Extended terpyridyl and triazine complexes of d6-metal centres

Article abstract of DOI:10.1039/b208211j

The reaction of a series of readily available extended terpyridyl and extended triazine ligands with several d⁶-metal centres has been investigated. This has led to the isolation and characterisation of nine new complexes, one of which is the first reported transition metal complex to contain the 2,4,6-tris(2-pyrimidyl)-1,3,5-triazine (tpymt) ligand. Two of the new complexes have had their molecular structures confirmed via X-ray crystallography studies. It has been shown that changes in the electronic properties of the coordinated ligand results in modulation of the electrochemical and photophysical properties of the complex to which it is coordinated. Furthermore, the emission properties of extended terpyridyl complexes incorporating the [Re(CO)₃(MeCN)]⁺ centre suggest that luminescence in these complexes is from an extended terpyridyl based intraligand state.

Full text of DOI:10.1039/b208211j

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Extended terpyridyl and triazine complexes of d6-metal centres
Clive Metcalfe, Sharon Spey, Harry Adams and Jim A. Thomas*
Department of Chemistry, University of Sheffield, Sheffield,
UK. E-mail: james.thomas@sheffield.ac.uk
Received 22nd August 2002, Accepted 14th October 2002
First published as an Advance Article on the web 14th November 2002
The reaction of a series of readily available extended terpyridyl and extended triazine ligands with several d6-metal
centres has been investigated. This has led to the isolation and characterisation of nine new complexes, one of which
is the first reported transition metal complex to contain the 2,4,6-tris(2-pyrimidyl)-1,3,5-triazine (tpymt) ligand. Two
of the new complexes have had their molecular structures confirmed via X-ray crystallography studies. It has been
shown that changes in the electronic properties of the coordinated ligand results in modulation of the electrochemical
and photophysical properties of the complex to which it is coordinated. Furthermore, the emission properties of
extended terpyridyl complexes incorporating the [Re(CO)3(MeCN)]ϩ centre suggest that luminescence in these
complexes is from an extended terpyridyl based intraligand state.
Introduction
In recent years ruthenium() and rhenium() complexes con-
taining polypyridyl chelating ligands have been extensively
studied. The rich photophysical and redox properties associated
with these complexes makes them potentially useful in areas as
diverse as light harvesting,1 electron transfer,2 non-linear
optics,3 photovoltaics,4 self-assembly,5 and probes for biologic-
ally relevant molecules such as DNA.6 Work in this latter area
has largely centred on bidentate extended phenanthroline type
ligands such as dipyrido[3,2-a:2Ј,3Ј-c]phenazine7 (dppz) and
4,7-diphenyl-1,10-phenanthroline (dpphen).8
Such work has produced metallo-intercalators with high
DNA binding affinities. However, despite the frequent use as
ligands for d8-metallo-intercalators,9 tridendate ligands such as
terpyridine (tpy) and its analogues are much less studied. Thorp
and colleagues have used tpy as an auxiliary ligand in the syn-
thesis of redox active ruthenium systems10 and also reported
that a RuIV complex that incorporates the commercially avail-
able extended triazine 2,4,6-tris(2-pyridyl)-1,3,5-triazine (tpt)
can redox cleave DNA.11 These ligands offer other attractive
features: they present a planar aromatic system projecting away
from the metal centre, can display η1, η2, or η3 coordination
modes, and are freely available or easily synthesised. By varying
the ligands and metal centres used, the charge, chirality, steric
demand and electronic properties of this basic architecture may
be modulated. Yet, despite recently reported work demonstrat-
ing that extended 2,2Ј:6Ј,2Љ-terpyridine ligands in themselves
are highly cytotoxic toward several human tumour cell lines,12
the DNA binding properties of complexes containing these
ligands and related extended triazines have yet to be studied.
As part of a long-term project involving the construction of
Scheme 1 Ligands used in this study.
a library of extended tpy complexes that may function as DNA
bpy = 2,2Ј-bipyridine), was then investigated. Of the 15 possible
probes, we report the syntheses of a series of RuII and ReI
combinations produced by this matrix only three, [Ru(tpy)-
(tpt)]2ϩ 11 [Ru(tpy)(phentpy)]2ϩ 13 and [Ru(tpy)(tpp)]2ϩ 14
, , have
,
complexes incorporating these ligands, several of which are
shown to possess interesting photophysical properties.
previously been reported. Consequently, we investigated the
syntheses of the other 12 members of this series.
The initial study described herein involved five well
characterised ligands including two extended triazines: 2,4,6-
tris(2-pyridyl)-1,3,5-triazine (tpt), and 2,4,6-tris(2-pyrimidyl)-
1,3,5-triazine (tpymt). Two extended terpyridines; 2,2Ј:
4,4Љ:6,2Љ-quaterpyridine (qtpy), 4Ј-phenyl-2,2Ј:6Ј,2Љ-terpyridine
(phentpy) and the structurally related tetra-2-pyridyl-1,4-
pyrazine (tpp) were also used—Scheme 1. The coordination of
these ligands to three d6-metal centres, [Ru(tpy)]2ϩ, [(phen)2-
Ru]2ϩ, and [Re(CO)3(MeCN)]ϩ (tpy = 2,2Ј:6Ј,2Љ-terpyridine,
Experimental
Materials and procedures
The ligands tpymt,15 qtpy,16 phentpy,17 and tpp18 and complexes
[Ru(tpy)Cl3]19 and [Ru(phen)2Cl2]20 were all synthesised via
literature methods. All other chemicals were purchased from
4732
J. Chem. Soc., Dalton Trans., 2002, 4732–4739
This journal is © The Royal Society of Chemistry 2002
DOI: 10.1039/b208211j

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commercial sources and were used as supplied unless otherwise
stated. Solvents were obtained from commercial sources and
were dried and purified using standard literature methods.
