Dynamic neighbouring participation of nitrogen lone pairs on the chromogenic behaviour of trans-bis(salicylaldiminato)Pt(ii) coordination platforms

Article abstract of DOI:10.1039/C6DT04005E

The participation of neighbouring nitrogen lone pairs in the chromogenic control of trans-bis(salicylaldiminato)Pt(ii) platforms was examined, using newly designed Pt analogues bearing salicylaldehyde hydrazone ligands. A series of non-vaulted and vaulted Pt complexes (1-5) with salicylaldehyde hydrazones as trans-coordinated bidentate ligands were synthesized and characterized with regard to the chromogenic behaviour of the trans-bis(salicylaldiminato)Pt(ii) coordination platforms. X-ray diffraction and 2D NMR data demonstrated that, in the case of the non-vaulted N-monomethyl complexes 1, there was significant participation of neighbouring N(2) lone pairs in the d-π conjugation of the trans-bis(salicylaldiminato)Pt(ii) platforms owing to conformational fixation arising from intramolecular hydrogen bonding. In contrast, the lone pairs of the N,N-dimethyl analogues 2 made a much less significant contribution to the extension of the d-π conjugation, due to their high conformational mobility. Complexes 1-5 were found to have structure-dependent chromogenic properties in the solution state, such that the absorption spectra of the N-methyl, short-vaulted complexes 1 and 3 exhibited significant hypsochromic shifts relative to the N,N-dimethyl, long-vaulted analogues 2 and 5, which had spectra very similar to that of the trans-bis(salicylaldiminato)Pt(ii) complex 6. The introduction of MeO groups at the 3- and 5 positions on the aromatic rings of 1 and 2 gave rise to significant hypsochromic and bathochromic shifts, respectively. In addition, ν_max - E_T(30) plots for various solvents revealed that complexes 1-5 exhibit negative solvatochromism, in which the data obtained in alcoholic solvents are hypsochromically separated from those in non-alcoholic solvents for 1 and 3, an effect that is not observed for 2 and 5. Complexes 1-5 also exhibit emission enhancement upon addition of excess CH₃SO₃H in dimethyl sulfoxide, and a significant effect of the linker on quantum yields (Φ_{77 K}) was observed in the case of the vaulted complexes. Density functional theory calculations (B3LYP/6-31G*, LanL2DZ) determined that the structure dependence of the chromogenic behaviour of these non-vaulted and polymethylene-vaulted hydrazone complexes can be attributed to variations in the participation of neighbouring nitrogen lone pairs in the d-π conjugation on the trans-bis(salicylaldiminato)Pt(ii) coordination platforms.

Full text of DOI:10.1039/C6DT04005E

Showcasing research from Takumi Hashimoto,
As featured in:
Kanako Fukumoto, Ngoc Ha Thu Le, Tatsuya Matsuoka,
Soichiro Kawamorita, Naruyoshi Komiya, and Takeshi Naota at
Graduate School of Engineering Science, Osaka University.
Volume 45 Number 48 28 December 2016 Pages 19143–19532
Dalton
Transactions
An international journal of inorganic chemistry
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Dynamic neighbouring participation of nitrogen lone pairs on
the chromogenic behaviour of trans-bis(salicylaldiminato)Pt(II)
coordination platforms
The participation of neighbouring nitrogen lone pairs in the
chromogenic control of trans-bis(salicylaldiminato)Pt(II) platforms
was examined, using newly designed Pt analogues bearing
salicylaldehyde hydrazone ligands. Short polymethylene linkers
provide strong solvatochromic behaviours for the molecules
upon backside bending of the coordination platforms.
ISSN 1477-9226
PAPER
C. Esmieu and G. Berggren
Characterization of a monocyanide model of FeFe hydrogenases –
highlighting the importance of the bridgehead nitrogen for catalysis
See Takeshi Naota et al.,
Dalton Trans., 2016, 45, 19257.
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PAPER
Dynamic neighbouring participation of nitrogen
lone pairs on the chromogenic behaviour of trans-
bis(salicylaldiminato)Pt(II) coordination platforms†
Cite this: Dalton Trans., 2016, 45,
19257
Takumi Hashimoto, Kanako Fukumoto, Ngoc Ha-Thu Le, Tatsuya Matsuoka,
Soichiro Kawamorita, Naruyoshi Komiya‡ and Takeshi Naota*
The participation of neighbouring nitrogen lone pairs in the chromogenic control of trans-bis(salicylaldimi-
nato)Pt(II) platforms was examined, using newly designed Pt analogues bearing salicylaldehyde hydrazone
ligands. A series of non-vaulted and vaulted Pt complexes (1–5) with salicylaldehyde hydrazones as trans-co-
ordinated bidentate ligands were synthesized and characterized with regard to the chromogenic behaviour of
the trans-bis(salicylaldiminato)Pt(II) coordination platforms. X-ray diffraction and 2D NMR data demonstrated
that, in the case of the non-vaulted N-monomethyl complexes 1, there was significant participation of neigh-
bouring N(2) lone pairs in the d–π conjugation of the trans-bis(salicylaldiminato)Pt(II) platforms owing to con-
formational fixation arising from intramolecular hydrogen bonding. In contrast, the lone pairs of the N,N-
dimethyl analogues 2 made a much less significant contribution to the extension of the d–π conjugation, due
to their high conformational mobility. Complexes 1–5 were found to have structure-dependent chromogenic
properties in the solution state, such that the absorption spectra of the N-methyl, short-vaulted complexes
1 and 3 exhibited significant hypsochromic shifts relative to the N,N-dimethyl, long-vaulted analogues 2 and
5, which had spectra very similar to that of the trans-bis(salicylaldiminato)Pt(II) complex 6. The introduction of
MeO groups at the 3- and 5 positions on the aromatic rings of 1 and 2 gave rise to significant hypsochromic
and bathochromic shifts, respectively. In addition, νmax − ET(30) plots for various solvents revealed that com-
plexes 1–5 exhibit negative solvatochromism, in which the data obtained in alcoholic solvents are hypsochro-
mically separated from those in non-alcoholic solvents for 1 and 3, an effect that is not observed for 2 and 5.
Complexes 1–5 also exhibit emission enhancement upon addition of excess CH3SO3H in dimethyl sulfoxide,
and a significant effect of the linker on quantum yields (Φ77 K) was observed in the case of the vaulted com-
plexes. Density functional theory calculations (B3LYP/6-31G*, LanL2DZ) determined that the structure depen-
dence of the chromogenic behaviour of these non-vaulted and polymethylene-vaulted hydrazone com-
plexes can be attributed to variations in the participation of neighbouring nitrogen lone pairs in the d–π con-
jugation on the trans-bis(salicylaldiminato)Pt(II) coordination platforms.
Received 19th October 2016,
Accepted 14th November 2016
DOI: 10.1039/c6dt04005e
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Much effort has been devoted to controlling the photophysical
properties of organometallic phosphors, primarily via the
Introduction
Both the extension and modulation of d–π conjugation on the extension of the π-conjugated systems on rigid ligands.2 In
coordination platforms of transition metal complexes are contrast to conventional methods for the synthetic extension
important with regard to the development of novel functional of rigid d–π conjugated frameworks, transition metal
materials with readily tuneable photoelectronic properties.1 complexes bearing flexible and mobile coordination platforms
are an attractive motif for the creation of novel functionalities
based on varying photophysical properties in association
with conformational changes in the flexible d–π conjugation
platforms.
