Catalytic and Regiospecific Extradiol Cleavage of Catechol ... · Catalytic and Regiospecific...

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Electronic Supplementary Information for

Catalytic and Regiospecific Extradiol Cleavage of Catechol by a Biomimetic Iron Complex

Sayanti Chatterjee, Debobrata Sheet and Tapan Kanti Paine*

Department of Inorganic Chemistry, Indian Association for the Cultivation of Science, 2A&2B Raja S. C. Mullick Road, Jadavpur, Kolkata-700032, India

Email: [email protected]

Electronic Supplementary Material (ESI) for Chemical CommunicationsThis journal is © The Royal Society of Chemistry 2013

mailto:[email protected]

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Experimental:

All chemicals and reagents were obtained from commercial sources and were used without further

purification unless otherwise noted. Solvents were distilled and dried before use. Preparation and

handling of air-sensitive materials were carried out under an inert atmosphere in a glove box. Fourier

transform infrared spectroscopy on KBr pellets was performed on a Shimadzu FT-IR 8400S instrument.

Elemental analyses were performed on a Perkin Elmer 2400 series II CHN analyzer. Electro-spray

ionization (ESI) mass spectra were recorded with a Waters QTOF Micro YA263 instrument. Solution

electronic spectra (single and time-dependent) were measured on an Agilent 8453 diode array

spectrophotometer. All room temperature NMR spectra were collected on a Bruker Avance 500 MHz

spectrometer. Room temperature magnetic data were collected on Gouy balance (Sherwood Scientific,

Cambridge, UK). Diamagnetic contributions were calculated for each compound using Pascal’s constants.

X-band EPR measurements were performed on a JEOL JES-FA 200 instrument. Labeling experiment was

carried out with 18O2 gas (99 atom %) from Icon Services Inc., USA. Synthesis of Ligand:

Scheme S1. Synthesis of the ligand.

Bis(6-methylpyridin-2-yl)methanone (A) was prepared according to a procedure described in the

literature.[1]

Bis(6-methylpyridin-2-yl)methanone oxime (B): Hydroxylamine hydrochloride (0.70 g, 10 mmol) and

triethylamine (2.1 mL, 15 mmol) were dissolved in ethanol (50 mL) in a round bottomed flask and stirred

for 1 h at room temperature. The mixture was then treated with bis(6-methylpyridin-2-yl)methanone (1.06

g, 5 mmol) and the reaction solution was refluxed for 1 h. The solution was then cooled to room

temperature and solvent was removed. The reaction mixture was then extracted with ethyl acetate. The


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organic extract was dried over anhydrous sodium sulfate and was concentrated to isolate a white solid.

Yield: 1.08 g (96%).1H NMR (DMSO-d6, 500 MHz) δ (ppm) 7.74 (m, 2H), 7.56 (d, 2H, J = 7.5 Hz), 7.25

(m, 2H), 2.44 (s, 3H), 2.33 (s, 3H). ESI-MS (positive ion mode, acetonitrile): m/z = 250.12 (100%,

[M+Na]+).

Bis(6-methylpyridin-2-yl)methanamine (C): A mixture of bis(6-methylpyridin-2-yl)methanone oxime

(1.02 g, 4 mmol) , ammonium actate (0.54 g, 7 mmol), aqueous ammonia (17 mL) and water (12 mL ) in

ethanol (20 ml) was taken in a round bottomed flask and was heated at 80ºC under stirring. To the

mixture, zinc (1.3 g, 20 mmol) was added slowly over a period of 2 h and then the solution was refluxed

for 5 h. The reaction mixture was cooled and filtered to remove any unreacted zinc. The pH of the

solution was maintained at 12 by adding 10(N) freshly prepared sodium hydroxide solution. The

precipitate was filtered and the pH of the filtrate was maintained at 12. The filtrate was then extracted

with dichloromethane. The organic layer was then dried over anhydrous sodium sulfate and the solvent

was removed to isolate a white crystalline solid. Yield: 0.88 g (92%). 1H NMR (CDCl3, 500 MHz): δ

(ppm) 7.48 (t, 2H, J = 7.5 Hz), 7.10 (d, 2H, J = 8 Hz), 7.00 (d, 2H, J = 7.5 Hz), 5.35 (s, 1H), 2.55 (s, 6H).

