Synthesis and characterization of bioorganometallic conjugates composed of NCN-pincer platinum(II) complexes and uracil derivatives

Article abstract of DOI:10.1016/j.jorganchem.2010.10.018

The conjugation of the NCN-pincer platinum(II) complexes as an oraganometallic compound and the uracil derivatives as a nucleobase was demonstrated to give the corresponding bioorganometallics. The NCN-pincer ligands bearing the 6-ethynyl-1-octyluracil, 5

Full text of DOI:10.1016/j.jorganchem.2010.10.018

Journal of Organometallic Chemistry 696 (2011) 1089e1095
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Synthesis and characterization of bioorganometallic conjugates composed
of NCN-pincer platinum(II) complexes and uracil derivatives
*
*
Toshiyuki Moriuchi , Shunichi Noguchi, Yuki Sakamoto, Toshikazu Hirao
Department of Applied Chemistry, Graduate School of Engineering, Osaka University, Yamada-oka, Suita, Osaka 565-0871, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
The conjugation of the NCN-pincer platinum(II) complexes as an oraganometallic compound and the uracil
derivatives as a nucleobase was demonstrated to give the corresponding bioorganometallics. The NCN-
pincer ligands bearing the 6-ethynyl-1-octyluracil, 5-ethynyl-1-octyluracil, and the furanopyrimidine
moiety were synthesized. In a crystal state, the NCN-pincer ligand bearing the 6-ethynyl-1-octyluracil
moiety was found to form a hydrogen-bonded dimer through intermolecular hydrogen bonds between the
Received 26 August 2010
Received in revised form
4 October 2010
Accepted 6 October 2010
uracil moieties, which was connected through pep interaction between the uracil and benzene moieties of
Keywords:
Bioorganometallic chemistry
Uracil
NCN-Pincer ligand
Platinum(II) complex
Crystal structure
Hydrogen bond
the NCN-pincer ligand. The reaction of the NCN-pincer ligand bearing the 6-ethynyl-1-octyluracil moiety
with [Pt(tolyl-4)2(SEt2)]2 led to the formation of the NCN-pincer platinum(II) complex bearing the
6-ethynyl-1-octyluracil moiety. The NCN-pincer platinum(II) complex bearing the furanopyrimidine
moiety was obtained by the reaction of the NCN-pincer ligand bearing the furanopyrimidine moiety with
[Pt(tolyl-4)2(SEt2)]2. The single-crystal X-ray structure determination of the NCN-pincer platinum(II)
complex bearing the furanopyrimidine moiety revealed the formation of the furanopyrimidine ring and the
p
stack dimer between the furanopyrimidine and benzene moieties of the NCN-pincer ligand in the crystal
packing. The NCN-pincer platinum(II) complexes bearing the 6-ethynyl-1-octyluracil moiety or the fur-
anopyrimidine moiety exhibited emission in both solution and solid states.
Ó 2010 Elsevier B.V. All rights reserved.
1. Introduction
interest, and considerable efforts have been devoted to conjugate
organometallic compounds with biomolecules such as DNA, amino
Highly-ordered molecular assemblies are constructed in bio-
systems to fulfill unique functions. The double helical DNA is
created by A-T and G-C base pairs, which are controlled mainly
acids, and peptides [6]. The transition metal complexes composed
of pincer ligands, which contain a stable metal-carbon bond, have
s
been extensively investigated and utilized as a variety of materials
and catalysts [6k,7]. A combination of pincer complexes with
nucleobases is allowed to design novel bioconjugates depending on
both properties. We herein report the characterization of bio-
organometallic conjugates composed of the NCN-pincer platinum
(II) complexes and the uracil derivatives.
by complementary hydrogen bonding,
p-stacking interaction,
and hydrophobic interaction [1]. Architectural control of molecular
self-organization is of importance for the development of func-
tional materials [2]. Regulation of hydrogen bonding [3] is a key
factor in the design of various molecular assemblies by virtue of
its directionality and specificity [4]. The reversibility and tune-
ability of hydrogen bonding is also of fundamental importance
in the chemical and/or physical properties of molecular assem-
blies. Nucleobases are known to have a specific ability to form
directionally controlled multiple and complementary hydrogen
bonding. The utilization of self-assembling properties of nucleo-
bases is considered to be a relevant strategy to design well-defined
molecular assemblies [5]. On the other hand, the research field of
bioorganometallic chemistry, which is a hybrid area between
biology and organometallic chemistry, has received extensive
2. Results and discussion
The synthesis of the NCN-pincer ligands 4e5 bearing the uracil
moiety and 6 bearing the furanopyrimidine moiety is outlined in
Scheme 1. Regioselective iodination of 1-octyluracil, which was
prepared by thealkylationofuracilwith1-iodooctane in the presence
of K2CO3, was performed as reported to afford 6-iodo-1-octyluracil
and 5-iodo-1-octyluracil [8], respectively. The Sonogashira coupling
reaction of 6-iodo-1-octyluracil or 5-iodo-1-octyluracil with trime-
thylsilylacetylene in the presence of
PdCl2(PPh3)2 and CuI, followed by removal of the TMS protecting
group with KOH in methanol gave 6-ethynyl-1-octyluracil (1) or
a catalytic amount of
* Corresponding author. Fax: þ81 6 6879 7415.