Unless otherwise stated all reactions were carried out under an
oxygen free nitrogen atmosphere.
purple solid. 1H NMR (d3-MeNO2): δH 7.15 (td, 2H), 7.42 (dd,
2H), 7.54 (dd, 2H), 7.88 (t, 1H), 8.00 (td, 2H), 8.17 (dd, 2H),
8.60 (d, 2H), 8.64 (t, 1H), 8.91 (d, 2H), 9.14 (dd, 2H), 9.31 (d,
2H). FAB-MS; m/z (%): 795 (30) [Mϩ Ϫ [PF6]], 325 (100)
[M2ϩ Ϫ 2[PF6]]. Anal. calc. for C30H20N12RuPF6 (Mϩ Ϫ [PF6]):
795.0619. Found:795.0590. Elementalanalysis:Calc. forC30H20-
N12RuP2F12: C, 38.35; H, 2.15; N, 17.89. Found: C, 38.75; H,
2.34; N, 18.24%.
Physical measurements
1
Unless otherwise stated, H NMR spectra were recorded on a
Bruker AM250 machine working in Fourier transform mode.
Mass spectral data was collected on a Micromass Prospec
spectrometer operating in positive ion fast atom bombardment
mode (FABϩ) with a NOBA matrix. UV/Vis spectra were
recorded on a Unicam UV2 or Varian-Carey bio-3 UV-Visible
spectrometer in twin beam mode. Spectra were recorded in
matched quartz cells (Helmer) and were baseline corrected.
Emission spectra were recorded on a Hitachi F4500 spectro-
photometer operating in luminescence wavelength scan mode.
Elemental analyses were obtained using a Perkin-Elmer 2400
analyser working at 975 ЊC. Cyclic voltammetry were recorded
using an EG&G model 362 potentiostat using the EG&G 270
Electrochemical Research Software or Electrochemistry Power-
suite software package. A three-electrode cell was used with an
Agϩ/AgCl reference electrode separated from a Pt disk working
electrode and Pt wire auxiliary electrode. 0.1 mol dmϪ3 tetra-n-
butylammonium hexafluorophosphate in acetonitrile, doubly
recrystallised from ethyl acetate/diethyl ether, was used as sup-
porting electrolyte. A scan rate of 200 mV sϪ1 was employed.
[Ru(phen)2(phentpy)][(PF6)2], 3[(PF6)2]. [Ru(phen)2Cl2]ؒ2H2O
(300 mg, 0.53 mmol) and phentpy (163 mg, 0.53 mmol) were
suspended in MeOH (40 cm3) and purged with nitrogen for
10 minutes. The suspension was then brought to reflux for 10
hours. After cooling to room temperature the solution was
reduced in vacuo and then loaded onto a silica chromatography
column. The product was eluted with 7 : 1 : 0.5 acetonitrile–
water–KNO3(sat.), with the desired product being collected as
the first main red band. The fractions containing the product
were concentrated and addition of NH4PF6 afforded precipit-
ation of the product as its hexafluorophosphate salt, which was
collected, washed with iced water (2.25 ml) and dried in vacuo.
1
Yield = 210 mg (37.4%), orange solid. H NMR (d3-MeCN):
δH 6.79 (td, 1H), 6.80 (m, 2H), 6.99 (dd, 1H), 7.21 (td, 1H), 7.32
(m, 2H), 7.46 (dd, 1H), 7.57 (m, 2H), 7.76 (dd, 1H), 7.80
(dd, 1H), 7.94 (m, 3H), 8.01–8.34 (m, 8H), 8.41 (dd,1H), 8.58
(dd, 1H), 8.71 (dd, 1H), 8.74 (dd, 1H), 8.79 (d, 1H), 8.87 (d,
2H). FAB-MS; m/z (%): 771 (15) [M2ϩ Ϫ 2[PF6]], 591 (30)
[Mϩ Ϫ phen Ϫ 2[PF6]]. Anal. calc. for C45H31N7RuPF6
(Mϩ Ϫ [PF6]): 916.1326. Found: 916.1348. Elemental analysis:
Calc. for C45H31N7RuP2F12: C, 50.95; H, 2.95; N, 9.24. Found:
C, 50.63; H, 2.74; N, 9.47%.
Syntheses
[Ru(tpy)(qtpy)][(PF6)2], 1[(PF6)2]. [Ru(tpy)Cl3]ؒ3H2O (220
mg, 0.50 mmol), and qtpy (2 eq., 310 mg, 1.0 mmol) were
heated to 180 ЊC with stirring in freshly distilled ethylene glycol
(15 cm3) for 2 hours. The cooled purple solution was diluted
with water (20 ml) and filtered to remove a fine black precipi-
tate. The solution was the treated with NH4PF6 (3 eq.), which
resulted in the precipitation of a purple solid, that was collected
on a sinter, washed with water (2 × 20 cm3) and diethyl ether
(2 × 20 cm3) and air dried. The crude product was dissolved in
acetonitrile (2 cm3) and chromatographed on silica eluted with
7 : 1 : 1, acetonitrile–water–KNO3 (sat.). The main purple band
containing the product was reduced in volume to 5 cm3, and
treated with NH4PF6 to precipitate the product. The precipitate
was filtered, washed with water (2 × 20 cm3), diethyl ether
(2 × 20 cm3) and dried in vacuo. Yield = 240 mg (51.3%),
purple solid. 1H NMR (d3-MeCN): δH 7.10–7.25 (m, 4H), 7.38
(dd, 2H), 7.43 (dd, 2H), 7.88–8.03 (m, 4H), 8.41 (dd, 2H), 8.51
(dm, 2H), 8.67 (m, 2H), 8.75 (dd 2H), 9.02 (m, 3H), 9.08
(d, 2H). FAB-MS; m/z (%): 791 (80) [Mϩ Ϫ [PF6]], 646 (100)
[Mϩ Ϫ 2[PF6]]. Anal. calc. for C35H25N7RuPF6 (Mϩ Ϫ [PF6]):
790.0858. Found:790.0792. Elementalanalysis:Calc. forC35H25-
N7RuP2F12: C, 44.97; H, 2.69; N, 10.49. Found: C, 44.99; H,
2.74; N, 10.44%.