ESI-MS (positive ion mode, acetonitrile): m/z = 214.15 (100%, [M+H]+), 197.12 (85%, [M-NH2]+).

Ligand tBu-LMe: To a solution of bis(6-methylpyridin-2-yl)methanamine (0.84 g, 4 mmol) in dry

tetrahydrofuran (30 mL) was added tert-butyl isocyanate (0.41 g, 4.43 mmol) in dry tetrahydrofuran (5

mL). The solution was stirred overnight at room temperature.The solvent was evaporated, water was

added and the content was extracted with dichloromethane. The organic layer was dried over anhydrous

sodium sulfate and concentrated under vacuum to isolate an off-white solid. Yield: 1.18 g (95%).

Elemental analysis calcd (%) for C18H24N4O (312.41 g/mol): C, 69.20; H, 7.74; N, 17.93. Found: C,

69.03; H, 7.94; N, 17.65. 1H NMR (CDCl3, 500 MHz): δ (ppm) 1.34 (s, 9H, tert-butyl), 2.57 (s, 6H, -

CH3), 5.83 (d, 1H, J = 5.5 Hz, CH), 6.83 (d, 1H, J = 5 Hz, NH), 7.03 (d, 2H, J = 7.5 Hz, 2PyH), 7.12 (d,

2H, J = 8 Hz, 2PyH), 7.51 (t, 2H, J = 7.75 Hz, 2PyH). 13C NMR (CDCl3, 125 MHz): δ (ppm): 24.4, 29.5,

50.4, 60.8, 119.2, 121.9, 137.1, 157.2, 157.5, 159.2. ESI-MS (positive ion mode, acetonitrile): m/z =

647.38 (100%, [M+M+Na]+), 335.20 (75%, [M+Na]+), 313.22 (55%, [M+H]+), 240.13 (40%, [M-

NHtertBu]+), 214.15 (25%, [M-NHCONHtertBu]+). [(tBu-LMe)FeII(Cl)2(MeOH)] (1). To a solution of the ligand (0.156 g, 0.5 mmol) in methanol was added

FeCl2 (0.064 g, 0.5 mmol). The resulting yellow solution was stirred for 1 h and the solvent was removed.

The residue was then washed with dichloromethane and filtered. The filtrate was concentrated under

vacuum and was layered with diethyl ether to isolate a yellow powder. X-ray quality yellow single

crystals were isolated by ether diffusion to a dichloromethane-methanol solution of the complex. Yield:


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0.20 g (89%). Elemental analysis calcd (%) for C19H28Cl2FeN4O2 (471.20 g/mol): C, 48.43; H, 5.99; N,

11.89. Found: C, 48.15; H, 5.72; N, 11.68. IR (KBr): 3438(br), 1641(s), 1552(s), 1458, 1269, 1217, 1166,

634 cm-1. ESI-MS (positive ion mode, acetonitrile): m/z = 403.12 ([1-(Cl+CH3OH)]+). µeff (298 K): 4.86

µB.

[(tBu-LMe)FeIII(DBC)]ClO4 (2). To a solution of the ligand (0.16 g, 0.5 mmol) in methanol was added

Fe(ClO4)3·xH2O (0.23 g, 0.5 mmol). To the yellow solution was added a methanolic solution (5 mL) of

3,5-di-tert-butylcatechol (0.11 g, 0.5 mmol) and triethylamine (130 µL). The resulting dark blue solution

was stirred at room temperature under nitrogen atmosphere for 2 h. The solvent was removed under

vacuum and the residue was repeatedly washed with water and dried to isolate a blue crystalline solid.

Yield: 0.27 g (78%). Elemental analysis calcd (%) for C32H44ClFeN4O7 (688.01 g/mol): C, 55.86; H,

6.45; N, 8.14. Found: C, 55.66; H, 6.23; N, 8.36. IR (KBr): 3440(br), 2954-2867, 2741, 2677, 2490,

1714(s), 1677-1647, 1589-1554, 1456, 1361, 1309, 1252, 1143, 1115, 1090 (vs), 1034, 985, 757, 631 cm-

1. ESI-MS (positive ion mode, MeCN): m/z = 688.18 ([2+H]+). UV-Vis in MeCN: λ, nm (ε, M−1 cm−1):

600 (1250). µeff (298 K): 5.98 µB.

