J = 8.54 Hz), 7.90 (d, 4H, J = 8.0 Hz), 8.62 (s, 4H). EI-MS
(m/z) = 512 (Mϩ).
J = 8.1 Hz), 8.68 (s, 4H), 8.74 (t, 2H, J = 8.1 Hz), 8.82 (d, 4H,
J = 8.1 Hz), 9.23 (d, 4H, J = 8.3 Hz), 9.53 (s, 4H). Anal. for
C74H50N16Ru2P4F24ؒ3H2O. Calc.: C 44.45, H 2.82, N 11.21.
Found: C 44.74, H 3.43, N 10.93%.
Hydrolysis of the isolated tetramethyl ester. The tetramethyl
ester (0.89 g, 1.5 mmol) was dissolved in chloroform (100 cm3),
in which potassium hydroxide (5 g) in ethanol (200 cm3) was
added. The solution was refluxed for ∼1 h. After the confirm-
ation of complete loss of the starting tetramethyl ester by TLC
(∼1 h), all the solvents were removed in vacuo. The yellow resi-
due was dissolved in water and neutralized with HCl. The
resulting pale yellow powder was collected and dried in vacuo.
[Ru2(terpy)2(H4L2)](PF6)4. The synthetic procedure was the
same as that used for the H4L1 analogue, substituting H4L1 for
1
H4L2. Yield: 75%. H NMR (400 MHz; solvent (CD3)2SO):
δ 5.97 (d, 4H, J = 8.5 Hz), 7.07 (t, 4H, J = 8.0 Hz), 7.27 (t, 4H,
J = 6.9 Hz), 7.34 (t, 4H, J = 7.7 Hz), 7.62 (d, 4H, J = 5.5 Hz),
7.78 (d, 4H, J = 8.2 Hz), 7.95 (t, 4H, J = 8.5 Hz), 8.41 (d, 4H,
J = 8.8 Hz), 8.50 (d, 4H, J = 8.2 Hz), 8.72 (t, 4H, J = 8.0 Hz),
8.81 (d, 4H, J = 7.7 Hz), 9.23 (d, 4H, J = 8.2 Hz), 9.35 (s, 4H).
Anal. for C80H54N16Ru2P4F24ؒH2O. Calc.: C 47.12, H 2.77, N
10.99. Found: C 47.54, H 3.02, N 10.63%.
Yield: 0.65 g (87%). IR (KBr): ν(C᎐O) 1725w cmϪ1
.
᎐
4,4Ј-Bis{2,6-bis(benzimidazol-2-yl)pyrid-4-yl}-1,1Ј-biphenyl
(H4L2). The preparation was the same as that of 1,4-bis{2,6-
bis(benzimidazol-2-yl)pyrid-4-yl}benzene, except that 4,4Ј-
bis(2Ј,2Љ,6Ј,6Љ-tetracarboxy-4,4Ј:4Ј,4Љ-pyridyl)-1,1Ј-biphenyl
was used. The ligand is sparingly soluble in common organic
solvents. This compound was used without further purification.
[Ru2(bpbbip)(H4L0)](PF6)4. A mixture of [Ru(Etbpbbip)-
(CH3CN)Cl2] (0.54 g, 0.6 mmol) and H4L0 in ethylene glycol
was heated for 4 min using a 650 W microwave oven. After
cooling to room temperature, water (80 cm3) and then saturated
NH4PF6 were added to the solution. The resulting precipitate
was collected in vacuo. The purification was performed by SP
Sephadex LH-20 column chromatography with methanol–
CH3CN (1 : 1 v/v) mixed solvent. Yield: 0.46 g (70%). 1H-NMR
(300 MHz, (CD3)2SO): δ 10.01 (s, 4H), 9.18 (d, J = 7.87 Hz, 4H),
8.99 (s, 4H), 8.82 (t, J = 7.87 Hz, 2H), 7.90 (d, J = 8.4 Hz,
4H), 7.68 (d, J = 7.7 Hz, 4H), 7.40 (t, J = 7.9 Hz, 4H), 7.34 (t,
J = 8.0 Hz, 4H), 7.20 (t, J = 7.1 Hz, 4H), 7.12 (t, J = 7.1 Hz, 4H),
6.39 (d, J = 8.4 Hz, 4H), 6.20 (d, J = 8.4 Hz, 4H), 5.08 (br t, 8H),
3.79 (q, J = 7.1 Hz, 16H), 2.02 (br q, 8H), 1.73 (br q, 8H), 1.52
(br t, 8H), 1.02 (td, J = 7.0 and 2.0 Hz, 24H).
1
Yield: 68%. H NMR (400 MHz; solvent (CD3)2SO ϩ CF3-
CO2D): δ 7.49 (m, 8H), 7.90 (m, 8H), 8.14 (d, 4H, J = 7.8 Hz),
8.23 (d, 4H, J = 7.9 Hz), 8.85 (s, 4H). Anal. for C50H32N10ؒ
6H2O. Calc.: C 68.20, H 5.13, N 15.94. Found: C 67.80, H 4.92,
N 15.45%.
