Synthesis, structure, and conformational mobility of a vaulted trans-bis(o-aminophenolato)platinum(II) complex

Article abstract of DOI:10.1007/s11243-013-9734-4

The synthesis, structure, and conformational mobility of a trans-bis(aminophenolato)platinum(II) complex bearing a dodecamethylene bridge, [Pt(L)] (1) [H ₂ L = N,N′-Dimethyl-N,N′-bis(2- hydroxyphenylmethyl)dodecane-1,12-diamine] are described. The 2D NMR and X-ray diffraction analysis revealed that the complex has a reversed U -shaped syn conformation in the solution state, which is mainly due to steric congestion of the vaulted structure and hydrogen bonding at the bis[(o-aminomethyl)phenolato] coordination site, while the complex unit is packed in the crystalline state with Z-shaped anti-conformation due to highly regulated molecular arrangement by 3D CH-π and hydrogen bonding interactions.

Full text of DOI:10.1007/s11243-013-9734-4

Transition Met Chem (2013) 38:659–664
DOI 10.1007/s11243-013-9734-4
Synthesis, structure, and conformational mobility of a vaulted
trans-bis(o-aminophenolato)platinum(II) complex
•
Naruyoshi Komiya Koichi Takahashi
•
•
Tomoya Tanaka Atsushi Yoshida
•
Takeshi Naota
Received: 25 April 2013 / Accepted: 17 May 2013 / Published online: 1 June 2013
Ó Springer Science+Business Media Dordrecht 2013
Abstract The synthesis, structure, and conformational
mobility of a trans-bis(aminophenolato)platinum(II) com-
plex bearing a dodecamethylene bridge, [Pt(L)] (1) [H2L =
N,N0-Dimethyl-N,N0-bis(2-hydroxyphenylmethyl)dodecane-1,
12-diamine] are described. The 2D NMR and X-ray diffrac-
tion analysis revealed that the complex has a ‘‘reversed U’’-
shaped syn conformation in the solution state, which is
mainly due to steric congestion of the vaulted structure and
hydrogen bonding at the bis[(o-aminomethyl)phenolato]
coordination site, while the complex unit is packed in the
crystalline state with ‘‘Z-shaped’’ anti-conformation due to
highly regulated molecular arrangement by 3D CH-p and
hydrogen bonding interactions.
studied in view of their inclusion properties [7, 9],
molecular aggregation [11, 12], optical properties [8, 12–
14], and catalytic activity for asymmetric transformation
[4–6, 19, 21].
As part of our program aimed at developing new func-
tionalities of flexible trans-ligating complexes with highly
controllable d-p conjugation, the dynamic behavior of
vaulted trans-ligating d8 transition metal complexes with
phenolato ligands-bearing o-imino [11–14] and o-NHC
[18] groups have been investigated. In this work, a novel
vaulted form of trans-bis[(o-aminomethyl)phenolato] Pt(II)
complex 1 was synthesized. Bis[(o-aminomethyl)phenola-
to] transition metals are an interesting platform for vaulted
structures because their small d-p conjugation provides
significant molecular mobility due to enhanced flexibility
of the metal platform. Cis-ligating complexes 2 of Cu(II)
[22, 23], Pd(II) [24], Ni(II) [25], and trans Pd(II) com-
plexes 3 [26–28] have been reported for this doubly
ligating platform, although Pt(II) complexes are limited to
mono-ligating complexes 4 with dichloro [29] and chlo-
ropyridine [30] ligands (Scheme 1). Complexes 2–4 were
studied with respect to their chemical [22, 24–28, 30] and
biological [23, 29] activities. This is the first example of
vaulted bis[(o-aminomethyl)phenolato]metal complexes,
and also, the first bis[(o-aminomethyl)phenolato)] Pt(II)
complex. The 2D NMR and X-ray diffraction (XRD)
studies revealed that complex 1 has ‘‘reversed U’’-shaped
syn conformation in solution, while the packing unit 1 in
the crystalline state has a contrastingly ‘‘Z’’-shaped anti-
conformation. The molecular flexibility of 1 is clearly
distinct from that of o-iminophenolato and o-NHC-phe-
nolato analogs 5 [13, 14] and 6 [18], which have much
more rigid planar and syn platforms, respectively, due to
enhanced d-p conjugation. This paper describes the syn-
thesis, structure, and dynamic behavior of complex 1, with
Introduction
Transition metal complexes vaulted with carbon chains
have been extensively studied as a new candidate for
functional materials due to their specific 3D superstructure
around bridged ligands and coordination planes [1–3].
Various vaulted complexes have been obtained by the
reaction of transition metals with a variety of tether-linked
ligands [4–21], and their specific functions have been
N. Komiya (&) ꢀ K. Takahashi ꢀ T. Tanaka ꢀ A. Yoshida ꢀ
T. Naota (&)
Department of Chemistry, Graduate School of Engineering
Science, Osaka University, Machikaneyama, Toyonaka,
Osaka 560-8531, Japan
e-mail: komiya@chem.es.osaka-u.ac.jp
T. Naota
e-mail: naota@chem.es.osaka-u.ac.jp
123