[Ru(phen)2(qtpy)][(PF6)2], 4[(PF6)2]. This complex was pre-
pared in an analogous way to 3, Yield = 31.4%, red solid. H
1
NMR (d6-acetone): δH 7.27 (td, 1H), 7.44 (dd, 1H), 7.74 (dd,
1H), 7.81 (dd, 1H), 7.92–8.06 (m, 4H), 8.23 (m, 4H), 7.36–8.55
(m, 7H), 8.22 (dd, 1H), 8.29 (dd, 1H), 8.32 (dd, 2H), 8.36 (m,
4H), 9.02 (dd, 1H), 9.23 (s, 2H), 9.39 (dd, 1H). FAB-MS; m/z
(%): 916 (25) [Mϩ Ϫ [PF6]], 772 (40) [M2ϩ Ϫ 2[PF6]]. Anal. calc.
for C44H32N8RuPF6 (Mϩ Ϫ [PF6]): 919.1435. Found: 919.1478.
Elemental analysis: Calc. for C44H32N8RuP2F12: C, 49.68; H,
3.03; N, 10.53. Found: C, 50.12; H, 2.95; N, 10.11%.
[Ru(phen)2(tpt)][(PF6)2], 5[(PF6)2]. This complex was pre-
1
pared in an analogous way to 3. Yield = 19.35%, red solid. H
NMR (d6-acetone): δH 6.94 (dd, 1H), 7.18 (m, 2H), 7.37 (td,
1H), 7.50 (dd, 1H), 7.59 (dd, 1H), 7.66 (td, 1H), 7.73 (td, 1H),
7.85 (dd, 1H), 7.96 (m, 2H), 8.06–8.25 (m, 4H), 8.33–8.51
(m, 6H), 8.69 (dd, 1H), 8.77 (dd, 1H), 8.84 (dd, 1H), 8.91 (dd,
1H), 8.96 (dd, 1H), 9.42 (dd, 1H), 9.94 (dd, 1H). FAB-MS;
m/z (%): 919 (40) [Mϩ Ϫ [PF6]], 774 (40) [M2ϩ Ϫ 2[PF6]]. Anal.
calc. for C42H28N10RuPF6 (Mϩ Ϫ [PF6]): 919.1184. Found:
919.1129. Elemental analysis: Calc. for C42H28N10RuP2F12ؒ
MeCN: C, 47.84; H, 2.83; N, 13.95. Found: C, 48.18; H, 2.85;
N, 13.56%.
[Ru(tpy)(tpymt)][(PF6)2], 2[(PF6)2]. [Ru(tpy)Cl3]3ؒ3H2O (200
mg, 0.45 mmol) and tpymt (3 eq., 429 mg, 1.362 mmol) were
heated to 180 ЊC in freshly distilled ethylene glycol (20 cm3) for
1 hour. The purple solution was diluted with water (20 cm3) and
filtered to remove unreacted ligand. NH4PF6 was added in
excess until precipitation of a purple solid was complete,
which was collected by filtration and washed with ice-cold
water (2 × 20 cm3) and air-dried. The crude product was taken
up in the minimum amount of 5 : 3 water–acetone and loaded
onto a Sephadex CM-C25 ion exchange chromatography col-
umn. Elution with 0.05 M NaCl in 5 : 3 water–acetone removed
a brown impurity that was discarded. The desired product was
eluted as a purple band with a 0.1 M NaCl solution, and
recovered by reducing the volume of eluent, precipitation with
NH4PF6 and filtration. The product was washed with ice-cold
water (2 × 20 cm3) and dried in vacuo. Yield = 209 mg (49.46%),
[Ru(phen)2(tpp)][(PF6)2], 6[(PF6)2]. This complex was pre-
pared in an analogous way to 3. Yield = 18.3%, orange solid. 1H
NMR (d6-acetone): δH 6.73 (br, 1H), 6.92 (br, 1H), 7.17 (m, 1H),
7.22 (td, 1H), 7.51 (dd, 1H), 7.57–7.91 (m, 9H), 8.04 (dd, 1H),
8.12 (m, 2H), 8.18–8.48 (m, 10H), 8.64 (dd, 1H), 8.75–8.84 (m,
2H), 8.98 (dd,1H), 9.16 (br, 1H). FAB-MS; m/z (%): 850 (60)
[M2ϩ Ϫ 2[PF6]], 670 (80) [Mϩ Ϫ phen Ϫ 2[PF6]]. Calc. for
C48H32N10RuPF6 (Mϩ Ϫ [PF6]): 995.1497. Found: 995.1511.
Elemental analysis: Calc. for C48H32N10RuP2F12: C, 50.58; H,
2.83; N, 12.29. Found: C, 50.44; H, 2.95; N, 12.52%.
