appeared at d 141.6, 135.6, 134.3 and 124.8 ppm and d 140.8, 135.8,
132.9 and 125.8 ppm, respectively, and also exhibited low intensity
[41]. Complex 2c reacts with Ag(CF3SO3) and pyridine to give
cationic complex 3c (Scheme 2). The IR spectrum of 3c shows a
number of strong absorptions at 1260e1000 cmꢀ1 due to the
presence of an uncoordinated CF3SOꢀ3 anion. The bands at 1257 and
1029 cmꢀ1 are assigned to the asymmetric and symmetric vibration
of the SO3 fragment respectively and the 1159 cmꢀ1 band is related
to the symmetric CF3 vibrational mode [42e44].
spectra are the presence of two resonances at
(2a) and four resonances at 3.46, 3.54, 3.65 and 3.76 ppm (3a),
corresponding to different OMe groups (Fig. 1). Moreover these
d 3.65 and 3.69 ppm
d
signals were observed at
d 51.0 and 52.0 ppm and d 51.2, 51.3, 51.8,
and 52.5 ppm in the 13C{1H} NMR spectra of 2a and 3a, respectively.
The signals due to the two and four types of carbon nuclei of the
ethylene (CaꢀCb) and butadienyl (CaeCg) units appeared at
d
126.7
The 1H and 13C{1H} NMR spectra of 3c show similar patterns to
those in 2b and 2c. However, in 3c, signals due to the pyridine
ligand are observed, and in its 1H NMR spectrum, one of the ortho-
protons of pyridine is significantly shifted to higher frequency
(9.48 ppm, 3JHH ¼ 6.4 Hz).
and 151.6 ppm and d 126.1,135.3, 143.4 and 155.0 ppm, respectively,
and exhibited low intensity [41]. In addition, the resonances cor-
responding to the CO carbon atoms ( 166.3 and 167.1 ppm for 2a)
and ( 157.8, 165.1, 168.0 and 171.0 ppm for 3a) of ester groups are
d
d
within the expected range [34]. These data strongly support the
hypothesis that mono- and di-insertion of MeO2CC^CCO2Me into
the palladiumecarbon bonds has occurred. Reaction of 1b and 1c
with PhC^CPh also afforded the nine-membered cyclopalladated
complexes 2b and 2c which were obtained from the insertion of
2.2. Single crystal X-ray diffraction studies
The molecular structures of 2b, 2c and 3c were determined by X-
ray diffraction studies. The X-ray molecular structures and selected
bond lengths and bond angles are shown in Figs. 2e4, respectively.
The crystal data and structural refinement parameters are listed in
Table 1. In complexes 2b and 2c, the palladium atom is effectively
four-coordinated, since it is bound to a chloro ligand, the nitrogen
two molecules of alkyne into the PdeC
s bond (Scheme 1). At-
tempts to gain the monoinsertion products of 1b and 1c in the
reaction with PhC^CPh were unsuccessful. A similar behavior has
already been observed in the reaction of cyclopalladated primary
and tertiary amines with PhC^CPh [29,34]. It was reported that,
with electron rich acetylenes like PhC^CPh, the synthesis of the di-
atom, the terminal carbon atom C11 or C7 of the
fragment, and the mid-pointof the C8]C9 or C4]C5 double bond in
h
3-butadienyl
Scheme 2. (i) Ag(CF3SO3), acetone, pyridine, r.t.

K. Karami et al. / Journal of Organometallic Chemistry 752 (2014) 152e160
155
Fig. 2. ORTEP diagram for palladacycle 2b with ellipsoids drawn at the 70% probability
level. The hydrogen atoms have been omitted for clarity. Selected bond lengths (A) and
Fig. 4. ORTEP diagram for palladacycle 3c with ellipsoids drawn at the 30% probability
level. The hydrogen atoms have been omitted for clarity. Selected bond lengths (A) and
ꢀ
ꢀ
angles (ꢁ): Pd1eCl1 2.3305(8), Pd1eN1 2.228(3), Pd1eC11 1.997(3), Pd1eC9 2.227(3),
Pd1eC8 2.210(3), N1eC5 1.481(4), C5eC6 1.513(4), C6eC7 1.406(5), C7eC8 1.507(5),
C8eC9 1.419(5), C9eC10 1.514(4), C10eC11 1.335(5), Cl1ePd1eN1 92.67(7), Cl1ePd1e
C9 150.29(8), Cl1ePd1eC8 165.84(8), Cl1ePd1eC11 91.80(9), N1ePd1eC11 167.93(11),
N1ePd1eC9 106.61(11), N1ePd1eC8 93.59(11), C11ePd1eC9 65.16(12), C11ePd1eC8
84.63(12), Pd1eN1eC5 106.05(19), N1eC5eC6 113.8(3), C5eC6eC7 124.2(3), C6eC7e
C8 125.2(3), C7eC8eC9 122.3(3), C8eC9eC10 117.0(3), C9eC10eC11 106.3(3), C10e
C11ePd1 48.46(17).
