Ru(II) complexes of polyarylated terpyridines: Unexpected side-chain C-metallation and photosensitization of electron transfer

Article abstract of DOI:10.1016/S0020-1693(01)00626-0

The new ligands 4,4″-diphenyl-6,6″-di(4-ethoxycarbonylphenyl)-2,2′:6 ′,2″-terpyridine (H4), its non-carboxylated 4,6,4″,6″-tetraphenyl analogue (H5) and the 4,4″-diphenyl-6,6″-di(4-methoxyphenyl) analogue were prepared in high yields via double Kr?hnke reactions. Reactions with activated (ttpy)RuCl₃ (ttpy is 4′-p-tolyl-2,2′:6′,2″-terpyridine) provided the symmetrical N₆-coordinated complexes, [Ru(H4)(ttpy)](PF₆)₂ and [Ru(H5)(ttpy)](PF₆)₂, along with the novel, unsymmetrical C-metallated analogues [Ru(4)(ttpy)]PF₆ and [Ru(5)(ttpy)]PF₆, in which an unprecedented side-chain metallation occurred in lieu of incomplete substitution. A crystallographic analysis of [Ru(5)(ttpy)]NO₃ confirmed the N₅C donor set in these products and revealed a distorted binding of 5^- as well as 'π-stacking' between its uncoordinated pyridine and the ttpy ligand. The diester [Ru(H4)(ttpy)](PF₆)₂ was hydrolyzed to the diacid complex [Ru(H₂3)(ttpy)](PF₆)₂ (H₂3 is 4,4″-diphenyl-6,6″-di(4-carboxyphenyl)-2,2′:6′, 2″-terpyridine). Measurements of the photogeneration of methyl viologen cation radical with [Ru(H5)(ttpy)](PF₆)₂ and [Ru(H₂3)(ttpy)](PF₆)₂ as sensitizers showed that the presence of carboxyl groups in the latter provided a distinct benefit, owing to the formation of the neutral form [Ru(3)(ttpy)]⁰ but this was insufficient to overcome the detrimental effect of inter-ligand repulsions.

Full text of DOI:10.1016/S0020-1693(01)00626-0

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Inorganica Chimica Acta 325 (2001) 1–8
Ru(II) complexes of polyarylated terpyridines: unexpected
side-chain C-metallation and photosensitization of electron transfer
Charles Mikel 1, Pierre G. Potvin *
Department of Chemistry, York Uni6ersity, 4700 Keele Street, Toronto, Ont., Canada M3J 1P3
Received 11 April 2001; accepted 28 June 2001
Abstract
The new ligands 4,4¦-diphenyl-6,6¦-di(4-ethoxycarbonylphenyl)-2,2%:6%,2¦-terpyridine (H4), its non-carboxylated 4,6,4¦,6¦-te-
traphenyl analogue (H5) and the 4,4¦-diphenyl-6,6¦-di(4-methoxyphenyl) analogue were prepared in high yields via double
Kro¨hnke reactions. Reactions with activated (ttpy)RuCl3 (ttpy is 4%-p-tolyl-2,2%:6%,2¦-terpyridine) provided the symmetrical
N6-coordinated complexes, [Ru(H4)(ttpy)](PF6)2 and [Ru(H5)(ttpy)](PF6)2, along with the novel, unsymmetrical C-metallated
analogues [Ru(4)(ttpy)]PF6 and [Ru(5)(ttpy)]PF6, in which an unprecedented side-chain metallation occurred in lieu of incomplete
substitution. A crystallographic analysis of [Ru(5)(ttpy)]NO3 confirmed the N5C donor set in these products and revealed a
distorted binding of 5− as well as ‘p-stacking’ between its uncoordinated pyridine and the ttpy ligand. The diester
[Ru(H4)(ttpy)](PF6)2 was hydrolyzed to the diacid complex [Ru(H23)(ttpy)](PF6)2 (H23 is 4,4¦-diphenyl-6,6¦-di(4-carboxyphenyl)-
2,2%:6%,2¦-terpyridine). Measurements of the photogeneration of methyl viologen cation radical with [Ru(H5)(ttpy)](PF6)2 and
[Ru(H23)(ttpy)](PF6)2 as sensitizers showed that the presence of carboxyl groups in the latter provided a distinct benefit, owing
to the formation of the neutral form [Ru(3)(ttpy)]0 but this was insufficient to overcome the detrimental effect of inter-ligand
repulsions. © 2001 Published by Elsevier Science B.V.
Keywords: X-ray crystallography; C-Metallation; Photoinduced electron transfer; Ruthenium(II) complexes; Aryl-substituted terpyridines
1. Introduction
attractive interactions between carboxylated sensitizers
and semiconductor surface [3], and ionizable complexes
are now routinely used for anchoring to such surfaces
[4].
A large number of Ru(II) complexes have been ex-
plored as photosensitizers which undergo photoinduced
electron transfer (PET) reactions with electron accept-
ing quencher molecules. PET generates charge-sepa-
rated states that can initiate useful redox chemistry,
such as the generation of H2 from H2O [1]. With
cationic electron acceptors such as methyl viologen
(MV2+, 1,1%-dimethyl-4,4%-bipyridinium), it has been
found that neutral or anionic Ru(II) complexes of
ionizable ligands, such as carboxylated or sulfonated
bipyridines, undergo faster PET than do their cationic
analogues, owing in part to electrostatic assistance [2].
PET to semiconductor particles can proceed from even
extremely short-lived excited states with the help of
There have been no analogous examples with ioniz-
able tridentate ligands, such as 2,2%:6%,2¦-terpyridine
(tpy). While tpy complexes generally suffer from com-
paratively short excited-state lifetimes, analogues bear-
ing electron-withdrawing groups [5,6] and cyclo-
metallated analogues [7–9] have displayed enhanced
triplet and luminescence lifetimes, and would further
benefit from electrostatic assistance. However, the few
known [10] examples of terpyridine carboxylic acids
required arduous methods for their preparation and/or
cannot be readily applied to our purposes.
We describe here the facile Kro¨hnke synthesis [11] of
such a ligand, its transformation to a Ru(II) complex,
the characterization of an unusual C-metallated side-
product, and the ability of the complex to undergo PET
* Corresponding author. Fax: +1-416-736 5936.
E-mail address: pgpotvin@yorku.ca (P.G. Potvin).