[Re(CO)3(MeCN)(phentpy)][CF3SO3], 7[CF3SO3]. tpt (256
mg, 0.83 mmol) was added to a refluxing solution of (CO)5ReCl
(300 mg, 0.83 mmol) in toluene (100 cm3). The mixture was
J. Chem. Soc., Dalton Trans., 2002, 4732–4739
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Table 1 Summary of crystallographic data for 3 and 6
3a
6
Empirical formula
M
C48H40F12N8O3P2Ru
1166.88
C50H40F12N12O5P2Ru
1279.95
Crystal system
Space group
Triclinic
P1 (Ci, no. 2)
Triclinic
P1 (Ci, no. 2)
1
1
¯
¯
Crystal dimensions/mm
T /K
0.40 × 0.12 × 0.10
150(2)
0.34 × 0.24 × 0.08
150(2)
a/Å
b/Å
c/Å
α/Њ
10.5019(13)
13.6177(17)
17.423(2)
87.481(2)
72.803(2)
86.833(3)
2375.6(5)
2
1.631
1178
497
0.0599
12.420(2)
12.765(3)
17.803(3)
86.927(4)
76.677(4)
87.185(4)
2740.7(9)
2
1.551
1292
0.443
0.0797
β/Њ
γ/Њ
U/Å3
Z
Dc/Mg mϪ3
F(000)
µ(Mo-Kα)/mmϪ1
Final R1 (on F)a
Final wR2 (on F)a
0.1577
0.2508
2
a A weighting scheme w = 1/[σ2(Fo ) ϩ (0.0740P)2 ϩ 0.00P] where P = (Fo2 ϩ 2Fc2)/3 was used in the latter stages of refinement. b A weighting scheme
2
scheme w = 1/[σ2(Fo ) ϩ (0.1756P)2 ϩ 1.32P] where P = (Fo2 ϩ 2Fc2)/3 was used in the latter stages of refinement.
refluxed under N2 for 4 hours and then cooled. The result-
ing precipitate was collected by filtration and was stirred
in DCM (50 cm3) for 10 min to remove any unreacted ligand.
The orange solid was filtered and washed with CH2Cl2 (2 ×
20 cm3) and Et2O (2 × 20 cm3) and dried in vacuo (quantitative
yield).
Crystal structure determination
Crystallographic data for 3 and 6 are summarised in Table 1.
For both complexes studied, data collected were measured on a
Bruker Smart CCD area detector with an Oxford Cryosystems
low temperature system and complex scattering factors were
taken from the program package SHELXTL21 as implemented
on the Viglen Pentium computer. Hydrogen atoms were placed
geometrically and refined with a riding model and with Uiso
constrained to be 1.2 times Ueq of the carrier atom.
150 mg (0.242 mmol) of the resultant solid and AgCF3SO3
(63 mg, 0.242 mmol) were refluxed for 10 hours in freshly dis-
tilled acetonitrile, after which the solvent was removed in vacuo.
The yellow solid was taken up into CH2Cl2 (10 cm3) and filtered
through Celite to remove the insoluble AgCl. The mother
liquor was reduced to 1 cm3, then added to cold pentane
(100 cm3), resulting in precipitation of the product, which was
filtered and dried in vacuo. Mass = 135 mg (72%), pale yellow
CCDC reference numbers 192147 and 192148.
See http://www.rsc.org/suppdata/dt/b2/b208211j for crystal-
lographic data in CIF or other electronic format.
1
solid. H NMR (d6-acetone): δH 2.09 (s, 3H), 7.32 (dd, 1H),
Results and discussion
7.63 (m, 3H), 7.76 (td, 1H), 7.96 (t, 1H), 8.11–8.24 (m, 3H),
8.42 (dd, 1H), 8.51 (td, 1H), 8.91 (dd, 1H), 9.1–9.35 (m, 3H).
FAB-MS; m/z (%): 702 (30) [Mϩ Ϫ MeCN Ϫ CO], 674 (100)
[Mϩ Ϫ MeCN Ϫ CO], 552 (80) [Mϩ Ϫ CF3SO3 Ϫ MeCN Ϫ
2CO]. Anal. calc. for C26H18N4O3Re (Mϩ Ϫ CF3SO3): 621.0937.
Found: 621.0947. Elemental analysis: Calc. for C27H18N4O6-
ReSF3: C, 42.13; H, 2.36; N, 7.28. Found: C, 42.13; H, 2.78; N,
7.01%.
Synthetic studies
Synthesis of complexes containing the RuII(tpy) domain. The
reaction of qtpy and tpymt with [Ru(tpy)Cl3] was first investi-
gated. It was found that the use of low boiling point solvents,
such as methanol, ethanol or water, resulted in low yields
(<15%) of the required product [Ru(tpy)(qtpy)]2ϩ, 1—Scheme 2.
However, at an elevated temperature of 180 ЊC using freshly
distilled ethylene glycol as the solvent the yield of 1, isolated as
a hexafluorophosphate salt, was increased to 50%. The low
yield at low temperatures is presumably due to other unisolated
kinetically favoured species, formed from the coordination of
the 4Ј-pyridyl moiety. The reaction of tpymt with [Ru(tpy)Cl3]
proved to be more problematical.
