- Kinetics and Mechanism of Oxygen Transfer in the Reaction of p-Cyano-N,N-dimethylaniline N-Oxide with Metalloporphyrin Salts. 5. The Influence of Imidazole Ligation of (meso-Tetrakis(2,6-dimethylphenyl)porphinato)manganese(III) Chloride on the Rates of Oxygen Transfer from N-Oxide to...
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Equilibrium constants for mono- and bisligation of imidazole (ImH) with (meso-tetrakis(2,6-dimethylphenyl)porphinato)manganese(III) chloride ((Me8TPP)MnIIICl) have been determined so that the concentrations (dry CH2Cl2) of the three species (Me8TPP)MnIIICl, III(ImH)>Cl, and III(ImH)2>Cl may be calculated at different ImH concentrations.The equilibrium constants for ligation of the one and two imidazoles are K1 = 245 M-1 and β2 = 1.80 x 105 M-2.The reaction of p-cyano-N,N-dimethylaniline N-oxide (NO) with the manganese(III) porphyrin (under the pseudo-first-order conditions of i >> IIICl>i and in the presence and absence of ImH) is first order in both NO and manganese(III) porphyrin, and the rate-controlling step involves oxygen transfer with formation of higher valent manganese-oxo porphyrin species plus p-cyano-N,N-dimethylaniline (DA).From the dependence of the pseudo-first-order rate constants (kobsd) upon i, and a knowledge of the equilibrium constants for imidazole ligation there has been calculated the second-order-rate constants for the kinetic terms k1IIICl>, k2III(ImH)>Cl>, and k3III(ImH)2>Cl>.Comparison of the second-order rate constants (k1 = 3.4 X 10-2 M-1 s-1, k2 = 5.53 M-1 S-1, and k3 = 7.32 X 10-2 M-1 s-1) establishes that ligation by one imidazole increases the rate of reaction of the manganese(III)porphyrin with NO by ca. 166-fold.Bis-imidazole ligated species are blocked to reaction with NO.The higher valent manganese-oxo porphyrin species formed from the reaction of NO with III(ImH)>Cl has been shown to be the principal epoxidizing agent from the dependence of the percentage yield of epoxide upon the concentration of ImH in reactions with cis-cyclooctene using constant initial concentrations of (Me8TPP)MnIIICl and NO.Epoxidation reactions are not rate controlling, and epoxide is formed in competitive processes that involve the reaction of higher valent manganese-oxo porphyrin species with DA (and its oxidation products) and alkene.With exception of the sterically hindered trans-β-methylstyrene, the percentage yield of epoxide at 1.0 M alkene is essentially independent of the type of alkene.Increase in the concentration of alkene and the 1e- oxidizable 2,4,6-tri-tert-butylphenol fails to trap all higher valent manganese-oxo porphyrin species.This result is interpreted as being due to the initial formation of an intimate pair of oxo species and DA with competition between dissociation of DA and oxo species and oxidation of DA within the intimate pair.Epoxidation of alkene by the oxo species occurs after the latter dissociates from the intimate pair.
- Wong, Wah-Hun,Ostovic, Drazen,Bruice, Thomas C.