E-mail addresses: moriuchi@chem.eng.osaka-u.ac.jp (T. Moriuchi), hirao@chem.
eng.osaka-u.ac.jp (T. Hirao).
0022-328X/$ e see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2010.10.018

1090
T. Moriuchi et al. / Journal of Organometallic Chemistry 696 (2011) 1089e1095
O
HN
O
O
HN
O
NMe2
Br
NMe2
Br
Pd(PPh3)4 (20 mol%)
CuI (5 mol%)
+
+
H
I
I
THF, i-Pr2NH, r.t., Ar, 18 h
in the dark
N
N
Oct
Oct
NMe2
NMe2
1
3
4, 57%
O
NMe2
Br
O
NMe2
Pd(PPh3)4 (5 mol%)
CuI (2.5 mol%)
HN
HN
N
O
H
O
Br
DMF, Et2NH, 0 °C, Ar, 1 h
then 55 °C, 18 h, in the dark
N
Oct
NMe2
Oct
NMe2
2
3
5, 61%
O
NMe2
Br
NMe2
Br
O
N
HN
N
AgNO3 (40 mol%)
acetone, r.t., Ar, 3 days
O
O
N
Oct
NMe2
Oct
NMe2
5
6, 97%
Scheme 1. Synthesis of the NCN-pincer ligands 4e6.
Fig. 1. (a) Molecular structure of 4, (b) a hydrogen-bonded dimer through intermolecular hydrogen bonds between the uracil moieties, and (c) a portion of a layer containing the
molecular assembly through interaction between the uracil and benzene moieties of the NCN-pincer ligand in a crystal packing of 4.
pep

T. Moriuchi et al. / Journal of Organometallic Chemistry 696 (2011) 1089e1095
1091
is 2.3(1)ꢀ (Fig. 1a and Table 1). Selected bond distances and angles
are listed in Table 2. The NCN-pincer ligand 4 was found to form
a hydrogen-bonded dimer through intermolecular hydrogen bonds
between the uracil moieties (N(4)/O(2), 2.818(4) Å; N(4)-H/O(2),
176(2)ꢀ) (Fig. 1b). Furthermore, each hydrogen-bonded dimer was
Table 1.
Crystallographic data for 4 and 9.
4
9
Empirical formula
Formula weight
Crystal system
Space group
a (Å)
C26H37N4O2Br1
517.51
Triclinic
C26H37N4O2Br1Pt1
712.60
Monoclinic
P21/a (No. 14)
16.9880(16)
9.0621(9)
connected through
the NCN-pincer ligand and the uracil moiety in a crystal packing as
shown in Fig.1c. This interaction might require the orientation
p-p interaction between the benzene moiety of
P-1 (No. 2)
8.67021(16)
12.2101(2)
13.1104(2)
91.8970(7)
100.4125(7)
106.8234(7)
1301.26(4)
2
pep
b (Å)
of the benzene moiety of the NCN-pincer ligand within a limited
range of location parallel to the uracil moiety.
c (Å)
17.5430(19)
a
b
g
(ꢀ)
(ꢀ)
(ꢀ)
91.325(3)
TheNCN-pincer platinum(II)complex 7 bearing the uracil moiety
was obtained quantitatively by the reaction of the NCN-pincer
ligand 4 with [Pt(tolyl-4)2(SEt2)]2 (Scheme 2). On the contrary, the
reaction of the NCN-pincer ligand 5 with 50 mol% amount of [Pt-
(tolyl-4)2(SEt2)]2 resulted in the complex mixture with the NCN-
pincer platinum(II) complexes 8 and 9 bearing the uracil and the
furanopyrimidine moiety, respectively. Deprotonation of the uracil
moiety is assumed to result in cyclization of the oxy anion of the
uracil moiety onto the triple bond, followed by protonation to afford
the furanopyrimidine moiety. An alternative mechanism might be
that the coordination of the triple bond 5 to [Pt(tolyl-4)2(SEt2)]2
enhances the electrophilicity of the triple bond, wherein the
subsequent nucleophilic attack of the carbonyl oxygen on the elec-
tron deficient triple bond to form the furanopyrimidine ring. The
separation of these platinum(II) complexes was unsuccessful at
this stage. The NCN-pincer platinum(II) complex 9 bearing the
furanopyrimidine moiety could be obtained quantitatively by
the reaction of the NCN-pincer ligand 6 with [Pt(tolyl-4)2(SEt2)]2.