[Re(CO)3(MeCN)(qtpy)][CF3SO3], 8[CF3SO3]. This complex
was prepared in an analogous way to 7. Yield = 72%, pale yel-
low solid. 1H NMR (d6-acetone): δH 2.09 (s, 3H), 7.64 (m, 3H),
7.78 (td, 1H), 7.89 (td, 1H), 8.05–8.28 (m, 3H), 8.41 (t, 1H),
8.52 (td, 1H), 8.90 (d, 1H), 9.11–9.34 (m, 3H). FAB-MS;
m/z (%): 582 (40) [Mϩ Ϫ CF3SO3 Ϫ MeCN], 554 (50)
[Mϩ Ϫ CF3SO3 Ϫ MeCN Ϫ CO], 525 (30) [Mϩ Ϫ CF3SO3 Ϫ
MeCN Ϫ 2CO]. Anal. calc. for C25H19N5O3Re (Mϩ Ϫ CF3SO3):
624.1046. Found:624.1051. Elementalanalysis:Calc. forC26H19-
N5O6ReSF3: C, 40.43; H, 2.48; N, 9.06. Found: C, 39.95; H,
2.50; N, 9.16%.
The synthesis of tpymt was first reported alongside tpt.15
This ligand would appear to be an attractive building block
for coordination chemistry as it possesses three terpyidyl-like
coordination sites. Yet, despite this, its coordination chemistry
is virtually undeveloped. Lippard and Lerner reported that the
reaction of tpymt with PbII results in polymetallic products
containing intact tpymt. In contrast to this, CuII centres cause
hydrolysis of tpymt producing coordinated bis(2-pyrimidyl-
carbonyl)amide anion.22 Since this work in the 1970s, the only
literature report involving non-hydrolyzed tpymt comes from
the Lehn lab, where it has been used in PbII templated self-
assembly.23 So, surprisingly, although tpymt has been known
for over 40 years, no transition metal complexes of this ligand
have been reported.
[Re(CO)3(MeCN)(tpt)][CF3SO3], 9[CF3SO3]. This complex
was prepared in an analogous way to 7. Yield = 67%, green
solid. 1H NMR (d3-MeNO2): δH 2.14 (s, 3H), 7.8 (m, 2H),
8.06 (td, 1H), 8.19 (m, 1H), 8.30 (d, 1H), 8.98 (m, 4H), 9.25
(m, 2H). FAB-MS; m/z (%): 624 (10) [Mϩ Ϫ CF3SO3], 583 (60)
[Mϩ Ϫ CF3SO3 Ϫ MeCN], 555 (30) [Mϩ Ϫ CF3SO3 Ϫ MeCN Ϫ
CO], 532 (10) [Mϩ Ϫ CF3SO3 Ϫ MeCN Ϫ 2CO]. Anal. calc. for
C23H15N7O3Re (Mϩ Ϫ CF3SO3): 624.0794. Found: 624.0810.
Elemental analysis: Calc. for C24H15N7O6ReSF3: C, 37.31; H,
1.96; N, 12.69. Found: C, 37.70; H, 1.69; N, 13.11%.
tpymt was synthesised via adapted literature procedures.15,22
The reaction of tpymt with [Ru(tpy)Cl3] was then investigated.
4734
J. Chem. Soc., Dalton Trans., 2002, 4732–4739

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Scheme 2 New complexes synthesised containing RuII(tpy) and RuII(phen)2 domains.
We initially used preparative conditions analogous to those
tpt analogues and this may well restrict its use as an oligotopic
ligand.
reported for tpt, but spectroscopic studies revealed evidence of
hydrolysis. A synthesis involving short reaction time and dry
degassed solvents was then investigated. Several solvent sys-
tems, such as methanol, ethanol, and nitromethane, were tried.
However, even when [RutpyCl3] was first treated with Agϩ,
no reaction occurred. Further studies revealed that a single
product could be obtained using anhydrous, N2 saturated,
ethylene glycol as a solvent and a large excess of tpymt. Heating
this mixture to 180 ЊC for 30 minutes resulted in a deep purple
solution from which the complex[Ru(tpy)(tpymt)]2ϩ, 2, was
isolated in good yields. As far as we aware this is the first
reported transition metal complex of intact tpymt. Indeed,
once synthesised 2 is relatively robust. Even after a period
of days, aqueous solutions of 1 show no detectable signs of
hydrolysis.
Synthesis of complexes containing the ReI(CO)3(L) domain.
Building on methodology developed by various groups in the
1980s and 1990s for polypyridyl complexes of rhenium(), we
used a two step procedure to obtain water soluble complexes
containing the [Re(CO)3(MeCN)]ϩ metal centre.
Reaction of Re(CO)5Cl with the relevant extended ter-
pyridine in refluxing toluene results in the precipitation of
the brightly coloured product complex in 90–95% yield.
These intermediates, two of which, [Re(CO)3Cl(phenpy)]24 and
([Re(CO)3Cl(tpt)],25 have been reported previously, are only
soluble in relatively nonpolar organic solvents, thus to enhance
solubilities in polar and protic solvents the complexes were
then treated with AgCF3SO3 in refluxing distilled acetonitrile,
resulting in the isolation of charged products 7–9—Scheme 4.
All three of the new complexes display good solubilities in a
wide range of solvents. Attempts to carry out analogous
reactions with both tpymt and tpp again proved to be problem-
atical, producing low yields of intractable materials. We are
currently investigating alternative procedures to obtain such
species.
Synthesis of complexes containing the RuII(phen)2 domain.
[Ru(phen)2Cl2ؒ2H2O] was refluxed in methanol with two equiv-
alents of the appropriate ligand, the resulting crude product
was purified by silica chromatography, leading to the isolation
of products 3 to 6 in ca. 20–40% yield—Scheme 2.
All attempts to synthesise the analogous tpymt complex in
this series failed due to the hydrolysis of the ligand resulting in
both bis(2-pyrimidyl)carboximidato and pyridine-2-carboxylic
acid amide species (Scheme 3).