Department of Chemistry, Graduate School of Engineering Science, Osaka University,
Machikaneyama, Toyonaka, Osaka 560-8531, Japan.
As part of a program aimed at the development of new func-
tional materials based on the controlled d–π conjugation of
square planar transition metal coordination platforms, we have
been investigating the ultrasound-induced aggregation,3 ultra-
sound-induced emission enhancement,3b solid-4 and liquid-
state5 phosphorescence, and molecular dynamics6 of various d8
E-mail: naota@chem.es.osaka-u.ac.jp
†Electronic supplementary information (ESI) available: Additional 1H NMR, 2D
NMR and spectroscopic data, and results of TD-DFT. CCDC 1485966–1485972.
For ESI and crystallographic data in CIF or other electronic format see DOI:
10.1039/c6dt04005e
‡Present address: Chemistry Laboratory, The Jikei University School of
Medicine, Kokuryo, Chofu, Tokyo 182-8570, Japan.
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the corresponding salicylaldehyde hydrazones in boiling
dimethyl sulfoxide (DMSO). Vaulted analogues, incorporating
octa- (3), deca- (4), and dodecamethylene (5) linkers, were
prepared by the reaction of 1a with the corresponding
1,ω-diiodoalkanes in the presence of NaH in N,N-dimethyl-
formamide (DMF), as depicted in eqn (1). This reaction pro-
vides a direct method for the preparation of the polymethyl-
ene-vaulted complexes, and is a convenient alternative to
the reaction of platinum salts with the corresponding
1,ω-dihydrazinoalkanes. Complexes 1–5 were characterized by
1H and 13C nuclear magnetic resonance (NMR) spectroscopy,
infra-red (IR) spectroscopy, high-resolution mass spectroscopy
(HRMS), and nuclear Overhauser effect spectroscopy (NOESY)
(Fig. S1–S4, ESI†).
Scheme 1 Modulation of the neighbouring participation of nitrogen
lone pairs in the d–π coordination of trans-bis(salicylaldiminato)Pt(II)
platforms.
ð1Þ
Scheme 2 Non-vaulted and vaulted hydrazone complexes 1–5.
transition metal complexes bearing flexible trans-bis(salicylald-
iminato) coordination platforms with three-dimensional super-
structures. The participation of nitrogen lone pairs in the d–π
conjugation of planar coordination platforms could be one
direct method for controlling the optical properties of transition
metal complexes upon modulation of their electronic configur-
ations. For this reason, the introduction of rigid nitrogen-
containing functionalities on π-conjugated ligands has been
extensively studied with the aim of modulating the optical pro-
perties of various transition metal complexes.4e,7,8
Transition metal complexes of salicylaldehyde hydrazones
in the trans-bis coordination mode9 represent interesting
analogues of trans-bis(salicylaldiminato) transition metal
complexes.3–6 These compounds have the potential to provide
various modes for the participation of neighbouring nitrogen
lone pairs in d–π conjugation on the coordination platforms,
as in the example of typical conformers I–III presented in
Scheme 1. In this paper, we describe the synthesis, structure
and chromogenic properties of a series of novel non-vaulted
and polymethylene-vaulted Pt(II) complexes (1–5) having trans-
bis coordination of salicylaldehyde hydrazone ligands
(Scheme 2). This work focussed on the correlation between the
photophysical properties of these complexes and the structure-
derived conformational fixation of the coordination platforms.
The molecular structures of the trans-bis(salicylaldehyde
hydrazone)Pt(II) complexes were unequivocally established by
X-ray diffraction (XRD) analysis at 113 K. The crystallographic
data and ORTEP drawings of complexes 1a, 1b, 2a, 2b, 3, 4 and
5 are provided in Table 1 and Fig. 1, in which the C(5)–Pt(1)–
C(5)′ (for 1 and 2) and C(5)–Pt(1)–C(12) (for 3, 4 and 5) angles
and the C(7)–N(1)–Pt(1)–O(1) dihedral angles are included to
express a macroscopic view of the coordination planarity of
the trans-bis(salicylaldiminato)Pt moieties. The coordination
blades in the non-vaulted complexes 1a, 1b, 2a and 2b were
highly planar, as indicated by the C(5)–Pt(1)–C(5)′ and C(7)–
N(1)–Pt(1)–O(1) angles (1a: 180°, 3.4°; 1b: 180°, 8.9°; 2a: 180°,
4.2°; 2b: 180°, 1.7°), while the corresponding angles [C(5)–
Pt(1)–C(12), C(7)–N(1)–Pt(1)–O(1)] in the vaulted complexes 3
(146°, 22.1°), 4 (163°, 9.8°) and 5 (165°, 9.4°) were smaller than
those in 1 and 2 due to additional bonding from the poly-
methylene linker. It is noteworthy that the coordination
planarity of the vaulted complexes decreases upon reducing
the linker length, as demonstrated by the above angles and the
molecular structures in Fig. 1e–g.
One of characteristic features of these complexes is that the
protons on the nitrogen atoms N(2)/N(2)′ in 1a and 1b interact
with remote oxygen atoms [O(1)′/O(1)], with typical hydrogen-
bonding distances of 2.04 and 2.03 Å, respectively. In the case
of these N-methyl complexes, the intramolecular hydrogen
bonding provides conformational fixation of the N-methyl
groups, which are located on the lateral sides of the coordi-
nation planes, as indicated by the smaller C(7)–N(1)–N(2)–C(8)
dihedral angles (1a: 33.0°; 1b: 24.9°) (Fig. 1a and b). This is in
contrast to the conformation of the N,N-dimethyl complexes 2,
Results and discussion
Synthesis and structure of non-vaulted and vaulted platinum
complexes of salicylaldehyde hydrazone
In the present study, trans-bis(salicylaldehyde hydrazone)Pt(II) in which four N-methyl groups are located on the upper and
complexes bearing N-methyl (1) and N,N-dimethyl (2) function- lower sides of the coordination platforms, as suggested by the
alities were prepared by the reaction of [PtCl2(CH3CN)2] with larger C(7)–N(1)–N(2)–C(8)/C(7)–N(1)–N(2)–C(9) dihedral angles
19258 | Dalton Trans., 2016, 45, 19257–19268
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Table 1 Crystallographic data for 1a, 1b, 2a, 2b, 3, 4 and 5
1a
1b
2a
2b
( )-3
( )-4
( )-5
Formula
Mr
T/K
C16H18N4O2Pt
493.43
113
C18H22N4O4Pt
553.49
113
C18H22N4O2Pt
521.49
113
C20H26N4O4Pt
581.54
113
C24H32N4O2Pt
603.63
113
C26H36N4O2Pt
631.69
113
C28H40N4O2Pt
659.74
113
Crystal color, habit
Crystal size/mm
Orange, block
0.20 × 0.20 ×
0.01
Orange, block
0.25 × 0.25 ×
0.15
Orange, block
0.30 × 0.30 ×
0.04
Yellow, block
0.20 × 0.20 ×
0.20
Orange, chunk
0.04 × 0.02 ×
0.01
Orange, block
0.16 × 0.10 ×
0.04
Yellow, chip
0.06 × 0.03 ×
0.01
Crystal system
Space group
a/Å
b/Å
c/Å
Orthorhombic
Pbca (#61)
10.8656 (4)
7.8537 (3)
18.2020 (6)
90
Monoclinic
P21/c (#14)
8.0049 (3)
7.4611 (3)
16.1764 (7)
90
Orthorhombic
Pbca (#61)
12.37580
8.61300
16.90670
90
Tetragonal
I41/a (#88)
16.814 (5)
16.814 (5)
14.083 (4)
90
Monoclinic
C2/c (#15)
19.267(3)
8.0479(12)
16.571(3)
90
Monoclinic
C2/c (#15)
22.571 (15)
12.924 (10)
18.991 (16)
90
Monoclinic
P21 (#4)
10.6527(16)
18.415(2)
14.174(2)
90
α/°
β/°
90
90
102.350 (2)
90
943.79 (7)
2
1.948
74.358
90
90
90
90
3981 (2)
8
1.940
70.563
2272.00
55.0
115.039(3)
90
2327.9(6)
4
115.35 (3)
90
5007 (7)
8
1.676
56.127
101.825(3)
90
2721.4(7)
4
γ/°
V/Å3
1553.27 (9)
4
2.110
90.130
944.00
54.9
1802.13191
4
1.922
77.740
1008.00
54.9
Z
ρcalcd/g cm−3
μ (MoKα)/cm−1
F(000)
1.722
1.610
60.310
1192.00
54.9
51.665
1320.00
55.0
536.00
54.9
2512.00
54.7
2θmax/°
No. of reflns measd
No. of obsd reflns
No. of variables
R1 (I > 2σ(I))a
wR2 (all reflns)b
Goodness of fit
28 631
1764
111
0.0198
0.0503
1.186
18 246
2149
130
0.0369
0.0992
1.076
12 615
2044
115
0.0646
0.2098
1.253
38 971
2272
133
0.0199
0.0632
1.273
11 176
2664
93
0.0242
0.0503
1.030
18 432
5518
298
0.1103
0.2288
1.134
27 987
11 471
595
0.0507
1.129
1.013
a R1 = ∑(|Fo| − |Fc|)/ ∑(|Fo|). b wR2 = [∑[w(Fo2 − Fc2)2]/∑w(Fo2)2]1/2
.