660
Transition Met Chem (2013) 38:659–664
Scheme 1 Structures of 1–6
(CH2)12
R'
R
N
M
L
O
N
O
N
O
N
O
N
N
O
M
Pt
Pt
O
O
L'
N
R
R
R R
R'
R'
R'
R'
L,L' = Cl, pyridine
2
4
3
1
(CH2)12
(CH2)12
13
9
16
N
14
11
10
1
2
N
2
N
1
2
12
O
O
Pt
1
N
Pt
1
1
O
O
3
2
N
N
1
5
4
7
6
5
6
Preparation of N,N0-dimethyldodecane-1,12-diamine
specific focus on the molecular mobility in the solution and
crystalline states.
A mixture of N,N0-bis(ethoxycarbonyl)dodecane-1,12-dia-
mine (2.30 g, 6.68 mmol) and LiAlH4 (1.59 g, 42.0 mmol)
in dry THF (50 mL) was refluxed for 24 h. After cooling
to 0 °C, excess LiAlH4 was quenched by adding
Na2SO4ꢀ10H2O (9.09 g, 28.2 mmol). Filtration followed
by evaporation under reduced pressure gave N,N0-dimeth-
yldodecane-1,12-diamine (1.42 g, 93 %) as a colorless
solid. 1H NMR (CDCl3, 500 MHz): d 1.23–1.35 (m, 14 H),
1.48 (tt, J = 7.1, 7.1 Hz, 4 H, N-CH2CH2CH2), 1.63–1.74
(m, 4 H), 2.43 (s, 6 H, NCH3), 2.56 (t, J = 7.1 Hz, 4 H,
NCH2CH2–); 13C NMR (CDCl3, 125 MHz): d 27.3, 29.6,
29.9, 30.1, 36.5, 52.2, 62.6.
Experimental section
All chemicals were commercially available and used as
received without further purification. Melting points were
measured in a glass capillary on a Bu¨chi B-545 melting
point apparatus. Mass spectra were obtained on a JEOL
JMS-DX 303. IR spectra were recorded on a Bruker
EQUINOX55/S spectrometer. 1H and 13C NMR spectra
were recorded on a Varian Unity-Inova 500 spectrometer.
X-ray analysis was carried out on a Rigaku R-AXIS
RAPID imaging plate diffractometer with graphite mono-
chromated MoKa radiation.
Preparation of H2L
Preparation of N,N0-bis(ethoxycarbonyl)dodecane-1,12-
A
mixture of N,N0-dimethyldodecane-1,12-diamine
(23.4 mg, 0.11 mmol), salicylaldehyde (25.0 g, 0.20 mmol),
and NaBH3CN (15.2 mg, 0.24 mmol) in methanol (4.0 mL)
was stirred at 20 °C for 17 h. The mixture was poured into
CH2Cl2 (20 mL) and extracted with 1 N HCl (20 mL 9 2).
After the acidity of the solution was adjusted to pH 12 by
adding NaOH, the mixture was extracted with CH2Cl2
(30 mL). The organic layer was dried over MgSO4, filtered,
and evaporated under reduced pressure to give H2L (25 mg,
diamine
A mixture of 1,12-diaminododecane (4.01 g, 20.1 mmol)
and ethyl chloroformate (5.43 g, 50.1 mmol) in pyridine
(40 mL) was refluxed at 100 °C for 13 h. After cooling to
room temperature, the mixture was poured into water
(100 mL) and extracted with ethyl acetate (100 mL). The
organic layer was washed successively with a saturated
Na2CO3 aqueous solution (100 mL 9 1), 2 N HCl
(100 mL 9 3), and water (100 mL 9 1), and dried over
MgSO4. After filtration, the residue was evaporated under
reduced pressure to give N,N0-bis(ethoxycarbonyl)dode-
1
58 %) as an orange oil: H NMR (CDCl3, 500 MHz): d
1.20–1.34 (m, 16 H), 1.54 (tt, J = 7.2, 7.2 Hz, 4 H,
N-CH2CH2CH2), 2.26 (s, 6 H, N-CH3), 2.46 (t, J = 7.2 Hz,
4 H, N-CH2CH2), 3.68 (s, 4 H, Ar-CH2-N), 6.76 (ddd,
J = 7.4, 7.4, 1.1 Hz, 2 H, H4), 6.81 (dd, J = 7.7, 1.1 Hz, 2
H, H6), 6.95 (dm, J = 7.4 Hz, 2 H, H3), 7.15 (ddd, J = 7.7,
7.4, 1.7 Hz, 2 H, H5); 13C NMR (CDCl3, 125 MHz): d 26.9,
27.1, 29.42, 29.45, 29.50, 41.1, 57.1, 61.5, 115.9, 118.8,
1
cane-1,12-diamine (3.35 g, 49 %) as a colorless solid. H
NMR (CDCl3, 500 MHz): d 1.17–1.35 (m, 22 H), 1.42–
1.53 (m, 4 H), 3.16 (q, J = 6.3 Hz, 4 H, NCH2CH2–), 4.10
(q, J = 6.7 Hz, 4 H, CH3CH2O–), 4.61 (br, 2 H, NH).
123

