Facile synthesis and platinum complexes of 4′,5,5′′- trisubstituted-2,2′:6′,2′′-terpyridines

Article abstract of DOI:10.1039/c1dt10465a

The synthesis of trisubstituted 4′,5,5′′ terpyridines is described. The strategy begins with synthesis of 2-acetyl-5-bromopyridine (3) from 2,5-dibromopyridine, substitution of the bromine in 3 using a variety of metal-catalyzed reactions and then formation of the terpyridine using the Krohnke reaction. The complexes have been prepared by reaction of [Pt(PhCN) ₂Cl₂] with the appropriate silver salt followed by addition of the terpyridyl ligand. The crystal structure of two complexes have been determined via X-ray diffraction and the MLCT (metal-to-ligand charge-transfer) emissions determined by UV/Vis spectroscopy. The Royal Society of Chemistry 2011.

Full text of DOI:10.1039/c1dt10465a

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PAPER
Facile synthesis and platinum complexes of 4¢,5,5¢¢-trisubstituted-2,
2¢:6¢,2¢¢-terpyridines†
Jianqiang Huo, Navamoney Arulsamy and John O. Hoberg*
Received 18th March 2011, Accepted 4th May 2011
DOI: 10.1039/c1dt10465a
The synthesis of trisubstituted 4¢,5,5¢¢ terpyridines is described. The strategy begins with synthesis of
2-acetyl-5-bromopyridine (3) from 2,5-dibromopyridine, substitution of the bromine in 3 using a
variety of metal-catalyzed reactions and then formation of the terpyridine using the Krohnke reaction.
The complexes have been prepared by reaction of [Pt(PhCN)2Cl2] with the appropriate silver salt
followed by addition of the terpyridyl ligand. The crystal structure of two complexes have been
determined via X-ray diffraction and the MLCT (metal-to-ligand charge-transfer) emissions
determined by UV/Vis spectroscopy.
Introduction
The use of terpyridine ligands in chelating metals has been in-
tensely studied since the 1970’s, with a view towards their biomed-
ical, energy and supramolecular applications.1 For example,
octahedral metal complexes of terpyridines offer unique electro-
chemical, magnetic, optical and photophysical properties,2 while
square planar complexes show unique luminescent properties,1,3
perform photocatalytic hydrogen production4 and photoinduced
electron transfer when connected to a porphyrin unit.5 Ter-
pyridines are also “potent G-quadruplex ligands that are highly
discriminating against duplex DNA”,6 and are thus potential anti-
cancer agents.7,8 Synthesis of terpyridines have primarily relied
on two strategies, one being the Claisen condensation of ethyl 2-
pyridinecarboxylate with acetone and base, Scheme 1 route A. The
resulting trione is then converted to the corresponding pyridone
with ammonium acetate, which gives the 4¢-chloroterpyridine
upon reaction with PCl5 and POCl3.8 The bromo analog9 can be
obtained with the use of PBr5 and POBr3 in slightly higher yield
and the OTf analog has also been reported.10,11
Alternatively, the Krohnke reaction allows for even further
functionalization via the use of functionalized benzaldehydes as
in Scheme 1 route B. In previous work, the use of commercially
available 2-acetylpyridine and benzaldehyde derivatives were used
to prepare terpyridines of type 1, in which R = H.12,6,13 The yields
of this one step reaction are typically modest (10–50%), but can
be improved upon by microwave heating.14 Newkome has also
Scheme 1
terpyridines based on the use of commercially available 4-methyl
and 4-cyano-2-acetylpyridines.15
reported the synthesis of a limited number of substituted 4,4¢¢
Functionalization of terpyridines at the 4¢ position is straight-
forward using derivatives of benzaldehyde, however functional-
ization at the 5 and 5¢¢ remains a challenge. In the course of our
work with terpyridines we required a range of these compounds,
and herein we report a facile method for entry into substituted
5,5¢¢-terpyridines, their complexation to platinum and UV/Vis
absorption results.
Department of Chemistry, University of Wyoming, Laramie, Wy, 82071,
USA. E-mail: hoberg@uwyo.edu; Fax: (307) 766-2807; Tel: (307) 766-
2795
† Electronic supplementary information (ESI) available: Experimental
details and characterization data for compounds 4a–4g, NMR spectra
for all compounds and X-ray crystallographic data for 6b and 6e. CCDC
reference numbers 818407 and 818408. For ESI and crystallographic data
in CIF or other electronic format see DOI: 10.1039/c1dt10465a
7534 | Dalton Trans., 2011, 40, 7534–7540
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Results and Discussion
Our strategy relied on the use of 2,5-dibromopyridine, an inexpen-
sive, commercially available starting material. Functionalization
at the 2-position is easily achieved using known procedures and
provides as one option methyl 5-bromopyridine-2-carboxylate (2)
via selective carbonylation, Scheme 2.16 Alternatively, 2-acetyl-
5-bromopyridine (3) can be obtained via selective lithiation and
trapping with N,N-dimethylacetamide (DMA).17 Initially, esters
2 (both with R = Me and Et) were used under a variety of route
A conditions in attempts to form the corresponding terpyridines,
however we were unable to procure any of the desired trione,
obtaining only intractable, viscous oils.