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p. 3428 - 3436
(2007/10/02)
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- Kinetics and Mechanism of Oxygen Transfer in the Reaction of p-Cyano-N,N-dimethylaniline N-Oxide with Metalloporphyrin Salts. 7. Oxygen Atom Transfer to and from (meso-Tetrakis(pentafluorophenyl)porphinato)iron(III) Chloride
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The decomposition of p-cyano-N,N-dimethylaniline N-oxide (NO) in the presence of (meso-tetrakis(pentafluorophenyl)porphinato)iron(III) chloride ((F20TPP)FeIIICl) provides p-cyano-N,N-dimethylaniline (DA) in 32 +/- 3percent, p-cyano-N-methylaniline (MA) in 50 +/- 5percent, 4-cyano-7-(dimethylamino)-2-benzofuranone-3-spiro-2'-cyano-5'-(dimethylamino)cyclopentadiene (BF) in 16 +/- 2percent, and formaldehyde in 30 +/- 3percent yield based upon (NO)i.Material balance may be accounted for in all components.Appearance of products is first order in both NO and (F20TPP)FeIIICl, and the second-order rate constant for the reaction has been determined to be (2.0 +/- 0.5) x 102 M-1 s-1.The observation that the formation of products DA, MA, and BF is associated with the same rate constant establishes the commitment step to be the bimolecular reaction of NO with (F20TPP)FeIIICl.It is proposed that this reaction directly yields DA and the iron(IV)-oxo porphyrin ?-cation radical ((+.F20TPP)FeIVO).That the formation of (+.F20TPP)FeIVO + DA is rate controlling is substantiated by use of the reagents 2,4,6-tri-tert-butylphenol (TBPH), N,N-dimethylaniline (DMA), and N,N-dimethyltoluidine (DMT) as traps for the (+.F20TPP)FeIVO species.The rates of oxidation of these trapping agents are independent of their concentration, and the rate constants calculated for the appearances of their oxidation products correspond to the turnover rate constant for the reaction of NO with (F20TPP)FeIIICl in the absence of trapping agents.Formation of the products MA and BF must then be attributed to the rapid oxidation of DA by (+.F20TPP)FeIVO.The formation of MA occurs by the oxidative demethylation of DA, and formation of BF is logically accounted for by the hydroxylation of DA to yield 2-hydroxy-4-cyano-N,N-dimethylaniline (DMP) which, on further stepwise oxidation, provides BF (much as in the stepwise 1 e- oxidation of p-cresol to yield Pumerer's ketone).Increase in the concentrations of DMA and DMT results in exponential increase in the percentage yield of DA and decrease in the percentage yield of MA.In each case the asymptotic percentage yields of 68 +/- 7percent DA and 17 +/- 2percent MA are approached.The percentage yield of BF (17 +/- 2percent) is not changed by the presence of DMA or DMT at various concentrations or by their absence.These results show that a substantial portion of the immediate products DA and (+.F20TPP)FeIVO reacts in a solvent-caged /(+.F20TPP)FeIVO*DA/ pair prior to their diffusion apart.Once free from the caged pair, the (+.F20TPP)FeIVO species oxidizes the traps DMA and DMT in preference to DA.The asymptotic yield of MA represents the percentage yield of MA obtained by oxidation of DA within the solvent caged pair.Since the percentage yield of BF is not influenced by the presence of DMA or DMT, all hydroxylation of DA must occur within the /(+.F20TPP)FeIVO*DA/ species.By this reasoning, both the caged oxidative demethylation and hydroxylation of DA occur in ca. 17percent yields.Thus, within the ....
- Ostovic, Drazen,Knobler, Carolyn B.,Bruice, Thomas C.