(2a: 114.5°/112.6°; 1b: 113.4°/115.0°) (Fig. 1c and d). Given the 2a appear as a singlet at 3.14 ppm, as shown in Fig. 2b,
contrasting conformations of crystalline 1 and 2, we can be suggesting that complex 2a has highly mobile N,N-dimethyl
reasonably certain that the lone pairs of the N(2)/N(2)′ atoms groups as a result of the absence of conformational fixation
of 1 participate significantly in d–π conjugation throughout via intramolecular hydrogen bonding. Notably, the H(7) signal
the trans-bis(salicylaldiminato)Pt(II) platforms, at least in the for the CvN moiety of 1a (7.90 ppm) appears upfield relative
crystalline state, while those in 2 have little involvement in to that of 2a (8.40 ppm) (Fig. 2a and b). This is attributed to
such conjugation, for steric reasons. This argument is in good the specific participation of neighbouring N(2) lone pairs in
agreement with the observations that (1) the N(1)–N(2) dis- the d–π conjugation on the coordination platform of 1a, such
tances in 1 (1a: 1.40 Å; 1b: 1.40 Å) are shorter than those in 2 that the reduced double bond character of the CvN moieties
(2a: 1.45 Å; 2b: 1.43 Å), and (2) the C(7)–N(1) distances in 1 (1a: diminishes the ring current and also the deshielding effect
1.30 Å; 1b: 1.31 Å) are longer than those in 2 (2a: 1.27 Å; 2b: experienced by the H(7) proton.
1.29 Å), indicating that the double bond character of the
Fig. 3 shows the 2D NOESY (500 MHz) spectrum of a solu-
N(1)–N(2) bond and single bond character of the C(7)–N(1) tion of 1a in CDCl3. Strong remote correlations are observed
bond in 1 are greatly enhanced by the participation of the between the NH (3.00 ppm) and H(3) (6.94 ppm) signals (corre-
neighbouring N(2) lone pairs.
lation A) and between the CH3 and H(7) signals (correlation B)
as well as the expected correlations between NH–CH3
(C), H(6)–H(7) (D), H(5)–H(6) (E), H(4)–H(5) (F) and H(3)–H(4)
Dynamic behaviour in the solution state
The dynamic behaviour of non-vaulted complexes 1 and 2 in (G). This is a good indication that the intramolecular hydro-
CDCl3 was examined by 1H NMR (500 MHz) analysis. As shown gen-bonding and the subsequent fixed conformation of 1
in Fig. 2a, the CH3 and neighbouring NH protons of 1a appear (Fig. 1a and b) are maintained in the solution state. Complex
as doublet and quartet signals at 3.00 and 7.58 ppm, respect- 2a exhibits remote NOESY CH3 (3.14 ppm)–H(3) (6.92 ppm) (A)
ively, with a coupling constant of 5.7 Hz. This is in contrast to and CH3–H(7) (8.40 ppm) (B) correlations in CDCl3, as shown
the observation that the CH3 and NH protons in secondary in Fig. 4. Given that the singlet CH3 signal of 2a does not split
methylamines (RNHCH3) generally appear as sharp and broad into two independent signals over the temperature range of
singlets, respectively, being unsplit due to the rapid exchange 243–298 K (Fig. S1†), the simultaneous correlations A and B of
of the NH protons. The clear quartet splitting of the NH the unsplit methyl signals suggest that, in the case of 2a, there
signals therefore indicates that the hydrogen-bonding fixation is an equilibrium between conformers II and III (inset to
of the NH protons in 1a evident in the crystalline state (Fig. 1a) Fig. 4) based on a rapid flipping motion resulting from the
is maintained even in solution. In contrast, the CH3 protons of N(sp3)–N(sp2) interconversion6b of the N(2) atoms, which
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Fig. 2 1H NMR spectra (500 MHz) of (a) 1a and (b) 2a in CDCl3 at 298 K.
Fig. 3 NOESY spectrum (500 MHz) of 1a in CDCl3 (298 K, mixing
time = 0.7 s, number of t1 increments = 1024, number of t2 increments
= 512, number of scans = 42).
occurs at a rate faster than the NMR time scale. A conformer
bearing two magnetically inequivalent methyl groups located
on the lateral and inner sides of the coordination platform can
evidently be rejected as a plausible single-species conformer of
2a, because the singlet CH3 signal is not split, even at lower
temperatures. An unsymmetrical conformer is also improbable
due to the associated steric congestion between the methyl
groups and phenoxy moieties of the cofacial ligand. A similar
flipping behaviour of N(2) atoms was apparent for the poly-
Fig. 1 ORTEP representations of trans-bis(salicylaldehyde hydrazone)
Pt(II) complexes (a) 1a, (b) 1b, (c) 2a (d) 2b, (e) 3, (f) 4 and (g) 5. Left
figures: overhead views. Right figures: side views. Thermal ellipsoids are
shown at the 50% probability level. Hydrogen-bonding distances (1a and
1b), C(5)–Pt(1)–C(5)’ (1 and 2)/C(5)–Pt(1)–C(12) angles (4 and 5) and the
C(7)–N(1)–Pt(1)–O(1) dihedral angle (in parentheses) are provided for
each structure.
