Electron Transfer to Photogenerated Ru(III)
J. Am. Chem. Soc., Vol. 121, No. 29, 1999 6841
retuning the instrument, the reaction mixture was replaced with fresh
solution for each magnetic field position employed. Time-mode EPR
spectra were obtained at each field position following the application
of a single laser flash using the following instrument settings:
modulation amplitude, 0.71 G; time constant, 0.16 ms; sweep time,
0.328 s; receiver gain, 1.25 × 105; microwave power, 17 mW;
microwave frequency, 9.7692 GHz. For each static field position used,
traces from 250 sequential laser flashes (523 nm, 5 Hz, 1.5 W) were
accumulated. The EPR recording was triggered to commence 500 µs
after each flash by means of a personal computer. A solution of
diphenylpicrylhydrazyl in acetonitrile was used as a g marker (as above).
An EPR “spectrum” was then constructed by plotting the initial signal
amplitude observed at each static field position.
and extracted with 3 × 50 mL CH2Cl2. The combined extracts were
dried over Na2SO4, and after evaporation of the solvent 510 mg of
(83%) 8 was isolated as a light yellow oil. 1H NMR (400 MHz, CDCl3)
δ in ppm 1.12 (t, J ) 7.0 Hz, 3H, CO2CH2CH3), 1.70 (br s, 2H, NH2),
2.72 (dd, J ) 7.9 and 13.4 Hz, 1H, CHCH2Tyr), 2.93 (dd, J1 ) 4.9
and 13.4 Hz, 1H, CHCH2Tyr), 3.59 (m, 1H, CHCH2Tyr), 3.74 (s, 4 H,
TyrCH2N), 3.81 (s, 8H, PyrCH2N), 4.04 (q, J ) 7.0 Hz, 2H, CO2CH2-
CH3), 6.99 (s, 2H, arom. Tyr-CH), 7.06 (m, 4H, Pyr-CH), 7.43 (m,
4H, Pyr-CH), 7.54 (m, 4H, Pyr-CH), 8.46 (m, 4H, Pyr-CH), 10.95 (s,
1H, TyrOH). 13C NMR (100.6 MHz, CDCl3, DEPT) δ in ppm 14.03
(+), 40.28 (-), 54.55 (-), 55.29 (+), 59.61 (-), 60.54 (-), 121.78
(+), 122.75 (+), 123.97 (Cquart), 126.58 (Cquart), 129.87 (+), 136.33
(+), 148.70 (+), 154.68 (Cquart), 159.05 (Cquart), 174.96 (Cquart). ESI-
MS found: m/z 654 (8 plus Na+ requires 654).
Materials. L-Tyrosine ethyl ester hydrochloride, 4,4′-dimethyl-2,2′-
bipyridine, 2,2′-bipyridine (bpy), 4,4′-bipyridine, rutheniumtrichloride,
silvertriflate, triethylamine, ammonium hexafluorophosphate, p-cresol,
and paraformaldehyde were purchased from Aldrich and used as
received. Silica gel 60 (230-400 mesh, Merck, Darmstadt, Germany)
and aluminum oxide (Aldrich) were used for column chromatography.
cis-Dichloro-bis(bpy)ruthenium (cis-Ru(bpy)2Cl2‚2H2O) was prepared
by the method reported by Meyer et al.36 All solvents were dried by
standard methods. Methylviologen (MV‚2PF6) was made by changing
the counterions from methylviologen (MV‚2Cl, Aldrich) followed by
two times recrystallization (2×) from ethanol/water (90/10). N,N-Di-
(2-picolyl)amine (dpa) was made by reaction of picolyl amine and
picolyl aldehyde followed by reduction with sodium borohydride.37
[Ru(bpy)2[4-Me-4′-CONH-CH(COOEt)(Hbpmp)]].(PF6)2 (4). Route
A. To compound 314 (0.177 g, 0.15 mmol) in EtOH/H2O (1.2 mL/1.5
mL) N,N-di(2-picolyl)amine (0.150 g, 0.75 mmol) and paraformalde-
hyde (0.023 g, 0.75 mmol) were added, followed by addition of 0.05
mL 2 N HCl, and the two-phase reaction mixture was heated under
reflux for 20 h under argon. After the solution was cooled to room
temperature, a solution of NH4PF6 (2 g) in 20 mL of H2O and 20 mL
of CH2Cl2 was added to the reaction mixture, and the organic phase
was isolated. To this organic solution, which contained the product 4
and the excess dpa, a 20 mL solution of 0.2 N HCl and NH4PF6 (1 g)
were added. The organic phase was washed with a solution of 30 mL
of H2O and Na2CO3 (3 g) and then with 30 mL of water. The organic
phase was finally separated and dried over anhydrous sodium sulfate.