Although the products were not separated they were easily
identified through FAB-MS and 1H-NMR studies. It seems
clear from these results that complexes containing coordinated
tpymt are appreciably more sensitive towards hydrolysis than
Spectral studies
All new complexes were characterised by 1-D and 2-D 1H-
NMR, FAB-, ES- and accurate mass spectroscopy. In several
cases, using a combination of 1-D and 2-D techniques such as
COSY, it was possible to fully assign spectra. For example, the
1
400 MHz H NMR spectrum of 1 in d3-nitromethane showed
only the signals associated with the complex and no impurities—
Fig. 1.
The spectrum is well defined and integrates to the required 20
protons. Although the complex shows two-fold symmetry the
exact assignments of the protons are still not obvious, but were
made with the help of COSY experiments The four doublets
residing at 9.15, 8.91, 8.60 and 8.16 ppm all have large coupling
constants of around 9 Hz, indicating they are adjacent to
ring nitrogens. In the 2-D experiment the doublet at 8.91 ppm
is cross-coupled to the triplet at 8.64 ppm, which integrates to
one proton, therefore these signals are assigned as protons j and
k respectively. As protons g and i are inequivalent due to
Scheme 3 Products identified from the reaction of [Ru(phen)2Cl2ؒ
2H2O] with tpymt.
J. Chem. Soc., Dalton Trans., 2002, 4732–4739
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Scheme 4 Complexes synthesised containing the ReI(CO)3(MeCN) domain.
Table 2 Selected bond lengths (Å) and angles (Њ) for [3][(PF6)2]
Ru–N(1)
Ru–N(2)
Ru–N(4)
2.114(4)
2.052(4)
2.064(4)
Ru–N(5)
Ru–N(6)
Ru–N(7)
2.065(4)
2.077(4)
2.062(4)
N(2)–Ru(1)–N(7)
N(2)–Ru(1)–N(4)
N(7)–Ru(1)–N(4)
N(2)–Ru(1)–N(5)
N(7)–Ru(1)–N(5)
N(4)–Ru(1)–N(5)
N(2)–Ru(1)–N(6)
N(7)–Ru(1)–N(6)
94.37(14)
90.01(14)
173.68(15)
96.86(14)
95.08(15)
79.86(15)
174.08(14)
79.71(14)
N(4)–Ru(1)–N(6)
N(5)–Ru(1)–N(6)
N(2)–Ru(1)–N(1)
N(7)–Ru(1)–N(1)
N(4)–Ru(1)–N(1)
N(5)–Ru(1)–N(1)
N(6)–Ru(1)–N(1)
95.88(15)
83.63(14)
78.51(14)
86.38(14)
98.97(14)
175.25(14)
101.09(14)
Fig. 1 The 400 MHz 1H NMR spectrum of 1 in d3-nitromethane.
coordination to ruthenium, they can be assigned to the double
doublets at 9.15 and 8.16 ppm. Again in COSY experiments,
both of these protons cross couple to the triplet at 7.54 ppm,
which is therefore assigned to proton h. The triplet at 7.88 ppm,
which integrates to only one proton, is assigned as the
central proton, a, on the tpy ligand, with the doublet at 9.30
ppm (J = 5 Hz) being protons b. The remaining doublet at 8.60
ppm with 9 Hz splitting can be assigned to proton f. Analysis of
cross coupling allowed the protons at 7.41 (doublet), 7.15 (trip-
let) and 8.00 ppm (triplet) to be assigned to protons c, d and e
respectively. The spectra of complexes incorporating (phen)2-
RuII and ReI(CO)3(MeCN) moieties are more complicated.
Although each of the spectra integrates to the expected num-
ber of protons, due to the asymmetric coordination mode
of the extended terpyridine ligands all aromatic protons are
inequivalent. In each ReI(CO)3(MeCN) complex the coordin-
ated acetonitrile ligand appears as a singlet, integrating to three
protons, at around 2.2 ppm. This shows a downfield shift of
around 0.5–1 ppm relative to free acetonitrile and is comparable
to values reported elsewhere.26
Fig. 2 ORTEP35 plot of the cation in [3][(PF6)2]. Hydrogens and lone
pairs are removed for clarity.
phen ligands vary from 2.062(4)–2.077(4) Å. The two coordin-
ated pyridyl rings are distorted away from planarity by a twist
angle of 16.1Њ, while the phenyl ring projects away from the
metal centre and displays a 33.8Њ twist relative to the attached
coordinated pyridyl ring. As has been observed in related sys-
tems,27 the uncoordinated pyridyl ring tends to coplanarity with
one of the phenanthroline ligands. This stacking leads to a twist
of 54.3Њ relative to the adjacent coordinated pyridyl ring.
Recent studies28,29 on the coordination chemistry of tpp have
demonstrated that it has two possible modes for bidentate
coordination. In mode A, η2-coordination involves nitrogens
on pyridine and pyrazine rings, while the other more sym-
metrical coordination mode, B, involves nitrogens on adjacent
pyridyl rings—Fig. 3.
The mass spectra of all the complexes were determined using
either FAB or positive ion ES techniques. Typically the spectra
show the sequential loss of any counter ions followed by loss of
any other monodentate ligands such as pyridine or carbonyl.
X-Ray crystallography studies
Crystallographic quality crystals of [3][(PF6)2] were obtained by
vapour diffusion—Fig. 2. Relevant bond lengths and angles are
shown in Table 2.
As expected, the phentpy ligand is coordinated in a bidentate
η2 mode, with the ruthenium centre taking up a distorted
octahedral coordination geometry. trans-angles at the RuII site
range from 171.85(14)–173.33(15)Њ. Ru–N bonds involving the
Fig. 3 Possible η2-coordination modes of tpp.