Synthesis of anchoring ligand
2,6-Bis(1-(4-diethylphosphonyl)butylbenzimidazol-2-yl)pyrid-
ine (Etbpbbip). NaH (oil dispersion 58%); 1.2 g, 50 mmol) was
washed with dry n-pentane and then suspended in dried dmf
(30 ml). To this suspension was added 2,6-bis(benzimidazol-2-
yl)pyridine (3.1 g, 10 mmol) under nitrogen atmosphere and the
mixture was heated to 80 ЊC for 2 h, during which time the
suspension slowly dissolved and became a yellow homogeneous
solution. The resulting solution, transferred to a dropping
funnel using cannula techniques, was added to 1-bromo-4-di-
ethylphosphonylbutane (7.30 g, 27 mmol) in dmf (10 ml) drop-
wise at room temperature and heated to 100 ЊC for 10 h. After
being cooled to room temperature, a small amount of methanol
(1 cm3) was added and then the solvent was removed under
reduced pressure. The resulting residue was dissolved in di-
chloromethane, purified by column chromatography on silica
gel with hexane–ethyl acetate (4 : 1 v/v). The desired compound,
eluted as a third band, was obtained as an oil. Yield: 6.65 g
(95%). Mass spectrum: m/z = 695.735 (M ϩ H)ϩ. 1H NMR (400
MHz; solvent (CD3)2SO): δ 1.20 (5, 12H), 1.25 (m, 4H), 1.50 (q,
4H), 1.79 (m, 4H), 3.73 (m, 8H), 4.83 (t, 4H), 7.30 (t, 2H), 7.38
(t, 2H), 7.74 (d, 2H), 7.78 (d, 2H), 8.23 (t, 1H), 8.32 (d, 2H).
Deprotection of ethyl ester groups. Deprotection of ethyl
ester groups in the ethylphosphonyl moiety of Etbpbbip was
made by the reaction of trimethylsilyl bromide (0.5 cm3) with
[Ru2(Etbpbbip)(H4L0)](PF6)4 (0.09 g, 0.041 mmol) in dry
acetonitrile at 70 ЊC for 20 h. After the addition of methanol
to the solution, the solvent was evaporated to dryness under
reduced pressure. The residue was dissolved in methanol
(10 cm3) and 40 cm3 of warter was added. After acidification by
the addition of HCl, the precipitation was affected by adding
saturated NH4PF6 to the solution. The precipitate was collected
1
and dried in vacuo. Yield: 0.07 g (86%). H NMR (400 MHz;
solvent (CD3)2SO): δ 9.99 (s, 4H), 9.16 (d, J = 8.3 Hz, 4H), 8.83
(t, J = 8.0 Hz, 2H), 8.30 (s, 4H), 7.87 (d, J = 8.3 Hz, 4H), 7.68 (d,
J = 8.0 Hz, 4H), 7.28 (t, J = 9.0 Hz, 4H), 7.20 (t, J = 8.0 Hz,
4H), 7.14 (t, J = 9.3 Hz, 4H), 7.03 (t, J = 9.0 Hz, 4H), 6.39 (d,
J = 8.3 Hz, 4H), 6.22 (d, J = 8.3 Hz, 4H), 5.05 (br t, 8H), 2.00
(br, 8H), 1.67 (br, 8H), 1.24 (br, 8H). Anal. for C92H86N20O12-
P8F24Ru2ؒ2H2O. Calc.: C 42.41, H 3.48, N 10.75. Found: C
42.18, H 3.82, N 11.16%.
Synthesis of dinuclear complexes
[Ru2(terpy)2(H4L1)](PF6)4. The microwave reactor used in
the present study, which was purchased from Shikoku Keisoku
Ltd., has an integral magnetic stirrer and a fitting for a reflux
condenser. The irradiation power of the reactor is 650 W at
multimode. The ligand, H4L1 (0.24 g, 0.34 mmol), was dis-
solved in ethylene glycol (30 ml) by microwave assisted heating
at 650 W, and then solid Ru(terpy)Cl3 (0.30 g, 0.68 mmol) was
added to the solution. The mixture was intermittently heated by
the microwave oven for 10 min. During heating the color of the
reaction mixture changed to brown. On cooling to room tem-
perature, water (30 ml) was added to the reaction mixture, fol-
lowed by filtration. To the filtrate 2 M HCl (0.5 cm3) and then a
saturated solution of NH4PF6 were added to complete precipit-
ation. The precipitate was collected and dried in vacuo. The
purification was performed by SP Sephadex LH-20 column
chromatography, using an acetonitrile–methanol mixture (1 : 1
v/v) as eluent. The desired complex was obtained by evapor-
Physical measurements
Electronic absorption spectra were obtained on a Hitachi
U-4000 spectrophotometer from 200 to 2500 nm. NMR
spectra were measured with a 400 MHz JEOL JNM-GSX 400
or 300 MHz Varian Mercury 300 spectrometer. IR were
recorded on a Nicolet FT-IR Magna 560 spectrometer. The
mass spectra were measured on a Shimadzu QP1000EX spec-
trometer for organic ligands and Micromass LCT electrospray
mass spectrometer equipped with an electrospray interface
(ESI) system for the ligands and Ru complexes. X-Ray photo-
electron spectra were measured on a Shimadzu/Krastos Axis
HSi X-ray photoelectron spectrometer with monochromated
Al-Kα radiation as an excitation source. Binding energies were
calibrated using C1s binding energy of 285.0 eV as a reference.
Electrochemical measurements were made at 20 ЊC with a
BAS 100 B/W electrochemical workstation or ALS/CH Model
660A electrochemical analyzer. The working electrode was a
BAS glassy-carbon (ꢀ 3 mm) or BAS platinum disk electrode
1
ation of the solvent. Yield: 0.20 g (37%). H NMR (400 MHz;
solvent (CD3)2SO): δ 6.00 (d, 4H, J = 8.5 Hz), 7.08 (t, 4H,
J = 7.8 Hz), 7.28 (t, 4H, J = 6.3 Hz), 7.35 (t, 4H, J = 7.8 Hz),
7.64 (d, 4H, J = 5.4 Hz), 7.78 (d, 4H, J = 8.1 Hz), 7.96 (t, 4H,
D a l t o n T r a n s . , 2 0 0 3 , 2 0 6 9 – 2 0 7 9
2071