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chromically upon shortening of the polymethylene bridges. It
is noteworthy that, in previous work, a series of polymethyl-
ene-vaulted trans-bis(salicylaldiminato)Pt(II) analogues did not
exhibit a significant linker dependence of absorption pro-
perties under similar conditions,10 indicating that the present
linker-dependent chromism can be attributed to the structure-
dependent participation of neighbouring N(2) lone pairs in
the d–π conjugation of the trans-bis(salicylaldiminato)Pt(II)
coordination platforms.
Another characteristic feature of the present platform is
chromogenic control, simply achieved by the introduction of a
single substituent at different positions on the aromatic ring.
Fig. 6 presents the absorption spectra of 1a–c and 2a–c in
CH3CN at 298 K, from which it can be seen that the absorption
maxima of the MLCT/ILCT bands vary significantly over a span
of 34 or 53 nm, depending on the position of the MeO group.
In addition, the non-vaulted and vaulted complexes 1–5
exhibited structure-dependent solvatochromism in various sol-
vents. The UV-vis spectra of 1–6 in various aliphatic, aromatic,
chlorinated and alcoholic solvents are shown in Fig. S6–S11.†
The absorption maxima of the MLCT/ILCT bands (νmax) of
these complexes are in good agreement with Reichardt’s
solvent parameter ET(30),11 and the correlations of the νmax
values of 1a, 2a and 6 with ET(30) for the various solvents are
plotted in Fig. 7. The slope of the 1a plot is steeper than that
for 2a, indicating that the solvent sensitivity of 1a is greater.
Fig. 4 NOESY spectrum (500 MHz) of 2a in CDCl3 (298 K, mixing
time = 0.4 s, number of t1 increments = 1024, number of t2 increments =
512, number of scans = 68).
methylene-vaulted complexes 3–5 in CDCl3 based on the
CH3–H(7)/H(14) and CH3–H(3)/H(10) NOESY correlations
shown in Fig. S2–S4.†
Structure-dependent changes in chromogenic properties
Hydrazone complexes 1–5 exhibited structure-dependent The absorption data for 1a in the non-alcoholic solvents
chromic behaviour in the solution state. Fig. 5a presents the demonstrates a strong correlation, as a result of negative solva-
UV-vis spectra of the non-vaulted hydrazone complexes with tochromism, between νmax and ET(30), while the data acquired
N-methyl (1a) or N,N-dimethyl groups (2a) and of the trans-bis in alcoholic solvents suggests a significantly different relation-
(N-isopropylsalicylaldiminato)Pt(II) (6) in CH3CN at 298 K, in ship, with lower wavenumbers (black circles in Fig. 7). This is
which the complexes exhibit broad bands attributable to a in contrast to the 2a data, which exhibit a strong correlation
mixture of metal-to-ligand charge transfer (MLCT) and intra with negligible deviation (black squares in Fig. 7). It is of inter-
ligand charge transfer (ILCT) transitions at 350–500 nm. The est that the νmax − ET(30) plot for the salicylaldiminato
MLCT/ILCT band of 1a is hyper- and hypsochromically shifted complex 6 (white circles in Fig. 7) is closer to the 2a data
relative to those of 2a and 6, as shown by the absorption rather than the 1a results, both in terms of deviations and
maxima. A difference similar to that between 1a and 2a is also slope. These plots indicate that (1) the coordination platform
observed in the case of the 4-methoxy (1b, 2b) and 5-methoxy- of the trans-bis(salicylaldiminato)Pt(II) complex 6 is similar to
substituted complexes (1c, 2c) in Fig. S5.† Vaulted complexes that of 2a but is significantly different from 1a in terms of
3–5, bearing various polymethylene linkages, also exhibited absorption properties in the solution state, and (2) the solvato-
linker-dependent absorption spectra, as can be seen in Fig. 5b, chromism increases in the order of 2a, 6 < 1a. Other para-
where the MLCT/ILCT transition bands are shifted hypso- meters, such as the solvent dipole moment (μ), dielectric
Fig. 5 UV-vis spectra of 2.0 × 10−4 M solutions of 1–6 in CH3CN at
298 K: (a) non vaulted complexes 1a, 2a and 6, and (b) polymethylene-
vaulted complexes 3, 4 and 5.
Fig. 6 Position-dependencies of the UV-vis spectra of non-, 4-MeO-
and 5-MeO-substituted complexes of (a) 1 and (b) 2 at 298 K in CH3CN
(2.0 × 10−4 M).
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Fig. 7 Plots of νmax (MLCT/ILCT) for 1a, 2a and 6 at 298 K against
Fig. 8 Plots of νmax (MLCT/ILCT) of short-vaulted 3 and long-vaulted 5
●
■
○
solvent ET(30) values. : 1a; : 2a; : 6. Solvents: 1, CCl4; 2, toluene;
3,2-methyl-2,3,4,5-tetrahydrofuran; 4, chlorobenzene; 5, CHCl3; 6, pyri-
dine; 7, CH2Cl2; 8, DMF; 9, DMSO; 10, CH3CN; a, 1-butanol; b, 2-propa-
nol; c, 1-propanol; d, ethanol; e, methanol.
●
○
at 298 K against ET(30) solvent values. : 3; :5. Solvents: 1, toluene;
2,2-methyl-2,3,4,5-tetrahydrofuran; 3, CHCl3; 4, CH2Cl2; 5, DMF; 6,
DMSO; 7, CH3CN; a, ethanol; b, methanol.
constant (ε),12 and Kamlet and Taft’s solvent polarity
scale (π*),13 were found to correlate poorly with the 1a and 2a
wavenumber values (Fig. S12–S14†).
The effect of the linker on the relationship between νmax
(MLCT/ILCT) and ET(30) in the case of the short- and long-
vaulted complexes 3, 4 and 5 in various solvents is summar-
ized in Fig. 8 and S15.† Notably, the deviation of alcoholic
solvent data from the other solvent data increases upon short-
ening of the polymethylene bridges. In addition, the slopes of
the νmax − ET(30) correlation for shorter vaulted 3 and 4 are
significantly larger than that for longer vaulted 5, indicating
that the solvatochromism of the vaulted complexes is
enhanced upon shortening of the linkers. Given the forgoing
solvatochromic behaviour of the non-vaulted complexes, it is
reasonable to conclude that the solvatochromic properties of
the vaulted complexes approach those of 1a from 2a as the
linker length is reduced.
Fig. 9 Solutions of (a) 1a and (b) 5 in DMSO (2.0 × 10−4 M) at 77 K with
(left) or without (right) CH3SO3H (100 equiv.). These photographs were
taken under room light (upper photos) and UV irradiation (365 nm,
lower photos) from the exterior of the quartz Dewar vessel in which the
sample cells were immersed in liquid nitrogen.
