Carbonyl group coordination preferences in square-planar NiII and PdII complexes of pentadentate ligands by electron-withdrawing/donating substituents

Article abstract of DOI:10.1016/j.ica.2015.04.029

A series of chirally switchable Ni^II and Pd^II complexes were synthesized and fully characterized by X-ray crystallography and additionally by NMR. It was found that control of the stereochemical preference between (S?,S?) and (S?,R?)

Full text of DOI:10.1016/j.ica.2015.04.029

Inorganica Chimica Acta 433 (2015) 3–12
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
II
II
Carbonyl group coordination preferences in square-planar Ni and Pd
complexes of pentadentate ligands by electron-withdrawing/donating
substituents
a
b
c
d
e
Jianlin Han , José Luis Aceña , Nobuhiro Yasuda , Hidehiro Uekusa , Taizo Ono ,
b,f,
⇑
g,h,
⇑
Vadim A. Soloshonok
, Karel D. Klika
a
School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210093, China
b
c
d
e
f
Department of Organic Chemistry I, Faculty of Chemistry, University of the Basque Country UPV/EHU, Paseo Manuel Lardizábal 3, 20018 San Sebastián, Spain
Japan Synchrotron Radiation Research Institute, SPring-8, 1-1-1 Kouto, Sayo-gun, 679-5198 Sayo-cho, Hyogo, Japan
Department of Chemistry and Materials Science, Tokyo Institute of Technology, Ookayama 2, Meguro-ku, Tokyo 152-8551, Japan
National Institute of Advanced Industrial Science and Technology (AIST), Anagahora 2266-98, Shimoshidami, Moriyama, 463-8560 Nagoya, Aichi, Japan
IKERBASQUE, Basque Foundation for Science, María Díaz de Haro 3, 48013 Bilbao, Spain
Department of Chemistry, University of Turku, Vatselankatu 2, FIN-20014 Turku, Finland
Molecular Structure Analysis, German Cancer Research Center (DKFZ), Im Neuenheimer Feld 280, D-69009 Heidelberg, Germany
g
h
a r t i c l e i n f o
a b s t r a c t
A series of chirally switchable NiII and PdII complexes were synthesized and fully characterized by X-ray
crystallography and additionally by NMR. It was found that control of the stereochemical preference
Article history:
Received 26 February 2015
Received in revised form 20 April 2015
Accepted 27 April 2015
⁄
⁄
⁄
⁄
between (S ,S ) and (S ,R ) diastereomers by substituent modification of the ligand sidearms was possible
in the process of crystallization with the preferred coordination of the sidearms generally consistent with
expectations based on the electron-donating or -withdrawing properties of the sidearm substituent
groups. There were however, quite interesting and unanticipated exceptions counter to chemical intu-
ition and it seems that only for complexes with ortho substituents are strong preferences for the coordi-
nation manner necessarily displayed in the solid state based on the electron-withdrawing or -donating
properties of the substituents.
Available online 7 May 2015
Keywords:
II
Ni complexes
II
Pd complexes
Trifluoromethyl group
Chiral switches
Ó 2015 Elsevier B.V. All rights reserved.
Coordination modes
Density functional theory
1
. Introduction
Molecules that can form supramolecular assemblies frequently
system based on the coordination of achiral pentadentate ligands
with d metals [4], and have since extended it to chiral ligands
8
[5]. Such chirally facile interconverting systems have been adopted
recently for their potential application as molecular switches [6],
though the authors drew attention to the inherent drawback in
that no chemical reaction can proceed with 100% conversion
[4a]. This is countered however, by the plethora of potential sys-
tems that could be applied for such purposes [6].
possess useful chemical and physical properties [1], and amongst
these coordination compounds are particularly prominent since
one of the major challenges is to attain a fine balance between
structural predictability and coordination flexibility, thereby
allowing the compounds to be responsive to external stimuli [2].
In this respect, one successful approach has been the application
of ligands containing carbonyl groups specifically intended to be
weakly coordinating [3]. We previously introduced a molecular
II
II
In our system consisting of square-planar Ni or Pd complexes
(Scheme 1), two elements of chirality are present: the stereogenic
center resulting from the fixation of the chirality at the benzy-
lamine nitrogen and the stereogenic axis arising from the
restricted rotation of the non-coordinated N-(o-benzophenone)
amide moiety about the N–C bond. Four species altogether, dis-
counting enantiomers, are possible when utilizing differently sub-
stituted sidearms of the ligand and facile interconversion could
conceivably occur between two preferred species. For example,
⇑
Corresponding authors at: Department of Organic Chemistry I, Faculty of
Chemistry, University of the Basque Country UPV/EHU, Paseo Manuel Lardizábal 3,
0018 San Sebastián, Spain. Tel.: +34 943 015177; fax: +34 943 015270 (V.A.
2
Soloshonok). Molecular Structure Analysis, German Cancer Research Center (DKFZ),
Im Neuenheimer Feld 280, D-69009 Heidelberg, Germany. Tel.: +49 6221 42 4515;
fax: +49 6221 42 2995 (K.D. Klika).
E-mail addresses: vadym.soloshonok@ehu.es (V.A. Soloshonok), klikakd@yahoo.
co.uk (K.D. Klika).
⁄
⁄
⁄
⁄
the switch between diastereomers (S ,S ) and (S ,R ) occurs via
the carbonyl de-coordination/coordination step resulting in
http://dx.doi.org/10.1016/j.ica.2015.04.029
0
020-1693/Ó 2015 Elsevier B.V. All rights reserved.

4
J. Han et al. / Inorganica Chimica Acta 433 (2015) 3–12
Horizontal transformations: if the trans (or cis) relationship between the N-benzyl group and the
coordinated ligand arm is favored and the coordination of a particular ligand arm is not important
Diagonal transformations: if
coordination of a particular
ligand arm is preferred and
the cis/trans relationship of
the N-benzyl group and the
coordinated ligand arm is
relatively unimportant
O
O
O
O
N
N
N
N
N
N
Ni
Ni
O
O
O
O
R
R
S*,S* diastereomer, substituted
S*,S* diastereomer, unsubstituted
Vertical transformations:
represent both a change in
the cis/trans relationship
between the N-benzyl
group and the coordinated
ligand arm together with a
change in the ligand arm
that is coordinated
arm of the ligand coordinated
arm of the ligand coordinated
O
O
O
O
N
N
N
N
N
N
Ni
Ni
O
O
O
O
R
R
S*,R* diastereomer, unsubstituted
arm of the ligand coordinated
S*,R* diastereomer, substituted
arm of the ligand coordinated
Scheme 1. Formation of diastereomerically switchable complexes from chiral ligands.
inversion of the stereogenic center chirality whilst retaining the
same sense of the axial chirality, i.e. the vertical transitions in
Scheme 1. If retention of the cis/trans relationship of the N-benzyl
2. Results and discussion
1
Continuing our modular approach for the design and synthesis
of pentadentate ligands and the consequent metal complexes [7],
we prepared ligands 5a–c in high yields, starting from the acetyl-
protected 2-aminobenzophenones 1a–c, readily available by aryl
group and the coordinated ligand arm is favored but the coordinat-
ing sidearm is not, then the horizontal transformations are in oper-
ation while conversely if the cis/trans relationship of the N-benzyl
group and the coordinated ligand arm is unimportant but the coor-
dinating sidearm is, then the diagonal transformations are in effect.