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p. 3444 - 3451
(2007/10/02)
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- Kinetics and Mechanism of Oxygen Transfer in the Reaction of p-Cyano-N,N-dimethylaniline N-Oxide With Metalloporphyrin Salts. 6. Oxygen Atom Transfer to and from the Iron(III) C2cap Porphyrin of Baldwin
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The decomposition of p-cyano-N,N-dimethylaniline N-oxide (NO) is catalyzed (CH2Cl2 solvent at 25 deg C) by the SbF6- salt of the C2-capped (meso-tetraphenylporphinato)iron(III) of Baldwin ((TPPC2cap)FeIIISbF6).Since neither NO nor the SbF6- anion can fit under the cap, this result establishes that oxygen transfer from NO to the iron(III) center can occur without the intermediate iron(IV)-oxo porphyrin ?-cation being hexacoordinated.The products of NO decomposition (p-cyano-N,N-dimethylaniline (DA) 68percent, p-cyano-N-methylaniline (MA) 12percent, p-cyanoaniline (A) 1percent, N-formyl-p-cyano-N-methylaniline (FA) 6percent, N,N'-dimethyl-N,N'-bis(p-cyanophenyl)hydrazine (H) 7percent, and CH2O 3percent) account for 100percent of p-cyanodimethylaniline moiety of NO, but ca. 40percent of the oxide oxygen of NO remains unaccounted for by product isolation.This is due to some loss of the catalyst and oxidation of the CH2Cl2 solvent during turnover.Oxidation of solvent results in the gradual exchange of the SbF6- axial ligand for Cl-.Product formation on reaction of NO with (TPPC2cap)FeIIISbF6 can be approximated by the first-order rate law.Since the observed first-order rate constants at a given i are a linear function of the iron(III) porphyrin, the reaction is first order in this catalyst and essentially so in NO.However, the finding that the initial rates are independent of i establishes that the iron(III) porphyrin catalyst is saturated with NO on initiation of the reaction.The exchange of Cl- for SbF6- axial ligand and some loss of catalyst during turnovers are responsible for the reactions changing from initial zero order to essentially first order in i.Trapping of the intermediate ((+.TPPC2cap)FeIVO) by the 2,4,6-tri-tert-butylphenol (TBPH), 2,3-dimethyl-2-butene (TME), and p-cyano-N-methylaniline (MA) prevents solvent oxidation and porphyrin oxidative destruction.Under these trapping conditions the reaction is rapid and zero order in NO to completion.That the zero-order kinetics are due to saturation of the 2cap)FeIII>+ catalysts by NO was established by following the time course of the reaction in the Soret and Q spectral regions.The products with TME are TME epoxide (100percent) and DA (100percent) while with TBPH the radical TBP. (100percent) and DA (100percent) are formed.The rate is also increased, but to a lesser extent, when using the poorer substrates, cyclohexene and norbornylene.These substrates also impart a zero-orderness to the appearance of products.The kinetics for the reaction of (TPPC2cap)FeIIISbF6 with NO using TME, TBPH, and MA as substrates have been computer simulated with the requirement of steady-state saturation in the intermediate (TPPC2cap)FeIIION.For successful simulations it is required that both the formation of (+.TPPC2cap)FeIVO + DA from (TPPC2cap)FeIIION and the reaction of (+.TPPC2cap)FeIVO with substrates (i.e., TME, TBPH, and MA) are partially rate limiting.At concentrations of added alkene less than that required for trapping of (+.TPPC2cap)FeIVO there are obtained, ...
- Bruice, Thomas C.,Dicken, C. Michael,Balasubramanian, P. N.,Woon, T. C.,Lu, Fu-Lung
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p. 3436 - 3443
(2007/10/02)
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- The Kinetics and Mechanisms of Oxygen Transfer in the Reaction of p-Cyano-N,N-dimethylaniline N-Oxide with Metalloporphyrin Salts. 4. Catalysis by meso-(Tetrakis(2,6-dimethylphenyl)porphinato)iron(III) Chloride
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meso-(Tetrakis(2,6-dimethylphenyl)porphinato)iron(III) chloride ((Me8TPP)Fe(III)Cl) is a catalyst for the conversion of p-cyano-N,N-dimethylaniline N-oxide (NO) to p-cyano-N,N-dimethylaniline (DA), p-cyano-N-methylaniline (MA), p-cyano-N-formyl-N-methylaniline (FA), p-cyanoaniline (A), N,N'-dimethyl-N,N'-bis(p-cyanophenyl)hydrazine (H), N,N'-bis(p-cyanophenyl)-N-methylmethylenediamine (MD), and CH2O.All evidence supports these reactions to occur by equilibrium ligation of NO to iron(III) porphyrin followed by rate-detrmining oxygen transfer to yields as intermediate products DA and the iron(IV)-oxo porphyrin ?-cation radical.Stepwise oxidation of DA by the higher valent iron-oxo porphyrin species is responsible for the formation of the other products (i.e., DA-->-->FA, DA-->MA-->A, 2MA-->MD, and 2MA-->H).The oxidation potentials of (Me8TPP)Fe(III)OCH3 are comparable to those of the unsubstituted meso-(tetraphenylporphinato)iron(III) methoxide ((TPP)Fe(III)OCH3).The following results are, therfore, not surprising: (i) The second-order rate constant (kakb/k-a) for reaction of (Me8TPP)Fe(III)Cl with NO is but 3.3-fold smaller than in the case of the reaction of NO with (TPP)Fe(III)Cl; (ii) the percentage yields of products (DA, 53percent; MA, 24percent; A, 3percent; FA, 8percent; H, 7percent; MD, 5percent) are comparable to when (TPP)Fe(III)Cl is employed; and (iii) oxidation and epoxydation of added substrates are not rate-determining.Of considerable interest is the finding that epoxidation reactions using NO with (Me8TPP)Fe(III)Cl occur in much higher yield (80percent to 100percent) than when (TPP)Fe(III)Cl is used as the catalyst.