One of the most important photophysical properties of the
hydrazone complexes is acid-induced emission enhancement,
in which the intensity and efficiency of phosphorescent emis-
sion in organic solvents increases upon the addition of an
excess of an organic acid. As an example, the addition of a
sufficient amount of CH3SO3H (100 equiv.) to non-emissive
solutions of non-vaulted and vaulted complexes in DMSO typi-
cally causes the solutions to exhibit intense yellow phosphor-
escence at 77 K, as shown in Fig. 9. Fig. 10 shows the changes
of 1a at 77 K (Φ77 K) also increased, from 0 to 0.44, with the
addition of 150 equiv. of the acid (Fig. 10b). Similarly, the
Φ77
values of the non-vaulted dimethyl complex 2a were
K
enhanced drastically, from 0 to 0.38, upon the addition of 150
equiv. of CH3SO3H. It is worth noting that the enhanced Φ77 K
value of the long-vaulted complex 5 under the same conditions
(0.59, 150 equiv., Fig. 10f) is greater than that of the short-
vaulted complex 4 (0.39, Fig. 10d).
in the emission spectra and quantum yields of 2.0 × 10−4
M
solutions of 1a, 4 and 5 in DMSO with varying concentrations
of CH3SO3H at 77 K. Upon increasing the equivalents of acid
from 1.0 to 150, the emission of 1a is gradually enhanced,
going from almost a non-emissive to a highly emissive state,
Mechanistic rationale for chromogenic behaviour
accompanied by a hypsochromic shift of the emission maxima To gain further insight into the chromogenic properties of the
(λmax) from 573 nm to 548 nm (Fig. 10a). The quantum yields hydrazone complexes, the optimized geometries of 1a, 2a, 3, 4
19262 | Dalton Trans., 2016, 45, 19257–19268
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This is quite consistent with the vertical orientation of the
lone pairs on the N(2) atoms of 1a with regard to the trans-bis
(salicylaldiminato)Pt(II) coordination platform (Fig. 11a). In
contrast, the lone pairs of 2a are situated horizontally
(Fig. 11b), as indicated by the X-ray structures (Fig. 1a and c).
The planarity of the coordination platforms of the vaulted
complexes 3–5 decreases upon shortening of the polymethyl-
ene linkers (Fig. 11c–e), as reflected in the C(5)–Pt(1)–C(12)
angles of 159° (for 3), 162° (for 4) and 172° (for 5), which is
also coincident with the molecular structures for 3–5 deter-
mined by XRD analysis (Fig. 1e–g).
The frontier orbitals associated with the optimized geome-
tries of 1a, 2a, 3, 5 and N,N′-diisopropyl-trans-bis(salicylaldimi-
nato)Pt(II) (6) are shown in Fig. 12. The highest occupied mole-
cular orbital (HOMO) of 1a is principally a hybrid of Pd(4d)
and π orbitals spread over the aromatic rings, imine moieties
and N(2) atoms, whereas the lowest unoccupied molecular
orbital (LUMO) is the π* orbital on the same ligand platform,
including the N(2) atoms (Fig. 12a). In contrast, the frontier
orbitals of 2a have no contribution from the N(2) atoms,
although the contribution of other atomic orbitals are almost
the same as those of 1a (Fig. 12b). Notably, the frontier orbitals
of 2a are very similar to those of 6 (Fig. 12b and c). The elec-
tronic configurations of the singlet states of 1a, 2a and 6 were
Fig. 10 Acid-induced emission enhancement of (a, b) non-vaulted 1a,
(c, d) short-vaulted 4, and (e, f) long-vaulted 5 in DMSO (2.0 × 10−4 M)
with CH3SO3H at 77 K (λex: 410 nm for 1a, 430 nm for 4 and 5). Changes
in (a, c, e) emission spectra, and (b, d, f) quantum yields (Φ77 K) as a func-
tion of initial equiv. of CH3SO3H.
and 5 were determined using density functional theory (DFT,
B3LYP/6-31G*, LanL2DZ) calculations on the basis of the struc-
tures derived from X-ray analysis (Fig. 11). The three bond
angles around the N(2) atom centre [N(1)–N(2)–C(8), N(1)–
N(2)–H, C(8)–N(2)–H] in 1a were found to be 111°, 104° and
107°, respectively, and these angles were smaller than those in
2a [N(1)–N(2)–C(8) (112°); N(1)–N(2)–C(9) (112°); C(8)–N(2)–
C(9) (115°)], indicating that the sp2 character of the N(2) atoms
in 1a was enhanced as a result of significant neighbouring par-
ticipation in the d–π conjugation of the coordination platform.
Fig. 12 Frontier orbitals and their eigenvalues [eV] for complexes (a) 1a,
(b) 2a, (c) 6, (d) 3, and (e) 5 as estimated from DFT calculations (B3LYP/
6-31G*, LanL2DZ) based on the optimized geometries.
Fig. 11 Optimized structures for (a) 1a, (b) 2a, (c) 3, (d) 4, and (e) 5 opti-
mized by DFT (B3LYP/6-31G*, LanL2DZ) calculations.
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estimated from time-dependent DFT (TD-DFT) calculations alcoholic and alcoholic solvent data for 2a with those for 6
(Table S1†). The primary electronic configuration of the S1 (black squares and white circles in Fig. 7) is also a good indi-
state was determined to be HOMO-to-LUMO for these com- cation that the solvation properties of 2a are almost
plexes, which implies that the absorption properties of the unchanged upon addition of non-conjugated mobile N(2) lone
hydrazone complexes are principally attributable to a mixture pairs to the trans-bis(salicylaldiminato)Pt(II) coordination plat-
of MLCT and ILCT transitions, as is the case with trans-bis(salicyl- form of 6.
aldiminato)Pt(II) complexes.4b The similarity in the frontier
The separated correlation of the alcoholic solvent data
orbitals of 2a and 6 indicates that the absorption properties of observed bathochromically in the νmax − ET(30) plots for 1a
2a are primarily due to the MLCT and ILCT transitions on (black circles, Fig. 7) can also be ascribed to the specific de-
the trans-bis(salicylaldiminato)Pt(II) coordination platforms, stabilization of the ground state of 1a in alcohols, such that
without the significant participation of neighbouring N(2) lone the hydrogen-bonding properties of 1a are diminished signifi-
pairs. This is highly consistent with the fact that the absorp- cantly upon strong participation of neighbouring, vertically
tion maxima for the MLCT/ILCT band of 2a (439 nm) is close locked N(2) lone pairs in the d–π conjugation on the coordi-
to that of 6 (433 nm) (Fig. 5a). Given the experimental results nation platform. The contrasting, unseparated correlations of
and the present theoretical support, we can conclude that the alcoholic and non-alcoholic solvent data for 2a (black squares,
participation of fixed or unfixed neighbouring N(2) lone pairs Fig. 7) demonstrate that the solvation of 2a in alcohols is
in the d–π conjugation of the coordination platforms is the key much higher than that of 1a due to the more pronounced
to the specific chromogenic properties of the hydrazone com- hydrogen-bonding character of the mobile N(2) lone pairs,
plexes. The effects of the position of the MeO functionality on which are free from neighbouring participation in the d–π con-
the absorption wavelengths of 1a–c and 2a–c (Fig. 7) can be jugation. The above discussion is in good agreement with pre-
explained by the strong correlation between the absorption vious reports on the solvatochromism of simple transition
wavenumbers of the MLCT/ILCT bands and the HOMO–LUMO metal complexes, in which strongly hydrogen-bonding com-
energy gaps, as shown in Fig. S16 and S17.†
plexes such as M(CN)2Lm exhibited unseparated νmax − ET(30)
Although the frontier orbitals of the long-vaulted complex 5 correlations for both alcoholic and non-alcoholic solvents,14d
have no contribution from N(2) atoms (Fig. 12e), similar to the while complexes such as M(CO)nLm with less hydrogen-
case of 2a and 6 (Fig. 12b and c), the short-vaulted analogue 3 bonding showed clearly separated correlations.14
exhibits significant contribution from N(2) atoms, likely due to
The steeper slope and separated correlation of alcoholic
the conformational fixation of their 2p orbitals with the short solvent data, observed specifically in the νmax − ET(30) plots for
polymethylene linker (Fig. 12d). The similarity between the shorter-vaulted 3 (Fig. 8) and 4 (Fig. S15†), can be also attribu-
frontier orbitals of 5 and those of 2a and 6 suggests that the ted to the enhancement of d–π conjugation on the coordi-
absorption properties of 5 are principally attributable to the nation platform of this complex, which would arise from stron-
MLCT/ILCT transitions on the trans-bis(salicylaldiminato)Pt(II) ger participation of less mobile, neighbouring N(2) lone pairs
coordination platform, which is consistent with the obser- upon conformational fixation of the short-vaulted structure.