1 Previously Charles M. Chamchoumis.
to MV2+
.
0020-1693/01/$ - see front matter © 2001 Published by Elsevier Science B.V.
PII: S0020-1693(01)00626-0

2
C. Mikel, P.G. Pot6in / Inorganica Chimica Acta 325 (2001) 1–8
2. Experimental
2.3. Preparation of
4,6,4¦,6¦-tetraphenyl-2,2%:6%,2¦-terpyridine (H5)
2.1. Preparation of 4,4¦-diphenyl-6,6¦-di(4-ethoxy-
carbonylphenyl)-2,2%:6%,2¦-terpyridine (H4)
In the same manner as for crude H23, 0.60 g of
3-phenyl-1-(2-pyridyl)propenone (1b) and 2 (1.00 g, 0.5
equiv.) were converted to H5, obtained as a white
powder (0.89 g, 98% yield). M.p.: 277–280 °C. 1H
NMR (CDCl3, l ppm):1 7.87 (s, 2H, H3/5), 7.75 (d, 2H,
H3%&5%), 7.56 (s, 2H, H5/3), 7.08 (d, 2H, 6-PhH2), 7.04 (d,
2H, 4-PhH2), 6.87 (t, 1H, H4%), 6.76 (m, 6H, 4,6-
PhH3&4). 13C NMR (TFA-d, l ppm): 151.2, 151.0,
147.4, 145.4, 139.0, 138.8, 130.7, 129.1, 122.0, 121.4,
120.7, 116.5, 115.1, 114.9, 114.6, 110.4. FAB MS; m/z
(%): 538 [M+H]. Anal. Found: C, 87.14; H, 5.01; N,
7.99. Calc. for C39H27N3: C, 87.12; H, 5.06; N, 7.82%.
2,6-Di[2-(1-pyridyl)-1-oxo-ethyl]pyridine diiodide [12]
(2) (0.30 g) and 3-(4-carboxy phenyl)-1-(2-pyridyl)-
propenone [13] (1a) (0.25 g, 2 equiv.) were added to
excess NH4OAc in glacial AcOH, with heating to reflux
for 3 h. After cooling, the precipitate was collected,
washed (CH3OH, 3×50 ml) and dried. The crude
diacid H23 was a tan powder (1.45 g, 95% yield). This
was taken up in SOCl2 (100 ml) and heated to reflux
under argon for 2 h. After removal of volatiles in
vacuo, absolute EtOH (100 ml) was added, and the
mixture again heated to reflux under argon for 2 h.
Once rid of solvent, the crude diester was dissolved in
warm CHCl3 and purified on a short column (alumina-
N, 2:98 CH3OH–CHCl3), then recrystallized (EtOH) to
give a white powder (1.58 g, 80% yield). M.p.: 270 °C.
1H NMR (CDCl3, l ppm):2 8.94 (s, 2H, H3/5), 8.75 (d,
2H, H3%&5%), 8.33 (d, 4H, 6-Ph), 8.22 (d, 4H, 6-Ph), 8.09
(t, 1H, H4%), 8.07 (s, 2H, H5/3), 7.88 (d, 4H, 4-PhH2),
7.54 (m, 6H, 4-PhH3&4), 4.37 (q, 4H, CH2), 1.47 (t, 6H,
CH3). 13C NMR (CDCl3, l ppm): 166.5, 156.6, 155.9,
155.3, 150.3, 143.5, 138.8, 137.9, 130.8, 130.0, 129.2,
127.2, 127.0, 121.6, 119.0, 118.4, 80.1, 29.6. FAB MS;
m/z (%): 682 (100) [M+H] 654 (5) [M−C2H5], 636
(15) [M−OC2H5]. Anal. Found: C, 79.24; H, 5.11; N,
6.09. Calc. for C45H35N3O4: C, 79.28; H, 5.17; N,
6.16%.
2.4. Preparation of [Ru(ttpy)(H4)](PF6)2 and
[Ru(ttpy)(N,N,C-4)]PF6
Ru(ttpy)Cl134 (0.030 g) was added to a solution of
AgBF4 (0.035 g, 3 equiv.) in acetone (10 ml) and the
mixture was heated to reflux under argon for 30 min.
The AgCl precipitate was filtered off, DMF (5 ml) was
added to the dark purple filtrate, and the acetone was
removed in vacuo. This was added to a warmed solu-
tion of H4 (0.045 g, 1.18 equiv.) in DMF (5 ml) and the
mixture was heated to reflux in the dark under argon
for 48 h, then freed of solvent in vacuo. The residue
was redissolved in minimal CH3CN and sufficient
aqueous NH4PF6 was added to cause precipitation of a
dark red powder. Some pure [Ru(H4)(ttpy)](PF6)2 was
isolated after trituration of this crude product with
CH3OH, filtration and evaporation of the filtrate to
provide a red powder. A further amount was obtained
by chromatography (silica, 14:2:1 CH3CN–satd.
KNO3–H2O) of the CH3OH-insoluble residue. The less
polar fraction was washed with H2O, reprecipitated
with NH4PF6 as before, then precipitated from CH3CN
with Et2O to provide [Ru(4)(ttpy)]PF6 as a purple
powder (0.010 g, 15% yield). 1H NMR (CD3CN, l
ppm):1 8.93 (s, 1H), 8.87 (d, 1H), 8.52 (s, 1H), 8.18 (d,
2H), 8.17 (s, 1H), 8.14 (d, 1H), 8.11 (s, 1H), 8.08 (d,
2H), 7.92 (d, 1H, H4/3A), 7.78 (m, 18H), 7.49 (d, 1H),
7.47 (d, 2H), 7.43 (s, 1H), 7.42 (d, 1H), 7.30 (d, 1H,
H3/4A), 7.23 (dd, 1H), 7.07 (dd, 1H), 7.20 (dd, 1H), 6.31
(s, 1H, HE), 5.78 (s, 1H, H6A), 4.48 (q, 4H, OCH2CH3),
3.89 (q, 4H, OCH2CH3), 2.60 (s, 3H, ArCH3), 1.46 (t,
6H, OCH2CH3), 0.90 (t, 6H, OCH2CH3). FAB MS;
m/z (%): 1104 (100) [M−H−PF6], 1031 (15) [M−
H−PF6−COOEt]. The more polar material
[Ru(H4)(ttpy)](PF6)2 was similarly treated and isolated
2.2. Preparation of 3-(4-methylphenyl)-1-
(2-pyridyl)-2-propenone (1b)
2-Acetylpyridine (3.43 g, 28 mmol) and 4-tolualde-
hyde (3.38 g, 28 mmol) were dissolved in 1:1 CH3OH–
5% aqueous KOH (100 ml) and the solution was stirred
for 2 h in an ice bath. The precipitate was collected,
washed with H2O and dried, giving pale yellow flakes
(5.50 g, 88%). A portion of the product was recrystal-
lized (CH3OH) as pale yellow flakes for characteriza-
1
tion. M.p.: 79–82 °C. H NMR (CDCl3, l ppm): 8.73
(d, 1H, pyꢀH6), 8.26 (d, 1H, vinyl H), 8.19 (d, 1H,
pyꢀH3), 7.91 (d, 1H, vinyl H), 7.88 (dd, 1H, pyꢀH4/5),
7.62 (d, 2H, ArH), 7.48 (dd, 1H, pyꢀH5/4), 7.21 (d, 2H,
ArH), 2.42 (s, 3H, CH3). 13C NMR (CDCl3, l ppm):
189.5, 154.4, 148.8, 144.9, 141.1, 137.0, 132.5, 129.6,
128.9, 126.8, 122.9, 119.9, 21.6. FAB MS; m/z (%): 224
(100) [M+H], 136 (44) [M−py]. Anal. Found: C,
80.89; H, 5.57; N, 6.22. Calc. for C15H13NO: C, 80.69;
H, 5.87; N, 6.27%.