Importantly, it should be noted that due to the structural rigidity of
the complexes, a process such as the vertical transition can occur
with near complete (>99%) stereoselectivity.
Grignard
additions
to
2-methyl-4H-3,1-benzoxazin-4-one
(Scheme 2). 1a–c were first hydrolyzed to the free 2-aminoben-
zophenones 2a–c, and then converted to amides 3a–c by treatment
with bromoacetyl bromide. These compounds encompassed elec-
tron-donating ortho-methyl, –o-Me, (3a) and para-methoxy, –p-
OMe, (3c) groups as well as an electron-withdrawing para-trifluo-
Previously, to evolve the molecular system with differently sub-
stituted sidearms in terms of predictability, we introduced elec-
tron-withdrawing or -donating substituents to influence the
preference for coordination of the N-(o-benzophenone) amide car-
bonyls [5]. While the reported data were quite convincing, we felt
romethyl, –p-CF , (3b) group. Compounds 3a–c were transformed
3
to pentadentate ligands 5a–c by reaction with the ring-unsubsti-
tuted benzlyamine moiety 4 [7c], also in high yields. Treatment
of 3c (Scheme 3) with benzylamine yielded intermediate 7 [5,8],
which upon reaction with 3b yielded pentadentate ligand 8 func-
tionalized on both sidearms, again in high yield.
II
II
that only two examples for the Ni and one for the Pd complexes
were insufficient to consider this approach for controlling the coor-
dination preferences completely explored and proven. Therefore,
we decided to extend our study to the synthesis of an additional
II
II
The synthesis of Ni and Pd complexes 6a–e (Schemes 2 and 3)
proceeded straightforwardly by the reaction of Ni(NO ) ꢀ6H O
3
2
2
II
II
series of fluorinated and non-fluorinated Ni and Pd complexes
to further understand the processes and factors involved in the sys-
tem interconversion, the preferential binding modes, as well as
peculiarities of the crystallographic packing. Characterization of
the complexes was enabled in the solid state by X-ray crystallo-
graphic analysis supported by NMR and MS measurements. The
relative energies of the structures with respect to configuration
and coordination site were evaluated by DFT calculations to further
complement and comprehend the results.
(6b,d,e) or PdCl (6a,c) together with the appropriate ligand (5a–
2
c or 8) in methanol under basic conditions [7c,9], though with only
modest (Ni complexes) or poor (Pd complexes) yields being
obtained.
Crystals of complexes 6a–e amenable for X-ray analysis were
obtained in each case by slow evaporation from either CH Cl2
(6b–e) or EtOAc (6a) solutions overlaid with n-hexane. This usually
required great perseverance and was very demanding and only
very small crystals could be obtained in some cases. The details
2
II
of X-ray crystallographic data collection and refinement for Ni
II
and Pd complexes 6a–e are summarized in Table 1.
1
The assignment of configuration at the stereogenic center, the N atom, follows the
II
II
Previously we have examined CF
plexes 6f–h (Fig. 1) and found full consistency between the
3
-containing Ni and Pd com-
convention outlined previously (Ref. [5]) in that covalent bonds are not considered to
take undue preference over coordinating bonds.

J. Han et al. / Inorganica Chimica Acta 433 (2015) 3–12
5
Br
Ac
NH
O
R1
H N
O
R1
O
NH
O
R1
2
HCl
BrCH COBr
2
R2
R2
R2
1
1
1
a R1 = Me, R2 = H
b R1 = H, R2 = CF3
c R1 = H, R2 = OMe
2a R1 = Me, R2 = H
2b R1 = H, R2 = CF3
2c R1 = H, R2 = OMe
3
3
3
a R1 = Me, R2 = H
b R1 = H, R2 = CF3
c R1 = H, R2 = OMe
NHBn
NH
O
O
O
O
O
N
O
N
NiII
N
N
NH
HN
M
or PdII
O
O
O
O
4
R1
R1
R2
R2
6
6
6
a M = Pd, R1 = Me, R2 = H
b M = Ni, R1 = H, R2 = CF3
c M = Pd, R1 = H, R2 = CF3
5a R1 = Me, R2 = H
5b R1 = H, R2 = CF3
5c R1 = H, R2 = OMe
6
d M = Ni, R1 = H, R2 = OMe
Scheme 2. Synthesis of ligands 5a–c and NiII and PdII complexes 6a–d. N.b. The actual coordinating sidearm is described in turn for each complex 6a–d.
NHBn
NH
contained eight molecules per unit cell consisting of four enan-
tiomeric pairs of molecules, R,R and S,S.
BnNH2
3b
II
The Ni complex 6b exhibited the expected coordination man-
O
O
3c
ner in the solid state (Fig. 2) in that the carbonyl oxygen of the
unsubstituted sidearm of the ligand was preferentially coordinated
OMe
to the Ni due to the electron-withdrawing property of the –p-CF
3
7
substituent group in the non-coordinated arm thus favoring pref-
erential coordination by the carbonyl oxygen to the Ni in the for-
mer sidearm. This same observation held true for Pd complex 6c
II
O
O
in the solid state (Fig. 3) via similar reasoning. Thus, re-positioning
O
O
N
N
II
the –CF
3
group from the ortho position, i.e. Ni complex 6f where
N
HN
N
NiII
NH
Ni
the resonance effects might be expected to be stronger in addition
to sigma effects, still results in the same preferred coordination
manner in the solid state.
O
O
O
O
In the previous study, we examined the tandem effect of mixing
electron-donating (–p-OMe) and -withdrawing (–o-CF
3
) sub-
stituent groups with one of each type on opposing arms [5].
OMe
OMe
CF3
CF3
II
II
Unsurprisingly, both the Ni (6g) and Pd complexes (6h) exhibited
the expected manner of coordination preference in the solid state
with the carbonyl oxygen of the sidearm containing the –p-OMe
substituent group being coordinated to the metal.
6
e
8
Scheme 3. Synthesis of NiII complex 6e.