vation that the absorption maxima for the MLCT/ILCT band of This is in contrast to the longer-vaulted complex 5, the coordi-
5 (440 nm) is close to those of 2a (439 nm) and 6 (433 nm) nation platforms of which is similar to that of non-vaulted 2a
(Fig. 5). The participation of the 2p orbitals of N(2) atoms in due to the high rotational and flipping mobility of the N(2)
the frontier orbitals of 3 (Fig. 12d) strongly implies that the atoms. Similarity in the solvatochromic properties between 3
characteristic hypsochromic shift in the absorption of 3 also and 4 (Fig. S15†) is probably due to their linker lengths, both
results from the significant participation of neighbouring, con- of which are sufficiently short for strong conformational
formationally locked N(2) lone pairs in the d–π conjugation on locking and subsequent extension of the d–π conjugation of
the coordination platforms.
the coordination platforms.
The structure-dependent changes in the correlations
Acid-induced emission enhancement (Fig. 10) would arise
between νmax and ET(30) (Fig. 7 and 8) can be explained by vari- from the protonation of N(2) lone pairs on the non-emissive
ations in the participation of N(2) lone pairs in the trans-bis coordination platforms of the hydrazone complexes. Given
(salicylaldiminato)Pt(II) coordination platforms. It has been that the emission spectra of the protonated complexes are
well documented that positive correlations in νmax − ET(30) close to that of 6, which exhibits emission maxima of 550 nm
plots arise primarily from significant solvation of polar under similar conditions (Fig. S18†), it is reasonable to con-
chromophores in polar solvents due to stabilization of the clude that the protonation of the N(2) lone pairs changes the
ground state.11 High solvent sensitivity, meaning the strong platform from a non-emissive electronic configuration to an
solvatochromism of 1a that is apparent from the steep slope of emissive one that is similar to that of the emissive trans-bis
its νmax − ET(30) plot (black circles in Fig. 7), is attributable to (salicylaldiminato)Pt(II) platform.3b,4,5 The linker-dependence
the foregoing strong participation of neighbouring locked N(2) of the emission enhancement of the vaulted complexes
lone pairs in the d–π conjugation of the coordination platform (Fig. 10d and f) can be ascribed to the difference in the
of 1a, such that the extended d–π conjugation increases the average planarity of the coordination platforms between short-
polarity of the coordination platform, leading to enhanced and long-vaulted analogues. The protonated platform of 5,
compatibility with polar solvents. The similarity in the non- with a high coordination planarity, would have a higher
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3
probability of the MLCT transition, leading to stronger emis-
sion, as reported for a series of corresponding long poly-
methylene-vaulted trans-bis(salicylaldiminato)Pt(II) analo-
gues.4a,b,5b The fact that the emission properties of vaulted 5
are enhanced to a greater extent (Φ77 K = 0.59) than those of
non-vaulted 1a (0.44) and 2a (0.38) under the same conditions
(Fig. 10) can be attributed to the barrier effect of the
polymethylene bridge, which would be expected to suppress
the energy dispersion through consecutive intermolecular
π-stacking interactions of the iminoaromatic rings.4
The relationship between the variations in the d–π conju-
gation of the non-vaulted trans-bis(salicylaldiminato)Pt(II)
coordination platforms and the photophysical properties of
these complexes is summarized schematically in Fig. 13. The
conformational fixation of the N(2) atoms of 1a by intra-
molecular hydrogen bonding gives rise to strong participation
of the neighbouring N(2) lone pairs in the d–π conjugation of
the coordination platform, which in turn induces significant
solvatochromic properties that can be rationalized according
to the forgoing discussion. Complex 2a undergoes much less
neighbouring participation due to the highly mobile N(2) lone
pairs with no hydrogen bonding fixation, leading to almost the
same scenario as for the trans-bis(salicylaldiminato)Pt(II)
complex 6 in terms of absorption and solvatochromic behav-
iour. Complexes 1a and 2a exhibit intense acid-induced
emission enhancement, since protonation of their N(2) lone
pairs induces an electronic configuration in their coordination
platforms similar to that of 6, which is emissive even under
non-acidic conditions.
Fig. 14 Linker length effects on the photophysical properties of (a)
short- and (b) long-vaulted complexes.
coordination planarity and so avoids steric congestion of the
amino moieties, resulting in weak solvatochromism similar to
that of the non-vaulted complex 2a. The long-linked complexes
demonstrate intense acid-induced emission enhancement
because the resulting highly planar protonated coordination
platforms resemble trans-bis(salicylaldiminato)Pt(II) and thus
have intense emission properties, while the emission pro-
perties of the short-linked complexes are greatly reduced due
to the weak MLCT/ILCT transitions on the bent protonated
platforms.
The effect of the linker length on the photophysical pro-
perties of the vaulted complexes is summarized in Fig. 14. The
bent coordination platforms of the short-vaulted complexes
result in significant participation of neighbouring N(2) lone
pairs in the d–π conjugation, owing to the conformational con-
straint, and this leads to pronounced solvatochromism. This is
Conclusions
in contrast to the behaviour of the long-vaulted complexes, This work examined the effects of the participation of neigh-
whose high conformational flexibility allows stability via bouring nitrogen lone pairs on the chromogenic behaviour of
trans-bis(salicylaldiminato)Pt(II) coordination platforms using
the newly designed Pt analogues 1–5 bearing salicylaldehyde
hydrazone as a trans-coordinated bidentate ligand. Structural
studies by XRD, NMR analyses and DFT calculations revealed
that the non-vaulted N-monomethyl complexes
1 have
extended d–π conjugation on the trans-bis(salicylaldiminato)
Pt(II) coordination platforms as a result of intense partici-
pation of neighbouring vertically-fixed N(2) lone pairs arising
from hydrogen bonding fixation. In contrast, the N,N-dimethyl
analogues 2 show much less d–π conjugation owing to the neg-
ligible participation of mobile N(2) lone pairs. The short-
vaulted complex 3 exhibits a greater extension of the d–π con-
jugation platforms than the longer vaulted 5 due to the confor-
mational fixation of the N(2) lone pairs by the short poly-
methylene bridge. Variations in the chromogenic behaviour of
these complexes were observed in terms of their absorption
wavelengths, solvatochromism and acid-induced emission
enhancement, all of which are controlled by structure-depen-
dent changes in the d–π conjugation of the coordination
Fig. 13 Schematic representation of the conformational differences
and relative photophysical properties of non-vaulted complexes (a) 1a,
(b) 2a, and (c) 6.
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platforms upon varying the participation of neighbouring 2 H, NH), 7.80 (s, 2 H, NvCH); 13C NMR (CDCl3, 125 MHz)
mobile N(2) lone pairs.
δ 38.8, 56.0, 113.5, 118.3, 120.3, 122.0, 145.3, 150.4, 155.5;
HRMS (FAB+) m/z calcd for C18H22N4O4195Pt (M)+: 553.1289;
found: 553.1286.