angles (ꢁ): Pd1eN2 2.014(3), Pd1eN1 2.156(3), Pd1eC13 1.985(4), Pd1eC11 2.140(3),
Pd1eC10 2.189(4), N1eC3 1.446(5), C3eC4 1.507(6), C4eC9 1.396(6), C9eC10 1.514(5),
C10eC11 1.395(5), C11eC12 1.504(5), C12eC13 1.289(5), N2ePd1eN1 91.08(13), N2e
Pd1eC11 155.64(14), N2ePd1eC10 160.69(14), N2ePd1eC13 92.73(14), N1ePd1eC13
169.15(15), N1ePd1eC11107.49(14), N1ePd1eC10 92.30(14), C13ePd1eC11 66.29(14),
C13ePd1eC10 87.45(14), Pd1eN1eC3 112.7(2), N1eC3eC4 114.1(4), C3eC4eC9
124.6(4), C4eC9eC10 126.3(4), C9eC10eC11 122.7(3), C10eC11eC12 119.8(3), C11e
C12eC13 107.8(3), C12eC13ePd1 99.3(3).
2b and 2c, respectively. The deviation of the metal from the mean
planes formed by Cl1, C11, N1, C8 and C9 for 2b and Cl1, C7, N1, C4 and
second one is cis, with the C7 or C11 carbon atom
palladium and trans coordinated to the amine N atom. As expected,
the carbonecarbon distances of the alkene units coordinated
2 to
s-bonded to
ꢀ
ꢀ
C5 for 2c is 0.124(2) A and 0.042(2) A, respectively. The first alkyne
fragment inserted as a trans group -bonded to palladium, while the
h
p
the palladium(II) are larger than those of the alkene units coordi-
nated k1 to the palladium(II): 1.419(5) and 1.335(5) A for 2b and
ꢀ
1.403(2) and 1.333(2) A for 2c. Also the alkene unit with an h2 co-
ꢀ
ordination mode in 2b does not deviate very much from planarity
[torsion angle C7eC8eC9eC10 ¼ ꢀ175.3(3)ꢁ] in relation to that in 2c
[torsion angle C3eC4eC5eC6 ¼ 171.48(14)ꢁ]. The complexes adopt
the structure found in most organopalladium complexes derived
from the insertion of two alkyne molecules into the PdeC
five- and six-membered cyclopalladated
[29,32,33,41,45,46]. The PdeCl distances (2.3305(8) A for 2b and
s
bonds of
complexes
ꢀ
ꢀ
ꢀ
2.3169(4) A for 2c) and the PdeN distances (2.228(3) A for 2b and
ꢀ
2.1534(14) A for 2c) are shorter and longer, respectively, than the
analogous distances in related cyclopalladated complexes of general
formulatrans-N,P-[Pd(C,N)Cl(phosphine)] [47e50]. Thisis due tothe
weaker trans influence of an h
2-coordinated alkene compared to a
metalated carbon atom and to the stronger trans influence of a
metalated carbon atom with respect to a phosphine ligand [51]. In
both complexes, bond lengths and angles around the palladium(II)
center are within the normal range for this kind of organopalladium
ꢀ
ꢀ
complexes [52e54]. The C8eC9 (1.419(5) A) and C4eC5 (1.403(2) A)
ꢀ
bond distances are slightly longer than the C10eC11 (1.335(5) A) and
C6eC7 (1.333(2) A) bond distances for 2b and 2c, respectively, due to
ꢀ
coordination to the palladium atom. Comparing 2b and 2c, the Pd1e
Fig. 3. ORTEP diagram for palladacycle 2c with ellipsoids drawn at the 70% probability
level. The hydrogen atoms have been omitted for clarity. Selected bond lengths (A) and
ꢀ
N1 distance (2.228(3) A) for 2b is longer than the Pd1eN1 distance
ꢀ
ꢀ
(2.1534(14) A) for 2c. Considering that the tert-butyl group in 2b is
angles (ꢁ): Pd1eCl1 2.3169(4), Pd1eN1 2.1534(14), Pd1eC7 2.0111(16), Pd1eC5
2.1972(15), Pd1eC4 2.2106(16), N1eC1 1.477(2), C1eC2 1.507(2), C2eC3 1.403(2), C3e
C4 1.512(2), C4eC5 1.403(2), C5eC6 1.508(2), C6eC7 1.333(2), Cl1ePd1eN1 86.77(4),
Cl1ePd1eC5 157.34(4), Cl1ePd1eC4 163.39(5), Cl1ePd1eC7 96.64(5), N1ePd1eC7
172.02(6), N1ePd1eC5 109.74(6), N1ePd1eC4 90.25(6), C7ePd1eC5 65.11(6), C7e
Pd1eC4 88.48(6), Pd1eN1eC1 112.67(10), N1eC1eC2 114.54(13), C1eC2eC3
124.86(14), C2eC3eC4 127.37(14), C3eC4eC5 118.70(14), C4eC5eC6 121.13(14), C5e
C6eC7 105.88(14), C6eC7ePd1 48.90(9).