Transition Met Chem (2013) 38:659–664
661
122.0, 128.3, 128.5, 158.1; HRMS (EI?): m/z [M]? calcd
X-ray structure determination
for C28H44N2O2: 440.3403; found: 440.3389.
Crystal suitable for XRD study was analyzed by using a
Rigaku R-AXIS RAPID imaging plate diffractometer with
Preparation of [Pt(L)] (1)
˚
graphite-monochromated MoKa radiation (k = 0.71075 A).
The structure of complex 1 was solved by direct methods
and refined by the full-matrix least-square method. In the
subsequent refinement, the function Rx(F2o - Fc2)2, in
which Fo and Fc were the observed and calculated structure
factor amplitudes, respectively, was minimized. The posi-
tions of non-hydrogen atoms were found from difference
Fourier electron density maps and refined anisotropically.
All calculations were performed using crystal structure
crystallographic software package. Details of the structure
determinations are given in Fig. 1 and Table 1.
A
mixture of PtCl2(CH3CN)2 (0.351 g, 1.01 mmol),
H2L (0.462 g, 1.05 mmol), and K2CO3 (1.02 g, 7.38 mmol)
in toluene (120 mL) and dimethylsulfoxide (30 mL) was
stirred at 140 °C for 24 h under argon atmosphere. After
evaporation of the solvent under reduced pressure, the
residual oil was diluted with ethyl acetate (100 mL). The
organic layer was washed successively with 1 N HCl
(50 mL 9 2) and water (100 mL) and dried over MgSO4.
After filtration and evaporation, the crude orange solid
was subjected to column chromatography (SiO2, n-hex-
ane/ethyl acetate = 5:1) to give [Pt(L)] (1) (27.8 mg,
4.4 %) as a yellow solid: mp 197.0–198.0 °C; IR (KBr):
3028, 2927, 2855, 1595, 1568, 1478, 1271, 1109, 1035,
Computational methods
883, 794, 763, 726, 614 cm-1
;
1H NMR (CDCl3,
All calculations were carried out based on the density
functional theory (DFT) with the B3LYP exchange–cor-
relation functional [31], using the Spartan 10 program
package (Wavefunction, Inc., Irvine, CA). The basic set
used was the effective core potential for platinum atom
[32] and 6-31G* for the remaining atoms [33].
500 MHz): d 1.26–1.53 (m, 16 H) 2.12–2.26 (m, 4 H),
2.65 (s, 6 H, N-CH3), 2.91 (d, J = 11.6 Hz, 2 H, Ar-
CHaHb-N), 3.15 (dddd, J = 16.2, 12.4, 11.7, 5.9 Hz, 2 H,
ArCH2NCH2CHaHb), 3.49 (ddd, J = 12.4, 12.4, 5.1 Hz,
2 H, N-CHaHbCH2), 4.16 (d, J = 11.6 Hz, 2 H, Ar-
CHaHb-N), 6.59 (ddd, J = 7.3, 7.3, 0.9 Hz, 2 H, H4), 6.72
(dd, J = 7.9, 0.9 Hz, 2 H, H6), 6.94 (dd, J = 7.3, 1.8 Hz,
2 H, H3), 7.06 (ddd, J = 7.9, 7.3, 1.8 Hz, 2 H, H5); 13C
NMR (CDCl3, 125 MHz): d 24.7, 25.90, 25.94, 26.9,
27.5, 49.2, 61.2, 63.4, 116.3, 117.9, 125.6, 130.0, 130.3,
167.6; HRMS (FAB?): m/z calcd for C28H42N2O1295Pt
(M)?: 633.2894; found: 633.2894.
Results and discussion
Complex 1 was prepared by the reaction of PtCl2(CH3CN)2
with H2L (1 equiv) and K2CO3 (7 equiv) in toluene/
Fig. 1 ORTEP drawing of complex 1. a Top view. b Side view.
Thermal ellipsoids are shown at the 30 % probability level. Hydrogen
˚
atoms are omitted for clarity. Selected bond distances (A) and angles
(°): Pt(1)–O(1), 2.021(8); Pt(1)–O(2), 2.017(8); Pt(1)–N(1), 2.065(9);
Pt(1)–N(2), 2.074(9); O(1)–Pt(1)–O(2), 179.3(3); N(1)–Pt(1)–N(2),
179.5(4); N(1)–Pt(1)–O(1)–C(1), 42.3(6); N(2)–Pt(1)–O(2)–C(21),
39.5(6); O(1)–Pt(1)–N(1)–C(7), 7.3(6); O(2)–Pt(1)–N(2)–C(27),
10.3(6); N(1)–C(7)–C(2)–C(1), 60.8(13); N(2)–C(27)–C(22)–C(21),
60.7(12)
123