Complex 2a: Orange block (7%); mp 272 °C (decomp.); IR
(KBr) 2929, 1604, 1537, 1447, 1320, 1195, 1152, 933, 758, 620,
599 cm−1; 1H NMR (CDCl3, 500 MHz) δ 3.14 (s, 12 H, N(CH3)2),
Experimental section
General
Salicylaldehyde hydrazones were prepared by reaction of the 6.59 (ddd, J = 8.3, 6.9, 1.2 Hz, 2 H, H5), 6.92 (d, J = 8.7, 1.2 Hz,
corresponding salicylaldehydes with N-methyl or N,N-di- 2 H, H3), 7.20 (dd, J = 8.3, 1.6 Hz, 2 H, H6), 7.33 (ddd, J = 8.7,
methylhydrazine in boiling ethanol. Melting points were deter- 6.9, 1.6 Hz, 2 H, H4), 8.40 (s, 2 H, NvCH); 13C NMR (CDCl3,
mined on glass plates using a Yanagimoto melting point 125 MHz) δ 46.2, 116.1, 118.5, 118.9, 133.5, 134.2, 158.9, 163.3;
apparatus. Mass spectra were acquired with a JEOL JMS-DX HRMS (FAB+) m/z calcd for C18H22N4O2195Pt (M)+: 521.1391;
1
303 spectrometer and H and 13C NMR spectra were recorded found: 521.1352. Elemental anal. calcd for C18H22N4O2Pt: C,
on a Varian Unity-Inova 500 spectrometer. IR spectra were 41.39; H, 4.03; N, 10.74; found: C, 41.46; H, 4.25; N, 10.74%.
acquired with
IR Prestige-21 spectrometers and UV–vis spectra were obtained IR (KBr) 2888, 1589, 1528, 1438, 1310, 1258, 1214, 1120, 1031,
on
Shimadzu MultiSpec-1500 spectrometer. Emission 980, 838, 556 cm−1; 1H NMR (CDCl3, 500 MHz) δ 3.11 (s, 12 H,
a
Bruker Equinox 55 s−1 or Shimadzu
Complex 2b: Yellow block (1%); mp 256 °C (decomp.);
a
spectra were generated using a Jasco FP-6500 spectrometer. N(CH3)2), 3.78 (s, 6 H, OCH3), 6.24 (dd, J = 8.7, 2.4 Hz, 2 H,
Quantum yields were measured by the absolute method using H5), 6.36 (d, J = 2.4 Hz, 2 H, H3), 7.08 (d, J = 8.7 Hz, 2 H, H6),
a Jasco FP-6500 spectrometer equipped with an integrating 8.29 (s, 2 H, NvCH); 13C NMR (CDCl3, 125 MHz) δ 46.2, 55.2,
sphere (Jasco ISN-470). Elemental analyses were performed 100.2, 106.3, 112.5, 134.8, 158.3, 164.8, 164.9; HRMS (FAB+)
with a Perkin-Elmer 2400II CHN elemental analyser.
Synthesis of non-vaulted complexes 1 and 2. A mixture of 582.1602.
m/z calcd for C20H26N4O4196Pt (M)+: 582.1603; found:
PtCl2(CH3CN)2 (1.22 g, 3.50 mmol), the corresponding salicyl-
Complex 2c: Orange block (6%); mp 225–226 °C; IR (KBr)
aldehyde hydrazone (7.00 mmol) and K2CO3 (6.29 g, 2897, 1579, 1540, 1473, 1460, 1297, 1221, 1163, 1043, 887,
45.5 mmol) in DMSO (20 mL) was refluxed at 120 °C under Ar 830 cm−1; 1H NMR (CDCl3, 500 MHz) δ 3.13 (s, 12 H, N(CH3)2),
for 24 h. The reaction mixture was subsequently dissolved in 3.74 (s, 6 H, OCH3), 6.63 (d, J = 3.2 Hz, 2 H, H6), 6.86 (d, J =
ethyl acetate (250 mL), washed with brine (250 mL) and dried 9.2 Hz, 2 H, H3), 7.02 (dd, J = 9.2, 3.2 Hz, 2 H, H4), 8.33 (s, 2 H,
over Na2SO4. After evaporation of the solvent under reduced NvCH); 13C NMR (CDCl3, 125 MHz) δ 46.3, 56.1, 113.5, 117.2,
pressure, the resulting crude solid was purified by column 119.8, 124.3, 150.2, 158.3, 158.7; HRMS (FAB+) m/z calcd for
chromatography (Fuji Silysia Chromatorex NH-DM1020, C20H26N4O4195Pt (M)+: 581.1602; found: 581.1606.
toluene) to give 1 or 2 as an orange or yellow solid.
Synthesis of polymethylene-vaulted platinum complexes 3–5
Complex 1a: Orange block (5%); mp 250 °C (decomp.); IR
(KBr) 3302, 1600, 1553, 1478, 1438, 1339, 1296, 1217, 1161, A mixture of 1a (34.7 mg, 0.05 mmol) and NaH (60% w/w oil
1
1122, 923, 860 cm−1; H NMR (CDCl3, 500 MHz) δ 3.00 (d, J = dispersion, 14 mg, 0.35 mmol) in DMF (5 mL) was stirred at
5.7 Hz, 6 H, NHCH3), 6.66 (ddd, J = 7.9, 7.0, 1.4 Hz, 2 H, H5), room temperature for 1 h under argon. After addition of the
6.94 (dd, J = 8.5, 1.4 Hz, 2 H, H3), 7.24 (dd, J = 7.9, 1.5 Hz, 2 H, corresponding 1,ω-diiodoalkane (0.05 mmol), the reaction
H6), 7.30 (ddd, J = 8.5, 7.0, 1.5 Hz, 2 H, H4), 7.58 (q, J = 5.7 Hz, mixture was stirred for 4 h at room temperature. The mixture
2 H, NH), 7.90 (s, 2 H, NvCH); 13C NMR (CDCl3, 125 MHz) was then dissolved in ethyl acetate (30 mL), washed with brine
δ 39.1, 116.5, 119.4, 119.7, 132.4, 132.9, 146.3, 160.6; HRMS (30 mL) and dried over Na2SO4. After evaporation of the
(FAB+) m/z calcd for C16H18N4O2195Pt (M)+: 493.1077; found: solvent under reduced pressure, the resulting crude solid was
493.1082.
purified by column chromatography (Fuji Silysia Chromatorex
Complex 1b: Orange block (8%); mp 224–225 °C; IR (KBr) NH-DM1020, hexane) to give products 3–5, each as an orange
3310, 1605, 1546, 1488, 1353, 1302, 1211, 1173, 1121, 1030, solid.