bulkier than the ethyl group in 2c, therefore, the sterically
demanding benzyl group at nitrogen atom in 2b increases the PdeN
length [39]. The Pd1/N1/C5eC8 (2b) and Pd1/N1/C1eC4 (2c) six-
membered rings assume half-chair conformations, with atoms N1,
C5 and N1, C1 displaced from opposite sides of the mean plane of the
ꢀ
remaining four atoms by 0.414(2), 0.496(3) A and 0.619(2),

156
K. Karami et al. / Journal of Organometallic Chemistry 752 (2014) 152e160
Table 1
coordinated alkene unit significantly deviates from the planarity
[torsion angle C20eC10eC11eC12 ¼ 14.9(6)ꢁ]. The PdeN bond
distance involving the N2 nitrogen atom of the pyridine molecule
Crystal data and refinement parameters for complexes 2b, 2c and 3c.
2b
2c
3c
ꢀ
(2.014(3) A) is remarkably shorter than that involving the N1 atom of
Empirical Formula
C39H36ClNPd
C37H32ClNPd
C43H37F3N2O3PdS$0.5
(C3H6O)
854.25
295 (2)
Monoclinic
C2/c
22.346 (3)
14.6118 (18)
25.145 (3)
90
105.6796 (19)
90
7904.7 (17)
8
0.58
ꢀ
the amine group (2.156(3) A). The six-membered metallacycle (Pd1/
Formula weight
T/K
660.54
100(1)
Triclinic
P-1
10.4190(10)
10.9540(11)
13.8890(12)
87.951(10)
78.443(10)
82.870(10)
1540.9(3)
2
0.72
1.424
680
1.0e35.0
4421
632.49
100(1)
Monoclinic
P21/n
10.0860(10)
17.7680(10)
16.2960(12)
90
95.670(10)
90
2906.1(2)
4
0.757
1.446
1296
N1/C3/C4/C9/C10) assumes a distorted twist boat conformation, as
indicated by the puckering parameters
q
¼ ꢀ115.4(4)ꢁ, 4 ¼ ꢀ94.0(4)ꢁ
Crystal system
Space group
ꢀ
and QT ¼ 0.565(4) A. In the crystal structure, complex cations are
linked into a three-dimensional network by NeH/O and CeH/O
bonds (Fig. 5) involving the triflate anions and acetone solvent
ꢀ
a/A
ꢀ
b/A
ꢀ
ꢀ
c/A
molecules, with H/O separations ranging from 2.11 to 2.50 A.
ꢁ
ꢁ
a
/
b
/
ꢁ
g
/
2.3. Theoretical approaches
3
ꢀ
V/A
Z
m
We have attempted to study important aspects of prepared
molecules by computational methods. Therefore, the optimization
of the structures of four isomers of complexes 3a, 2b and 2c was
performed. We named four isomers as cc, ct, tt or tc, in which, the
first double bond of alkyne attached to the aromatic ring is cis, cis,
trans or trans and the second one is cis, trans, trans or cis. It should
be noted that we did not succeed to find a stable geometry with
minimum energy for tt isomers of each complex. According to the
X-ray structures, 3a, 2b and 2c have tc geometry, respectively. The
calculation of relative Gibbs free energies (Rel G) and enthalpies
(Rel H) of three complexes (Table 2) showed that the tc isomers are
(mmꢀ1
)
Dcal/mg mꢀ3
F(000)
1.436
3504
7.5e21.6
7139
q
Ranges/ꢁ
3.05e27.23
6093
Independent
reflections
Data/restraints/
parameters
4421/0/372
6093/0/365
7139/96/518
Goodness-of-fit on F2 1.100
1.105
R1 ¼ 0.0230
1.040
R1 ¼ 0.0454
Final R indices
R1 ¼ 0.0289
wR2 ¼ 0.0787 wR2 ¼ 0.0590 wR2 ¼ 0.1155
R indices (all data)
R1 ¼ 0.0300
R1 ¼ 0.0235
R1 ¼ 0.0588
wR2 ¼ 0.0794 wR2 ¼ 0.0593 wR2 ¼ 0.1250
more stable than the others. Calculated
DGccetc for 3a, 2b and 2c are
6.78, 10.39 and 7.05 kcal/mol in the solvent, and also
D
Gctetc for
ꢀ
0.212(2) A for 2b and 2c, respectively. Structureof complex 3c (Fig. 4)
is similar to those of the related complexes 2b and 2c, and the new
butadienyl fragment (C10, C11, C12, C13) presents a transecis
configuration. Complex 3c is the second cationic complex of this
family structurally characterized by X-ray analysis and all the others
are neutral di-inserted complexes [30]. In 3c, the remarkably tetra-
hedrally distorted square planar coordination geometry about the
Pd metal is provided by two nitrogen atom of the cis-arranged pyr-
them are 25.27, 49.25 and 45.25 kcal/mol. As we can see from the
calculated relative energies, the stability of the isomers for each
complex is as followed: tc > cc > ct. This result is completely in
agreement with the proposed mechanism by Ryabov [25] about the
insertion of the second alkyne into the palladiumecarbon bond of
amine palladacycles. According to this mechanism after addition of
second alkyne which coordinates in form of cis, the resulting cis-
configuration
h
2-coordinated alkenyl fragment will be in the Pd
idine molecule and amine group, the terminal C11 atom of the h3
butadienyl fragment, and the mid-point of the C8]C9 double bond.