1
as a red powder (total 0.048 g, 61% total yield). H
NMR (CD3CN, 330 K, l ppm):1 9.05 (d, 2H, H3&5C),
8.80 (s, 2H, H3/5B), 8.60 (t, 1H, H4C), 8.35 (d, 2H,
H3/6E), 8.04 (dd, 2H, H4/5E), 7.84 (s, 2H, HF), 7.80 (d,
4H, H2/3D), 7.80 (d, 2H, HG), 7.56 (d, 2H, H6/3E), 7.51
2 H NMR assignments use the standard tpy numbering for H4, H5
and 6, and the ring labels of Scheme 1 for the Ru complexes.

C. Mikel, P.G. Pot6in / Inorganica Chimica Acta 325 (2001) 1–8
3
(m, 4H, H3/2D), 7.51 (m, 2H, H4D), 7.51 (d, 2H, HG),
7.40 (m, 4H, H3A), 7.31 (dd, 2H, H5/4E), 7.14 (s, 2H,
H5/3B), 6.20 (d, 4H, H2A), 3.92 (q, 4H, OCH2), 2.54 (s,
3H, ArCH3), 1.15 (t, 6H, OCH2CH3). 13C NMR
(CD3CN, l ppm): 167.0, 165.9, 160.1, 157.3, 153.5,
150.2, 148.2, 141.8, 139.4, 137.2, 135.5, 133.7, 131.8,
131.5, 130.8, 130.3, 130.0, 128.4, 128.3, 128.2, 127.9,
125.5, 124.4, 121.5, 120.8, 61.9, 21.2, 14.0. FAB MS;
m/z (%): 1250 (100) [M−2PF6], 1105 [M−PF6]. Anal.
Found: C, 54.43; H, 3.55; N, 6.26. Calc. for
C67H52F12N6O4P2Ru·1/2NH4PF6: C, 54.46; H, 3.68; N,
6.16%.
was collected by vacuum filtration, washed with H2O,
and dried. A second crop was isolated by adding an
additional 50 ml of H2O to the filtrate and cooling the
solution overnight. The combined crops recrystallized
(CH3OH) as white needles (1.08 g, 68%). M.p.: 104–
105 °C. 1H NMR (CDCl3, l ppm): 8.08 (d, 2H, ArꢀH),
7.82 (d, 1H, vinyl-H), 7.69 (d, 2H, ArꢀH), 7.58 (d, 2H,
vinyl-H), 7.43 (m, 3H, ArꢀH), 7.05 (d, 2H, ArꢀH), 3.95
(s, 3H, OCH3). 13C NMR (CDCl3, l ppm): 188.7,
163.7, 143.9, 135.1, 131.1, 130.8, 130.3, 128.9, 128.4,
121.9, 113.9, 55.5. EI MS; m/z (%): 238 (100) [M], 135
(50) [M−PhCHꢁCH]. Anal. Found: C, 79.98; H, 5.94.
Calc. for C16H14O2: C, 80.65; H, 5.92%.
2.5. Preparation of [Ru(ttpy)(H5)](PF6)2 and
[Ru(ttpy)(N,N,C-5)]PF6
2.7. Preparation of 4,4¦-diphenyl-6,6¦-di(4-methoxy-
phenyl)-2,2%:6%,2¦-terpyridine (6)
The reaction of Ru(ttpy)Cl3 (0.035 g) with H5 (0.035
g, 1.0 equiv.) and work-up were carried out in the same
manner as with H4. The less polar material was isolated
as the PF6−, salt, [Ru(5)(ttpy)]PF6, a purple powder
2,6-Di[2-(N-pyridyl)-1-oxo-ethyl]pyridine diiodide (2)
[12] (0.30 g, 0.500 mmol) and 4%-methoxychalcone (1c)
(0.25 g, 1.00 mmol) were added to a solution of excess
NH4OAc (2.0 g) in glacial AcOH (5 ml), and the
resulting solution was heated to reflux for 5 h. The
precipitate, which formed upon cooling overnight, was
collected, washed with CH3OH (3×50 ml) and dried,
yielding a white powder which recrystallized (CHCl3–
CH3OH) as white needles (0.54 g, 90%). M.p.: 293–
1
(0.005 g, 7% yield). H NMR (CD3CN, l ppm):1 8.89
(s, 1H, HB), 8.87 (d, 1H, H3/5C), 8.48 (s, 1H, HB), 8.21
(d, 2H), 8.16 (s, 1H, HJ), 8.13 (t, 1H, H4C), 8.07 (s, 1H,
HJ), 7.88 (d, 1H, H3/6A), 7.77–7.48 (m, 22H), 7.43 (d,
2H), 7.29 (d, 1H, H5/3C), 7.09 (dd, 1H), 7.08 (dd, 1H),
6.66 (t, 1H, H4/5A), 6.40 (t, 1H, H5/4A), 6.26 (s, 1H, HE),
5.15 (d, 1H, H6/3A), 2.47 (s, 3H, ArCH3). FAB MS; m/z
(%): 961 (100) [M−H−PF6]. A crystallographic sam-
ple of [Ru(ttpy)(N,N,C-5)]NO3 was obtained by omit-
ting the second NH4PF6 treatment and diffusion of
Et2O into an acetone solution. The more polar fraction
provided red [Ru(H5)(ttpy)](PF6)2 (0.055 g, 68% yield).
