C O M M U N I C A T I O N S
Figure 3. 3D-plots showing the initial rates of 2e-catalyzed bleaching of Orange II by H2O2 as a function of [H2O2] and [Orange II] at pH 7 (A), 9 (B),
and 11 (C) at [2e] 2 × 10-7 M, 0.01 M phosphate, 25 °C. The bars on the right of each plot compare catalytic activity referred to the highest activity at pH
9. Each data point is a mean value of three determinations. The meshes are calculated using the rate constants in Table 1.
II to indicate that first-order kinetics in the dye prevail and that no
catalyst degradation occurs while the process is ongoing. The
calculated pseudofirst-order rate constant kobs could thus be used
for the calculation of kII simply by dividing the kobs ) 0.029 (
0.001 s-1 by the 2e concentration. The resulting value of 1.45 ×
105 M-1 s-1 agrees well with that reported in Table 1 at pH 11
obtained from all the data points in Figure 3C.
Acknowledgment. Dedicated to Prof. W. F. Boldridge on his
92nd birthday. Support (T.J.C.): Heinz Endowments, C. E. Kaufman
Foundation; HHMI (C.T.). We thank R. Gil for NMR assistance
and the NSF for NMR Instrumentation (CHE-0130903).
Supporting Information Available: Synthetic procedures, details
of X-ray experiment and kinetic measurements. This material is
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Figure 4. Catalytic bleaching by 2e at pH 11: Inset shows that the bleaching
follows exponential kinetics over approximately 10 half-lives.
Table 1. Rate Constants (M-1 s-1) for the FeIII-TAML Catalyzed
Bleaching of Orange II by [H2O2] at 25 °C in 0.01 M Phosphate
pH
Fe-TAML
kI
kII
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7
9
11
11
11
2e
2e
(1.9 ( 0.1) × 103
(16 ( 2) × 103
(10 ( 1) × 103
3.5 × 103
(5.2 ( 0.7) × 105
(10 ( 1) × 105
(1.2 ( 0.1) × 105
1.5 × 104
2e
1a5
1b (SI)
(8.4 ( 0.6) × 103
(1.1 ( 0.1) × 105
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In conclusion, by focusing on the electronegativity of groups
within the TAML framework, we have been able to iteratively
design a new type of iron-TAML activator, called Fe-D*, that is
comprised exclusively of the common elements of biochemistry15
and that exhibits the highest reactivity and stability, especially at
pH 7, found to date. So this is a case where the singular electronic
effects of fluorine’s high electronegativity have been mimicked by
the type of detailed iterative design that green chemists are working
to develop. Future work will quantify the relationship between pH,
stability, and reactivity in the Fe-D* system.
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S. T.; Kauffmann, K. E.; Mu¨nck, E.; Kostka, K. L.; Uffelman, E. S.;
Rickard, C. E. F.; Noon, K. R.; Collins, T. J. Coord. Chem. ReV. 1998,
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(19) Chahbane, N.; Popescu, D.-L.; Mitchell, D. A.; Chanda, A.; Lenoir, D.;
Ryabov, A. D.; Schramm, K.-W.; Collins, T. J. Green Chem. 2007, 9, 49.
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