We again examined the tandem effect of mixing electron-
donating and -withdrawing substituent groups with one of each
anticipated and the observed coordination in the solid state as
determined by X-ray crystallographic analysis [5]. The anticipated
coordination preference was considered in light of the electron-do-
nating or -withdrawing properties of the sidearm substituent
groups and can be construed as ‘‘chemical intuition’’.
type on opposing arms, but this time with –p-OMe and –p-CF sub-
3
stituent groups, i.e. the –CF3 group was re-positioned from the
II
ortho position to the para position in Ni complex 6e with respect
to complexes 6g,h. The ensuing result was remarkable. The molec-
ular structure of 6e displayed structural disorder at the two termi-
II
All five Ni complexes 6b,d–g from these two studies were
ꢀ
found to crystallize in the triclinic system and space group P1 with
nal functional groups, –p-CF
of –p-CF and –p-OMe are exchanged (i.e. the coordinating side-
arms are interchanged). These disordered –p-CF and –p-OMe
3
and –p-OMe, in which the positions
two molecules per unit cell consisting of an enantiomeric pair of
3
II
molecules, R,R and S,S. All three Pd complexes 6a,c,h on the other
3
hand, were found to crystallize in the orthorhombic system,
though formerly 6h was found to crystallize in the space group
Pbca while in this study 6a,c both were found to crystallize in
groups are almost completely overlapped at the two sites as they
have very similar geometric volumes, so such disorder can thus
occur without steric hindrance in the crystal structure and disrup-
tion of the crystal packing forces. Though this is a known
II
the space group Pccn. All three Pd crystal structures however,

6
J. Han et al. / Inorganica Chimica Acta 433 (2015) 3–12
Table 1
Summary of crystal data for complexes 6a–e.
6
a
6b
6c
6d
6e
Formula
C
38
H
31
N
3
O
4
Pd
C
39
H30Cl
2
F
N
3 3
O
4
Ni
C
38
H
28
F
3 3
N O
4
Pd
C
39
H
33Cl
2
N
3
O
5
Ni
40 2 3 3 5
C H32Cl F N O Ni
M
700.06
123(2)
0.68972
791.27
143(2)
1.54186
754.03
123(2)
0.83136
753.27
123(2)
0.83136
821.30
123(2)
0.71073
Temperature (K)
Wavelength (Å)
Crystal size (mm)
Crystal system
Space group
a (Å)
0.0879 ꢁ 0.0159 ꢁ 0.005 0.07 ꢁ 0.02 ꢁ 0.02
0.0876 ꢁ 0.0164 ꢁ 0.005 0.170 ꢁ 0.0143 ꢁ 0.0043 0.40 ꢁ 0.06 ꢁ 0.04
orthorhombic
Pccn
triclinic
P1ꢀ
orthorhombic
Pccn
triclinic
P1ꢀ
triclinic
P1ꢀ
23.474(3)
31.104(5)
8.5425(15)
–
–
–
6237.3(17)
8
1.491
8.5200(2)
13.6980(3)
15.8800(4)
75.748(1)
75.510(1)
83.215(1)
1735.97(7)
2
23.5859(9)
31.8655(10)
8.3357(3)
–
–
–
6265.0(4)
8
1.599
8.5849(4)
13.7098(8)
15.4024(9)
78.1456(19)
73.6561(17)
82.8312(16)
1698.13(16)
2
8.6277(7)
14.1581(12)
15.9486(13)
71.537(2)
78.720(2)
86.163(2)
1812.2(3)
2
b (Å)
c (Å)
a
(°)
b (°)
(°)
c
3
V (Å )
Z
D
ꢂ3
calc (Mg m
)
1.514
1.473
1.505
F(000)
2869
812
3056
780
844
h Range for data collection (°)
Index ranges, hkl
1.68–24.55
ꢂ27 to 28, ꢂ37 to 37,
ꢂ10 to 10
5705/38442
0.248
2.95–68.23
2.46–27.89
2.63–27.83
3.03–27.45
ꢂ10 to 9, ꢂ16 to 16, ꢂ19 to 26, ꢂ30 to 30, ꢂ8 ꢂ8 to 7, ꢂ15 to 15, ꢂ17 ꢂ11 to 11, ꢂ18 to 18,
ꢂ18 to 19
to 9
3664/21851
1.055
to 17
4249/8751
1.084
ꢂ20 to 20
Reflections unique/observation
6237/20534
1.000
8045/17496
1.070
Goodness-of-fit on F2
Final R indices {I > 2
R indices (all data), R
Largest diff. peak, hole (e Å
r
1
(I)}, R
1
, wR
2
0.0298, 0.0422
0.1710, 0.0598
0.379 and ꢂ0.443
0.1641, 0.3545
0.4261, 0.5224
0.713 and ꢂ0.607
0.0514, 0.1089
0.0870, 0.1244
0.681 and ꢂ1.162
0.0978, 0.2350
0.1435, 0.2881
1.179 and ꢂ0.961
0.0608, 0.1418
0.1087, 0.1757
1.293 and ꢂ0.964
, wR
2
ꢂ3
)
O
O
N
N
N
O
M
O
F3C
R
6
6
6
f M = Ni, R = H
g M = Ni, R = OMe
h M = Pd, R = OMe
Fig. 3. X-ray structure of PdII complex 6c; only the (R,R)-enantiomer is shown from
the unit cell containing both enantiomers.
Fig. 1. The previously reported NiII and PdII complexes 6f–h [5].
to the Ni) however, is only 0.103(5) and this is somewhat unusual.
The occupancy anomaly may originate from crystallographic
sources [10], e.g. insufficient void space around the two groups
resulting in less than rigid but not totally slack packing or insuffi-
cient molecular size to completely negate the differences in surface
charge between the two groups. Alternatively, minor stability dif-
ferences in the adopted coordinations could result in both species
being present to a high degree in solution. Clearly the latter must
be an important factor in this case and therefore the conclusion
must be that the effect of the electron-donating properties of the
–
p-OMe substituent group and the electron-withdrawing proper-
ties of the –p-CF substituent group can be considered quite weak
despite the contrary indications for the latter from complexes 6b,c
3
II
(
vide supra). The structure of Ni complex 6e with an indication of
the disorder at the substituent sites is displayed in Fig. 4.
II
The Pd complex 6a with an –o-Me substituent group exhibited
Fig. 2. X-ray structure of NiII complex 6b; only the (S,S)-enantiomer is shown from
the unit cell containing both enantiomers.
the expected coordination manner in the solid state (Fig. 5) in that
the carbonyl oxygen of the substituted sidearm of the ligand was
preferentially coordinated to the Pd due to the electron-donating
property of the –o-Me substituent group in the coordinating arm
thus favoring preferential coordination by its carbonyl oxygen to
the Pd.
phenomenon – the isomorphic or ‘‘chloro–methyl’’ exchange rule
[
10] – the occupancy factor of the minor component (the carbonyl
oxygen of the sidearm bearing the –p-CF group being coordinated
3

J. Han et al. / Inorganica Chimica Acta 433 (2015) 3–12
7
Fig. 6. X-ray structure of NiII complex 6d; only the (S,S)-enantiomer is shown from
the unit cell containing both enantiomers.
Fig. 4. X-ray structure of NiII complex 6e; only the (S,S)-enantiomer is shown from
the unit cell containing both enantiomers. The disorder at the –p-OMe and –p-CF3
substituent groups is portrayed.