The single-crystal X-ray structure determination of 9 revealed
the formation of the furanopyrimidine ring, which is nearly parallel
to the benzene moiety of the NCN-pincer ligand with the dihedral
angle between the two planes of 8.0(4)ꢀ (Fig. 2a). In a crystal packing,
V (Å3)
2700.0(5)
4
1.753
Z
Dcalcd (g cmꢁ3
)
)
1.321
23.783
m
m
(Cu K
(Mo K
T (ꢀC)
a
a
) (cmꢁ1
) (cmꢁ1
)
66.898
ꢁ150
ꢁ150
l
l
(Cu K
a
a
) (Å)
) (Å)
1.54187
(Mo K
0.71075
0.084
0.230
R1 a
wR2
0.058
0.157
b
a
R1 ¼ S||Fo| ꢁ |Fc||/S|Fo|.
b
wR2 ¼ [Sw(F2o ꢁ F2c)2/Sw(Fo2)2]1/2
.
5-ethynyl-1-octyluracil (2), respectively. The Pd-catalyzed coupling
reaction of 1 or 2 with 4-bromo-3,5-bis(dimethylaminomethyl)
iodobenzene (3), which was prepared according to the literature
method [9], afforded the desired NCN-pincer ligands 4 or 5 bearing
the uracil moiety in 61 or 57% yields, respectively. The NCN-pincer
ligand 6 bearing the furanopyrimidine moiety was obtained quanti-
tatively by treatment with a catalytic amount of AgNO3.
The single-crystal X-ray structure determination of the NCN-
pincer ligand 4 revealed that the benzene moiety of the NCN-pincer
ligand is nearly parallel to the uracil moiety probably due to the p-
a
p
stack dimer between the furanopyrimidine and benzene moie-
conjugation; the dihedral angle between the least squares planes of
the benzene moiety of the NCN-pincer ligand and the uracil moiety
ties of the NCN-pincer ligand was observed as shown in Fig. 2b.
Table 2
Selected bond distances (Å) and angles (ꢀ) for 4 and 9
4
9
4
9
Bond distances (Å)
C(1)eBr(1)
Pt(1)eBr(1)
C(1)eC(2)
C(1)eC(6)
C(2)eC(7)
1.895(4)
C(15)eC(18)
C(17)eC(18)
O(2)eC(13)
O(2)eC(18)
N(3)eC(15)
N(3)eC(16)
N(3)eC(17)
N(4)eC(16)
N(4)eC(17)
N(4)eC(18)
O(1)eC(16)
O(1)eC(17)
O(2)eC(17)
1.361(5)
1.439(5)
1.415(15)
2.6241(13)
1.494(16)
1.407(15)
1.470(16)
1.494(16)
1.528(13)
1.511(14)
2.077(8)
1.402(4)
1.401(5)
1.527(5)
1.533(4)
1.460(4)
1.445(5)
1.416(12)
1.344(12)
1.380(4)
1.395(5)
C(6)eC(10)
N(1)eC(7)
1.362(14)
1.396(15)
N(2)eC(10)
Pt(1)eN(1)
Pt(1)eN(2)
C(4)eC(13)
C(13)eC(14)
C(14)eC(15)
C(15)eC(16)
1.379(5)
1.382(4)
1.385(15)
1.290(14)
2.083(9)
1.431(5)
1.209(5)
1.426(5)
1.450(14)
1.335(14)
1.452(14)
1.352(14)
1.207(4)
1.234(4)
1.202(15)
Bond angles (ꢀ)
C(1)eC(2)eC(7)
C(1)eC(6)eC(10)
C(2)eC(7)eN(1)
C(6)eC(10)eN(2)
Pt(1)eC(1)eC(2)
Pt(1)eC(1)eC(6)
C(1)ePt(1)eN(1)
C(1)ePt(1)eN(2)
Pt(1)eN(1)eC(7)
Pt(1)eN(2)eC(10)
C(1)ePt(1)eBr(1)
N(1)ePt(1)eBr(1)
N(2)ePt(1)eBr(1)
C(15)eN(3)eC(16)
N(3)eC(16)eN(4)
120.5(3)
121.7(3)
113.9(3)
112.7(3)
113.7(10)
110.8(9)
108.9(9)
110.1(9)
117.5(7)
123.3(8)
83.6(4)
C(16)eN(4)eC(17)
N(4)eC(17)eC(18)
C(15)eC(18)eC(17)
N(3)eC(15)eC(18)
C(13)eC(14)eC(15)
C(14)eC(15)eC(18)
C(15)eC(18)eO(2)
C(18)eO(2)eC(13)
O(2)eC(13)eC(14)
C(15)eC(16)eN(3)
C(16)eN(3)eC(17)
N(3)eC(17)eN(4)
C(17)eN(4)eC(18)
N(4)eC(18)eC(15)
C(16)eC(15)eC(18)
127.7(3)
114.6(3)
119.9(3)
121.6(3)
178.6(3)
121.4(3)
106.6(9)
106.1(8)
109.1(9)
107.6(7)
110.5(8)
118.6(10)
123.8(9)
117.4(10)
116.4(10)
128.4(10)
115.0(9)
80.4(4)
110.4(6)
110.2(6)
176.9(3)
98.2(2)
97.8(2)
122.0(3)
114.2(3)

1092
T. Moriuchi et al. / Journal of Organometallic Chemistry 696 (2011) 1089e1095
O
HN
O
NMe2
Br
O
HN
O
NMe2
Pt Br
NMe2
[Pt(tolyl-4)2(SEt2)]2 (50 mol%)
benzene, reflux, Ar, 6 h
N
Oct
N
Oct
NMe2
4
7, quant.