Scheme 4
Table 1 Synthesis of acylpyridines 4 from 3
Entry Conditions
Product
Yielda
90%
1
ArB(OH)2, Pd(PPh3)4
PhMe/H2O
105 ◦C, 12h
2
3
”
”
4b R = Ph
81%
85%
4
”
30%
Scheme 2
5
6
alkyne, Cu(OAc)2
PdCl2(PhCN)2
iPr2NH, PPh3
80 ◦C, 4h
84%
94%
Subsequently, acyl pyridine 3 was reacted with benzaldehyde
under conditions reported by Wang and Hanan, Scheme 3.12
Gratifyingly, an acceptable yield of 41% for the formation of 1a
was obtained. In attempts to form derivatives, reaction of 1a under
a variety of metal-catalyzed cross couplings such as Sonogashira,
Suzuki and Stille reactions were then undertaken but in all cases
no transmetallation products were obtained. This is not altogether
surprising, as coordination of the metal catalyst used in these
reactions with the terpyridine ligand may have occurred resulting
in an impaired catalyst.
alkyne, CuI
Pd(PPh3)4
Et2NH
50 ◦C, 10h
7
8
”
83%
94%
C3H5SnBu3 Pd(PPh3)4, 12h
PhMe, 105 ◦
C
a Yield of purified product.
Table 2 entries 1–3. Use of 4e, R = TMS-acetylene, provided
a useful secondary reaction in that cleavage of the TMS group
was also observed. This leads to formation of terpyridines 1e–1g,
entries 4–6, in which the R groups consist of only the ethynyl
moiety. In many respects, this alleviates the need for an additional
deprotection step in any future coupling reactions. Alternatively,
if the ethynyl group needs to remain protected, the THPO group
appears to be robust enough to survive the reaction, entry 7. For
the purpose of our studies, it was gratifying to see that entries 8–10
produced decent yields of the expected terpyridines. It also appears
that electron-withdrawing groups on 4 prohibit the formation of
terpyridines, in which the use of 4c and 4d, entries 11 and 12,
fail to produce any terpyridine. For entry 13, an intractable oil
was produced in which no terpyridine could be identified, while in
entry 14 reaction of only one equivalent of 4h with 5 occurred.
Scheme 3
In order to circumvent this issue, 3 was transformed to mul-
tiple 5-substituted-2-acylpyridines under a variety of conditions,
Scheme 4. These conditions involved Suzuki, Sonogashira and
Stille reactions all of which resulted in the expected products in
mostly excellent yields. Table 1 illustrates these conditions and
as seen only entry 4, transmetallation of nitrobenzene, resulted
in a poor yield. Synthesis of 4a18 and 4b,19 entries 1 and 2, have
previously been reported however in only 41% and 39% yields,
respectively.
With the new derivatives in hand, formation of terpyridines was
next attempted, Scheme 5. The use of 4b, R = Ph, gave excellent
results, in which high yields of the terpyridines were obtained,
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esters, which are then deprotected to the boronic acid.22–25 Thus,
an attempt was made to perform the reaction with a trifluoro
borate salt, entry 15, however no product was observed.
Platinum-terpyridine complexes
Formation of terpyridine metal complexes was initially attempted
using the procedure of Annibale26 and a variety of terpyridines
listed in Table 2, however none of the desired complexes were
formed. Subsequently, the method of Buchner27 and co-workers
was adopted, Scheme 6. Thus, treatment of a refluxing solution
of Pt(PhCN)2Cl2 with one equivalent of AgOTf gave a white
precipitate of AgCl, which was removed via filtration. The
resulting yellow solution was reacted with select terpyridines
to form the colored solids 6a–6e. Successful reactions occurred
with terpyridines 1a–1c, 1i and 1l, while terpyridine 1f did not
produce any of the desired complex. Yields ranged from 69–78%
and the complexes were characterized using NMR, and X-ray
crystallography was used to characterize two of these complexes.
