J. Am. Chem. SOC.1985, 107, 512-513
512
limit, P-MoZCl4(dmpe),displays a '(6 6*) transition at 12500 sufficient to supply the water molecules for the disproportionation cm-l, only 4700 cm-' red shifted from that of M O ~ C ~ ~ ( P M ~ reaction.) ~)~. Thus, CICr'I'TPP may be used as a trap for O= CrV(C1)TPP. The rapid trapping of the chromium(V) species by The sum of this red shift and the 3(&3*) energy of @-MozC14( d m ~ e ) -5200 ~, cm-I (15 kcal/mol), which approximates the the chromium(II1) species has allowed us to study oxygen transfer position of the 3(6S*) state of Mo2CI4(PMe3),(Figure 3), is an from percarboxylic acids and hydroperoxides to CICr"'TPP (eq experimental measure of the &bond component of the barrier to 2). rotation about a quadruple bond. ROOH + C1Cr"'TPP ROH + O=CrV(C1)TPP (2a) Acknowledgment. This research was supported by National k2 Science Foundation Grant CHE8 1-20419. Magnetic susceptibility CICr'I'TPP f ~ 2 20=CrIVTPP 0 + 2HCl O=CrV(C1)TPP measurements were made at the University of Southern California (2b) SQUID Instrumentation Facility (supported by NSF Grant The kinetics of the reactions of percarboxylic acids and hyCHE82-11349). M.D.H. and T.C.Z. acknowledge graduate droperoxides with CICr'I'TPP were carried out in CHzC12(25 OC, fellowships from the Sun Co. Nz atmosphere), under the pseudo-first-order conditions of Registry No. Mo2CI,(PMe3),, 67619-17-4; @-M~,Cl,(dmpe)~, 851 15[ROOH] >> [CICrl"TPP]. The reactions were monitored by 86-2. observing the decrease in C1Cr'"TPP at 446 nm and were found to follow the first-order rate law to 6 to 7 half-lives. Plots of initial [ROOH] vs. the determined pseudo-first-order rate constant (koM) Mechanism of "Oxygen Atom" Transfer to were linear. The slopes of such plots provided the second-order rate constants kRooH of eq 2a. In Figure 1 there is plotted the (Tetrapheny1porphinato)chromic Chloride log kRooH values for the reaction of ROOH species with CILung-Chi Yuan and Thomas C. Bruice* Cr'I'TPP vs. the pK, of ROH. The lack of a break in the plot Department of Chemistry, University of California is in accord with consistency of mechanism for species of great at Santa Barbara, Santa Barbara, California 931 06 monooxygen-donation potential (m-CIC6H4C03H)and little oxygen-donation potential (t-BuOOH). That this mechanism inReceived July 9, 1984 volves RO-OH bond heterolysis follows from the recovery of Herein are described results obtained in a study of the reaction >90% phenylacetic acid (as methyl ester with CHzN,) when of C1Cr"'TPP with a variety of oxygen-donor molecules. This ROOH is phenylperacetic acid. Homolysis would yield phenyinvestigation is an extension of studies of oxygen transfer from lacetoxyl radical which decarboxylates rapidly." aniline N-oxides to (porphinato)Fe"'X and (porphinato)Mn"'X The log of the second-order rate constants (kNuc)for heterosalts'-3 and to cytochrome P-450 enzyme^.^ The objectives of lytic-nucleophilic cleavage of the 0-0 bond of a series of hythe present study are to ascertain the effect of donor structure droperoxides and percarboxylic acids [ ROOH] have previously on the ease and the mechanism of oxygen transfer. been shown to be a linear function (PI, = -0.6) of the pK, of the The reaction of iodosylbenzene with C1Cr"'TPP is not well leaving groups (ROH) when the nucleophilic species are thioxane, In this study, the reaction of C1Cr"'TPP with N,N-dimethylbenzylamine, and I-.1o The reaction of C1Cr"'TPP PhIO was initiated (spectral grade dichloromethane, 25 OC, N2 with ROOH follows the same linear free energy relationship with atmosphere) by mixing various volumes of a freshly prepared PI, = -0.34. If one wishes to ignore the difference in solvent for solution saturated in PhIO with a solution of C1Cr"'TPP (1 X nucleophilic attack by I-, : N f , :S< (t-BuOH) and by