662
Transition Met Chem (2013) 38:659–664
Trans-coordination and vaulted structures of 1 have
been unequivocally established from XRD analysis of a
crystal obtained by recrystallization from hexane/AcOEt
(Table 1). An ORTEP drawing of 1 is shown in Fig. 1.
Complex 1 has anti-conformation, where the dihedral
angles between the coordination plane [Pt(1)–O(1)–N(1)/
Pt(1)–O(2)–N(2)] and aromatic plane [C(1)–C(3)–C(5)/
C(21)–C(23)–C(25)] are 43.8° and 39.3°, respectively
(Fig. 1b). Large torsion angles of [N(1)–Pt(1)–O(1)–C(1)]
(42.3°) and [N(2)–Pt(1)–O(2)–C(21)] (39.5°) indicate that
the bent structure is mainly due to folding along the lines
O(1)–C(7) and O(2)–C(27). Intraligand H-bonding inter-
actions between phenoxy oxygen atoms O(1)/O(2) and
linker protons H(20a)/H(9b) are observed with H-bonding
Table 1 Crystal data and structure refinement details for compound 1
Formula
C28H42N2O2Pt
633.74
293
Formula weight
Temperature (K)
Crystal size (mm)
Crystal system
Space group
0.20 9 0.20 9 0.02
Monoclinic
P21/c (#14)
19.561(2)
9.7112(6)
14.467(1)
90
˚
a (A)
˚
b (A)
˚
c (A)
a (°)
b (°)
c (°)
100.241(1)
90
3
˚
V (A )
2704.4(4)
4
˚
distance of 2.41 and 2.73 A. Noteworthy is strong contact
Z value
Dcalcd (gcm-3
between H(10a) and C(2) with sufficiently short distance of
˚
2.44 A, which indicates that the unprecedented anti-con-
)
1.556
l(MoKa) (mm-1
)
5.194
formation of 1 in the crystalline state is partially the result
of intramolecular CH-p interactions between linker
hydrogen and aromatic planes. The dodecamethylene-
vaulted analogs of bis(o-iminophenoxy) and bis(o-NHC-
phenoxy) platinum(II) complexes 5 [13, 14] and 6 [18]
have contrastingly planar and syn conformations, respec-
tively, as shown in Fig. 2.
F(000)
1272.00
54.8
2hmax (°)
No. of reflections measured
No. of observed reflections
No. of variables
52780
6130
298
R1 [I [ 2r(I)]a
wR2 (all reflections)b
0.080
1
0.144
The H NMR (500 MHz) spectrum of 1 in CDCl3 at
Goodness of fit
1.11
298 K has one set of aromatic protons H(3), H(4), H(5),
and H(6) in the range of 6.57–7.07 ppm, which indicates
that the complex has symmetrical conformation in the
solution state (Fig. 3). Clear splitting and a significant
downfield shift of H(7b)/H(27b) protons at 4.16 ppm
indicate that these protons undergo intraligand H-bonding
interactions with O(1)/O(2), which are similar to those in
the crystalline state. A strong remote correlation in the
NOESY (500 MHz) spectrum is observed between N-
methyl H(8) and aromatic H(6) protons on the other
side of the aromatic region (correlation A in Fig. 3), in
a
R1 = R(|Fo|-|Fc|)/R(|Fo|)
wR2 = [R[w(F2o-F2c)2]/Rw(Fo2)2]1/2
b
dimethyl sulfoxide (4:1) at 140 °C. Ligand H2L was
prepared from 1,12-diaminododecane in three steps
(Scheme 2). Complex 1 was characterized by spectro-
scopic methods including H–H correlation spectroscopy
(COSY) and nuclear Overhauser effect spectroscopy
(NOESY).
Scheme 2 Synthetic route for
[Pt(L)] 1
123