Scheme 5
Table 2 Synthesis of terpyridines 1 from 4 and 5
Entry
Reactants
Product (% yield)a
1
2
3
4
5
6
7
4b, 5 R1 = H
4b, 5 R1 = Br
4b, 5 R1 = Cl
4e, 5 R1 = Cl
4e, 5 R1 = Br
4e, 5 R1 = H
4f, 5 R1 = H
1b R = Ph, R1 = H (74)
1c R = Ph, R1 = Br (70)
1d R = Ph, R1 = Cl (51)
1e R = ethynyl, R1 = Cl (46)
1f R = ethynyl, R1 = Br (43)
1g R = ethynyl, R1 = H (25)
Scheme 6
Crystal structures of 6b+A- and 6e+A-, where A =
tetrakis(perfluorophenyl)borate anion
R1 = H (45)
8
4a, 5 R1 = H
1i, R = p-MeOC6H4, R1 = H (70)
In order to obtain X-ray suitable crystals, the triflate salts of 6b and
6e were reacted with potassium tetrakis(perfluorophenyl)borate
(K+A-) to produce the tetrakis(perfluorophenyl)borate salts of
both 6b and 6e. The crystallographic asymmetric unit of [6b]A
contains three [6b]+ cations, three tetrakis(perfluorophenyl)borate
anions and five heavily disordered dichloromethane solvent
molecules. In spite of the disorder, the structural features of the
cations and anions are well characterized (due to the sensitivity
of square-planar Pt(II) compounds to anions and solvent, this
large, noncoordinating anion may impact packing). All of the
non-hydrogen atoms of the ions except for two carbon atoms are
refined anisotropically. All atoms of the solvent molecules are
refined isotropically. Their hydrogen atoms were neither located
nor placed in calculated positions. Two of the dichloromethane
molecules are found in sites with 100% occupancy, whereas the
rest are refined with partial occupancies.
9
4a, 5 R1 = Br
1j, R = p-MeOC6H4, R1 = Br (51)
10b
11
12
13
14
15
4 R = H, 5 R1 = Br
4c, 5 R1 = H
1l R = H, R1 = Br (44)
No Rx
4d, 5 R1 = H
No Rx
4g, 5 R1 = H
No Rx
4h, 5 R1 = H
No Rx
4 R = Ph, 5 R1 = BF3K
No Rx
a Yield of purified product; b reported previously, see reference 20.
Importantly, the use of 5 in which a para bromo20 or chloro
benzaldehyde is used allows for the further manipulation of the
terpyridines via transmetallation reactions or transformation into
carboxylic or phosphoric acids.21 Previous papers on the synthesis
of boronated phenylterpyridines involve the use of pinnacolate
The three complex cations are chemically identical but exhibit
significant twists of the three phenyl rings. A view of one of the
complex cations is shown in Fig. 1, in which the metal ion assumes
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Table 3 Structural data for [6b]A·5/3CH2Cl2
˚
Bond Distances (A)
Pt(1)–N(2)
Pt(1)–N(1)
Pt(1)–N(3)
Pt(1)–Cl(1)
Pt(1)–Pt(2)
1.937(7)
2.016(8)
2.016(7)
2.292(2)
3.6545(4)
Pt(2)–N(5)
Pt(2)–N(4)
Pt(2)–N(6)
Pt(2)–Cl(2)
Pt(2)–Pt(2A)
1.907(8)
2.016(7)
2.030(7)
2.300(2)
3.4430(4)
Pt(3)–N(8)
Pt(3)–N(9)
Pt(3)–N(7)
Pt(3)–Cl(3)
Pt(3)–Pt(1)
1.940(6)
2.019(7)
2.026(6)
2.303(2)
3.9450(4)
Bond Angles (◦)
N(2)–Pt(1)–N(1)
N(2)–Pt(1)–N(3)
N(1)–Pt(1)–N(3)
N(2)–Pt(1)–Cl(1)
N(1)–Pt(1)–Cl(1)
N(3)–Pt(1)–Cl(1) ◦
Dihedral Angles ( )a
vs pyridine-N1
vs pyridine-N2
vs pyridine-N3
81.3(3)
81.4(3)
162.7(3)
179.3(2)
98.9(2)
98.4(2)
N(5)–Pt(2)–N(4)
N(5)–Pt(2)–N(6)
N(4)–Pt(2)–N(6)
N(5)–Pt(2)–Cl(2)
N(4)–Pt(2)–Cl(2)
N(6)–Pt(2)–Cl(2)
83.4(3)
78.4(3)
161.7(3)
177.7(2)
98.8(2)
99.5(2)
N(8)–Pt(3)–N(9)
N(8)–Pt(3)–N(7)
N(9)–Pt(3)–N(7)
N(8)–Pt(3)–Cl(3)
N(9)–Pt(3)–Cl(3)
N(7)–Pt(3)–Cl(3)
80.4(3)
81.1(3)
161.5(3)
179.2(2)
98.9(2)
99.5(2)
2.9(8)
21.4(6)
6.2(6)
vs pyridine-N4
vs pyridine-N5
vs pyridine-N6
31.5(4)
28.8(8)
17.6(7)
vs pyridine-N7
vs pyridine-N8
vs pyridine-N9
3.9(6)
23.4(6)
24.4(6)
a Dihedral angles between mean planes of phenyl rings and associated pyridine rings.