The metal is displaced by 0.0246(3) A from the mean plane through
-
plane. This position is thermodynamically less favorable, therefore,
the cis / trans isomerization of the olefinic fragment takes place,
ꢀ
and the h
2-coordinated alkenyl fragment will be perpendicular to
the donor atoms. As observed in 2b and 2c, the C10eC11 bond length
the palladium plane. So, the tc geometry is more stable structure in
such related complexes. In addition, we have been calculated the
dipole moment of four complexes. The calculated dipole moments
of the h2-coordinated alkene unit (1.395(5) A) was the larger than
ꢀ
that of the k1-coordinated alkene unit (1.289(5) A). The h2
-
ꢀ
Fig. 5. Crystal packing of 3c approximately viewed down the b axis. Only the major component of the disordered triflate anions are shown. Hydrogen atoms not involved in
hydrogen bonding (dashed lines) are omitted.

K. Karami et al. / Journal of Organometallic Chemistry 752 (2014) 152e160
157
Table 2
Calculated relative Gibbs free energies and enthalpies of cc, ct and tc isomers of 3a,
2b and 2c and their dipole moments.
R'
Molecule
Rel H
Rel G
Rel G
Dipole
(gas phase)
(gas phase)
(in solvent)
moment (Debye)
C5
R'
C3
3a-cc
3a-ct
3a-tc
2b-cc
2b-ct
2b-tc
2c-cc
2c-ct
2c-tc
15.07
35.78
0.00
9.27
25.76
0.00
14.28
35.69
0.00
12.10
51.65
0.00
7.09
25.90
0.00
12.48
51.69
0.00
7.05
45.25
0.00
6.78
25.27
0.00
10.39
49.25
0.00
12.50
8.34
4.84
8.65
8.56
6.66
8.62
8.70
7.36
C6
C7
C4
C2
C1
Hb
R'
R'
N1
Pd
Ha
H
R
of 3a, 2b and 2c (with their isomers) are shown in Table 2. As it is
shown, the isomer with less dipole moment (tc in each complex) is
more stable. Also, the dipole moment of the cationic complex 3c
(9.83 Debye) is greater than that of the 3a-tc, 2b-tc and 2c-tc. From
the optimized structures of 2b, 2c and 3c, molecular parameters
can be obtained. Most important parameters for optimized struc-
tures, in comparison with the X-ray parameters, were listed in
Table 3. The atom numbering depicted in Fig. 6 for the di-inserted
products was used. The comparison between calculated parameters
of 2b-tc, 2c-tc and 3c-tc with those in X-ray structures confirms that
these structures are closer to the real structures.
X
Fig. 6. Numbering scheme adopted for the di-inserted products.
facilitates the oxidation process. The reactivity of the complexes is
different and the energy values of 10 frontier orbitals (Table 4)
confirm these differences. By comparison between the energies of
frontier orbitals, the LUMOeHOMO energy gaps in 3a and 3c are
less than that in other complexes, which shows these structures are
more reactive than 2b and 2c. For a more exact determination of the
partial atomic charges, NBO calculations were used. The results of
these calculations for four complexes (Table 5) showed that the
We also employed population analyses for tc geometric isomers
of 3a, 2b, 2c and 3c to extract the energies of frontier molecular
orbitals (FMOs). Graphical presentations of LUMO and HOMO of the
structures and their energy gaps (eV) are shown in Fig. 7. In the
studied systems the presence of electron-donor groups, Ph, in the
carbon atoms connected to Pd via
h
2-bond (C3]C4) in the com-
plexes 2b, 2c and 3c with electron-donor group (Ph), have great
negative charges comparing to those in complex 3a which has
electron-withdrawing groups (CO2Me). Moreover, the Pd atom in
the cationic complex 3c has a greater positive charge in comparison
with that in other neutral complexes.
h
2-butadienyl moiety decreases the energy of the HOMO. On the
contrary, the presence of electron-withdrawing groups, CO2Me,
Table 3
Selected molecular parameters for calculated isomers (tc) in comparison with those
ꢀ
3. Conclusion
in the X-ray structures of 2b, 2c and 3c. Bond lengths are in (A) and bond angles are
in (ꢁ).