NMe2
Pt Br
NMe2
O
NMe2
Br
O
NMe2
Pt Br
NMe2
O
N
HN
N
HN
N
[Pt(tolyl-4)2(SEt2)]2 (50 mol%)
benzene, reflux, Ar, 6 h
O
+
O
O
N
Oct
Oct
NMe2
Oct
9
5
8
NMe2
NMe2
Pt Br
NMe2
O
N
O
N
[Pt(tolyl-4)2(SEt2)]2 (50 mol%)
benzene, reflux, Ar, 6 h
O
O
Br
N
N
Oct
Oct
NMe2
6
9, quant.
Scheme 2. Synthesis of the NCN-pincer platinum(II) complexes 7-9.
The UV/Vis spectrum of a solution of the platinum(II) complex 7
in dichloromethane showed a broad absorption at around 370 nm,
assignable to an intramolecular charge transfer band, wherein the
NCN-PtBr moiety behaves as a donor (Fig. 3a). The platinum(II)
complex 7 in dichloromethane exhibited an emission at around
450 nm (Fig. 3b). It should be noted that the emission at around
a hydrogen-bonded dimer through intermolecular hydrogen bonds
between the uracil moieties. Furthermore, each hydrogen-bonded
dimer was connected through pep interaction in a crystal packing.
The NCN-pincer platinum(II) complexes bearing the uracil or the
furanopyrimidine moiety, respectively, were found to exhibit
emission in both solution and solid states. The NCN-pincer palla-
dium(II) complexes have been demonstrated to serve as homoge-
neous catalysts [6k,7]. The NCN-pincer platinum(II) complexes
bearing the uracil or the furanopyrimidine moiety are envisioned to
exhibit catalytic activities by the formation of the corresponding
cationic complexes. Such application and dynamic control of
aggregated platinum(II) complexes as a catalyst are now in progress.
550 nm probably due to the aggregation based on pep interaction
was observed in a solid state together with an emission at around
450 nm as shown in Fig. 3b. The platinum(II) complex 9 in
dichloromethane also showed a broad absorption assignable to an
intramolecular charge transfer band at around 380 nm in the UV/
Vis spectrum (Fig. 3c) and an emission at around 450 nm in the
emission spectrum (Fig. 3d). In the solid state spectrum of 9, the
emission probably due to the aggregation based on pep interaction
was observed at around 600 nm together with an emission at
around 450 nm as shown in Fig. 3d. This result is consistent with
4. Experimental
4.1. General materials and experimental procedures
the formation of the
p stack dimer in a crystal packing (Fig. 2).
All reagents and solvents were purchased from commercial
sources and were further purified by the standard methods, if
necessary. 1-Octyluracil [8], 5-ethynyl-1-octyluracil (2) [8], 4-
bromo-3,5-bis(dimethylaminomethyl)iodobenzene (3) [9], and [Pt
(tolyl-4)2(SEt2)]2 [10] were prepared by the literature methods.
Melting points were determined on a Yanagimoto Micromelting
Point Apparatus and were uncorrected. Infrared spectra were
3. Conclusion
The bioorganometallic conjugates composed of the NCN-pincer
platinum(II) complexes as an oraganometallic compound and
the uracil derivatives as a nucleobase were designed. The NCN-
pincer ligand bearing the uracil moiety was demonstrated to form
Fig. 2. (a) Molecular structure of 9 and (b) a
p stack dimer between the furanopyrimidine and benzene moieties of the NCN-pincer ligand in a crystal packing of 9.