Fig. 1 View of one of the complex cations in the crystals of [6b]
A·5/3CH2Cl2. Hydrogen atoms are omitted and the thermal ellipsoids
are drawn at 50% probability.
Fig. 2 View of packing in the crystals of 6b A·5/3CH2Cl2as viewed along
the c-axis. Hydrogen atoms of the cations, anions and solvent molecules
are omitted and the thermal ellipsoids are drawn at 50% probability.
Non-platinum atoms are unlabeled for clarity.
distorted square planar geometry. The PtN3Cl units in the three
cations are nearly coplanar, but the N–Pt–Cl bond angles in the
range of 98.4(2)–99.5(2) and the N–Pt–N bond angles in the ranges
of 78.4(3)–83.4(4)◦ deviate from the expected angle of 90◦ for
a square-plane. Similarly, the trans N–Pt–N angles observed in
the range of 161.5(3)–162.7(3)◦ also deviate from 180◦ reflecting
distortion from square planar geometry. The Pt–N and Pt–Cl
bond distances are unexceptional and are comparable to those
in other platinum-tpy complexes reported in the literature.28–30
The dihedral angles between the mean planes passing through the
phenyl and the associated pyridine rings are also listed in Table 3.
We attribute the dissimilarity of the dihedral angles to the loose
packing of the constituents in the crystal lattice. The three complex
cations are arranged on top of each other with two of them being
disposed head-to-tail to each other, and the third being oriented
orthogonal to the first two. A view of the packing is shown in
Fig. 2. The platinum centers of neighboring cations form a zig–zig
For the crystal structure of [6e]A·CH3OH, the coordination
geometry of the platinum center in the [6e]+ complex cation is
also distorted square planar as in the previous cation. However,
this structure is more precisely refined as all of the constituents
of the unit cell are well ordered. A view of the complex cation is
shown in Fig. 3 and selected bond distances and angles are listed in
Table 4. The cation exhibits striking similarity to the [6b]+ cation.
The bromophenyl substituent on the central pyridine ring also
exhibits a small twist at 24.20(9)◦. The cations exclusively pack
in a head-to-tail fashion with the Pt ◊ ◊ ◊ Pt distance of 3.500(2)
˚
A indicating the absence of any inter-metallic interaction. The
solvated methanol molecules are present as pairs due to strong
◦
˚
Table 4 Bond Distances (A) and Bond Angles ( ) for [6e]A·CH3OH
Pt(1)–N(2)
Pt(1)–N(3)
N(2)–Pt(1)–N(1)
N(1)–Pt(1)–N(3)
N(1)–Pt(1)–Cl(1)
1.9352(16)
2.0179(17)
81.12(6)
161.98(7)
98.98(5)
Pt(1)–N(1)
Pt(1)–Cl(1)
N(2)–Pt(1)–N(3)
N(2)–Pt(1)–Cl(1)
N(3)–Pt(1)–Cl(1)
2.0143(16)
2.3003(5)
80.87(7)
179.48(5)
99.03(5)
˚
arrangement, in which the Pt ◊ ◊ ◊ Pt distances of 3.443 A or longer
rule out any inter-metallic bonding interaction, and this pattern is
commonly seen in related Pt-tpy complexes as discussed above.28–30
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Fig. 4 UV/VIS for complexes 6a–6e.
a point of reference, replacement with an electron-withdrawing
group as in 6a (R = Br) appears to slightly shift the absorption
to a shorter wavelength. Contrarily, use of a modest electron-
donating group, as in 6b (R = Ph) does shift the wavelength
noticeably in the opposite direction, while the stronger donating
group in 6c (R = p-MeOC6H4) produces a substantial shift to
a longer wavelength. Thus, it is apparent from this data that the
absorption of terpyridine complexes can be influenced via changes
at the 5/5¢¢ position. McMillin and co-workers observed similar
effects in [Ru(terpy)]2+ systems and have attributed this to the low-
lying p* orbital of the substituted terpy ligands.32 Thus, increasing
the energy difference between the ligand-field and the MLCT
excited states provides a method of constructing long-lived excited-
state complexes. Apparently, this condition can be achieved with
modifications at the 5/5¢¢ position as well.
Fig. 3 View of the complex cation in the crystals of [6e]+A-·CH3OH.
Hydrogen atoms are omitted and the thermal ellipsoids are drawn at 50%
probability.
hydrogen bonds, but are not involved in any bonding interaction
with the complex cation.
1H NMR data for both metal-free ligands and the metal com-
plexes are very straightforward to interpret due to the symmetry
(see Scheme 6 for numbering). In all cases for the ligands, H6 is the
furthest downfield and H3¢ is just slightly upfield of it, with both
resonating between 8.7–9.0 ppm. H3 also resonates in the vicinity
of 8.7 while H4 appears most often at around 8.0 ppm. Coupling
between the protons is similar to typical pyridine systems with
H6 appearing as a doublet with long-range coupling to H4 of J =
2.0 Hz. H4 is a doublet of doublets with J = 2.0 and ~8.0 Hz.
Finally, H3¢ appears as the expected singlet, and depending on
the substitution on the ligand, additional aromatic protons will
overlap. For example, in 1a protons on the phenyl ring attached
at C4¢ appear at 7.88 (doublet, 2H) and 7.55 (multiplet, 3H).