In this paper, the synthesis of new mono- and di-inserted pal-
ladacycles of secondary benzylamine along with their character-
ization is reported. Complexes 1a, 1b and 1c react with dimethyl
acetylenedicarboxylate and diphenylacetylene producing mono-
and di-nuclear palladacycles (2a, 3a, 2b and 2c) derived from single
2b (tc)/X-ray
2c (tc)/X-ray
3c (tc)/X-ray
ꢀ
Bond lengths (A)
PdeCl(N2)
PdeN1
PdeC1
PdeC3
PdeC4
C1eC2
C2eC3
C3eC4
C4eC5
C5eC6
C6eC7
C7eN
2.504/2.3305(8)
2.225/2.228(3)
2.030/1.997(3)
2.250/2.227(3)
2.280/2.210(3)
1.344/1.335(5)
1.526/1.514(4)
1.413/1.419(5)
1.514/1.507(5)
1.416/1.406(5)
1.524/1.513(4)
1.505/1.481(4)
2.446/2.3169(4)
2.198/2.1534(14)
2.037/2.0111(16)
2.254/2.1972(15)
2.276/2.2106(16)
1.347/1.333(2)
1.526/1.508(2)
1.412/1.403(2)
1.515/1.512(2)
1.417/1.403(2)
1.519/1.507(2)
1.500/1.477(2)
2.283/2.014(3)
2.231/2.156(3)
2.039/1.985(4)
2.271/2.140(3)
2.270/2.189(4)
1.341/1.289(5)
1.530/1.504(5)
1.418/1.395(5)
1.518/1.514(5)
1.417/1.396(6)
1.516/1.507(6)
1.506/1.446(5)
and double insertion of the corresponding alkynes into the PdeC
s
bonds. The 1H and 13C{1H} NMR spectra of 2a and 3a showed clearly
two and four resonances corresponding to methoxy groups in
mono- and di-inserted products, respectively. Complex 2c reacts
with Ag(CF3SO3) and pyridine to give cationic complex 3c. The
crystal structure of di-inserted complexes 2b, 2c and 3c show the
newly formed butadienyl fragments present a transecis confor-
mation and are h2 k1 coordinated to the palladium(II) center.
e
Theoretical calculations also confirm the greater stability of this
conformation for di-inserted products.
Bond angles (ꢁ)
Cl(N2)ePdeN
83.35/92.67(7)
83.84/86.77(4)
99.10/96.64(5)
150.54/157.34(4)
173.12/163.39(5)
88.61/91.08(13)
90.88/92.73(14)
127.27/66.29(14)
162.14/87.45(14)
169.81/169.15(15)
108.13/107.49(14)
91.75/92.30(14)
64.43/66.29(14)
85.65/87.45(14)
Cl(N2)ePdeC1 96.03/91.80(9)
Cl(N2)ePdeC3 131.06/150.29(8)
Cl(N2)ePdeC4 164.62/165.84(8)
NePdeC1
NePdeC3
NePdeC4
C1ePdeC3
C1ePdeC4
PdeN1eC7
PdeC1eC2
C1eC2eC3
C2eC3eC4
C3eC4eC5
C4eC5eC6
C5eC6eC7
C6eC7eN
172.09/167.93(11) 171.67/172.02(6)
109.29/106.61(11) 108.20/109.74(6)
93.58/93.59(11)
65.26/65.16(12)
84.94/84.63(12)
4. Experimental
92.39/90.25(6)
65.63/65.11(6)
85.43/88.48(6)
4.1. General
107.89/106.05(19) 108.44/112.67(10) 106.19/112.7(2)
Starting materials and solvents were purchased from Sigmae
Aldrich or Alfa Aesar and used without further purification. Infrared
spectra were recorded on an FT-IR JASCO 680 spectrophotometer in
the spectral range 4000e400 cmꢀ1 using the KBr pellets. NMR
spectra were measured on a Bruker spectrometer at 400.13 MHz
(1H) and 100.61 MHz (13C) using standard pulse sequences at 298 K.
Elemental analysis was performed on Leco, CHNS-932 apparatus.