The complexes 6a–h, unfortunately, were only very poorly sol-
uble in suitable solvents, thus limiting their comprehensive analy-
sis by NMR, limited especially by the consequent unavailability of
1
3
C acquisition. With appreciable conformational mobility includ-
ing the flexible benzyl moiety, fluxional motion of the heteroatom
rings formed by coordination to the metal, and other bond rota-
tions etc., in addition to the chiral switching arising from the de-
coordination/coordination steps of the carbonyl oxygen atoms to
the metal, the NMR spectra were either extremely broad or con-
tained multiple resonances from the various contributing species
wherein interconversion between the species was confirmed by
variable-temperature NMR. Thus pertinently, the solution-state
flexibility extends to the solid state as discussed above.
Nevertheless, the evaluation of Gibbs’ Free Energies (
equilibria based on signal integration to access populations
enabled comparison to G values provided by DFT-calculations
DG) for the
D
and is discussed in conjunction with the modeling results (vide
infra). For characterization purposes of these complexes, sufficient
H and F NMR data were nonetheless attained and were consis-
1
19
Fig. 5. X-ray structure of PdII complex 6a; only the (S,S)-enantiomer is shown from
the unit cell containing both enantiomers.
tent with the expected structures. Irrespective of these limitations
however, the dynamic behaviors exhibited by the complexes
clearly indicate the potential for facile switching between diastere-
omers and clearly chiral switching must be a principle process in
effect based on the magnitude of the energies involved.
Moreover, it was evident that the introduction of electron-with-
drawing or -donating substituents on the sidearms in ligands 5a–
c and 8 was insufficient for providing a predictable, overwhelm-
ingly biased coordination of a particular carbonyl group in solu-
II
Finally, the solid state structure of Ni complex 6d with an elec-
tron-donating –p-OMe substituent group – previously indicated to
be only weakly effective from the results of 6e – is presented in
Fig. 6. The result is, in spite the aforementioned assertion, still
unexpected and quite extraordinary. The carbonyl oxygen in the
unsubstituted sidearm is preferentially coordinated to the Ni coun-
ter to chemical intuition. It can only be assumed that crystal pack-
F
tion. An interesting point however, is that the d of the coalesced
ing forces may play
a
determinate role in exhibiting the
signal for the –CF group for complexes 6b,c,e is essentially identi-
3
unexpected coordination manner in the solid state. To rationalize
this intriguing result, it is worth noting that complexes 6b–d are
all isostructural and it is the carbonyl oxygen of the unsubstituted
sidearm that is coordinated to the metal: It seems therefore that
only for complexes with ortho substituents (complexes 6a,f–g)
are strong preferences necessarily displayed in the solid state
based on the electron-withdrawing or -donating properties of the
substituents. In other cases with only para substituents present
cal in all three cases (ca. ꢂ65 ± 1 ppm), thus pertaining to at least
some dominance of the species where the carbonyl oxygen in the
ligand arm bearing the –CF
otherwise it could be expected that differences in d
apparent – notwithstanding some quite improbable coincidences
in d and equilibria positions. This is analogous to complexes 6f–
h which also displayed [5] an essentially identical d of the coa-
lesced signal for their –CF
group (ca. ꢂ61 ppm) with the difference
in d between the two sets attributed to the ortho/para positioning
of the –CF substituent group.
3
group is not coordinated to the metal,
F
s would be
F
F
3
(
complexes 6b–e), the observed preference for the coordination
F
manner may align with the expected preference, though this may
simply be incidental (complexes 6b,c), or it may provide an unex-
pected mixture (complex 6e), or it may provide a seemingly
anomalous result counter to chemical intuition (complex 6d). As
a final note, the cis isomers were not observed at all, and thus only
the (S,S)- and (R,R)-enantiomers were present representing the
trans isomers.
3
For comparison to the experimental NMR results, four coordina-
tion site/relative configuration permutations were selected for
intrastructural evaluation of each complex and interstructural
comparison between the complexes following geometry optimiza-
tion and calculation of their corresponding energies by density
functional theory (DFT) quantum chemical calculations. The four
structural permutations of each complex were the coordination
of either carbonyl of each ligand arm to the metal and then with
To try and comprehend these anomalous solid-state results,
recourse was made to NMR measurements and DFT calculations.

8
J. Han et al. / Inorganica Chimica Acta 433 (2015) 3–12
respect to the relative configuration of the free ligand arm as either
⁄
⁄
⁄
⁄
cis (i.e. R ,S ) or trans (i.e. R ,R ) to the benzyl group. Each structure
for optimization was conveniently modified from an optimized
structure taken from a set for a compound previously optimized.
This ensured firstly, computational efficiency, and secondly, fair
comparison between the analogous structures across the sets.
Calculations were performed firstly in the gas phase, and then by
inclusion of a solvent model (polarizable continuum model using
2 2
the integral equation formalism variant, IEFPCM) for CH Cl . The
non-metallic atoms were adequately handled using the restricted
B3LYP functional with the 6-31G(d,p) basis set while the Ni and
Pd entities necessitated the selective use of the LanL2DZ basis
II
set. Example depictions for Ni complex 6b of the four structural
permutations are presented in Figs. 7–10 while Table 2 lists the
Fig. 9. Complex 6b with coordination of the unsubstituted ligand arm and with the
ligand arm bearing the –CF group cis to the benzyl group.
3
Fig. 7. Complex 6b with coordination of the ligand arm bearing the –CF
with the unsubstituted ligand arm cis to the benzyl group.
3
group and
Fig. 10. Complex 6b with coordination of the unsubstituted ligand arm and with
the ligand arm bearing the –CF group trans to the benzyl group.
3
D
G values for the four structural permutations of complexes 6a–
h without and upon inclusion of the solvent model.
Overall though, the results with respect to relative energies are
heavily dependent upon inclusion of the solvent model considering
each complex individually with respect to the dominance of one
structure over the other three with respect to coordination site
and relative configuration (for example, complex 6f has three
close-in-energy minima structures). It is worth noting that while
the relative energies change, the geometrical changes of each
structure from the gas phase upon inclusion of the solvent were
quite small by inspection, thus pertaining to the important role
that the solvent plays in stabilizing the complexes without struc-
tural changes.
With respect to the coordination site, with the exception of the
methyl-substituted complex 6a, the expected ligand arm coordina-
tion preference for each complex is predicted to be energetically
favored, though the pronounced differences in the gas phase could
be quite muted when the solvent model was included, e.g. com-
plexes 6b,d,f. For the methyl-substituted complex 6a, the methyl
group is a weak electron donor and thus it is not too surprising that
Fig. 8. Complex 6b with coordination of the ligand arm bearing the –CF
with the unsubstituted ligand arm trans to the benzyl group.
3
group and

J. Han et al. / Inorganica Chimica Acta 433 (2015) 3–12
9
Table 2
DFT-calculated Gibbs’ Free Energies (
D
G) of four selected coordination site/relative configuration permutations for complexes 6a–h, both without and upon inclusion of a solvent
2 2
model for CH Cl .