1H NMR (CD3CN, 330 K, l ppm):1 9.05 (d, 2H,
H3&5C), 8.77 (s, 2H, HB), 8.60 (t, 1H, H4C), 8.23 (d, 2H,
H3/6E), 8.00 (dd, 2H, H4/5E), 7.88 (d, 2H, H2/3G), 7.85 (s,
2H, HF), 7.80 (d, 4H, H2A/D), 7.68 (d, 2H, H6/3E), 7.57
(m, 4H, H3A/D), 7.57 (m, 2H, H4A/D), 7.57 (d, 2H, HG),
7.29 (dd, 2H, H5/4E), 7.10 (s, 2H, HB), 7.09 (t, 2H,
H4D/A), 6.80 (dd, 4H, H3D/A), 6.10 (d, 4H, H2D/A), 2.62
(s, 3H, ArCH3). 13C NMR (CD3CN, l ppm):1 168.1,
160.4, 159.9, 156.8, 156.6, 153.1, 149.9, 148.1, 141.4,
138.9, 138.3, 137.0, 135.6, 135.0, 131.5, 131.0, 130.2,
129.4, 129.3, 128.5, 128.2, 127.9, 127.8, 128.6, 125.3,
125.2, 121.7, 121.1, 21.3. FAB MS; m/z (%): 1107 (100)
[M−PF6], 962 (35) [M−2PF6]. Anal. Found: C, 57.61;
H, 3.70; N, 6.80. Calc. for C61H44F12N6P2Ru·H2O: C,
57.69; H, 3.65; N, 6.62%.
1
296 °C. H NMR (TFA-d, l ppm): 8.78 (s, 2H, H3/5),
8.72 (d, 2H, H3%&5%), 8.55 (t, 1H, H4%), 8.50 (s, 2H, H5/3),
8.06 (d, 4H, 4-PhH2), 8.02 (d, 4H, 6-PhH2), 7.75 (m,
6H, 4-PhH3&4), 7.29 (d, 4H, 6-PhH3). 13C NMR (TFA-
d, l ppm): 156.6, 154.0, 147.0, 140.1, 139.0, 134.3,
126.7, 125.6, 122.5, 122.3, 120.2, 118.3, 115.7, 115.4,
112.3, 108.5, 47.7. FAB MS; m/z (%): 597 (100) [M].
Anal. Found: C, 81.29; H, 5.25; N, 6.91. Calc. for
C41H31N3O2: C, 82.39; H, 5.23; N, 7.03%.
2.8. Crystal structure determination of
[Ru(ttpy)(N,N,C-5)]NO3
Diffraction intensities were collected on a Nonius
Kappa CCD instrument using a fine-focus sealed tube
Mo Ka source and graphite monochromator (u=
,
0.71073 A). C61H43N7O3Ru·0.25H2O, M=1027.60,
purple needle (0.20×0.15×0.12 mm); monoclinic, a=
,
12.6538(12), b=17.077(2), c=22.5488(18) A, i=
3
104.524(6)°, V=4717.0(8) A , Dcalc=1.447 g cm−3
,
;
,
space group P21/n, Z=4, v (Mo Ka)=0.391 mm−1
T=150.0(1) K, 37 511 reflections collected (q=4.09–
23.26°, completeness to q=23.26° 98.9%, 05h514,
05k518, −255l524), 6698 unique (Rint=0.271),
corrected for absorption (Denzo-SMN) and used in all
calculations. Heavy atom positions were determined by
direct methods (SHELXS-97). The remaining non-hydro-
gen atoms were located by difference Fourier maps,
while the hydrogen atoms were assigned idealized posi-
tions. Structure refinement used full-matrix least-
2.6. Preparation of
3-(4-methoxyphenyl)-1-(2-pyridyl)-2-propenone (1c)
4-Methoxyacetophenone (1.00 g, 6.67 mmol) was
added to a cooled solution of 4-tolualdehyde (0.71 g,
6.67 mmol) in 70:30 CH3OH–5% KOH (100 ml) and
the resulting solution was stirred at ꢀ50 °C for 5 h.
The precipitate, which formed upon cooling overnight,

4
C. Mikel, P.G. Pot6in / Inorganica Chimica Acta 325 (2001) 1–8
squares on F2 (SHELXL-97). Rings D and L were con-
(s, 2H, H5/3B), 6.21 (d, 4H, H2A), 2.57 (s, 3H, ArCH3).
ES MS; m/z: 525 [M−2PF6]2+. The product was
]95% pure but attempts at recrystallization of an
analytical sample resulted in the partial loss of the
elements of HPF6, producing insoluble material.
,
strained to fit regular hexagons (CꢀC 1.39 A). Ring
F/G was disordered over two equally populated rota-
tional orientations. All but the hydrogen atoms and the
solvent oxygen atoms were refined anisotropically.
With 665 refined parameters, the final wR(F2)3 was
0.2055 (all data), goodness-of-fit2 1.047, with R(F)=
2.10. Electron transfer measurements
0.0826 for the 3458 reflections where I\2|(I); largest
−3
,
difference peak and hole 0.555 and −0.540 e A
Table 1 presents selected bond lengths and angles.
.