T. Moriuchi et al. / Journal of Organometallic Chemistry 696 (2011) 1089e1095
1093
a
b
1.0
0.5
0
300
400
500
400
500
600
700
800
Wavelength / nm
Wavelength / nm
c
d
1.0
0.5
0
300
400
500
400
500
600
700
800
Wavelength / nm
Wavelength / nm
Fig. 3. (a) Electronic spectrum of 7 in dichloromethane (2.0 ꢂ 10ꢁ4 M), (b) emission spectra of 7 in dichloromethane (- (a long solid line) 2.0 ꢂ 10ꢁ4 M, lex ¼ 350 nm) and a solid
state (/, lex ¼ 350 nm), (c) Electronic spectrum of 9 in dichloromethane (2.0 ꢂ 10ꢁ4 M), and (d) emission spectra of 9 in dichloromethane (- (a long solid line), 2.0 ꢂ 10ꢁ4 M,
lex ¼ 350 nm) and a solid state (/, lex ¼ 350 nm).
obtained with a JASCO FT/IR-480 Plus spectrometer. 1H NMR
spectra were recorded on a JNM-ECS 400 (400 MHz) spectrometer
with tetramethylsilane as an internal standard. Mass spectra were
run on a JEOL JMS-700 mass spectrometer.
NMR (400 MHz, CDCl3, TMS, 1.0 ꢂ 10ꢁ2 M)
d 8.34 (br s, 1H), 6.41 (s,
1H), 4.05 (t, 2H, J ¼ 8.1 Hz), 1.64e1.72 (m, 2H), 1.26e1.37 (m, 10H),
0.89 (t, 3H, J ¼ 7.0 Hz); HRMS (FAB) m/z calcd for C12H19N2O2I
(([M]þ)), 350.0486; found, 350.0493.
4.1.1. Synthesis of 6-iodo-1-octyluracil
4.1.2. Synthesis of 6-ethynyl-1-octyluracil (1)
To a THF solution (25 mL) of diisopropylamine (2.8 mL,
20 mmol) was added BuLi (1.66 M hexane solution, 18 mL,
30 mmol) dropwise at ꢁ78 ꢀC, and the resulting solution was
stirred under Ar at ꢁ78 ꢀC for 10 min and 0 ꢀC for 10 min. To the
resulting solution, was added a THF solution (20 mL) of 1-octylura-
cil (1.8 g, 8.0 mmol) dropwise at ꢁ78 ꢀC, and the resulting solution
was stirred under Ar at ꢁ78 ꢀC for 1.5 h. A THF (10 mL) solution of I2
(4.1 g, 16 mmol) was added dropwise to the resulting solution and
the reaction mixture was stirred under Ar at ꢁ78 ꢀC for 2 h. The
resulting solution was then treated with glacial acetic acid (5 mL)
and the resulting solution was stirred at room temperature for 10 h.
The resulting mixture was diluted with dichloromethane, washed
with saturated Na2S2O3 aqueous solution, saturated NaHCO3
aqueous solution, brine, and then dried over Na2SO4. The solvent
was evaporated in vacuo and purification of the crude product by
silica-gel column chromatography (from CHCl3 to 4/1 CHCl3/EtOAc)
gave 6-iodo-1-octyluracil (1.7 g, 61%) as a white solid.
To a toluene (30 mL) solution of 6-iodo-1-octyluracil (0.70 g,
2.0 mmol), PdCl2(PPh3)2 (70.2 mg, 0.10 mmol), CuI (9.5 mg,
0.050 mmol), and triethylamine (3.0 mL, 22 mmol) was added
trimethysilylacetylene (1.7 mL, 12 mmol) dropwise at room
temperature. The resulting mixture was stirred under Ar at room
temperature for 12 h and the solvent was evaporated. The residue
was poured into water and extracted with dichloromethane. The
dichloromethane solution was washed with brine, and then dried
over Na2SO4. The solvent was evaporated in vacuo and purification
of the crude product by silica-gel column chromatography (from
CHCl3 to 4/1 CHCl3/EtOAc) yielded 1-octyl-6-[(trimethysilyl)
ethynyl]uracil (0.47 g, 73%) as a white solid. The mixture of 1-octyl-
6-[(trimethysilyl)ethynyl]uracil (100 mg, 0.31 mmol) and KOH
(26 mg, 0.46 mmol) in methanol (5 mL) was stirred under Ar at
room temperature for 2 h. Water was added, and the organic phase
was extracted with dichloromethane. The dichloromethane solu-
tion was washed with brine, and then dried over Na2SO4. The
solvent was evaporated in vacuo and purification of the crude
product by silica-gel column chromatography (from CHCl3 to 4/1
6-Iodo-1-octyluracil: mp 127e128 ꢀC (uncorrected); IR (KBr)
3148, 3016, 2952, 2920, 1690, 1562, 1444, 1406, 1173, 1070 cmꢁ1; 1H

1094
T. Moriuchi et al. / Journal of Organometallic Chemistry 696 (2011) 1089e1095
CHCl3/EtOAc) afforded 6-ethynyl-1-octyluracil (1) quantitatively as
a white solid.
12H), 1.76e1.83 (m, 2H), 1.25e1.39 (m, 10H), 0.88 (t, 3H, J ¼ 7.0 Hz);
HRMS (FAB) m/z calcd for C26H37N4O2Br ([M þ H]þ), 517.2173;
found, 517.2159.