ꢂ1
ꢂ1
D
G in the gas phase (kJ mol
)
D
G with the solvent model for CH
2
Cl
2
(kJ mol )
Coordination site:
First sidearm listed
Second sidearm listed
First sidearm listed
Second sidearm listed
⁄
⁄
⁄
⁄
⁄
⁄
⁄
⁄
⁄
⁄
⁄
⁄
⁄
⁄
⁄ ⁄
Relative configuration:
trans (R ,R )
cis (R ,S )
trans (R ,R )
cis (R ,S )
trans (R ,R )
cis (R ,S )
trans (R ,R )
cis (R ,S )
6
6
6
6
6
6
6
6
a: –p-H, –o-Me
0.00
0.00
0.00
2.12
0.00
0.00
0.00
0.00
5.10
5.34
4.52
5.92
13.43
4.44
3.65
7.13
2.84
4.98
6.18
0.00
7.92
5.36
7.20
6.83
7.19
9.05
9.82
0.00
0.00
0.00
0.83
0.00
0.00
0.00
0.00
2.74
3.65
4.76
5.76
6.40
0.15
3.80
8.85
1.75
0.79
4.79
0.00
9.39
0.46
2.69
1.87
3.74
6.47
7.43
3.97
13.80
2.54
5.85
7.52
b: –p-H, –p-CF
3
c: –p-H, –p-CF
3
d: –p-H, –p-OMe
e: –p-OMe, –p-CF
2.66
3
15.25
12.30
10.30
11.99
f: –p-H, –o-CF
g: –p-OMe, –o-CF
3
3
h: –p-OMe, –o-CF
3
ꢂ1
the expected results were not forthcoming though for complex 6a
the difference is quite small at 1.75 kJ mol with inclusion of the
to coordination in the gas phase, 5.36 kJ mol ). In two other cases
where the dynamic behavior could be comprehended – complexes
ꢂ1
ꢂ1
ꢂ1
solvent model. It is worth noting that steric effects do not appear to
play a role in the calculational results as the methyl group is ori-
ented away from any potential steric interactions. These results
tally well with the X-ray crystal structure determinations of com-
plexes 6b,c,f–h wherein the expected coordination configuration
was indeed observed for these complexes in the solid state. For
complex 6a, the expected coordination configuration was observed
in the solid state in contrast to the calculational result.
Interestingly, for complex 6d, the unexpected coordination config-
uration observed in the solid state was in opposition to intuition
and the calculational results, but it must be noted that for this
complex the difference in energies – at least with inclusion of
the solvent model – between the two coordination configurations
6e (exp. 2.47 kJ mol
;
calc. 9.39 kJ mol
)
and 6h (exp.
ꢂ1
ꢂ1
5.54 kJ mol ; calc. 1.87 kJ mol ) – experimental observations
were less in concert with calculated values. For these two cases,
inclusion of the solvent model actually led to poorer predicted val-
ues. The reasons for these anomalies may again reside with the
complex conformational behavior of the molecules stemming from
their promiscuity with respect to conformational space. Clearly
inclusion of a solvent model influences the results greatly and
therefore must be considered mandatory for these complexes.
Nonetheless, modeling calculations hold promise for predicting
favorable selection of systems for coordination configuration and
stereochemical preference and hence potential application as opti-
cally switchable devices. The challenge is in surmounting the
encumbrance arising from the complex behavior of these highly
conformationally promiscuous molecules.
ꢂ1
was near the lowest of all the complexes at 0.83 kJ mol thereby
suggesting that the presence of the unexpected coordination con-
figuration isomer is not altogether untoward. Perhaps even more
surprising was the result for complex 6e where both coordination
configuration isomers were observed in the solid state with the
expected isomer – in concert with calculations – predominant
3
. Conclusions
It was found that control of the stereochemical preference
(
ratio adjudged to be ca. 9:1). Here though, the difference in ener-
⁄
⁄
⁄
⁄
between (S ,S ) and (S ,R ) diastereomers by substituent modifica-
tion of the ligand sidearms was possible in the solid state with the
preferred coordination of the sidearms generally consistent with
expectations based on the electron-donating or -withdrawing
properties of the sidearm substituent groups. However, it seems
that only for complexes with ortho substituents (complexes 6a,f–
g) are strong preferences for the coordination manner necessarily
displayed in the solid state based on the electron-withdrawing or
gies between the two coordination configurations was near the
ꢂ1
highest of all the complexes (9.39 kJ mol
model).
with the solvent
In four cases fine or reasonable agreement was found between
prediction and observation for the position of the coordination site
equilibrium in solution, viz. complexes 6b,c,f,g, which is respect-
able considering the complexity of the systems involved, their con-
formational mobility and the need to include a solvent model. In
-
donating properties of the substituents. In other cases with only
the case of complex 6b, the experimental value of
DG was
para substituents present (6b–e), the observed preference for the
coordination manner may align with the expected preference,
though this may simply be incidental (6b,c), or it may provide an
unexpected mixture (6e), or it may provide a seemingly anomalous
result counter to chemical intuition (6d). The unusual observation
of mixed species in one crystal lattice in the case of 6e is an inter-
esting crystallographic result and may be the consequence of the
state of the system in solution.
These results indicate that the design of molecular systems sen-
sitive to external stimuli with macromolecular structure may be
less predictable than originally thought, but this could lead to
greater potential in terms of response sensitivity and fine tuning.
ꢂ1
evaluated as 0.69 kJ mol between the global minimum and the
next lowest energy structure with other structures of minimal con-
tribution and this compared well with the calculations which pro-
ꢂ1
vided a value of 0.79 kJ mol ; for complex 6f, the experimental
ꢂ1
value of
D
G was evaluated as 1.04 kJ mol between the preferred
coordination configuration isomer and the alternative coordination
configuration isomer while calculations provided
a
value
ꢂ1
of 0.46 kJ mol
; for complex 6g, the observed value of
ꢂ1
4
2
.42 kJ mol was somewhat higher than the predicted value of
ꢂ1
.69 kJ mol ; and by contrast, for complex 6c the observed value
ꢂ1
of 2.86 kJ mol was somewhat lower than the predicted value of
ꢂ1
4
.79 kJ mol . Of note, in the case of complex 6c, considerable
improvement was forthcoming by inclusion of the solvent model
calculated G with respect to coordination in the gas phase,
(
D
4. Experimental
ꢂ1
6
.18 kJ mol ). For complex 6b, inclusion of the solvent model
was absolutely critical for the good result (calculated
respect to coordination in the gas phase, 4.98 kJ mol ) and simi-
D
G with
4.1. X-ray experimental
ꢂ1
larly for complexes 6g (calculated
in the gas phase, 7.20 kJ mol ) and 6f (calculated
D
G with respect to coordination
G with respect
The crystal data and details of data collection are given in
Table 1. X-ray diffraction data for complexes 6a,c,d were measured
ꢂ1
D

1
0
J. Han et al. / Inorganica Chimica Acta 433 (2015) 3–12
at 123(2) K using synchrotron radiation on the BL40XU (6c,d) and
BL02B2 (6a) instruments at SPring-8 utilizing a high precision
diffractometer [11] and large cylindrical image-plate camera [12],
respectively, because of the extremely small crystal sizes of the
samples provided. The data for complexes 6b,e were measured
using a Rigaku R-AXIS RAPD imaging plate diffractometer {gra-
polarizable continuum model using the integral equation formal-
ism variant solvent model (IEFPCM) – followed previous protocol
[21] with parameter values for CH Cl as the selected solvent.