Curiously, no change in chemical shifts of the protons are observed
upon complexation of the platinum. Thus, in complexing platinum
to 1a to produce 6a, H6 continues to resonate at 8.78 ppm, and
both H4 and H3 are also exactly the same chemical shift.
Conclusions
Previous to this work, a limited amount of 5/5¢¢ substituted
terpyridines were available, and these were limited to alkyl groups
such as methyl, tert-butyl or amides. We have developed a
facile method to permit the construction of 5/5¢¢ substituted
terpyridines that also enable the further manipulation at this
position in addition to the 4¢ position. Thus, further coupling
via the halides at the 4¢-phenyl unit or the bromides and
acetylinic units at the 5/5¢¢ position can be envisioned to further
manipulate these ligands. Finally, platinum complexes of these
newly modified terpyridines do show significant UV/VIS absorp-
tion changes, which should be useful in future applications of
terpyridines.
A range of colors were observed for the metal complexes, which
are formed as powdery solids. For example, 6c and 6e are yellow
colored, while 6a and 6b were red and 6d dark orange. A primary
goal of this study was to ascertain the effects of electron-donating
and withdrawing groups on the terpyridine rings at the 5/5¢¢
position. Gratifyingly, a change in the UV absorption for the
MLCT regions is observed, Fig. 4. The spectra were obtained in
degassed acetonitrile solutions at room temperature, and contrary
to work published by Che and co-workers,31 no change in the
absorption was observed when changing only the para group
on the 4¢-phenyl ring from a proton to a bromine (6b vs. 6d).
Che reported that the absorption is sensitive to changes when
modifying this position, although only one result is presented in
our study compared to the three previously reported. However,
changes made to the 5/5¢¢ position (R group in Scheme 6) do not
have significant effects on the absorption. Using 6e (R = H) as
Experimental
General
All reactions were performed under an Argon atmosphere and
solvents were purified prior to use. NMR spectra were recorded on
a Bruker ARX400 MHz Bruker Spectrometer. Mass Spectra were
recorded on a Voyager-DE PRO MALDI-TOF mass spectrometer.
Fourier transform infrared spectra were recorded in pressed KBr
pellets on a Perkin Elmer 1000 FTIR spectrometer. UV-visible
absorption spectra were recorded on a Perkin Elmer Lambda 950
UV/vis spectrometer.
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General procedure for the synthesis of 2,2¢:6¢,2¢¢-terpyridyl
derivatives
1600, 1500 cm-1. HRMS m/z calculated for 435.0371 C25H14BrN3,
found 435.0368 (M)+.
4¢-Phenyl-5,5¢¢-diacetylene-2,2¢:6¢,2¢¢-terpyridine
(1g). 1H
4¢-Phenyl-5,5¢¢-dibromo-2,2¢:6¢,2¢¢-terpyridine (1a). 2-acetyl-5-
bromopyridine (3) (480 mg, 4.00 mmol) was added to a solution of
benzaldehyde (210 mg, 2.00 mmol) and KOH (308 mg, 4.00 mmol)
in freshly distilled EtOH (10 mL). NH4OH (5.8 mL, 29%,
5.0 mmol) was added and the reaction was heated at reflux for
12 h. The resulting precipitate was filtered, washed with EtOH
and dried to afford 4¢-phenyl-5,5¢¢-dibromo-2,2¢:6¢,2¢¢-terpyridine
1a (385 mg, 41%) as a white solid. 1H NMR (400 MHz, CDCl3):d
8.78 (d, J = 2.5 Hz, 2H), 8.74 (s, 2H), 8.56 (dd, J = 8.4 Hz, 2H), 8.01
(dd, J = 8.4, 2.5 Hz, 2H), 7.89 (dd, J = 8.2, 1.5 Hz, 2H), 7.54 (td,
J = 7.0, 1.7 Hz, 2H), 7.50 (d, J = 7.0 Hz, 1H) 13C NMR (100 MHz,
CDCl3): d = 155.7, 155.1, 150.3, 147.6, 138.5, 137.7, 136.6, 135.2,
129.1, 129.0, 128.9, 128.2, 127.3, 127.1, 121.3, 118.9. IR (KBr)
2990, 2920, 1025 cm-1. HRMS m/z calculated for C21H13Br2N3
466.9456, found 466.9375(M)+.