Sample solutions (2.5 ml) containing [Ru(H5)(ttpy)]-
(PF6)2 (4.03×10−5 M), [Ru(H23)(ttpy)](PF6)2 (3.97×
10−5 M) or [Ru(ttpy)2](PF6)2 (3.99×10−5 M),
MV(PF6)2 (9.45×10−3 M) and triethanolamine (5×
10−2 M) in CH3CN were prepared in 3 ml cuvettes for
measurements and data treatment as detailed elsewhere
[15]. The absorbance due to MV+ (umax 600 nm, mmax
10 060 M−1 cm−1) [16] was monitored over time first
under irradiation, then in the dark, and this cycle was
2.9. Preparation of [Ru(H23)(ttpy)](PF6)2
A sample of [Ru(H4)(ttpy)](PF6)2 (0.1001 g, 71.7
mmol) in 5 ml of DMF was heated to reflux with NaOH
(10 ml 0.10 N) while stirring for 4 h. After cooling and
quenching with HPF6 (60% in H2O), the precipitates
were collected and washed with H2O. The solid was
redissolved in CH3CN and washed with hexanes, fol-
lowed by a removal of volatiles in vacuo to yield 0.0854
repeated twice more with each sample. After converting
+
’
the absorbance data to MV concentrations, the aver-
+
’
age maximum MV
yields and the average initial
growth rates were assessed. The pseudo-first-order rate
1
g (89%) of [Ru(H23)(ttpy)](PF6)2. H NMR (CD3CN,
constants for the formation (kf) and quenching (kq) of
330 K, l ppm):1 9.05 (d, 2H, H3&5C), 8.79 (s, 2H, H3/5B),
8.60 (t, 1H, H4C), 8.34 (d, 2H, H3/6E), 8.01 (dd, 2H,
H4/5E), 7.88 (s, 2H, HF), 7.78 (d, 2H, HG), 7.75 (d, 4H,
+
’
MV
were obtained from application of the kinetic
model [15]
’
H2/3D), 7.65 (d, 2H, H6/3E), 7.52–7.47 (m, 6H, H3/2D
,
d[MV +
]
’
=kf[MV2+]0−(kf+kq+kd1)[MV +
]
t
H4D, HG), 7.39 (m, 4H, H3A), 7.30 (dd, 2H, H5/4E), 7.14
dt
’
−kd2[MV + 2
]
(1)
t
Table 1
,
Selected bond lengths (A) and bond angles (°) for [Ru(ttpy)(5)]NO3
using kd parameter values measured from a prior analy-
sis of the subsequent aerobic decays in the dark (where
kf=kq=0).
Bond lengths
Ru(1)ꢀC(71)
Ru(1)ꢀN(21)
Ru(1)ꢀN(11)
Ru(1)ꢀN(61)
Ru(1)ꢀN(31)
Ru(1)ꢀN(51)
1.992(11)
1.944(7)
2.016(8)
2.024(7)
2.047(9)
2.216(8)
3. Results and discussion
3.1. Synthesis
Bond angles
N(21)ꢀRu(1)ꢀC(71)
N(21)ꢀRu(1)ꢀN(11)
C(71)ꢀRu(1)ꢀN(11)
N(21)ꢀRu(1)ꢀN(61)
C(71)ꢀRu(1)ꢀN(61)
N(11)ꢀRu(1)ꢀN(61)
N(21)ꢀRu(1)ꢀN(31)
C(71)ꢀRu(1)ꢀN(31)
N(11)ꢀRu(1)ꢀN(31)
N(61)ꢀRu(1)ꢀN(31)
N(21)ꢀRu(1)ꢀN(51)
C(71)ꢀRu(1)ꢀN(51)
N(11)ꢀRu(1)ꢀN(51)
N(61)ꢀRu(1)ꢀN(51)
N(31)ꢀRu(1)ꢀN(51)
C(72)ꢀC(71)ꢀRu(1)
C(76)ꢀC(71)ꢀRu(1)
N(51)ꢀC(52)ꢀC(91)
95.0(4)
79.7(3)
92.1(4)
174.6(3)
79.6(3)
101.0(3)
79.0(3)
The chalcone derivative 1a [13] and the dipyridinium
salt 2 [12] were condensed in the presence of NH4+ to
give the new terpyridinediacid H23 (Scheme 1). The full
characterization of H23 and its use in complexation
were precluded by its low solubility, but its identity was
determined by NMR spectroscopy in CF3COOD. Es-
terification provided the soluble and fully characterized
H4 in 76% isolated yield from 1a. Unfortunately, reac-
tions of H4 with RuCl3 or Ru(DMSO)4Cl2 were not
clean and incomplete. But, after activation with Ag+,
reaction of the known [14] (ttpy)RuCl3 (ttpy is 4%-p-
tolyl-2,2%:6%,2¦-terpyridine) with H4, followed by an an-
ion exchange, provided a mixture of two PF−6 salts.
One was a red complex, the expected [Ru(H4)(ttpy)]-
(PF6)2 (61% isolated yield), and the other was a purple
salt later assigned the C-metallated structure [Ru(4)-
(ttpy)]PF6 (15% isolated yield). Complex [Ru(H4)-
(ttpy)](PF6)2 was hydrolyzed with NaOH, then treated
89.1(4)
158.7(3)
100.2(3)
109.1(3)
155.8(3)
90.5(3)
76.3(3)
97.1(3)
130.9(7)
114.4(7)
120.8(10)
3 w=[|2(Fo2 )+(0.0550P)2+16.1243P]−1, where P=(Fo2 +2Fc2)/
3; goodness-of-fit={ꢀ[w(F2o −F2c )2]/(Nrflns−Nparams)}1/2
.

C. Mikel, P.G. Pot6in / Inorganica Chimica Acta 325 (2001) 1–8
5
Scheme 1. Reagents and conditions: (i) excess NH4OAc, HOAc, reflux, 2 h; (ii) SOCl2, reflux, then EtOH, reflux; (iii) Ru(ttpy)Cl3, AgBF4, acetone,
reflux, 0.5 h, then H4 or H5, DMF, reflux, 8 h; (iv) excess NH4PF6 in H2O, CH3CN; (v) NaOH, DMF, reflux, 4 h, then HPF6.
is analogous to that seen at the 6 positions of N3-coor-
dinated terpyridines and is also attributable to the ring
current of the orthogonal ligand (ttpy, in this instance).
Another example is provided by our new N3-coordi-
nated terpyridine complexes [Ru(H4)(ttpy)](PF6)2,
[Ru(H5)(ttpy)](PF6)2 and [Ru(H23)(ttpy)](PF6)2, all of
which have 6/6¦-phenyl ortho H (ring A) lying above
the terminal pyridines of the ttpy ligand (ring E), and
all three show a doublet near 6.2 ppm. Analogously,
[Ru(4)(ttpy)]PF6 and [Ru(5)(ttpy)]PF6 showed singlets
near 6.3 ppm that were assigned to the uncoordinated
pyridine H (ring E), and the strong upfield shift was
again ascribed to the same ring current effect.