2 2
4.4. Synthesis
phite-monochromated Mo K
nique, k = 0.71073 (6e) or 1.54186 (6b) Å} at 123(2) (6e) or
43(2) (6b) K. The crystal structures were solved by direct methods
a
or Cu K
a
radiation,
x
-scan tech-
4.4.1. General procedure for the syntheses of 2-aminobenzophenones 2
To a solution of the corresponding acetamide 1a–c in acetone
(0.15 m), aqueous 6 m HCl (40 eq.) was added. The solution was
1
2
using SHELXS-97 [13] and all non-H atoms were refined on F
anisotropically using SHELXL-97 [14] except for 6a. H atoms were
located by geometrical calculations and included refinement using
riding models with constrained isotropic displacement parameters.
The structure for 6a was refined isotropically except for the Pd
atom due to the very weak diffraction intensities as a result of
the small crystal size. However, the molecular structure of 6a is
considered sufficiently reliable and the R1 factor converged to
stirred at 70 °C for 2 h followed by the addition of K
basic. The crude amine was extracted with CH Cl and the organic
layer dried over Na SO and then concentrated in vacuo after filtra-
2 3
CO until
2
2
2
4
tion. The resulting 2-aminobenzophenones 2a–c were used with-
out further purification.
0
1
4.4.1.1. 2-Amino-2 -methylbenzophenone (2a). 97% yield. H NMR d
2.31 (3H, s), 6.44 (2H, br), 6.56 (ddd, J = 8.1, 7.6, 1.1 Hz), 6.75 (dd,
1
3
0
.0298 without significant residual electron density peak.
J = 8.3, 0.7 Hz), 7.23–7.41 (6H, m). C NMR d 19.1, 115.1, 116.6,
Depictions of the X-ray derived structures in Figs. 2–6 were pro-
duced using the GUI GaussView [15].
117.7, 124.9, 126.7, 128.8, 130.2, 134.4, 134.5, 134.6, 140.3,
+
151.1, 200.9. HRMS: calcd for C14H14NO [M+H] 212.1075, found
2
12.1079.
4
.2. NMR experimental
0
4
.4.1.2. 2-Amino-4 -(trifluoromethyl)benzophenone (2b). 90% yield.
1
NMR spectra were acquired using a Bruker Avance NMR spec-
H NMR d 6.25 (2H, brs), 6.64 (ddd, J = 8.1, 7.6, 1.1 Hz), 6.79 (dd,
1
3
trometer equipped with a 5 mm normal configuration dual coil
probe with z-gradient capability at a field strength of 9.4 T operat-
ing at 400 and 376 MHz for H and F nuclei, respectively. NMR
spectra for the intermediates and the free ligands were measured
at a field strength of 7.05 T operating at 300 and 75.5 MHz for H
and C nuclei, respectively Measurements were conducted at
2
6
6
J = 8.3, 0.6 Hz), 7.33–7.41 (2H, m), 7.76 (4H, s). C NMR d 115.6,
1
3
117.2, 123.9 (qt,
J
F,C = 272.6 Hz), 125.2 (qt,
JF,C = 3.6 Hz), 127.4,
1
19
2
129.1, 132.4 (qt, JF,C = 32.5 Hz), 134.4, 134.9, 143.5, 151.4, 197.7.
1
9
+
F NMR d ꢂ62.8. HRMS: calcd for C14
found 266.0799.
11 3
H F NO [M+H] 266.0793,
1
1
3
0
5 °C (or at other temperatures as indicated for the complexes
a–e) with samples contained in CDCl (in CD Cl for the complexes
a–e). The chemical shifts of H and C nuclei are reported relative
4.4.1.3. 2-Amino-4 -(methoxy)benzophenone (2c). 98% yield; data
3
13
2
2
consistent with literature [22].
1
1
to TMS incorporated as an internal standard (d = 0 ppm for both H
4.4.2. General procedure for the syntheses of bromoacetamides 3
1
3
and C) and externally to CF
3
CO
2
H in CDCl
3
[2–3%v/v] at 25 °C for
To a suspension of the corresponding 2-aminobenzophenone
1
9
F (d = ꢂ78.5 ppm). Correction of the recorded temperature was
2a–c and K
(2 eq.) was added dropwise. The mixture was stirred at rt for 2 h
followed by the addition of H O. The crude amide was extracted
with CH Cl and the organic layer dried over Na SO and then con-
centrated in vacuo after filtration. The resulting bromoacetamides
2 3
CO (5 eq.) in MeCN (0.3 m), bromoacetyl bromide
effected by a Pt100 thermocouple inserted into the probe. General
NMR experimental details have been previously described [16].
2
2
2
2
4
4.3. Molecular modeling experimental
3
a–c were used without further purification.
DFT quantum chemical calculations were performed using the
Gaussian09 [17] program and analyzed using the GUI GaussView
15]. Depictions of the structures in Figs. 7–10 were produced
0
4.4.2.1.
2-(Bromoacetamido)-2 -methylbenzophenone
(3a). 95%
1
[
yield. H NMR d 2.34 (3H, s), 4.09 (2H, s), 7.11 (ddd, J = 8.1, 7.6,
1.0 Hz), 7.27–7.35 (3H, m), 7.40–7.47 (m), 7.47 (dd, J = 8.0,
1.5 Hz), 7.63 (ddd, J = 8.8, 7.9, 1.6 Hz), 8.76 (dd, J = 8.4, 0.7 Hz),
12.18 (brs). C NMR d 19.7, 29.5, 120.7, 123.0, 123.3, 125.2,
128.9, 130.2, 130.8, 134.3, 134.9, 135.9, 138.8, 140.3, 165.2,
using the GUI GaussView [15]. The modeling protocol consisted
of initial optimization in the gas phase using the restricted B3LYP
functional [18] with the 6-31G(d,p) basis set for non-metallic
atoms and the LanL2DZ basis set for Ni and Pd whereby for these
entities core electrons were substituted by a model potential by
invoking the keyword pseudo = read. Geometry optimizations were
conducted in tandem with vibrational analysis and thermochem-
istry calculations at the same level of theory. Vibrational analyses
were conducted to confirm that optimized structures were true
minima on the potential energy surface by not providing imaginary
1
3
+
202.3. HRMS: calcd for C16
332.0286.
H
15BrNO
2
[M+H] 332.0286, found
0
4.4.2.2.