After evaporation of the solvent, a red solid was obtained. Further
purification was conducted by three successive flash column chro-
matographies on Al2O3 with eluents of MeOH/2M HCl (95:5, v/v).
The desired fractions were combined and concentrated to about 10 mL
and then neutralized by adding an aqueous solution of Na2CO3.
Extraction with CH2Cl2, drying over Na2SO4, and evaporation of the
2,6-Bis[[N,N-di(2-pyridylmethyl)amino]methyl]-4-methylphe-
nol (Hbpmp). This compound was made by following a modification
of the literature method.37 To N,N-di(2-picolyl)amine (2.50 g, 12.5
mmol) in EtOH/H2O (15 mL/45 mL) was added p-cresol (0.54 g, 5.0
mmol) and paraformaldehyde (0.75 g, 25.0 mmol). To the mixture was
added 0.3 mL of 2 N HCl, and the two-phase reaction mixture was
heated under reflux for 20 h and then allowed to cool to room
temperature. CH2Cl2 (100 mL) and H2O (100 mL) were added to the
reaction mixture, and the organic phase was separated after washing
with another 100 mL of H2O and dried over anhydrous sodium sulfate.
A yellow oil was obtained after evaporation of solvent. Medium-
pressure column chromatography on silica gel with gradient eluents
CH2Cl2 and CH2Cl2/MeOH (94/6) afforded a pale yellow oil (2.25 g,
85% yield) which became a solid upon standing, mp 112 °C (uncor-
1
solvent afforded 4 (0.149 g, 65% yield) as a red solid. H NMR (400
MHz, DMSO-d6) δ in ppm 1.01 (t, J ) 7.0 Hz, 3H, CO2CH2CH3),
2.51 (s, 3H, Me), 3.01-3.12 (m, 2H, CHCH2Tyr), 3.55-3.72 (m, 12H,
CH2N), 3.99 (q, J ) 7.0 Hz, 2H, CO2CH2CH3), 4.62-4.74 (m, 1H,
CHCH2Tyr), 7.09 (s, 2H, Tyr), 7.19 (dd, J ) 4.8 and 7.0 Hz, 4H, Pyr),
7.39 (d, J ) 7.4 Hz, 4H, Pyr), 7.43-7.57 (m, 4H, Bpy), 7.63-7.72
(m, 8H, Bpy, Pyr), 7.72-7.77 (m, 1H, Bpy), 7.80-7.85 (m, 1H, Bpy),
8.09-8.19 (m, 5H, Bpy), 8.39 (dd, J ) 4.8 and 5.4 Hz, 4H, Pyr), 8.69
(d, J ) 19.8 Hz, 1H, Bpy), 8.77-8.86 (m, 5H, Bpy), 9.05 (d, J ) 19.8
Hz, 1H, Bpy), 9.45 (br s, 1H, NH), 10.95 (s, 1H, TyrOH). 13C NMR
(100.6 MHz, DMSO-d6, DEPT) δ in ppm 13.77 (+), 20.61 (+), 35.77
(-), 53.78 (-), 54.84 (+), 58.63 (-), 60.56 (-), 121.55 (+), 122.05
(+, Pyr), 122.49 (+, Pyr), 123.48 (Cquart), 124.34 (+), 125.39 (+),
126.13 (Cquart), 127.80 (+), 128.85 (+), 129.82 (+), 136.51 (+, Pyr),
137.89 (+), 140.80 (Cquart), 148.53 (+, Pyr), 149.79 (Cquart), 149.84
(Cquart), 150.28 (+), 150.97 (+), 151.82 (+), 154.14 (Cquart), 155.48
(Cquart), 156.27 (Cquart), 156.31 (Cquart), 156.36 (Cquart), 156.40 (Cquart),
156.45 (Cquart), 157.31 (Cquart), 157.34 (Cquart), 158.50 (Cquart, Pyr), 162.91
(Cquart), 162.97 (Cquart), 171.02 (Cquart). IR (cm-1) 1669 (ν(CdO)), 1732
(ν(CdO)), 3405 (ν(OH)). Electrospray ionization mass spectrometry
(ESI-MS) spectrum of 4 from acetonitrile gave a mono charged peak
at m/z 1386 (calcd for [M - PF6-]+, 1386) and doubly charged peaks
1
rected). H NMR (400 MHz, CDCl3) δ in ppm 2.23 (s, 3H, -CH3),
3.77 (s, 4H, ph-CH2-N), 3.86 (s, 8H, N-CH2-py), 6.98 (s, 2H, ph-H),
7.11 (m, 4H, py-H), 7.48 (d, J ) 7.8 Hz, 4H, py-H), 7.59 (m, 4H,
py-H), 8.50 (m, 4H, py-H). 13C NMR (100 MHz, CDCl3), δ in ppm
20.6, 54.8, 59.8, 121.9, 122.9, 123.8, 127.3, 129.7, 136.5, 148.9, 153.6,
159.4.