Analysis of organic products after reaction with oxygen: The iron(III) complex 2 (0.020 mmol) was

dissolved in 10 mL of a dioxygen-saturated acetonitrile solution in the presence of different proton donors.

For complex 1, a similar procedure was followed along with the addition of one eqv of H2DBC and 2 eqv

of triethylamine to generate the catecholate complexes. For catalytic experiments, acetonitrile and

ammonium acetate/acetic acid buffer solution (4 mL acetonitrile and 1 mL acetic acid-acetate buffer, the

concentration of the original buffer solution is 1.18 M) was used for all the complexes (0.02 mmol) in the

presence of excess H2DBC. The solutions were allowed to stir at room temperature. After the reaction,

the solvent was removed under vacuum and the residue was treated with 10 mL of 3M hydrochloric acid

solution. The organic products were extracted with diethyl ether (3×15 mL), and the organic layer was

dried over anhydrous sodium sulfate. After removal of solvent, the colorless residue was analyzed by

ESI-MS and 1H-NMR spectroscopy. 1H NMR data for 3,5-di-tert-butylcatechol cleavage products (500

MHz, CDCl3): 4,6-di-tert-butyl-2-pyrone: δ (ppm) 1.22 (s, 9H), 1.36 (s, 9H), 6.05 (m, 2H). ESI-MS

(positive ion mode, MeCN): m/z = 209.03 (100%, [M+H]+), 231.01 (10%, [M+Na]+]. X-ray crystallographic data collection and refinement and solution of the structure of 1: X-ray

single-crystal data for 1 were collected at 120 K using Mo Kα (λ = 0.7107 Å) radiation on a SMART-

APEX diffractometer equipped with CCD area detector. Data collection, data reduction, structure solution

and refinement were carried out using the software package of APEX II.[2] The structure was solved by

direct method and subsequent Fourier analyses and refined by the full-matrix least-squares method based


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on F2 with all observed reflections.[3] The non-hydrogen atoms were treated anisotropically. In each of the

asymmetric unit one methanol molecule was found to be present. The hydrogen atom (O2-H) of methanol

molecule could not be assigned in structure refinement. Crystal data of 1: MF = C19H27Cl2FeN4O2, Mr = 470.2, monoclinic, space group Cc, a = 13.3894(8), b =

14.7280(9), c = 10.9907(7) Å, α = 90.00° β = 96.691(2)°, γ = 90.00°, V = 2152.6(2) Å3, Z = 4, ρ = 1.451

mg m-3, µ Mo-Kα = 0.971 mm-1, F(000) = 980, GOF = 1.180, A total of 12356 reflections were collected

in the range 2.06≤ θ ≤ 24.99, 3507 of which were unique (Rint = 0.0175). R1(wR2) = 0.0205 (0.0786) for

263 parameters and 3507 reflections (I > 2σ(I)).

Table S1. Selected bond distances (Ǻ) and angles (°) for complex 1.

Fe(1)-N(1) 2.237(2) Fe(1)-N(2) 2.336(2)

Fe(1)-N(3) 2.345(3) Fe(1)-O(2) 2.1410(19)

Fe(1)-Cl(1) 2.5063(7) Fe(1)-Cl(2) 2.3640(7)

C(7)-N(3) 1.480(3) C(14)-N(3) 1.426(4)

C(14)-N(4) 1.343(3) C(14)-O(1) 1.219(3)

N(2)-Fe(1)-N(3) 69.64(8) N(1)-Fe(1)-N(3) 74.50(8)

N(1)-Fe(1)-N(2) 84.12(8) N(1)-Fe(1)-O(2) 158.56(8)

N(2)-Fe(1)-O(2) 83.62(7) N(3)-Fe(1)-O(2) 84.75(8)

Cl(1)-Fe(1)-Cl(2) 93.09(3) Cl(1)-Fe(1)-O(2) 94.43(6)

Cl(2)-Fe(1)-O(2) 91.86(6) Cl(1)-Fe(1)-N(1) 92.00(6)

Cl(1)-Fe(1)-N(2) 162.51(6) Cl(1)-Fe(1)-N(3) 92.88(6)

Cl(2)-Fe(1)-N(1) 108.22(6) Cl(2)-Fe(1)-N(2) 104.34(6)

Cl(2)-Fe(1)-N(3) 173.35(6)


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Figure S1. Optical spectra of iron(II)-chloro complex (1) and iron(III)-catecholate complex (2) in acetonitrile (Concentration = 0.5 mM) at 298 K.