1: mp 142e143 ꢀC (uncorrected); IR (KBr) 3195, 3040, 2919,
2852, 2107, 1722, 1690, 1590, 1453, 1414, 1178 cmꢁ1 1H NMR
;
(400 MHz, CDCl3, TMS, 1.0 ꢂ 10ꢁ2 M)
d
8.25 (br s, 1H), 5.99 (s, 1H),
4.1.6. Synthesis of the NCN-pincer platinum(II) complex 7
A mixture of the NCN-pincer ligand 4 (35 mg, 0.068 mmol) and
[Pt(tolyl-4)2(SEt2)]2 (32 mg, 0.034 mmol) was stirred in benzene
(2.0 mL) under Ar at reflux temperature for 6 h. After evaporation of
the solution, the NCN-pincer platinum(II) complex 7 was isolated
quantitatively as a yellow solid by reprecipitation from dichloro-
methane and diethyl ether.
3.97 (t, 2H, J ¼ 7.7 Hz), 3.66 (s, 1H), 1.66e1.74 (m, 2H), 1.25e1.40 (m,
10H), 0.88 (t, 3H, J ¼ 7.1 Hz); HRMS (FAB) m/z calcd for C14H20N2O2
(([M]þ)), 248.1519; found, 248.1526.
4.1.3. Synthesis of the NCN-pincer ligand 4
A mixture of 6-ethynyl-1-octyluracil (1, 410 mg, 1.65 mmol), 4-
bromo-3,5-bis(dimethylaminomethyl)iodobenzene (3, 600 mg,
1.51 mmol), Pd(PPh3)4 (300 mg, 0.26 mmol), CuI (14 mg,
0.074 mmol), and diisopropylamine (24 mL, 171 mmol) was stirred
under Ar at room temperature for 18 h and the solvent was evap-
orated. Water was added, and the organic phase was extracted with
dichloromethane. The dichloromethane solution was washed with
brine, and then dried over Na2SO4. The solvent was evaporated in
vacuo and purification of the crude product by silica-gel column
chromatography (AcOEt) gave the NCN-pincer ligand 4 (447 mg,
57%) as a white solid.
7: mp 238e242 ꢀC (decomp.); IR (KBr) 3152, 3005, 2925, 2857,
2199, 1706, 1675, 1573, 1466, 1447, 1399, 1217, 1081, 1017 cmꢁ1 1H
;
NMR (400 MHz, CD2Cl2, 1.0 ꢂ 10ꢁ2 M)
d 8.49 (br s, 1H), 7.00 (s, 2H),
5.90 (s, 1H), 3.99e4.08 (m, 6H), 3.09 (s, 12H), 1.71e1.79 (m, 2H),
1.21e1.41 (m, 10H), 0.87 (t, 3H, J ¼ 7.0 Hz); HRMS (FAB) m/z calcd for
C26H37N4O2Br194Pt ([M]þ), 710.1721; found, 710.1722.
4.1.7. Synthesis of the NCN-pincer platinum(II) complex 9
A mixture of the NCN-pincer ligand 6 (30 mg, 0.058 mmol) and
[Pt(tolyl-4)2(SEt2)]2 (30 mg, 0.032 mmol) was stirred in benzene
(2.0 mL) under Ar at reflux temperature for 6 h. After evaporation of
the solution, the NCN-pincer platinum(II) complex 9 was isolated
quantitatively as a yellow solid by reprecipitation from dichloro-
methane and diethyl ether.
4: mp 166e168 ꢀC (uncorrected); IR (KBr) 3148, 3025, 2928,
2857, 2821, 2773, 2214, 1711, 1671, 1575, 1464, 1352, 1017 cmꢁ1; 1H
NMR (400 MHz, CD2Cl2, 1.0 ꢂ 10ꢁ2 M)
d 8.54 (br s, 1H), 7.57 (s, 2H),
5.96 (s, 1H), 4.03 (t, 2H, J ¼ 7.8 Hz), 3.54 (s, 4H), 2.30 (s, 12H),
1.73e1.80 (m, 2H), 1.21e1.42 (m, 10H), 0.85 (t, 3H, J ¼ 6.9 Hz); HRMS
(FAB) m/z calcd for C26H37N4O2Br ([M þ H]þ), 517.2173; found,
517.2153.
9: mp 229e233 ꢀC (decomp.); IR (KBr) 3080, 3008, 2924, 2854,
1668, 1598, 1574, 1450, 1412, 1375, 1163, 1126 cmꢁ1 1H NMR
;
(400 MHz, CD2Cl2, 1.0 ꢂ 10ꢁ2 M)
d 7.85 (s, 1H), 7.25 (s, 2H), 6.64 (s,
1H), 4.07 (s, 4H), 3.96 (t, 2H, J ¼ 7.3 Hz), 3.10 (s, 12H), 1.75e1.82 (m,
2H), 1.25e1.38 (m, 10H), 0.88 (t, 3H, J ¼ 7.0 Hz); HRMS (FAB) m/z
calcd for C26H37N4O2Br194Pt ([M]þ), 710.1721; found, 710.1745.