100.75/48.46(17)
107.36/106.3(3)
118.44/117.0(3)
121.44/122.3(3)
126.99/125.2(3)
125.55/124.2(3)
115.50/113.8(3)
99.82/48.90(9)
102.14/99.3(3)
108.37/105.88(14) 106.66/107.8(3)
118.72/121.13(14) 117.48/119.8(3)
122.43/118.70(14) 121.73/122.7(3)
126.71/127.37(14) 126.65/126.3(4)
124.42/124.86(14) 124.10/124.6(4)
112.45/114.54(13) 111.49/114.1(4)

158
K. Karami et al. / Journal of Organometallic Chemistry 752 (2014) 152e160
Fig. 7. Graphical presentation of LUMO and HOMO for optimized structures of (tc) isomers of 3a, 2b, 2c and 3c and their energy gaps (eV).
4.2. Synthesis of [Pd2{(C,N)eC(CO2Me)]C(CO2Me)C6H4CH2NH(t-
Bu)}2( -Br)2] (2a)
1670. 1H NMR (DMSO-d6, ppm):
d
¼ 1.46 (m, 9H, CH3), 3.08 (m, 1H,
m
NH), 3.46, 3.54, 3.65, 3.76 (s, 12H, 4OMe), 4.04 (d, Ha, CHaH
2JHH ¼ 13.2 Hz), 4.39e4.44 (dd, Hb, CHbH, JHH ¼ 13.2 Hz,
2
To a solution of palladacycle 1a (0.040 g, 0.056 mmol) in acetone
(15 mL) was added MeO2CC^CCO2Me (13.7 L, 0.112 mmol). After
3JHH ¼ 6.0 Hz), 7.03 (d, 1H, C6H4), 7.30e7.45 (m, 3H, C6H4); 13C{1H}
m
NMR (DMSO-d6, ppm):
d
¼ 28.5, 49.8 (t-Bu), 51.2 (OMe), 51.3 (OMe),
6 h, a yellow solution was formed, which was filtered through a
plug of MgSO4. The solvent was removed to ca. 2 mL, and n-hexane
(15 mL) was added to precipitate 2a as a yellow solid, which was
51.8 (OMe), 52.5 (OMe), 59.5 (CH2), 128.0, 128.1, 129.6, 131.4, 134.5,
134.8 (Caromatic), 126.1, 135.3, 143.4, 155.0 (Ca, C,, Cd, C,), 157.8
(CO), 165.1 (CO), 168.0 (CO), 171.02 (CO). Anal. calcd for
collected and air-dried. Yield: 70%. IR (KBr, cmꢀ1):
n
(NH) ¼ 3228,
C23H28NO8BrPd: C, 43.65; H, 4.45; N, 2.21. Found: C, 43. 86; H, 4.39;
N, 2.16%.
n
(CO) ¼ 1709,1628. 1H NMR (DMSO-d6, ppm):
d
¼ 1.35e1.42 (m, 9H,
CH3), 3.50e3.62 (m, Ha, CHaH), 3.65, 3.69 (s, 6H, 2OMe), 5.36 (dd,
Hb, CHbH, 2JHH ¼ 11.4 Hz, 3JHH ¼ 4.8 Hz), 4.4 (br, 1H, NH), 7.37e7.50
4.4. Synthesis of [Pd{(C,N)eC(Ph)]C(Ph)C(Ph)]C(Ph)}
C6H4CH2NH(t-Bu)Cl] (2b)
3
(m, 3H, C6H4), 7.63 (d, 1H, C6H4 JHH ¼ 6.8 Hz); 13C{1H} NMR
(DMSO-d6, ppm):
d
¼ 29.0, 47.0 (t-Bu), 51.0 (OMe), 52.0 (OMe), 57.0
(CH2), 128.0, 128.4, 131.8, 134.7, 138.4, 138.9 (Caromatic), 126.7, 151.6
(Ca, C,), 166.3 (CO), 167.1 (CO). Anal. calcd for C34H44N2Br2Pd2: C,
42.12; H, 4.57; N, 2.88. Found: C, 42.41; H, 4.58; N, 2.82%.
To a suspension of palladacycle 1b (0.050 g, 0.082 mmol) in
dichloromethane (15 mL) was added PhC^CPh (0.058 g,
0.327 mmol). After 6 h, a yellow solution was formed, which was
filtered through a plug of MgSO4. The solvent was removed to ca.