C1Cr"'TPP M). As the ratio of PhIO/C1Cr1"TPP, present at the time (CH2C1,), though probably not wise, one would conclude that 0-0 of mixing, was increased from 1 to 20 the Soret band of the bond cleavage has not proceeded as far in the transition state in product was found to shift from 429 (O=Cr'VTPP) to 415 nm the instance where the Cr"' moiety of C1Cr"'TPP is the nucleo(O=CrV(Cl)TPP). Thus, at high concentrations of PhIO relative phile. With the percarboxylic acids the product is a mixture of to ClCr'I'TPP, there is obtained as product O=CrV(C1)TPP. An porphinato Cr" and CrV species, whereas with all the hydroinvestigation of the kinetics of the reaction was not attempted due peroxides the A,, of the Soret peak at t, corresponds to the Cr" to the known polymeric nature of PhIO e t c 9 Nevertheless, it species. This result is as should be expected from the results with would appear that the logical explanation for these experimental iodosylbenzene. As the pK, of ROH increases the ease of oxyresults is found in eq 1 . When the product kl [PhIO] is sufficiently gen-oxygen bond breaking in R M H decreases as does the value ki kRooHIROOH] (eq 2a) and this allows the term k2[0=CrvPhI=O C1Cr"'TPP PhI O=CrV(C1)TPP ( l a ) (Cl)TPP] to compete for the C1Cr"'TPP species to yield O= k2 Cr'VTPP. O=CrV(C1)TPP C1Cr"'TPP 20=CrIVTPP + 2HCl 2-(Phenylsulfonyl)-3-(p-nitrophenyl)oxaziridine (Oxa) has been (1b) employed in the epoxidation of alkenes12 (60 OC, CHCI,) and on this basis would appear as a worthy agent to explore as an oxygen large, all C1Cr"'TPP is converted into O=CrV(C1)TPP. At lower donor to metalloporphyrins. The kinetics of reaction of Oxa (1.9 concentrations of PhIO the oxidant O=CrV(C1)TPP competes X 1 r 2to 1.9 X M) with C1Cr"'TPP (1.3 X M) to provide with PhIO for C1Cr"'TPP and a disproportionation reaction enslies O=CrIVTPP were followed at 429 nm (CH2CI2,20 "C). Reto yield O=CrIVTPP. (Traces of moisture in the solvent were actions were first order to at least 6 half-lives and plots of kobsd vs. [Oxa] were linear with slope 8.25 M-' s-l. The appearance ( 1 ) Shannon, P.; Bruice, T. C. J . Am. Chem. SOC.1981, 103, 4500. (2) Nee, M. W.; Bruice, T. C. J . Am. Chem. SOC.1982, 104, 6123. of O=CrIVTPP rather than O=CrV(C1)TPP as product is ex(3) Powell, M. F.; Pai, E. F.; Bruice, T. C. J . Am. Chem. SOC.1984, 106, pected since the rate constant is but -2 times greater than that 3277 ._ for the reaction of triphenylmethyl hydrogen peroxide with (4) Heimbrook, D. C.; Murray, R . I.; Egeberg, H. D.; Sligar, S. G.; Nee, ClCr'I'TPP (Figure 1). M . W .; Bruice, T. C. J . Am. Chem. SOC.1984, 106, 1514. Though p-cyano-N,N-dimethylaniline N-oxide @-CNDMA( 5 ) Groves, J. T.; Haushalter, R. C. J . Chem. SOC.,Chem. Commun.1981, 1165. Groves, J. T.; Kruper, W. J., Jr. J . Am. Chem. SOC.1979, 101,7613. NO) is comparable to PhIO as an oxygen donor to ClFeII'TPP (6) Budge, J. R.; Gatehouse, B. M. K.; Nesbit, M. C.; West, B. 0. J . in the epoxidation of alkenes,2it does not react with CICr"'TPP Chem. SOC.,Chem. Commun. 1981, 370. (25 OC, CHzC12solvent, N z atmosphere). With photoexcitation (7) Buchler, J. W.; Lay, K. L.; Castle, L.; Ullrick, V. Inorg. Chem. 1982, 21. 842. of the reaction mixture, p-CNDMANO does transfer an oxygen (8) Groves, J . T.; Kruper, W. J., Jr.; Haushalter, R. C.; Butler, W. M. to yield O=CrTVTPP.The photoreaction is presumably associated -+
-
+
-
+
+
+
3
Inorg. Chem. 1982, 21, 1363. (9) Bell, R.; Morgan, K. J. J . Chem. SOC.1960, 1209. (10) Bruice, T. C. J . Chem. SOC.,Chem. Commun.1983, 14. Bruice, T. C.; Noar, J. B.; Ball, S. S.; Venkataram, U. V. J . A m . Chem. SOC.1983, 105, 2452.
0002-7863/85/1507-0512$01.50/0
(11) Bartlett, P. D.; Ruchardt, C. J . Am. Chem. SOC.1960, 82. 1756. (12) Davis, F. A.; Abdul-Malik, N. F.; Awad, S. B.; Harakal, M . E. Tetrahedron Lett. 1981, 22, 917.