NH2-CH(COOEt)-Hbpmp (8). To a suspension of dpa (500 mg,
2.51 mmol) and paraformaldehyde (100 mg, 3.33 mmol) in 2 mL of
ethanol and 6 mL of water were added HCl (0.5 m, 0.5 mL) and the
tyrosine derivative 6 (300 mg, 0.970 mmol).38 The mixture was heated
under reflux for 4 days, cooled to room temperature and all volatile
fractions were evaporated in vacuo. The remaining highly viscous oil
was dissolved in 5 mL CH2Cl2 at 0 °C, 5 mL of trifluoroacetic acid
were added and the mixture was stirred for additional 12 h while it
warmed to room temperature. The solvents were evaporated in vacuo
and 100 mL of aqueous ammonia, saturated with NaCl, were added.
The mixture was extracted with 5 × 50 mL CH2Cl2, the combined
organic phases were dried over Na2SO4 and again the solvent was
subsequent evaporated in vacuo. Column chromatography was per-
formed on silica gel (30 g) with the following eluents: CH3CN/CH3-
COOH ) 20:1, 100 mL; CH3CN/H2O/CH3COOH ) 100:10:1, 200 mL;
CH3CN/NH3(aqueous) ) 10:1, 200 mL; eluating the desired compound
as the last fraction. This fraction was concentrated in vacuo to 30 mL
at m/z 693 (calcd for [M - PF6- + H+]2+, 693) and m/z 621 (calcd for
-
[M - 2PF6
]
2+, 621). Fast atom bombardment mass spectrometry
(FAB-MS) using 1-thioglycerol as matrix, showed the mono charged
peaks at m/z 1532 (calcd for [M + H+]+, 1532) and 1386 (calcd for
[M - PF6-]+, 1386).
Route B. To Ru-complex-acid 9 (300 mg, 0.33 mmol) was added
freshly distilled SOCl2 (5 mL). The resulting red solution was stirred
for 2 h under reflux and then cooled to room temperature. The SOCl2
was evaporated in vacuo, and CH3CN (10 mL) was added followed by
8 (210 mg, 0.33 mmol) dissolved in CH3CN (5 mL). After 30 min,
K2CO3 (800 mg, 5.79 mmol) was added, and the resulting suspension
was stirred for 24 h at room temperature. The mixture was then diluted
with water (100 mL) and extracted with CH2Cl2 (3 × 80 mL). The
combined organic phases were concentrated by evaporation to 10 mL
and subsequently chromatographed on 30 g silica gel (eluent: CH3-
CN/H2O/KNO3(aq)/CH3COOH ) 100:10:5:2). To the obtained shiny red
(36) Sullivan, B. P.; Salmon, D. J.; Meyer, T. J. Inorg. Chem. 1978, 17,
3334.
(37) Lubben, M.; and Feringa, B. L. J. Org. Chem. 1994, 59, 2227-
2233.
(38) Houlihan, F.; Bouchard, J.; Frechet, J. M.; Willson, C. G. Can. J.
Chem. 1985, 63, 153-162.
(39) Due to the low solubility of the complex 4 in water, it has not been
possible to perform NOESY studies to verify this result.