2-(Bromoacetamido)-4 -(trifluoromethyl)benzophenone
(3b). 97% yield. H NMR d 4.07 (2H, s), 7.20 (t, J = 7.6 Hz), 7.57
(dd, J = 7.9, 1.3 Hz), 7.68 (t, J = 7.9 Hz), 7.81 (2H, d, J = 8.4 Hz),
7.84 (2H, d, J = 8.4 Hz), 8.67 (d, J = 8.4 Hz), 11.55 (brs). C NMR d
29.4, 121.6, 123.1, 123.2 (qt,
1
1
3
frequencies and to obtain the thermodynamic contributions to
D
G
1
at 298.15 K and 1 atm wherein frequencies were scaled by a factor
of 0.9806 [19]. Each structure for optimization was conveniently
modified from an optimized structure taken from a set for a com-
pound previously optimized, this ensured not only computational
efficiency but that direct comparisons were valid and meaningful.
The first structure of a set to be optimized was taken from an X-ray
crystallographic structure as this has proven a useful tactic in past
studies [20] with the optimized structure then providing a basis for
the set of structures for that first complex by appropriate modifica-
tion. Re-optimization at the same level of theory of each gas phase-
optimized structure with inclusion of a solvent model – the
F,C
J = 270.7 Hz), 125.3 (qt,
3
2
J
F,C = 3.5 Hz), 129.8, 130.0, 133.5, 133.8 (qt, JF,C = 33.1 Hz), 134.8,
1
9
139.8, 141.4, 165.0, 198.1. F NMR d ꢂ63.0. HRMS: calcd for
+
16
C H12BrF
3
NO
2
[M+H] 386.0004, found 386.0007.
0
4.4.2.3. 2-(Bromoacetamido)-4 -(methoxy)benzophenone (3c). 88%
yield; data consistent with literature [5].
4.4.3. General procedure for the synthesis of ligands 5
To a solution of the corresponding bromoacetamide 3a–c and
2
benzylamine 4 [7c] (1 eq.) in MeCN (0.3 m), i-Pr NEt (2 eq.) was

J. Han et al. / Inorganica Chimica Acta 433 (2015) 3–12
11
added. The mixture was stirred at 70 °C for 16 h and then concen-
trated in vacuo. The product was purified by column chromatogra-
phy over silica (hexane–EtOAc, gradient from 5:1 to 1:1) to provide
the resulting ligands 5a–c.
2 2
(CH Cl –acetone, gradient from 2:1 to 1:10) to provide the result-
ing complexes 6a,c.
II
4.4.5.1. Pd complex 6a. 8% yield. Detailed assignment of proton
absorptions was not possible due to intense molecular movements
+
4.4.3.1.
N-(2-Benzoylphenyl)-2-(benzyl(2-((2-(2-methylben-
HRMS: calcd for C38H32N O Pd [M+H] 700.1428, found 700.1458.
3
4
zoyl)phenyl)amino)-2-oxoethyl)amino)acetamide (5a). 85% yield.
H NMR d 2.26 (3H, s), 3.47 (2H, s), 3.48 (2H, s), 3.96 (2H, s), 7.08
1
II
1
4
3
7
7
.4.5.2. Pd complex 6c. 26% yield. H NMR (major isomer, 35 °C) d
.44 (2H, vbs), 3.59 (1H, vbs), 3.68 (1H, vbs), 3.82 (2H, vbs), 7.23–
.31 (5H, m), 7.39–7.48 (8H, m), 7.533 (2H, ꢃt, J = 7.51 Hz), 7.57–
(
ddd, J = 8.2, 7.6, 1.1 Hz), 7.15 (td, J = 7.6, 1.1 Hz), 7.21–7.31 (6H,
m), 7.38–7.47 (4H, m), 7.48–7.52 (4H, m), 7.54–7.61 (2H, m),
7
1
1
1
1
.66–7.71 (2H, m), 8.22 (d, J = 8.0 Hz), 8.67 (dd, J = 8.4, 0.8 Hz),
0.89 (brs), 11.95 (brs). 13C NMR d 19.6, 58.7, 59.0, 59.5, 121.1,
22.6, 123.1, 124.0, 125.1, 127.1, 127.6, 128.0, 128.2, 128.3,
29.5, 129.8, 130.2, 130.8, 131.8, 132.3, 132.7, 133.9, 134.6,
.62 (1H, m), 7.647 (3H, ꢃdAB, J = 8.14 Hz), 7.807 (3H, ꢃdAB
,
19
J = 7.01 Hz).
F
NMR (35 °C)
d
ꢂ64.07. HRMS: calcd for
+
C
38
29
H F
3
N
3
O
4
Pd [M+H] 754.1145, found 754.1169.
36.3, 137.8, 137.9, 138.8, 140.1, 169.1, 169.5, 197.4, 201.7.
II
4
.4.6. General procedure for the synthesis of Ni complexes 6b,d,e
+
HRMS: calcd for C38
H
34
N
3
O
4
[M+H] 596.2549, found 596.2561.
To a solution of the corresponding ligand 5b–c or 8 in MeOH
0.1 m), Ni(NO O (2 eq.) and KOH (7 eq.) were added. The
ꢀ6H
mixture was stirred at 70 °C for 7 h followed by the addition of
O. The crude complex was extracted with CH Cl and the organic
layer dried over Na SO and then concentrated in vacuo after filtra-
tion. The product was purified by column chromatography over sil-
ica (CH Cl –acetone, gradient from 2:1 to 1:10) to provide the
(
3
)
2
2
4.4.3.2.
N-(2-Benzoylphenyl)-2-(benzyl(2-oxo-2-((2-(4-(trifluo-
(5b). 85%
yield. H NMR d 3.39 (2H, s), 3.41 (2H, s), 3.84 (2H, s), 7.13–7.23
5H, m), 7.41–7.48 (5H, m), 7.50–7.63 (4H, m), 7.65–7.70 (4H,
m), 7.79 (2H, d, J = 8.1 Hz), 8.25 (dd, J = 8.3, 0.6 Hz), 8.40 (dd,
romethyl)benzoyl)phenyl)amino)ethyl)amino)acetamide
H
2
2
2
1
2
4
(
2
2
13
J = 8.2, 0.5 Hz), 11.01 (brs), 11.15 (brs). C NMR d 59.2, 59.3,
resulting complexes 6b,d,e.
5
J
9.7, 122.2, 122.9, 123.3, 123.5 (qt, 1
F,C = 3.4 Hz), 125.7, 126.4, 127.8, 128.2, 128.4, 129.6, 130.0,
J
F,C = 272.7 Hz), 125.1 (qt,
3
II
1
4
.4.6.1. Ni complex 6b. 52% yield. H NMR (35 °C) d 3.004 (1H, dAB
,
2
1
30.1, 131.9, 132.5, 132.6, 133.5, 133.5, 133.6 (qt, JF,C = 32.5 Hz),
J = ꢂ15.38 Hz), 3.116 (1H, dAB, J = ꢂ15.73 Hz), ꢃ3.37 (1H, vbs),
.542 (1H, bdAB, J = ꢂ15.51 Hz), ꢃ3.63 (1H, vbs), 3.825 (1H, bdAB
J = ꢂ11.07 Hz), 7.055 (1H, ꢃt, J = 7.58 Hz), 7.18–7.39 (8H, m),
.40–7.59 (6H, m), 7.60–7.72 (4H, m), 7.875 (3H, ꢃd, J = 7.27 Hz).