0 1985 American Chemical Society
J. Am. Chem. SOC.1985, 107, 513-514
513
CH3-(CH )
-C03H
1
D
D 0
0.8-
-J
Ph3COOH
-\
CH3-C-OOH I
12
7
2
17
ROH
12
8
4
16
ROH Figure 1. A plot of the log of the second-order rate constants for the reaction CICr"'TPP with percarboxylic acids and hydroperoxides (kROOH) vs. the pK, of the carboxylic acid and alcohol leaving groups (see eq 2a). pK,
with a high 9. Thus, with diffuse room fluorescent lighting a solution containing [p-CNDMANO] = 2.38 X M and [ClCr"'TPP] = 1.34 X M provides O=CrlVTPP in >95% yield in just a few minutes. The reactions of p-CNDMANO with chromium TPP species will be considered in greater detail in a full paper. Acknowledgment. This work was supported by the National Institutes of Health. Registry No. Oxa, 86428-23-1; m-CPBA, 937-14-4; p-CNDMANO, 62820-00-2;CH3(CH2),,CO3H, 2388-12-7;Ph,C(CO,Me)OOH, 57272-44-3;Ph,C(CN)OOH, 5233-67-0;Ph,COOH, 4198-93-0;(CH,),COOH, 75-91-2;HzOZ,7722-84-1;(tetrapheny1porphinato)chromic chloride, 281 10-70-5;iodosylbenzene, 536-80-1.
Figure 1. Plot of log kRooH vs. pK, of corresponding ROH. The reactions were studied under an argon atmosphere in spectral grade methanol employing collidine buffer at pH 6.5 ([collidine]/[collidine.HCI] = 0.126). kRooH was determined from the intercept of plots of kobidvs. [collidine] at zero collidine buffer concentration. Values of kRooHso determined are in close agreement with rate constants determined in methanol without buffer present. [CIFe"'TPP] = (0.15-1.5)X M; [TBPH] = 0.1-0.3M; [ROOH] = (0.2-1.5)X IO-' M; T = 30 "C.
Table I. Second-Order Rate Constants for Oxygen Transfer to M) by Non-Peroxidic Oxygen Donor CIFeII'TPP (1.5 X Molecules (IO-, M) ( T = 30 "C)
iodosobenzenediacetate p-cyano-N,N-dimethylaniline N-oxide 2-(phenylsulfonyl)-3-(p-nitrophenyljoxaziridine
(3.2f 0.1) x 103 12 f 3 (7.5 k 0.1) X lo-'
as oxygen donors to the ferric state of cytochrome P-450. The question as to whether heterolysis (eq l a ) or homolysis (eq 1 b)
+ ROOH F? PFe"'-O-OR H PFe"' + ROOH e PFe"'-O-OR H
PFe"'
-
+ ROH ( l a ) PFe'"-O(H) + RO-
PFeV=O
-
(1b)
Homolytic and Heterolytic Oxygen-Oxygen Bond Scissions Accompanying Oxygen Transfer to Iron(111) Porphyrins by Percarboxylic Acids and Hydroperoxides. A Mechanistic Criterion for Peroxidase and Cytochrome P-450 William A. Lee and Thomas C. Bruice*
Department of Chemistry, University of California at Santa Barbara, Santa Barbara, California 931 06 Received July 9, 1984 The monooxygenase enzymes are of current interest to biochemists and pharmacologists, as well as to organic and inorganic chemists. The cytochrome P-450 enzymes have received most of the attention because of their key roles in metabolism, their inducibility by xenobiotics, and their ability to catalyze specific oxidation reactions that are not easily reproduced in purely chemical A variety of peracids and alkyl hydroperoxides have been used (1) White, R. E.;Coon, M. J. Annu. Reo.. Biochm. 1980, 49, 315-356. (2)Guengerich, F.P.;MacDonald, T. L. Acc. Chem. Res. 1984, 17, 9-16.
0002-7863/85/ 1507-05 13$01.50/0
[ P = porphyrin] occurs in these reactions is of particular c o n c e ~ n . ~ - ' ~ We have attempted a comparative evaluation of the secondorder r a t e constants for oxygen transfer t o (tetrapheny1porphyrin)iron chloride (C1Fe"'TPP) from a series of peracids and hydroperoxides. An ideal method to study these reactions employs 2,4,6-tri-tert-butylphenol(TBPH) to trap the reactive intermediate formed (eq 2) and has been offered by
PFe"'
+ ROOH 7
[PFeV=O
~RCOH
TBPH + R O H or PFeIV-0(H) + RO.] 7 2TBP. + R O H + PFe"' (2)
Traylor et al.'l~14The reactions were shown to be first order in
(3) Kadlubar, F. F.;Morton, K. C.; Ziegler, D. M., Biochem. Biophys. Res. Commun. 1973, 54, 1255-1261. (4) Nordblom, G. D.;White, R. E.; Coon, M. J. Arch. Biochem. Biophys. 1976, 175, 524-533. ( 5 ) Blake, R. C.; Coon, M. J. J . B i d . Chem. 1980, 255, 4100-4111. (6)Hamilton, G.A. In "Molecular Mechanisms of Oxygen Activation"; Hayaishi, 0.. Ed.; Academic Press: New York, 1974;pp 405-451. (7) Blake, R. C.; Coon, M. J. J . Biol. Chem. 1981, 25'6, 12127-12133.
0 1985 American Chemical Society