NMR (400 MHz, CDCl3):d 8.84 (d, J = 2.0 Hz, 2H), 8.77 (s, 2H),
8.66 (d, J = 8.3 Hz, 2H), 7.98 (dd, J = 8.3, 2.0 Hz, 2H), 7.91 (d,
J = 8.4 Hz, 2H), 7.55 (t, J = 7.0, 2H), 7.50 (d, J = 7.4 Hz, 1H),
3.35 (s, 2H) 13C NMR (100 MHz, CDCl3): d = 155.3, 155.1, 152.2,
150.5, 139.9, 138.2, 129.2, 129.0, 127.3, 120.5, 119.6, 119.2, 81.4,
80.7. IR (KBr) 3260, 900, 860 cm-1. HRMS m/z calculated for
357.1266 C25H15N3, found 357.1256 (M)+.
4¢-Phenyl-5,5¢¢-di(3-methyl-3-(THP-2-yloxy)but-1-ynyl)-2,2¢:6¢,
2¢¢-terpyridine (1h). 1H NMR (400 MHz, CDCl3):d 8.76 (s, 4H),
8.60 (d, J = 8.3 Hz, 2H), 7.90 (m, 4H), 7.57 ~ 7.46 (m, 3H), 5.19 (s,
1H), 3.94 (m, 1H), 3.48 (m 1H), 1.84 ~ 1.37 (m, 12H). 13C NMR
(100 MHz, CDCl3): d = 155.3, 154.8, 151.7, 150.4, 139.4, 138.3,
129.1, 129.0, 127.3, 120.5, 120.0, 119.4, 96.3, 81.0, 71.4, 63.4,
32.0, 30.4, 29.9, 26.9, 25.4, 20.5. IR (KBr) 1120, 1005, 960 cm-1.
HRMS m/z calculated for 641.3254 C41H43N3O4, found 641.3329
(M)+.
5,4¢,5¢¢-Triphenyl-2,2¢:6¢,2¢¢-terpyridine (1b). 1H NMR (400
MHz, CDCl3):d 9.00 (d, J = 2.3 Hz, 2H), 8.82 (s, 2H), 8.79 (d,
J = 8.3 Hz, 2H), 8.12 (dd, J = 8.3, 2.3 Hz, 2H), 7.96 (d, J = 7.0 Hz,
4¢-Phenyl-5,5¢¢-di(4-methoxylphenyl)-2,2¢:6¢,2¢¢-terpyridine (1i).
1H NMR (400 MHz, CDCl3):d 8.96 (d, J = 2.0 Hz, 2H), 8.79
(s, 2H), 8.75 (d, J = 8.3 Hz, 2H), 8.06 (dd, J = 8.3, 2.0 Hz, 2H),
7.96 (d, J = 7.4 Hz, 2H), 7.65 (d, J = 8.6, 4H), 7.54 (m, 3H), 7.08
(d, J = 8.7 Hz, 4H), 3.91 (s, 6H) 13C NMR (100 MHz, CDCl3):
d = 159.8, 155.8, 154.5, 150.3, 147.2, 138.6, 136.2, 134.6, 130.1,
128.9, 128.2, 127.3, 121.29, 118.7, 114.6, 55.4. IR (KBr) 1620,
1450, 1190 cm-1. HRMS m/z calculated for 521.2103 C35H27N3O2,
found 521.2122 (M)+.
2H), 7.72 (d, J = 7.0, 4H), 7.56 (t, J = 7.2 Hz, 6H), 7.48 (m, 3H) 13
C
NMR (100 MHz, CDCl3): d = 155.1, 154.5, 150.2, 139.5, 129.3,
129.4, 127.3, 126.7, 122.6, 121.3, 120.3, 119.1. IR (KBr) 1600,
1550, 1460 cm-1. HRMS m/z calculated for 461.1892 C33H23N3,
found 461.1761(M)+.
4¢-Bromophenyl-5,5¢¢-diphenyl-2,2¢:6¢,2¢¢-terpyridine (1c). 1H
NMR (400 MHz, CDCl3):d 9.00 (d, J = 2.4 Hz, 2H), 8.79 (d,
J = 8.1 Hz, 2H), 8.77 (s, 2H), 8.12 (dd, J = 8.1, 2.4 Hz, 2H), 7.83
(d, J = 8.6 Hz, 2H), 7.71 (m, 6H), 7.55 (t, J = 6.7 Hz, 4H), 7.47 (t,
J = 7.3, 2H) 13C NMR (100 MHz, CDCl3): d = 155.9, 154.8, 149.1,
147.6, 137.6, 137.4, 136.7, 135.2, 132.1, 129.1, 128.9, 128.2, 127.1,
123.5, 122.9, 121.3, 118.5. IR (KBr) 2921, 1001, 822 cm-1. HRMS
(m/z) calculated for 539.0977 C33H22N3Br, found 539.1002 (M)+.