2 mL, and n-hexane (15 mL) was added to precipitate 2b as a yellow
solid, which was collected and air-dried. Yield: 75%. IR (KBr, cmꢀ1):
4.3. Synthesis of [Pd{(C,N)eC(R0)]C(R0)C(R0)]C(R0)}
C6H4CH2NH(t-Bu)Br] (R0 ¼ CO2Me) (3a)
n
(NH) ¼ 3226, 1H NMR (CDCl3, ppm):
¼ 1.11 (m, 9H, CH3), 3.33 (dd,
d
2
3
Ha, CHaH, JHH ¼ 12.6 Hz, JHH ¼ 3.2 Hz), 3.63 (dd, Hb, CHbH,
To a solution of palladacycle 1a (0.040 g, 0.056 mmol) in acetone
(15 mL) was added MeO2CC^CCO2Me (27.4 mL, 0.224 mmol) and
2JHH ¼ 10.2 Hz, 3JHH ¼ 3.2 Hz), 3.91 (br, 1H, NH), 6.81e7.51 (m, 24H,
Ph and C6H4); 13C{1H} NMR (CDCl3, ppm):
d
¼ 29.5, 48.9 (t-Bu), 57.7
the resulting solution was refluxed for 3 h. A yellow solution was
formed which was filtered through a plug of MgSO4. The solvent
was removed to ca. 2 mL, and n-hexane (15 mL) was added to
precipitate 3a as a yellow solid, which was collected and air-dried.
(CH2), 125.3, 125.7, 126.0, 126.4, 126.5, 126.6, 127.4, 127.5, 127.8,
128.9, 129.0, 129.1, 129.3, 129.4, 130.6, 130.8, 130.9, 131.6 (Caromatic),
141.6, 135.6, 134.3, 124.8 (Ca, C,, Cd, C,). Anal. calcd for
Yield: 68%. IR (KBr, cmꢀ1):
n
(NH) ¼ 3250, (CO) ¼ 1725, 1713, 1690,
n
C39H36NClPd: C, 70.90; H, 5.49; N, 2.12. Found: C, 70.73; H, 5.38; N,
2.10%.
Table 4
The energy values of 10 frontier molecular orbitals (FMOs) of tc isomers of 3a, 2b, 2c
and 3c.
4.5. Synthesis of [Pd{(C,N)eC(Ph)]C(Ph)C(Ph)]C(Ph)}
C6H4CH2NH(Et)Cl] (2c)
Molecule
3a-tc
2b-tc
2c-tc
3c
To a suspension of palladacycle 1c (0.050 g, 0.090 mmol) in
dichloromethane (15 mL) was added PhC^CPh (0.064 g,
0.36 mmol). After 6 h, a yellow solution was formed, which was
filtered through a plug of MgSO4. The solvent was removed to ca.
2 mL, and n-hexane (15 mL) was added to precipitate 2c as a yellow
solid, which was collected and air-dried. Yield: 82%. IR (KBr, cmꢀ1):
LUMO energy (eV)
ꢀ0.121
ꢀ0.148
ꢀ0.156
ꢀ0.165
ꢀ0.170
ꢀ0.173
ꢀ0.186
ꢀ0.191
ꢀ0.204
ꢀ0.306
ꢀ0.164
ꢀ0.167
ꢀ0.169
ꢀ0.171
ꢀ0.173
ꢀ0.181
ꢀ0.192
ꢀ0.208
ꢀ0.230
ꢀ0.293
ꢀ0.164
ꢀ0.166
ꢀ0.169
ꢀ0.171
ꢀ0.172
ꢀ0.182
ꢀ0.193
ꢀ0.207
ꢀ0.232
ꢀ0.293
ꢀ0.165
ꢀ0.168
ꢀ0.168
ꢀ0.170
ꢀ0.176
ꢀ0.179
ꢀ0.190
ꢀ0.208
ꢀ0.225
ꢀ0.287
HOMO energy (eV)
n
(NH) ¼ 3200, 1H NMR (CDCl3, ppm):
d
¼ 0.98 (t, 3H, CH3, 3JHH ¼ 7.2
Hz), 1.24 (m, 2H, CH2), 2.33 (m, Ha, CHaH), 2.9 (br, 1H, NH), 4.57 (m,
Hb, CHbH), 6.55e7.83 (m, 24H, Ph and C6H4); 13C{1H} NMR (CDCl3,

K. Karami et al. / Journal of Organometallic Chemistry 752 (2014) 152e160
159
Table 5
The net charge on the atoms around the nine-membered cycle in the di-inserted products; the atom numbering refers to the scheme in Fig. 6.
Molecule
Atom
C1
C2
C3
C4
C5
C6
C7
N1
Pd
Cl (N2)
3a-tc
2b-tc
2c-tc
3c
ꢀ0.124
ꢀ0.113
ꢀ0.142
ꢀ0.152
ꢀ0.152
0.061
0.059
0.093
ꢀ0.055
ꢀ0.207
ꢀ0.247
ꢀ0.285
ꢀ0.079
ꢀ0.179
ꢀ0.219
ꢀ0.196
ꢀ0.037
ꢀ0.114
ꢀ0.037
ꢀ0.019
0.0373
0.003
0.002
0.006
ꢀ0.321
ꢀ0.292
ꢀ0.351
ꢀ0.357
ꢀ0.583
ꢀ0.596
ꢀ0.606
ꢀ0.649
0.348
0.666
0.686
0.836
ꢀ0.444
ꢀ0.476
ꢀ0.434
ꢀ0.736
ppm):
d
¼ 12.6, 18.4 (Et), 48.5 (CH2), 126.5, 126.6, 126.7, 127.5, 127.8,
and F/F distances were constrained to 1.44(1), 2.42(2), 1.32(1) and
2.15(2) A, respectively. Moreover the anisotropic displacement
parameters of the disordered atoms were restrained to be
approximately isotropic and constrained to be equivalent for paired
components of the disorder.