The electronic spectrum of [Ru(4)(ttpy)]PF6 revealed
two bands, at 530 nm (m 17 200 M−1 cm−1) and 380
nm (m 10 000 M−1 cm−1) in accordance with similar
MLCT bands observed with other C-metallated species
[8,9]. The latter is assigned to metal-to-ligand charge
transfer [9] to 4−. The main product, [Ru(H4)(ttpy)]-
with HPF6 to provide an 89% isolated yield of the
diacid [Ru(H5)(ttpy)](PF6)2, the first carboxylated ter-
pyridine complex of Ru(II).
In an entirely analogous manner, the new chalcone
1b was transformed to the 4,6,4¦,6¦-tetraphenyl ligand
H5 (86% overall isolated yield from commercially avail-
able materials), then to a mixture of its complexes
(Scheme 1). The major product was again the red,
N6-ligated product [Ru(H5)(ttpy)](PF6)2 in 68% yield,
and the minor, purple product (7% yield) was assigned
the N5C-coordinated structure [Ru(N2C-5)(ttpy)]PF6,
on the basis of spectral similarities with [Ru(4)(ttpy)]-
PF6, whose crystallography confirmed its structure
(vide infra).
As an illustration of the generality of the ligand
synthesis, we also prepared the 6,6¦-di(4-methoxy-
phenyl)-4,4¦-diphenyl analogue 6 from the new chal-
cone 1c (61% overall isolated yield from commercially
available materials) as an example bearing an electron-
releasing substituent, though it was not transformed to
a Ru(II) complex.
(PF6)2, absorbed at
−1 cm−1) more typical of terpyridine complexes.
The new C-metallated complexes are distinctive in
a position (488 nm, 22 600
M
The identification of the C-metallated products
[Ru(4)(ttpy)]PF6 and [Ru(5)(ttpy)]PF6 involved a num-
ber of techniques. The lack of symmetry was immedi-
ately evident from the 1H NMR spectra and was
confirmed by a dtd splitting pattern for the central
pyridine ring signals revealed by the COSY spectra.
Not all resonances were assignable but a strongly upfi-
eld-shifted singlet (5.8 ppm) undergoing long-range
coupling to one of the pair of doublets was assigned to
the hydrogen next to the site of metallation (H-3) on a
p-phenylene ring (ring A). Such a shift has been found
in other instances of C-metallation [8,9]. The shielding
several respects. They are, to our knowledge, the first
instances of optional C-metallation by ligands otherwise
able to bind exclusively through pyridine nitrogens.
Previous instances of C-metallation with tridentates
have been intentional in that the ligands bore fewer
than three nitrogens. Optional C-metallation may have
occurred previously but has not been reported: for
instance, a purple side-product was noted during the
complexation of 6,6¦-diphenylterpyridine [17], but it
was not isolated nor characterized. Secondly, side-chain
metallation occurs here in lieu of an incomplete substi-
tution. When the N3 donor set along the meridional

6
C. Mikel, P.G. Pot6in / Inorganica Chimica Acta 325 (2001) 1–8
plane is misaligned, the usual result is a ‘hypo-chelated’
N5Cl-coordinated species [18]. Here, the availability of
C-metallation sites on the 6 and 6¦ side-chains in either
misaligned orientation precludes ‘hypo-chelation’. Al-
though there are many examples of terpyridines acting
as bidentates with pendant, non-coordinated pyridines
[9,18,19], H4 and H5 provide the first examples of
C-metallated varieties, acting moreover as tridentates.
Thus, the pendant pyridine groups constitute protona-
tion, alkylation or perhaps metal coordination sites not
previously available in C-metallated complexes.
The solvent may have an effect on the distribution of
N6- and N5C-coordinated products [9], as can the oc-
currence of ‘p-stacking’ [19], but we note that the
observed preference for N6-coordination is consistent
with an initial coordination by a distal pyridine at one
of two axial metal sites, as opposed to the one equato-
rial site, whereas an excess of the N5C-coordinated
product would have been expected from an initial bind-
ing of the central pyridine. This preference may be a
result of the steric hindrance to an approach of the
central pyridine nitrogens by the 4- and 4¦-phenyl
groups when H4 or H5 are in their free-ligand (anti,
anti ) conformations [20]. We note that C-metallation
at terminal pyridines would have provided no steric
advantage. Thus, the highly congested ligands H4 and
H5 behaved much like less-congested terpyridines, dif-
fering only in the nature of the product of
misalignment.
the structure (Fig. 1) confirmed the ‘p-stacking’ of the
ttpy ligand with the uncoordinated pyridine of 5−.
Indeed, the centroid-to-centroid separation between
,
rings D and F is 3.39 A and they lie virtually parallel to
one another (8° interplanar angle). Perhaps to accom-
modate this, ring C is pulled away from the metal,
,
resulting in a long RuꢀN(51) bond (2.22 A), but there is
no detectable distortion of the ring C–ring E junction
(N(51)ꢀC(52)ꢀC(91) 12191°). Nevertheless, the coordi-
,
nation to ring B (RuꢀN(61) 2.02 A) is weaker than is
,
usual (viz. RuꢀN(21) 1.94 A), while the bond to the
,
carbanionic ring A is shorter (RuꢀC(71) 1.99A). It
would appear that the strong RuꢀC bond to ring A
forces a weaker coordination of ring B and especially
ring C, and allows the uncoordinated ring E to tilt
away from the ttpy central pyridine ring J, thereby
avoiding inter-ligand steric congestion.
It is also noteworthy that those phenyl and tolyl rings
attached to the metal-coordinated pyridine rings D and
L are essentially coplanar (interplanar angles of 16.3
and 10.0°, respectively) to permit conjugation, as we
have observed before [21], but the rings F/G attached
to the uncoordinated pyridine are tilted out of plane
(30.6–38.7° interplanar angles) to avoid steric conges-
tion at the ortho positions.
3.3. Photoinduced electron transfer
The homoleptic 6,6%-diphenyl-2,2%:6%,2¦-terpyridine
(dptpy) complex of Ru(II) was non-luminescent even at
77 K, with an immeasurably short excited-state lifetime
(~) [22]. In this and other instances of steric congestion
in the vicinity of the metal [23], inter-ligand steric
interactions were deemed responsible for weakening the
ligand fields and thereby rendering a metal-centred,
triplet d–d state (3MC) more accessible from the lig-
3.2. Molecular structure of [Ru(5)(ttpy)]NO3
Although attempts were made to obtain high quality
crystals of all complexes, useable crystals were instead
obtained with the NO3− salt of [Ru(5)(ttpy)]+. In addi-
tion to supporting the N5C binding assigned by NMR,
Fig. 1. ORTEP diagram of [Ru(5)(ttpy)]NO3 showing 50% probability ellipsoids and disorder in a phenyl ring. H atoms and the counteranions have
been omitted for clarity.