1
9
1
35.9, 138.0, 138.2, 138.6, 141.0, 169.0, 169.2, 196.5, 198.5.
F
3
,
+
NMR d ꢂ63.0. HRMS: calcd for C38
31 3 3 4
H F N O [M+H] 650.2267,
found 650.2270.
7
1
9
F NMR (35 °C) d ꢂ66.08. HRMS: calcd for C38
29 3 3 4
H F N O Ni
4
.4.3.3.
phenyl)amino)-2-oxoethyl)amino)acetamide (5c). 84% yield.
NMR d 3.35 (4H, s), 3.79 (2H, s), 3.88 (3H, s), 6.87–6.92 (2H, m),
N-(2-Benzoylphenyl)-2-(benzyl(2-((2-(4-methoxybenzoyl)
+
[
M+H] 706.1464, found 706.1666.
1
H
II
4
.4.6.2. Ni complex 6d. 58% yield. Detailed assignment of proton
7
7
.11–7.23 (5H, m), 7.37–7.44 (4H, m), 7.50–7.60 (5H, m), 7.66–
.73 (4H, m), 8.26–8.31 (2H, m), 10.87 (brs), 11.00 (brs). C NMR
1
3
absorptions was not possible due to intense molecular movements
HRMS: calcd for C38
+
32
H N
3
O
5
Ni [M+H] 668.1695, found 668.1889.
d 55.4, 59.1, 59.1, 59.5, 113.4, 122.5, 122.6, 123.0, 123.1, 126.8,
1
1
1
6
27.2, 127.6, 128.0, 128.3, 129.6, 129.9, 130.4, 131.6, 132.2,
II
1
4
.4.6.3. Ni complex 6e. 41% yield. H NMR (35 °C) d 2.966 (1H, dAB
,
32.4, 132.5, 133.0, 136.0, 137.8, 138.0, 138.2, 163.3, 168.9,
+
J = ꢂ15.56 Hz), 3.118 (1H, dAB, J = ꢂ15.83 Hz), ꢃ3.26 (1H, vbs),
69.0, 196.3, 197.8. HRMS: calcd for
12.2498, found 612.2513.
C
38
H
34
N
3
O
5
[M+H]
3
.561 (1H, bdAB, J = ꢂ15.80 Hz), ꢃ3.58 (1H, vbs, ol), 3.807 (3H, s),
ꢃ3.84 (1H, vbd, ol), 6.778 (2H, ꢃd, J = 8.97 Hz), 7.038 (1H, ꢃt,
J = 7.54 Hz), 7.11–7.20 (2H, m), 7.22–7.29 (1H, m), 7.30–7.37 (3H,
m), 7.38–7.52 (5H, m), 7.654 (2H, ꢃdAB, J = 8.28 Hz), 7.72–7.81
4.4.4. Synthesis of 2-(benzyl(2-((2-(4-methoxybenzoyl)phenyl)
amino)-2-oxoethyl)amino)-N-(2-(4-(trifluoromethyl)benzoyl)phenyl)
acetamide (8)
19
(
(
2H, m), 7.82–7.89 (2H, m), 7.913 (1H, ꢃd, J = 8.51 Hz). F NMR
39 31 3 3 5
C H F N O
Ni [M+H]+
35 °C)
d
ꢂ66.02. HRMS: calcd for
To a solution of the bromoacetamide 3c and benzylamine 7 [5]
7
36.1569, found 736.1759.
(
2
1 eq.) in MeCN (0.3 m), i-Pr NEt (2 eq.) was added. The mixture
was stirred at 70 °C for 16 h and then concentrated in vacuo. The
Acknowledgments
product was purified by column chromatography over silica (hex-
1
ane–EtOAc, gradient from 2:1 to 1:1) to provide 8 in 87% yield. H
Guangqian Zhang is thanked for assistance with parts of the
experimental work; financial support from the Center for
International Mobility (CIMO) and Turun Yliopistosäätiö,
Ikerbasque, Basque Foundation for Science, and the Basque
Government (SAIOTEK S-PE13UN098) is gratefully acknowledged;
the CSC–IT Center for Science Ltd. is thanked for providing compu-
tational resources and assistance with modeling calculations (Nino
Runeberg); the Japan Synchrotron Radiation Research Institute
(JASRI) is thanked for the synchrotron radiation experiments which
were performed on the BL02B1 and BL40XU instruments at SPring-
8 (Proposal Nos. 2010A1976, 2010B1489, and 2010B1494), and
SGIker (UPV/EHU) is thanked for HRMS analyses.
NMR d 3.37 (2H, s), 3.38 (2H, s), 3.80 (2H, s), 3.90 (3H, s), 6.89–6.94
(
7
(
2H, m), 7.13–7.25 (5H, m), 7.41–7.61 (6H, m), 7.64–7.72 (4H, m),
.80 (2H, d, J = 8.1 Hz), 8.24 (d, J = 7.6 Hz), 8.33 (d, J = 7.7 Hz), 10.93
1
3
brs), 10.99 (brs). C NMR d 55.4, 59.1, 59.3, 59.6, 113.5, 122.4,
1
1
22.9, 123.0, 123.4, 123.5 (qt,
JF,C = 272.5 Hz), 125.0 (qt,
3
J
F,C = 3.4 Hz), 126.6, 126.7, 127.7, 128.4, 129.6, 130.1, 130.3,
2
1
1
31.8, 132.6, 132.7, 133.4, 133.5 (qt, JF,C = 32.5 Hz), 135.9, 138.0,
38.1, 141.0, 163.4, 168.8, 169.1, 196.3, 196.7. F NMR d ꢂ63.0.
19
+
HRMS: calcd for C39
H
33
F
3
N
3
O
5
[M+H] 680.2372, found 680.2387.
II
4
.4.5. General procedure for the synthesis of Pd complexes 6a,c
To a solution of the corresponding ligand 5a–b in MeOH
0.04 m), PdCl (2 eq.) and K CO (6 eq.) were added. The mixture
was stirred at 70 °C for 16 h followed by the addition of H O. The
crude complex was extracted with CH Cl and the organic layer
dried over Na SO and then concentrated in vacuo after filtration.
The product was purified by column chromatography over silica
(
2
2
3
2
Appendix A. Supplementary material
2
2
2
4
CCDC 990583 for (6a), 990584 for (6b), 990585 for (6c), 990586
for (6d), and 990587 for (6e) contains the supplementary

1
2
J. Han et al. / Inorganica Chimica Acta 433 (2015) 3–12
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. Supplementary data
associated with this article can be found, in the online version, at
http://dx.doi.org/10.1016/j.ica.2015.04.029.
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