ꢀ
127.9, 128.0, 128.2, 128.3, 128.4, 128.5, 128.7, 128.9, 130.6, 130.7,
131.3, 132.6, 132.8 (Caromatic), 140.8, 135.8, 132.9, 125.8 (Ca, C,, Cd,
C,). Anal. calcd for C37H32NClPd: C, 70.25; H, 5.09; N, 2.21. Found:
C, 70.12; H, 4.96; N, 2.16%.
4.8. Computational methods
4.6. Synthesis of [Pd{(C,N)eC(Ph)]C(Ph)C(Ph)]C(Ph)}
C6H4CH2NH(Et)(py)]CF3SO3 (3c)
DFT method was applied to optimize all structures and calculate
molecular and spectral parameters of prepared compounds in the
gas phase. The energy values in the solvent (dichloromethane)
were calculated using SCRF keyword with Tomasi’s polarized con-
tinuum (PCM) model [59]. Gaussian 09 program package [60] was
employed for optimizing the structures and calculation of molec-
ular properties. To perform DFT calculations, Becke’s three-
parameter exchange functional [61] was used in combination
with the LeeeYangeParr correlation functional (B3LYP) with
LANL2DZ basis set [62]. All molecules have been used without any
symmetry restriction and C1 symmetry was assumed for all mol-
ecules. NBO analyses [63] were carried out as implemented in the
Gaussian program package using B3LYP/LANL2DZ level of theory.
To a solution of complex 2c (0.030 g, 0.047 mmol) in acetone
(15 mL) was added Ag(CF3SO3) (0.010 g, 0.047 mmol), and the
mixture was stirred for 30 min under light protection and then
filtered through a plug of MgSO4 to remove AgCl. Pyridine (3.78 mL,
0.047 mmol) was added to the filtrate, and the resulting yellow
solution was stirred for 45 min and then filtered again through
MgSO4. The solvent was removed to ca. 2 mL, and n-hexane (15 mL)
was added to precipitate complex 3c as a pale yellow solid, which
was collected and air-dried. Yield: 80%. IR (KBr, cmꢀ1):
n
(NH) ¼ 3217,
n
(CF3SO3) ¼ 1029, 1H NMR (CDCl3, ppm):
¼ 1.65 (br,
d
3H, CH3), 2.19 (m, 2H, CH2), 3.25 (d, Ha, CHaH, 2JHH ¼ 14.4 Hz), 3.66
2
(d, Hb, CHbH, JHH ¼ 14.0 Hz), 4.54 (br, 1H, NH), 6.15 (d, HAr
,
3JHH ¼ 7.2 Hz), 6.87e7.72 (m, 28H, 4Ph þ C6H4 þ 4Hpy), 9.48 (d, 1H,
o-py, JHH ¼ 6.4 Hz); 13C{1H} NMR (CDCl3, ppm):
d
¼ 13.15, 30.97
Acknowledgments
3
(Et), 43.75 (CH2), 125.91, 126.03, 126.12, 126.40, 127.05, 128.12,
128.27, 128.66, 128.84, 128.91, 128.94, 128.98, 129.05, 129.12, 129.27,
129.33, 131.10, 131.41, 131.94, 132.78, 134.41, 135.17, 136.61, 137.30
(Caromatic), 151.78, 139.95, 138.82, 124.91 (Ca, C,, Cd, C,). Anal.
calcd for C37H32NClPd: C, 62.58; H, 4.51; N, 3.39. Found: C, 62.41; H,
4.45; N, 3.30%.
We are grateful for the financial support from the Department of
Chemistry, Isfahan University of Technology (IUT).
Appendix A. Supplementary material
CCDC 924332, 924333 and 945922 contain the supplementary
crystallographic data for this paper. These data can be obtained free
of charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
4.7. X-ray structure determinations
Single crystals for the X-ray molecular structure determination
of 2b, 2c and 3c were obtained by slow evaporation of a solution of
2b in chloroform/ n-hexane and solution of 2c and 3c in dichloro-
methane/ n-hexane. The X-ray diffraction experiments for 2b and
2c were done at 100 K with the use of Agilent SuperNova single
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