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Electrochemistry data (in volts) for the complexes in
acetonitrile solution vs. an Ag/AgCl reference electrode
Table 3 Selected bond lengths (Å) and angles (Њ) for [6][(PF6)2]
Table 4
Ru–N(1)
Ru–N(4)
Ru–N(7)
2.118(4)
2.053(4)
2.076(4)
Ru–N(8)
Ru–N(9)
Ru–N(10)
2.088(4)
2.062(4)
2.076(4)
Compound
Oxidationsa
Reductions
1
2
3
4
5
6
7
8
9
1.37
1.62
1.28
1.34
1.49
1.43
1.36b
1.41b
1.66b
Ϫ1.10, Ϫ1.41, Ϫ1.78b
Ϫ0.45, Ϫ1.25,b Ϫ1.45,b Ϫ1.62b
Ϫ1.25, Ϫ1.37, Ϫ1.45b
Ϫ1.13, Ϫ1.39, Ϫ1.67b
Ϫ0.96, Ϫ1.41, Ϫ1.72b
Ϫ0.87, Ϫ1.37, Ϫ1.59,b Ϫ1.71b
Ϫ1.15, Ϫ1.36,b Ϫ1.55b
Ϫ1.11, Ϫ1.28,b Ϫ1.60b
Ϫ0.57, Ϫ1.02,b Ϫ1.28b
N(4)–Ru(1)–N(9)
N(4)–Ru(1)–N(10)
N(9)–Ru(1)–N(10)
N(4)–Ru(1)–N(7)
N(9)–Ru(1)–N(7)
N(10)–Ru(1)–N(7)
N(4)–Ru(1)–N(8)
N(9)–Ru(1)–N(8)
88.49(16)
93.84(16)
79.60(15)
98.43(16)
172.75(15)
97.70(15)
173.33(15)
93.44(15)
N(10)–Ru(1)–N(8)
N(7)–Ru(1)–N(8)
N(4)–Ru(1)–N(1)
N(9)–Ru(1)–N(1)
N(10)–Ru(1)–N(1) 171.85(14)
N(7)–Ru(1)–N(1)
N(8)–Ru(1)–N(1)
80.25(15)
79.44(16)
78.60(15)
97.00(14)
86.53(15)
107.46(15)
a Unless otherwise stated couples are reversible with |Ipc/Ipa| = 1 and
∆Ep < 100 mV. b Chemically irreversible couple, therefore only Ep value
quoted.
1
An analysis of the H-NMR data for 6 suggested that for
the RuII(phen)2 centres coordination of tpp was via the less
symmetric A mode. This hypothesis was confirmed via X-ray
crystallography studies on the hexafluorophosphate salt of 6,
obtained via vapour diffusion of diethyl ether into a nitro-
methane solution of this complex—Fig. 4. Relevant bond
lengths and angles are printed in Table 3.
relative to [(tpy)2Ru]2ϩ 30
The first ligand-based reduction,
.
which is reversible, is observed at 0.44 V. Further irreversible
ligand-based reductions are seen at more cathodic potentials.
While, for reductions above Ϫ1.46 V, a stripping peak at 1.15 V
is observed on the return sweep—Fig. 5.
Fig. 5 CV of [6][(PF6)2] in acetonitrile/0.1 M Bu4NPF6.
The other RuII complexes all display similar RuIII/II oxidation
couples, with potentials being dependant upon the nature of
the extended terpyridine ligand. For both the tpyRu2ϩ and
(phen)2Ru2ϩ series, coordinated ligands with a higher number
of nitrogen atoms result in more anodic oxidation couples—
Table 4.
This is consistent with previous studies showing that as
ligands become more electron deficient there is concomitant
lowering of the ligand LUMO, resulting in enhanced π acceptor
properties and more anodic RuIII/II oxidation couples.31 The first
ligand-based reduction also reflects the relative electron
deficiency within the series, with couples becoming more facile
as the number of nitrogens in a ligand increases. As expected,
for the corresponding rhenium complexes, the ReII/I couple is
characteristically irreversible, but nevertheless the same trend in
redox potentials are observed.
Fig. 4 ORTEP plot of the cation in [6][(PF6)2]. Hydrogens and lone
pairs are removed for clarity.
The coordination geometry at the Ru atom is distorted
octahedral with trans-angles at the RuII site ranging from
171.85(14)–173.33(15)Њ. Ru–N bonds involving the phen
ligands vary from 2.062(4)–2.076(4) Å. As observed in related
structures,29 while the Ru–N bond length for the coordinated
pyridyl ligand of tpp is comparable to that seen for the phen
ligands (2.053(4) Å), the Ru–N distance for the coordinated
pyrazine is slightly longer at 2.118(4) Å. There is significant
twisting between the pyrazine and coordinated pyridyl rings
(21.3Њ). However, dihedral angles between the pyrazine and
uncoordinated pyridyl rings are much higher, ranging between
44.1 and 70.4Њ. As observed in 3, this latter value is due to
stacking between the uncoordinated pyridyl ring and one of the
phenanthroline ligands—the distance between the two rings
being 3.354 Å.
Photophysical studies
Small crystals of 2 were also obtained by diethyl ether vapour
diffusion into acetonitrile solutions of its hexafluorophosphate
salt. However, due to a poor quality data set and a high degree
of counter-ion disorder, consequent X-ray crystallography
studies produced a solution that is not of publishable quality.
Nevertheless, these studies did confirm the cationic connectivi-
ties obtained from NMR studies.