Transition Met Chem (2013) 38:659–664
663
Fig. 2 Contrasting conformations of dodecamethylene-vaulted plat-
inum(II) complexes 1 (a), 5 [13, 14] (b), and 6 [18] (c) determined by
single crystal XRD. Values in parentheses are dihedral angles
between the coordination and aromatic planes. Coordination planes:
[Pt(1)–O(1)–N(1)/Pt(1)–O(2)–N(2)] for 1; [Pt(1)–O(1)–N(1)/Pt(1)–
O(2)–N(2)] for 5; [Pt(1)–O(1)–C(1)/Pt(1)–O(2)–C(10)] for 6. Aro-
matic planes: [C(1)–C(3)–C(5)/C(21)–C(23)–C(25)] for 1; [C(2)–
C(4)–C(6)/C(9)–C(11)–C(13)] for 5; [C(3)–C(5)–C(7)/C(12)–C(14)–
C(16)] for 6. Numbering of the atoms for these structures is shown in
Fig. 1 for 1 and Scheme 1 for 5 and 6
C
H10b
N
H7b
H10a
O
Pt
O
H9b
N
H9a
H7a
H8
E
F
H6
H3
A
D
B
Fig. 3 1H NMR/NOESY (500 MHz) spectra and the major NOE correlation of 1 in CDCl3 (298 K, mixing time = 0.700 s)
DFT calculations (B3LYP/LACVP*) based on the opti-
mized structure in gas phase indicate that the syn con-
formation of 1 is more stable than the anti-conformation
by 2.3 kcal/mol (Fig. 4). The rigid syn conformation of 1
in the solution state can be ascribed to the steric repulsion
around the aromatic moiety and molecular constraint
caused by hydrogen bonding at H(7b)/H(27b)–O(1)/O(2)
and H(9b)/H(20a)–O(2)/O(1).
The molecular packing of crystal 1 is shown in Fig. 5.
The most important feature evident in this crystal is the
herringbone packing motif, which consists of intermo-
lecular hydrogen bonding between aromatic protons and
˚
phenoxy oxygens [H(3)–O(2) (2.68 A, broken line A),
˚
H(23)–O(1) (2.51 A, B)]. Intermolecular [H(8a)–C(25)
Fig. 4 Optimized structure and relative energy for syn- and anti-1 in
gas phase estimated by DFT calculations (B3LYP/LACVP*) based on
the geometries of the anti-form obtained from single crystal XRD
˚
(2.93 A, broken line C), H(20b)–C(5) (2.89 A, D)] and
˚
˚
intramolecular [H(10a)–C(2) (2.44 A)] CH-p interactions
are also observed between methyl/methylene protons and
aromatic ring. Therefore, the anti-form of the molecular
unit is the result of sufficient stabilization achieved by
these inter- and intra-molecular interactions in the crys-
talline state, although this is thermodynamically unfa-
vorable in the solution state. Such dynamic molecular
addition to expected correlations of H(3)–H(7a) (B),
H(7b)–H(9a) (C), H(7a)–H(8) (D), H(8)–H(9a) (E), and
H(8)–H(9b) (F). This indicates that complex 1 has rigid
syn conformation in the solution state, which is in contrast
to the anti-conformation in the crystalline state (Fig. 1b)
123

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Transition Met Chem (2013) 38:659–664
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Conclusions
In summary, we have synthesized the first vaulted trans-
bis(o-aminomethylphenolato)Pt(II) complex 1 bearing a
polymethylene bridge. The flexible coordination plane with
weak d-p conjugation generates bistability for syn and anti-
conformations in the solution and crystalline states,
respectively. Further research is currently underway to
apply the related vaulted complexes with high flexibility as
new functional materials.
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CCDC 937955 contains the supplementary crystallographic
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Acknowledgments This work was supported by Grant-in-Aid for
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