C. Mikel, P.G. Pot6in / Inorganica Chimica Acta 325 (2001) 1–8
7
Table 2
With just one 6,6¦-diarylated ligand, complex
[Ru(H5)(ttpy)](PF6)2 was still a much weaker sensitizer
than [Ru(ttpy)2]2+ (~ 0.95 ns) [25], presumably because
of a very low ~ value despite the opportunity for added
conjugation. The presence of carboxyl groups in
Kinetic parameters (uncertainties in least-significant digits in brack-
ets) for the photogeneration of MV
+
’
+
kf×105
(s−1
kq×103
(s−1
’
Complex
[MV
]
max
(mM)
)
)
[Ru(H23)(ttpy)](PF6)2 was evidently beneficial, leading
[Ru(H5)(ttpy)](PF6)2
[Ru(H23)(ttpy)](PF6)2
[Ru(ttpy)2](PF6)2
1.9
4.0(3)
5.5(5)
0.072(1)
0.17(2)
1.12(1)
0.5(1)
2.4(6)
8.8(6)
+
’
to faster MV
formation and quenching than with
[Ru(H5)(ttpy)](PF6)2, and this can be ascribed to fa-
vourable intermolecular interactions involving the de-
protonated form [Ru(3)(ttpy)]0. Nevertheless, this
benefit was insufficient to overcome the deficit in ~ of
[Ru(H5)(ttpy)](PF6)2, relative to [Ru(ttpy)2]2+. We are
currently exploring new sensitizer designs that incorpo-
and-centred, charge-transfer state (3CT) that is involved
in the photoinduced electron transfer. The MC state
3
provides an efficient route of non-radiative energy loss
and a shortened ~. This steric effect was expected to be
milder in the heteroleptic complexes [Ru(H5)(ttpy)]-
(PF6)2 and [Ru(H23)(ttpy)](PF6)2, where only one lig-
and bears substituents at the 6-positions. Indeed,
[Ru(dptpy)2]2+ was photoreactive in the presence of
SCN− due to the congestion [22], but no such sensitiv-
ity was noted in [Ru(H4)(ttpy)](PF6)2 or [Ru(H5)-
(ttpy)](PF6)2. The 4,4%,4¦-triphenyl-2,2%:6%,2¦-terpyridine
analogue was a much better emitter (~ ca. 0.2 ms in 4:1
EtOH–MeOH) than was [Ru(dptpy)2]2+ or even the
unsubstituted tpy complex [24], presumably because of
rate carboxylate substituents on
framework.
a less-congested
Acknowledgements
This work was funded by a grant from the Natural
Sciences and Engineering Research Council (Canada).
We thank Ms. Phuong Uyen Luyen for the photochem-
ical work.
3
References
conjugation by the phenyl groups stabilizing the CT
3
state relative to the MC state. We anticipated that the
[1] (a) A. Harriman, M.A. West (Eds.), Photogeneration of Hydro-
gen, Academic Press, New York, 1983;
4- and 4¦-phenyl groups in [Ru(H5)(ttpy)](PF6)2 and
[Ru(H23)(ttpy)](PF6)2 would serve the same purpose,
with conjugation exemplified by rings D and L in the
crystal structure of [Ru(5)(ttpy)]NO3 and elsewhere
[21]. We also expected that 4,4¦-diphenyl substitution
would help to rigidify the complex, thereby increasing
the barrier to the structural reorganization that accom-
panies the 3CT“3MC transition, and hinder solvent-in-
duced quenching. These factors, combining to mitigate
a reduced congestion, constitute improvements over the
dptpy case [22].
(b) J.R. Norris, D. Meisel (Eds.), Photochemical Energy Conver-
sion, Elsevier, New York, 1989;
(c) K. Kalyanasundaram, in: Photochemistry of Polypyridine
and Porphyrin Complexes, Academic Press, London, 1992;
(d) in: K. Kalyanasundaram, M. Gra¨tzel (Eds.), Photosensitiza-
tion and Photocatalysis using Inorganic and Organometallic
Compounds, Kluwer Academic Press, Dordrecht, 1993.
[2] (a) G.L. Gaines, J. Phys. Chem. 83 (1979) 3088;
(b) S. Anderson, E.C. Constable, K.R. Seddon, J.E. Turp, J.E.
Baggott, M.J. Pilling, J. Chem. Soc., Dalton Trans. (1985) 2247.
[3] (a) N. Vlachopoulos, P. Liska, J. Augustynski, M. Gra¨tzel, J.
Am. Chem. Soc. 110 (1988) 1216;
Methodology developed earlier [15] was used to com-
paratively assess the ability of [Ru(H5)(ttpy)](PF6)2 or
[Ru(H23)(ttpy)](PF6)2 to sensitize the production of
(b) O. Kohle, S. Ruile, M. Gra¨tzel, Inorg. Chem. 35 (1996) 4779;
(c) R. Argazzi, C.A. Bignozzi, G.M. Hasselman, G.J. Meyer,
Inorg. Chem. 37 (1998) 4533.
methyl viologen cation radical (MV +) from methyl
’
[4] (a) T.J. Meyer, G.J. Meyer, B.W. Pfennig, J.R. Schoonover, C.J.
Timpson, J.F. Wall, C. Kobusch, X. Chen, B.M. Peek, Inorg.
Chem. 33 (1994) 3952;
viologen as an electron acceptor by oxidative quench-
ing, under continuous irradiation in CH3CN and with
(b) R. Argazzi, C.A. Bignozzi, T.A. Heimer, F.N. Castellano,
G.J. Meyer, Inorg. Chem. 33 (1994) 5741;
triethanolamine as a sacrificial reductant. Table 2 re-
+
’
ports the steady-state yields of MV and the pseudo-
(c) R. Argazzi, C.A. Bignozzi, T.A. Heimer, F.N. Castellano,
G.J. Meyer, J. Am. Chem. Soc. 117 (1995) 11815;
(d) K. Vinodgopal, X. Hua, R.L. Dahlgren, A.G. Lappin, L.K.