Electronic absorption spectra. The UV-visible absorption
spectra of all the complexes were recorded in acetonitrile
solution at room temperature. These data are summarised in
Table 5.
The low energy bands (350–550 nm) present in all of the RuII
complexes are characteristic of Ru(d)
L(π*) MLCT transi-
tions involving the various pyridyl components of the coordin-
ated ligands. These low energy transitions are similar in both
energy and intensity (5000–20000 molϪ1 dm3 cmϪ1) to those
observed in the numerous tris-phenanthroline and bis-terpyrid-
ine type complexes present in the literature, giving rise to
their intense red through to purple colours. The intense higher
energy bands, typically <300 nm, can be assigned to ligand
Electrochemical studies
Using cyclic voltammetry the electrochemical properties of the
new complexes were studied. All of the ruthenium complexes
show characteristic reversible RuIII/II oxidation couples. For
example, 2 shows a reversible RuIII/II oxidation couple at 1.62 V
(vs. Ag/AgCl) which is anodically shifted by around 300 mV
centred π
π* and n
π* transitions.
J. Chem. Soc., Dalton Trans., 2002, 4732–4739
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Table 5 Photophysical data for complexes 1–9 recorded in acetonitrile solution
Absorption
Emission
λem/nm (λex/nm)
Compound
λmax/nm (ε/molϪ1 dm3 cmϪ1
)
1
2
3
4
5
6
7
8
9
229 (sh), 238 (25584), 273 (36438), 309 (35498), 324 (sh), 485 (15204)
269 (35121), 296 (20531), 316 (14572), 330 (18346), 474 (13796)
220 (60272), 264 (72782), 310 (sh), 385 (7134), 450 (9775)
244 (31138), 287 (45977), 450 (10428)
264 (62239), 284 (sh), 402 (sh), 432 (9912), 470 (7519)
264 (75751), 344 (21820), 427 (11308), 488 (7306)
251 (26207), 277 (26735), 328 (17372)
—
—
595 (450)
674 (450)
725 (450)
715 (430)
370 (310))
417 (310)
—
253 (28110), 279 (sh), 330 (12727)
251 (26604), 295 (27103), 302 (25108), 377 (5171)
The rhenium() complexes show much simpler absorption
Luminescence in these complexes is only observed on exci-
tation at 310 nm, resulting in high energy structured emis-
sions, suggesting that luminescence in these complexes is not
spectra, typically consisting of a sharp Re(d)
tion appearing around 300–320 nm with a tail extending to
around 450 nm in the visible region. The ligand centred π π*
and n π* transitions appear as either two bands or one broad
L(π*) transi-
from the dπ(Re)
π*(diimine) MLCT manifold. It is
known that luminescence from intraligand ππ* states results
in well-resolved vibronic structure. Thus it seems likely that
emission from 7 and 8 is from phentpy and qtpy based states
respectively, which is consistent with the energy of the observed
luminescence.
band in the 230–300 nm region of the spectrum. Again these
values are typical of other ReI polypyridyl complexes found in
the literature.
Electronic emission spectra. 1 and 2 are not luminescent at
Complex 8 possesses the relatively electron deficient qtpy
ligand. This will result in a lower ππ* energy gap than that
of phentpy, and as would be expected from this argument,
emission from 8 is at appreciably longer wavelength than that of
7. At present more detailed photophysical studies are underway
to confirm this hypothesis. Complex 9 showed no emission even
when excited at a range of different wavelengths. To our know-
ledge, this is first time the emission properties of ReI(CO)3-
(triazine) systems have been studied and this may or may not be
a general phenomenon.
room temperature. This behaviour is consistent with reports
3
on analogous compounds. The lowest lying excited MLCT,
normally centered on the ligand π* LUMO, is very low lying
in complexes related to [(tpy)2Ru]2ϩ, undergoing fast non-
radiative deactivation.32
3–6 show characteristic emission spectra for complexes
containing RuII(phen)2 domains.30 Excitation at 450 nm results
in broad unstructured emissions occurring between 595 and
725 nm—Table 5, that are typical of emission from a dπ
(Ru)
π*(diimine) MLCT. The energy of this emission again
correlates with the nature of the ligand incorporated into the
complex. The more nitrogen atoms present in the extended
terpyridyl ligand, the lower the energy of the emission. These
observations are consistent with the trends observed in the
electrochemical data, indicating that as the ligand π* orbital,
which is the LUMO complex, becomes lower in energy, there is
a corresponding shift to longer wavelength emission. Corre-
sponding studies on the analogous ReI complexes reveal con-
trasting properties.
It has been pointed out that the photophysical properties of
[Re(CO)3(L)(diimine)] complexes are often more easy to inter-
pret than corresponding RuII systems as they usually only
possess one chomophoric diimine ligand.33 However, it is also
known that, in several cases, [Re(CO)3(L)(diimine)] complex
emission is actually from intraligand ππ* states.33,34 Within this
context, the results of the excitation of the rhenium complexes
7 and 8 are revealing—Fig. 6.
Conclusions
Nine new complexes containing extended tpy ligands and three
different d6 metal centres have been synthesised. It has been
found that the electrochemical and photophysical properties of
the complexes are highly dependent on the nature of the
incorporated extended terpyridyl ligand. All the complexes
show good solubility in a variety of organic solvents. By
counterion metathesis such systems are easily rendered water-
soluble. Future work will focus on the interaction of this matrix
of compounds with biologically significant molecules.
Acknowledgements
We gratefully acknowledge the support of The Royal Society
(J. A. T.) and the EPSRC (C. M. and J. A. T.).
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