Figure S2. 1H NMR spectrum (500 MHz, CDCl3, 295 K) of complex 1.


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Figure S3. X-band EPR spectrum of complex 2 in dichloromethane and acetonitrile (1:1). (Experimental parameters: temperature = 77 K, microwave frequency = 9.13 GHz, microwave power = 0.998 mW, modulation frequency = 100 kHz, modulation width = 1 mT, time constant = 0.03 s)

Figure S4. Optical spectral changes with time (time interval = 60 s) during the reaction of 2 (0.5 mM) with dioxygen in acetonitrile at 298 K. Inset: ESI-mass spectrum of the catechol-derived product, 4,6-di-tert-butyl-2-pyrone.


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Figure S5. 1H NMR spectrum (500 MHz, CDCl3, 295 K) of organic products derived from 3,5-di-tert-butylcatechol after the reaction of 2 with dioxygen in acetonitrile. *-marked peaks are from solvents.

Figure S6. ESI-MS spectra of the catechol-cleavage product in the reaction with (a) 16O2 and (b) 18O2.


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Figure S7. Percentage of catechol-cleavage product in the presence of different protic acids.

Figure S8. Extradiol cleavage by iron complexes in the presence of different concentration of pyridinium perchlorate.


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Figure S9. Optical spectral changes with time (time interval = 30 s) during the reaction of 2 (0.5 mM solution in acetonitrile and NH4OAc/AcOH buffer mixture (4:1) of pH = 5.5) with dioxygen at 298 K. Inset: plot of absorbance vs time.

Figure S10. Plot of turnover numbers (TON) vs equivalents of H2DBC added.


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Figure S11. Time-dependent 1H NMR spectral plot and TON with time for complex 2 in acetonitrile-NH4OAc/AcOH buffer solution (pH = 5.5) at room temperature (*-marked peaks are from residual CHCl3 solvent).

Figure S12. Plot of TON vs reaction time for complex 2.


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Figure S13. Optical spectrum of [(TACN)FeIII(DBC)(Cl)] (3) (concentration = 0.5 mM) in a mixture of CH3CN and NH4OAc/AcOH (4:1) buffer of pH = 5.5 at 298 K.

Figure S14. 1H NMR spectra (500 MHz, CDCl3, 295 K) of organic products derived from 3,5-di-tert-butylcatechol after the reaction of 3 with dioxygen in acetonitrile-NH4OAc/AcOH buffer solution (pH = 5.5) in the presence of (i) 100 eqv H2DBC, (ii) 20 eqv N-methyl imidazole and 100 eqv H2DBC, (iii) 1 eqv AgBF4 and 100 eqv H2DBC and (iv) 1 eqv AgBF4, 20 eqv N-methyl imidazole and 100 eqv H2DBC. *-marked peaks are from solvents.


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Table S2. Percentage of organic products derived from 3,5-di-tert-butylcatechol after the reaction of 3 with dioxygen in acetonitrile-NH4OAc/AcOH buffer solution (pH = 5.5).

Experimental conditions H2DBC

(D)

Pyrone

(A)

Pyrone

(B)

Quinone

(C)

(i) 3 in CH3CN and NH4OAc/AcOH buffer (4:1) + 100 eqv H2DBC 10 % 5% 2% 83%

(ii) 3 in CH3CN and NH4OAc/AcOH buffer (4:1)+20 eqv N-methyl imidazole + 100 eqv H2DBC

12% 4% 2% 82%

(iii) 3 in CH3CN and NH4OAc/AcOH buffer (4:1) + 1 eqv AgBF4 + 100 eqv H2DBC

61% 2% 1% 36%

(iv) 3 in CH3CN and NH4OAc/AcOH buffer (4:1) + 1 eqv AgBF4 + 20 eqv N-methyl imidazole + 100 eqv H2DBC

27% 2% 1% 70%

References: [1] G. R. Newkome, G. E. Kiefer, Y. A. Frere, M. Onishi, V. K. Gupta and F. R. Fronczek,

Organometallics, 1986, 5, 348. [2] APEX 2 v2.1–0, Bruker AXS, Madison, WI, 2006. [3] G. M. Sheldrick, SHELX97 Programs for Crystal Structure Analysis (Release 97-2), (1998) University of Göttingen, Germany.


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