4¢-Bromophenyl-5,5¢¢-di(4-methoxylphenyl)-2,2¢:6¢,2¢¢-terpyri-
dine (1j). 1H NMR (400 MHz, CDCl3):d 8.96 (d, J = 2.0 Hz,
2H), 8.75 (d, J = 8.3 Hz, 2H), 8.74 (s, 2H), 8.06 (dd, J = 2.0, 8.3
Hz, 2H), 7.83 (d, J = 8.6 Hz, 2H), 7.67 (t, J = 8.6 Hz, 6H), 7.08 (d,
J = 8.6 Hz, 4H), 3.92 (s, 6H). 13C NMR (100 MHz, CDCl3): d =
159.9, 156.0, 154.3, 147.2, 141.9, 137.5, 136.3, 134.6, 132.1, 130.0,
128.9, 123.4, 121.3, 118.3, 114.6, 55.4. IR (KBr) 1598, 1245, 822
cm-1. HRMS m/z calculated for 599.1208 C35H26BrN3O2, found
599.1185 (M)+.
4¢-Chlorophenyl-5,5¢¢-diphenyl-2,2¢:6¢,2¢¢-terpyridine (1d). 1H
NMR (400 MHz, CDCl3):d 8.98 (d, J = 2.0 Hz, 2H), 8.76 (d, J = 8.3
Hz, 2H), 8.75 (s, 2H), 8.09 (dd, J = 8.3, 2.0 Hz, 2H), 7.87 (d, J = 8.6
Hz, 2H), 7.70 (d, J = 8.6, 4H), 7.52 (m, 8H) 13C NMR (100 MHz,
CDCl3): d = 155.8, 154.8, 148.9, 147.6, 137.65, 136.95, 136.69,
135.19, 129.19, 128.63, 128.2, 127.1, 121.3, 118.5. IR (KBr) 1480,
1020, 850 cm-1. HRMS m/z calculated for 495.1502 C33H22ClN3,
found 495.1205(M)+.
General procedure for the synthesis of complexes 6a–6e
[Pt(4¢-Bromophenyl-2,2¢:6¢,2¢¢-terpyridine)Cl]OTf (6e). To a
suspension of [PtCl2(PhCN)2] (100 mg, 0.21 mmol) in CH3CN
(10 mL) was added AgOTf (54 mg, 0.21 mmol) in CH3CN
(5 mL). The reaction mixture was heated under reflux for 16 h, the
precipitated AgCl removed by filtration and solid 4¢-bromophenyl-
2,2¢:6¢,2¢¢-terpyridine (81 mg, 0.21 mmol) added to the filtrate.
The mixture was refluxed for an additional 24 h, following which
the volume of the solution was reduced in vacuo resulting in the
precipitation of a yellow solid. The solid was filtered, washed
with diethyl ether and dried in vacuo to give [Pt(4¢-bromophenyl-
4¢-Chlorophenyl-5,5¢¢-diacetylene-2,2¢:6¢,2¢¢-terpyridine
(1e).
1H NMR (400 MHz, CDCl3):d 8.82 (d, J = 2.0 Hz, 2H), 8.71 (s,
2H),.63 (d, J = 8.3 Hz, 2H), 7.97 (dd, J = 8.3, 2.0 Hz, 2H), 7.83
(d, J = 8.6 Hz, 2H), 7.51 (d, J = 8.6, 2H), 3.35 (s, 2H) 13C NMR
(100 MHz, CDCl3): d = 155.3, 155.1, 152.2, 149.1, 140.0, 136.6,
135.4, 129.2, 128.5, 120.5, 119.3, 119.2, 81.6, 80.7. IR (KBr) 3280,
1490, 1100 cm-1. HRMS m/z calculated for 391.0876 C25H14ClN3,
found 391.0880 (M)+.
1
2,2¢:6¢,2¢¢-terpyridine)Cl]OTf 6e (133 mg, 78%). H NMR (400
4¢-Bromophenyl-5,5¢¢-diacetylene-2,2¢:6¢,2¢¢-terpyridine
(1f).
MHz, CD3CN):d 8.66 (d, J = 5.5 Hz, 2H), 8.33 (s, 2H), 8.24 (t,
J = 7.8 Hz, 4H), 7.87 (s, 4H), 7.66 (t, J = 5.5, 2H) 13C NMR (100
MHz, CD3CN): d = 158.0, 154.5, 152.6, 151.5, 142.5, 134.2, 132.8,
129.6, 129.2, 126.0, 125.6, 121.6 IR (KBr) 1261.9, 1147.6, 1023.8,
633.3 cm-1. UV/Vis 385, 405 nm. MS (m/z) calculated for 616.97
C21H13Br2ClN3Pt, found 616.99 (M)+.