Patterson, P.V. Kamat, J. Phys. Chem. 99 (1995) 10883;
(e) R.W. Fessenden, P.V. Kamat, J. Phys. Chem. 99 (1995)
12902;
first-order rate constants for its formation (kf) and
quenching (kq). We found that [Ru(H23)(ttpy)](PF6)2
+
’
led to a concentration of MV about double that with
[Ru(H5)(ttpy)](PF6)2. Kinetic analysis suggested that
this improvement arose from a faster electron transfer
(larger kf) tempered by a concomitant increase in MV
(f) P. Pechy, F.P. Rotzinger, M.K. Nazeeruddin, O. Kohle, S.M.
Zakeeruddin, R. Humphry-Baker, M. Gra¨tzel, J. Chem. Soc.,
Chem. Commun. (1995) 65;
(g) T.A. Heimer, S.T. D’Arcangelis, F. Farzad, J.M. Stipkala,
G.J. Meyer, Inorg. Chem. 35 (1996) 5319.
+
’
quenching (larger kq). With much larger kf and kq
values, [Ru(ttpy)2]2+ produced only about 1.4 times
+
’
higher steady-state concentrations of MV
than did
[5] Bidentates: W.F. Wacholz, R.A. Auerbach, R.H. Schmehl, In-
org. Chem. 25 (1986) 227.
[Ru(H23)(ttpy)](PF6)2 under identical conditions.

8
C. Mikel, P.G. Pot6in / Inorganica Chimica Acta 325 (2001) 1–8
[6] Terpyridines: M. Maestri, N. Armaroli, V. Balzani, E.C. Con-
[11] F. Kro¨hnke, Synthesis (1976) 1.
stable, A.M.W. Cargill Thompson, Inorg. Chem. 34 (1995) 2759.
[7] (a) F. Barigelletti, D. Sandrini, M. Maestri, V. Balzani, A. Von
Zelewsky, L. Chassot, P. Jolliot, U. Maeder, Inorg. Chem. 27
(1988) 3644;
[12] F. Kro¨hnke, Angew. Chem. 74 (1962) 811; Angew. Chem., Int.
Ed. Engl. 2 (1963) 386.
[13] H. Iida, H. Iida, Kogyo Kagaku Zasshi 71 (1968) 525 (Chem.
Abstr. 69 (1968) 60027y).
(b) J.-P. Collin, M. Beley, J.-P. Sauvage, F. Barigelletti, Inorg.
Chim. Acta 186 (1991) 91;
[14] J.-P. Collin, S. Guillerez, J.-P. Sauvage, J. Chem. Soc., Chem.
Commun. (1989) 776.
(c) J.-P. Collin, R. Kayhanian, J.-P. Sauvage, G. Calogero, F.
Barigelletti, A. De Cian, J. Fischer, J. Chem. Soc., Chem.
Commun. (1997) 775;
[15] P.U. Luyen, P.G. Potvin, F. Al-Mutlaq, New J. Chem. 25 (2001)
839.
[16] E.M. Kosower, J.L. Cotter, J. Am. Chem. Soc. 86 (1964) 5524.
[17] C.O. Dietrich-Buchecker, P.A. Marnot, J.-P. Sauvage, Tetrahe-
dron Lett. 23 (1982) 5291.
[18] E.C. Constable, A.M.W. Cargill Thompson, Inorg. Chim. Acta
223 (1994) 177.
[19] Y. Jahng, R.P. Thummel, S.G. Bott, Inorg. Chem. 36 (1997)
3133.
[20] J. Zadykowicz, P.G. Potvin, J. Coord. Chem. 47 (1999) 395.
[21] C.M. Chamchoumis, P.G. Potvin, J. Chem. Soc., Dalton Trans.
(1999) 1373.
[22] J.R. Kirchoff, D.R. McMillin, P.A. Marnot, J.-P. Sauvage, J.
Am. Chem. Soc. 107 (1985) 1138.
(d) E.C. Constable, A.M.W. Cargill Thompson, J. Cherryman,
T. Liddiment, Inorg. Chim. Acta 235 (1995) 165.
[8] (a) E.C. Constable, D.G.F. Rees, New J. Chem. 21 (1997) 369;
(b) M. Beley, J.-P. Collin, R. Louis, B. Metz, J.-P. Sauvage, J.
Am. Chem. Soc. 113 (1991) 8521;
(c) E.C. Constable, A.M.W. Cargill Thompson, New J. Chem.
20 (1996) 65;
(d) D.A. Bardwell, J.C. Jeffery, E. Schatz, E.E.M. Tilley, M.D.
Ward, J. Chem. Soc., Dalton Trans. (1995) 825;
(e) D.A. Bardwell, A.M.W. Cargill Thompson, J.C. Jeffery, J.
McCleverty, M.D. Ward, J. Chem. Soc., Dalton Trans. (1996)
873;
[23] (a) R.H. Fabian, D.M. Klassen, R.W. Sonntag, Inorg. Chem. 19
(1980) 1977;
(f) Review: A.M.W. Cargill Thompson, Coord. Chem. Rev. 160
(1997) 1.
(b) A. Juris, V. Balzani, P. Belser, A. von Zelewsky, Helv. Chim.
Acta 64 (1981) 2175;
[9] E.C. Constable, M.J. Hannon, Inorg. Chim. Acta 211 (1993)
101.
(c) F. Barigelletti, A. Juris, V. Balzani, P. Belser, A. von
Zelewsky, Inorg. Chem. 22 (1983) 3335.
[10] (a) V.-M. Mukkala, M. Helenius, I. Hemmila¨, J. Kanare, H.
Takalo, Helv. Chim. Acta 76 (1993) 1361;
[24] M.L. Stone, G.A. Crosby, Chem. Phys. Lett. 79 (1981) 169.
[25] J.-P. Sauvage, J.-P. Collin, J.-C. Chambon, S. Guillerez, C.
Coudret, V. Balzani, F. Barigelletti, L. De Cola, L. Flamigni,
Chem. Rev. 94 (1994) 993.
(b) K.T. Potts, K.A. Gheysen Raiford, M. Keshavarz-K, J. Am.
Chem. Soc. 115 (1993) 2793;
(c) A.P. Da Silva, H.Q.N. Gunaratne, T.E. Rice, Angew. Chem.,
Int. Ed. Engl. 35 (1996) 2116.