973, 840 cm−1; 1H NMR (CDCl3, 500 MHz) δ 2.94 (d, J = 6.2 Hz,
Complex 3: Orange block (6%); mp 181–182 °C; IR (KBr)
6 H, NHCH3), 3.80 (s, 6 H, OCH3), 6.31 (dd, J = 8.7, 2.5 Hz, 2 H, 2925, 2851, 1654, 1607, 1540, 1444, 1309, 1200, 936, 846 cm−1
;
H5), 6.40 (d, J = 2.5 Hz, 2 H, H3), 7.13 (q, J = 6.2 Hz, 2 H, NH), 1H NMR (CDCl3, 500 MHz) δ 1.21–1.31 (m, 4 H, CH2),
7.14 (d, J = 8.7 Hz, 2 H, H6), 7.94 (s, 2 H, NvCH); 13C NMR 1.41–1.54 (m, 4 H, CH2), 1.96 (dddd, J = 12.8, 12.5, 11.2, 4.0
(CDCl3, 125 MHz) δ 40.5, 55.5, 102.1, 106.8, 113.6, 134.1, Hz, 2H, NCH2CH2), 2.32 (dddd, J = 12.8, 12.4, 11.0, 6.1 Hz, 2H,
149.3, 163.2, 164.2; HRMS (FAB+) m/z calcd for NCH2CH2), 2.52 (ddd, J = 13.4, 11.2, 6.1 Hz, 2 H, NCHaHb),
C18H22N4O4195Pt (M)+: 553.1289; found: 553.1281.
3.12 (s, 6 H, NCH3), 4.26 (ddd, J = 13.4, 11.0, 4.0 Hz, 2 H,
Complex 1c: Orange block (2%); mp 218 °C (decomp.); IR NCHaHb), 6.56 (ddd, J = 8.0, 7.0, 1.1 Hz, 2 H, H5), 6.88 (dd, J =
(KBr) 3303, 1483, 1404, 1284, 1229, 1042, 830 cm−1; H NMR 8.7, 1.1 Hz, 2 H, H3), 7.14 (dd, J = 8.0, 1.8 Hz, 2 H, H6), 7.25
1
(CDCl3, 500 MHz) δ 3.00 (d, J = 5.7 Hz, 6 H, NHCH3), 3.76 (s, (ddd, J = 8.7, 7.0, 1.8 Hz, 2 H, H4), 8.17 (s, 2 H, NvCH);
6 H, OCH3), 6.69 (d, J = 3.2 Hz, 2 H, H6), 6.87 (d, J = 9.2 Hz, 13C NMR (CDCl3, 125 MHz) δ 24.7, 25.86, 25.92, 47.6, 55.0,
2 H, H3), 6.97 (dd, J = 9.2, 3.2 Hz, 2 H, H4), 7.65 (q, J = 5.7 Hz, 116.1, 118.6, 119.3, 133.1, 134.0, 159.5, 164.5; HRMS (FAB+)
19266 | Dalton Trans., 2016, 45, 19257–19268
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m/z calcd for C24H33N4O2195Pt (M + H)+: 604.2251; found: 09W17 program package. The basis sets were the effective core
604.2245.
potential (LanL2DZ) for the platinum atom18 and 6-31G* for
Complex 4: Orange block (10%); mp 182–183 °C; IR (KBr) the remaining atoms.19 Molecular orbitals and their eigen-
2926, 2851, 1607, 1540, 1444, 1319, 1148, 752 cm−1; H NMR values for complexes 1a, 2a, 3, 5 and 6 were calculated using
1
(CDCl3, 500 MHz) δ 1.07–1.16 (m, 2 H, CH2), 1.25–1.35 (m, the geometries obtained from the structural optimization.
4 H, CH2), 1.38–1.49 (m, 6 H, CH2), 1.66 (dddd, J = 13.2, 12.5,
12.3, 4.7 Hz, 2H, NCH2CH2), 2.10 (dddd, J = 13.0, 12.5, 12.1,
4.5 Hz, 2 H, NCH2CH2), 2.53 (ddd, J = 12.6, 12.3, 4.5 Hz, 2 H,
NCHaHb), 3.19 (s, 6 H, NCH3), 3.99 (ddd, J = 12.6, 12.1, 4.7 Hz,
Acknowledgements
2 H, NCHaHb), 6.58 (ddd, J = 7.8, 6.8, 1.0 Hz, 2 H, H5), 6.91 This study was supported by JSPS KAKENHI (grant numbers
(dd, J = 8.8, 1.0 Hz, 2 H, H3), 7.18 (dd, J = 7.8, 1.8 Hz, 2 H, H6), JP15H03796 and JP16H06516).
7.30 (ddd, J = 8.8, 6.8, 1.8 Hz, 2 H, H4), 8.35 (s, 2 H, NvCH);
13C NMR (CDCl3, 125 MHz) δ 24.8, 25.80, 25.81, 27.4, 47.2,
55.9, 115.9, 118.4, 133.5, 134.1, 160.6, 163.8; HRMS (FAB+) m/z
Notes and references
calcd for C26H37N4O2195Pt (M
632.2568.
+
H)+: 632.2564; found:
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Complex 5: Orange block (17%); mp 169–170 °C; IR (KBr)
2928, 2854, 1606, 1540, 1444, 1319, 754 cm−1; 1H NMR (CDCl3,
500 MHz) δ 1.11–1.40 (m, 16 H, CH2), 1.50 (dddd, J = 12.3,
12.2, 11.3, 4.7 Hz, 2 H, NCH2CH2), 1.77 (dddd, J = 12.7, 12.5,
10.9, 5.5 Hz, 2 H, NCH2CH2), 2.71 (ddd, J = 12.6, 11.3, 5.5 Hz,
2 H, NCHaHb), 3.15 (s, 6 H, NCH3), 3.96 (ddd, J = 12.6, 10.9,
4.7 Hz, 2 H, NCHaHb), 6.58 (ddd, J = 7.9, 6.8, 1.1 Hz, 2 H, H5),
6.91 (dd, J = 8.5, 1.1 Hz, 2 H, H3), 7.20 (dd, J = 7.9, 1.8 Hz, 2 H,
H6), 7.32 (ddd, 8.5, 6.8, 1.8 Hz, 2 H, H4), 8.37 (s, 2 H, NvCH);
13C NMR (CDCl3, 125 MHz) δ 25.3, 26.8, 26.9, 27.3, 27.6, 46.6,
55.6, 115.8, 118.3, 118.8, 133.6, 134.1, 160.3, 163.5; HRMS
(FAB+) m/z calcd for C28H41N4O2195Pt(M + H)+: 660.2877;
found: 660.2870.
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X-ray structure determination
Crystals suitable for XRD studies were prepared by recrystalli-
zation from ethyl acetate–CHCl3 for 1a and 2a, CH2Cl2 for 1b,
ethyl acetate for 2b, DMSO for ( )-3, hexane for ( )-4, and
CHCl3–ethanol for ( )-5, and analyzed using a Rigaku R-AXIS
RAPID imaging plate diffractometer and a Rigaku Mercury
CCD diffractometer with graphite monochromated Mo Kα radi-
ation (λ = 0.71075 Å). The structures of 1a, 1b, 2a, 2b, ( )-3,
( )-4, and ( )-5 were solved using direct methods and refined
with the full-matrix least-squares method. In subsequent
2
2 2
refinements, the function ∑ω(Fo − Fc ) was minimized,
where Fo and Fc are the observed and calculated structure
factor amplitudes, respectively. The positions of non-hydrogen
atoms were determined from difference Fourier electron
density maps and refined anisotropically. All calculations were
performed using the Crystal Structure crystallographic software
package, and illustrations were drawn using ORTEP.15 Details
of the structural determinations are given in Fig. 1 and
Table 1. CCDC 1485966 (1a), 1485967 (1b), 1485968 (2a),
1485969 (2b), 1485970 [( )-3], 1485971 [( )-4], and 1485972
[( )-5] contain the supplementary crystallographic data for this
paper.
Computational methods
All DFT calculations were conducted using the B3LYP
exchange–correlation functional,16 employing the Gaussian
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