1H NMR (400 MHz, CDCl3):d 8.83 (d, J = 2.0 Hz, 2H), 8.73 (s,
2H), 8.64 (d, J = 8.3 Hz, 2H), 7.97 (dd, J = 8.3, 2.0 Hz, 2H), 7.78
(d, J = 8.6 Hz, 2H), 7.67 (d, J = 8.6, 2H), 3.35 (s, 2H) 13C NMR
(100 MHz, CDCl3): d = 155.3, 155.1, 152.2, 149.2, 140.0, 137.1,
133.4, 132.2, 128.8, 123.7, 120.5, 119.2, 81.5, 80.7. IR (KBr) 3300,
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Dalton Trans., 2011, 40, 7534–7540 | 7539
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[Pt(4¢-Phenyl-5,5¢¢-dibromo-2,2¢:6¢,2¢¢-terpyridine)Cl]OTf (6a).
Yield 74%, H NMR (400 MHz, CD3CN):d 8.79 (d, J = 2.2 Hz,
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1
2H), 8.74 (s, 2H), 8.56 (d, J = 8.3 Hz, 2H), 8.01 (dd, J = 8.3, 2.2
Hz, 2H), 7.85 (d, J = 8.9 Hz, 2H), 7.44 ~ 7.34 (m, 3H) 13C NMR
(100 MHz, CDCl3): d = 155.1, 154.5, 150.2, 139.4, 138.2, 137.5,
129.2, 129.0, 127.3, 122.5, 121.3, 119.1 IR (KBr) 1252.3, 1152.3,
1028.5, 633.3 cm-1. UV/Vis 388, 408 nm. MS (m/z) calculated for
697.69 C21H32ClBr2N3Pt, found 697.82 (M)+.
[Pt(5,4¢,5¢¢-triphenyl-2,2¢:6¢,2¢¢-terpyridine)Cl]OTf (6b). Yield
1
75%, H NMR (400 MHz, CD3CN):d 8.72 (d, J = 2.0 Hz, 2H),
8.33 (dd, J = 2.0, 8.3 Hz, 2H), 8.16 (s, 2H), 8.14 (s, 2H), 7.70 (d,
J = 7.1 Hz, 2H), 7.55 (t, J = 7.3 Hz, 1H), 7.50 ~ 7.33 (m, 12H) 13
C
NMR (100 MHz, CD3CN): d = 155.7, 153.9, 149.2, 146.9, 140.7,
139.1, 137.5, 135.1, 134.3, 132.7, 131.9, 130.7, 129.7, 127.8, 126.,
125.6, 121.1 IR (KBr) 1252.3, 1157.0, 1028.5, 633.3 cm-1. UV/Vis
394, 415 nm. MS (m/z) calculated for 691.12 C33H23ClN3Pt, found
691.29 (M)+.
[Pt(4¢-Phenyl-5,5¢¢-di(4-methoxylphenyl)-2,2¢:6¢,2¢¢-terpyridine)-
1
Cl]OTf (6c). Yield 69%, H NMR (400 MHz, CD3CN):d 8.24
(s, 2H), 7.90 (d, J = 8.3 Hz, 2H), 7.71 (m, 4H), 7.44 ~ 7.34 (m,
3H), 7.24 (t, J = 6.7 Hz, 2H), 6.98 (d, J = 8.5 Hz, 4H), 6.61 (d,
J = 8.5 Hz, 4H), 3.61 (s, 6H). 13C NMR (100 MHz, CD3CN): d =
161.8, 153.7, 153.2, 149.2, 147.6, 146.8, 139.7, 138.6, 137.5, 135.1,
133.6, 131.8, 129.5, 128.9, 127.6, 127.2, 123.7, 120.8, 119.8, 114.9,
114.8 IR (KBr) 1247.6, 1180.9, 1028.5, 633.3 cm-1. UV/Vis 407,
429 nm. MS (m/z) calculated for 751.14 C35H27ClO2N3Pt, found
750.92 (M)+.
[Pt(4¢-Bromophenyl-5,5¢¢-diphenyl-2,2¢:6¢,2¢¢-terpyridine)Cl]OTf
1
(6d). Yield 70%, H NMR (400 MHz, CD3CN):d 8.86 (s, 2H),
8.47 (d, J = 6.6 Hz, 2H), 8.26 (d, J = 8.0 Hz, 2H), 8.19 (s, 2H),
7.68 (s, 4H), 7.60 ~ 7.46 (m, 10H). 13C NMR (100 MHz, CD3CN):
d = 167.2, 153.9, 149.1, 139.1, 132.8, 132.7, 130.8, 129.7, 129.1,
126.7, 125.6, 120.8 IR (KBr) 1463.3, 1084.8, 978.8 cm-1. UV/Vis
395, 415 nm. MS (m/z) calculated for 769.03 C33H22ClBrN3Pt,
found 769.17 (M)+.
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Acknowledgements
29 E. Sakuda, A. Funahashi and N. Kitamura, Inorg. Chem., 2006, 45,
We thank the School of Energy Resources for financial support of
this work.
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7540 | Dalton Trans., 2011, 40, 7534–7540
This journal is
The Royal Society of Chemistry 2011
©