4.1.4. Synthesis of the NCN-pincer ligand 5
To a mixture of 4-bromo-3,5-bis(dimethylaminomethyl)iodo-
benzene (3, 200 mg, 0.50 mmol), Pd(PPh3)4 (29 mg, 0.025 mmol),
CuI (2.3 mg, 0.012 mmol), and diethylamine (6 mL, 58 mmol) was
added the DMF (6 mL) solution of 5-ethynyl-1-octyluracil (2,
137 mg, 0.55 mmol) dropwise at 0 ꢀC. The resulting mixture was
stirred under Ar at 55 ꢀC for 18 h and the solvent was evaporated.
Water was added and the organic phase was extracted with
dichloromethane. The dichloromethane solution was washed with
brine, and then dried over Na2SO4. The solvent was evaporated in
vacuo and purification of the crude product by silica-gel column
chromatography (from dichloromethane to 93/7 dichloromethane/
methanol) yielded the NCN-pincer ligand 5 (0.16 g, 62%) as a white
solid.
4.2. General procedure of UV/Vis measurement
UV/Vis spectra were obtained using a Hitachi U-3500 spectro-
photometer in a dichloromethane solution with the concentration
2.0 ꢂ 10ꢁ4 M for the platinum(II) complexes 7 and 9 under Ar at
298 K. UV/Vis spectra were measured using 1-mm pathlength
quartz cuvettes.
4.3. General procedure of emission measurement
5: mp 173e174 ꢀC (uncorrected); IR (KBr) 3164, 3053, 2949,
2925, 2855, 2772, 2219, 1691, 1627, 1427, 1354, 1175, 1026 cmꢁ1; 1H
NMR (400 MHz, CD2Cl2, 1.0 ꢂ 10ꢁ2 M)
d 8.49 (br s, 1H), 7.56 (s, 1H),
Emission spectra were measured using a Shimadzu RF-5300PC
spectrofluorophotometer in a dichloromethane solution with the
concentration 2.0 ꢂ 10ꢁ4 M for the platinum(II) complexes 7 and 9
under Ar at 298 K. Emission spectra were measured using 1-mm
pathlength quartz cuvettes.
7.48 (s, 2H), 3.74 (t, 2H, J ¼ 7.5 Hz), 3.51 (s, 4H), 2.28 (s, 12H),
1.67e1.74 (m, 2H),1.26e1.36 (m,10H), 0.88 (t, 3H, J ¼ 6.8 Hz); HRMS
(FAB) m/z calcd for C26H37N4O2Br ([M þ H]þ), 517.2173; found,
517.2165.
4.1.5. Synthesis of the NCN-pincer ligand 6
A mixture of the NCN-pincer ligand 5 (30 mg, 0.058 mmol) and
AgNO3 (4.0 mg, 0.024 mmol) was stirred in acetone (2.5 mL) under
Ar at room temperature for 3 days and the solvent was evaporated.
Water was added and the organic phase was extracted with
dichloromethane. The dichloromethane solution was washed with
brine, and then dried over Na2SO4. The solvent was evaporated in
vacuo and purification of the crude product by alumina column
chromatography afforded the NCN-pincer ligand 6 (29 mg, 97%) as
a white solid.
4.4. X-ray structure analysis
All measurements for 4 were made on a Rigaku RAXIS-RAPID
Imaging Plate diffractometer with graphite monochromated Cu K
radiation. All measurements for 9 were made on a Rigaku RAXIS-
RAPID Imaging Plate diffractometer with graphite monochromated
a
Mo Ka radiation. The structures of 4 and 9 were solved by direct
methods and expanded using Fourier techniques. The non-
hydrogen atoms were refined anisotropically. The H atoms involved
in hydrogen bonding were located in electron density maps. The
remainder of the H atoms were placed in idealized positions and
allowed to ride with the C atoms to which each was bonded.
Crystallographic details are given in Table 1.
6: mp 191e193 ꢀC (uncorrected); IR (KBr) 3104, 3016, 2925,
2854, 2815, 2766, 1667, 1604, 1572, 1453, 1379, 1260, 1171, 1130,
1019 cmꢁ1; 1H NMR (400 MHz, CD2Cl2, 1.0 ꢂ 10ꢁ2 M)
d 7.90 (s, 1H),
7.77 (s, 2H), 6.83 (s, 1H), 3.98 (t, 2H, J ¼ 7.5 Hz), 3.58 (s, 4H), 2.31 (s,

T. Moriuchi et al. / Journal of Organometallic Chemistry 696 (2011) 1089e1095
[4] (a) M.M. Conn, J. Rebek Jr., Chem. Rev. 97 (1997) 1647e1668;
1095
Acknowledgement
(b) E.A. Archer, H. Gong, M.J. Krische, Tetrahedron 57 (2001) 1139e1159;
(c) L.J. Prins, D.N. Reinhoudt, P. Timmerman, Angew. Chem. Int. Ed. 40 (2001)
2382e2426.
This work was supported by Grant-in-Aids for Science Research
on Priority Areas (No. 20036034) and Innovative Areas (No.
22108516) from the Ministry of Education, Culture, Sports, Science
and Technology, Japan. Thanks are also due to the Analytical Centre,
Graduate School of Engineering, Osaka University, for the use of the
NMR and MS instruments.
[5] Forrecentreviews, see:(a) S. Sivakova, S.J. Rowan, Chem. Soc. Rev.34(2005) 9e21;
(b) J.T. Davis, G.P. Spada, Chem. Soc. Rev. 36 (2007) 296e313;
(c) J.L. Sessler, C.M. Lawrence, J. Jayawickramarajah, Chem. Soc. Rev. 36 (2007)
314e325;
(d) K. Tanaka, M. Shionoya, Coord. Chem. Rev. 251 (2007) 2732e2742;
(e) J. Müller, Eur. J. Inorg. Chem. (2008) 3749e3763;
(f) S. Lena, S. Masiero, S. Pieraccini, G.P. Spada, Chem. Eur. J. 15 (2009) 7792e7806;
(g) G.H. Clever, M. Shionoya, Coord. Chem. Rev. 254 (2010) 2391e2402.
[6] (a) G. Jaouen, A. Vessiéres, I.S. Butler, Acc. Chem. Res. 26 (1993) 361e369;
(b) R. Severin, R. Bergs, W. Beck, Angew. Chem. Int. Ed. 37 (1998) 1634e1654;
(c) R.H. Fish, G. Jaouen, Organometallics 22 (2003) 2166e2177;
(d) T. Moriuchi, T. Hirao, Chem. Soc. Rev. 33 (2004) 294e301;
(e) D.R. van Staveren, N. Metzler-Nolte, Chem. Rev. 104 (2004) 5931e5986;
(f) C. Baldoli, P. Cerea, C. Giannini, E. Licandro, C. Rigamonti, S. Maiorana,
Synlett (2005) 1984e1994;
Appendix A. Supplementary material
CCDC 790374 and 790375 contain the supplementary crystal-
lographic data (excluding structure factors) for compounds 4 and 9
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.
(g) G. Jaouen (Ed.), Bioorganometallics; Biomolecules, Labeling, Medicine,
Wiley-VCH, Weinheim, 2006 (and references therein);
(h) R. Alberto, J. Organomet. Chem. 692 (2007) 1179e1186;
(i) G. Erker, J. Organomet. Chem. 692 (2007) 1187e1197;
(j) C.G. Hartinger, P.J. Dyson, Chem. Soc. Rev. 38 (2009) 391e401;
(k) B. Wieczorek, H.P. Dijkstra, M.R. Egmond, R.J.M. Klein Gebbink, G. van
Koten, J. Organomet. Chem. 694 (2009) 812e822;
References
[1] (a) W. Saenger, Principles of Nucleic Acid Structure. Springer-Verlag, New
York, 1984;
(l) W. Beck, Z. Naturforsch. B. 64 (2009) 1221e1245;
(m) A. Lataifeh, S. Beheshti, H.-B. Kraatz, Eur. J. Inorg. Chem. (2009)
3205e3218;
(b) V.A. Bloomfield, D.M. Crothers, I. Tinoco Jr., Nucleic Acids: Structures,
Properties, and Functions. University Science Books, Sausalito, CA, 2000.
[2] (a) D. Braga, F. Grepioni, G.R. Desiraju, Chem. Rev. 98 (1998) 1375e1406;
(b) V. Balzani, A. Credi, F.M. Raymo, J.F. Stoddart, Angew. Chem. Int. Ed. 39
(2000) 3348e3391;
(c) G.F. Swiegers, T.J. Malefetse, Chem. Rev. 100 (2000) 3483e3538.
[3] G.A. Jeffrey, An Introduction to Hydrogen Bonding, first ed. Oxford University
Press, New York, 1997.
(n) T. Moriuchi, T. Hirao, Acc. Chem. Res. 43 (2010) 1040e1051.
[7] M. Albrecht, G. van Koten, Angew. Chem. Int. Ed. 40 (2001) 3750e3781.
[8] M. Takase, M. Inoueye, J. Org. Chem. 68 (2003) 1134e1137.
[9] G. Rodríguez, M. Albrecht, J. Schoenmaker, A. Ford, M. Lutz, A.L. Spek, G. van
Koten, J. Am. Chem. Soc. 124 (2002) 5127e5138.
[10] B.R. Steele, K. Vrieze, Transit. Met. Chem. 2 (1977) 140e144.