- Woon, T. C.,Dicken, C. Michael,Bruice, Thomas C.
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p. 7990 - 7995
(2007/10/02)
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- Kinetics and Mechanisms of Oxygen Transfer in the Reaction of p-Cyano-N,N-Dimethylaniline N-Oxide with Metalloporphyrin Salts. 3. Catalysis by iron(III) Chloride
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Decomposition of p-cyano-N,N-dimethylaniline N-oxide (NO) catalyzed by iron(III) chloride ((Cl8TPP)FeIIICl) yields as products p-cyano-N,N-dimethylaniline (DA), p-cyano-N-methylaniline (MA), and formaldehyde (CH2Cl2 solvent, 25 deg C, N2 atmosphere).Intermediate in the reaction are mono and bis NO complexes (Cl8TPP(Cl)FeIIINO and Cl8TPP(NO)FeIIINO, respectively).Oxygen transfer from the complexed NO species to the iron porphyrin is rate-limiting and provides the higher valent iron(IV) salts (IVO>+. and IVO>+.) and DA.The observed kinetics for reactions involving 10-100 turnovers of catalyst dictate that the catalyst is saturated in the formation of Cl8TPP(Cl)FeIIINO and that formation of Cl8TPP(NO)FeIIINO is unfavorable.The two iron(IV)-oxo porphyrin ?-cation radical species are converted back to the iron(III) porphyrin catalytic moieties by oxidation of DA -> MA + CH2O and oxidation of CH2O.Addition of 2,4,6-tri-tert-butylphenol (TBPH), 2,3-dimethyl-2-butene (TME), and cyclohexene results in the formation of TBP. and the respective epoxides, thus inhibiting the oxidation of DA and CH2O.The kinetics of the overall reaction and formation of each product may be simulated by employing the reactions of Scheme II and eq l-r, and from the simulations, the rates and equilibria, leading to the formation of the two iron(IV)-oxo porphyrin ?-cation radical species may be determined as can minimal rate constants for the oxidations of DA, CH2O, and TBPH and the epoxidation of TME and cyclohexene.The results obtained herein with the electron-deficient porphyrin, (Cl8TPP)Fe(III)Cl, are discussed and compared to those obtained previously when employing (TPP)FeIIICl as the catalyst.
- Dicken, C. Michael,Woon, T. C.,Bruice, Thomas C.
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p. 1636 - 1643
(2007/10/02)
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- Kinetics and Mechanisms of Oxygen Transfer in the Reaction of p-Cyano-N,N-dimethylaniline N-Oxide with Metalloporphyrin Salts. 2. Amine Oxidation and Oxygen Transfer to Hydrocarbon Substrates Accompanying the Reaction of p-Cyano-N,N-dimethylaniline N-Oxide with meso-(Tetraphenylporphi...
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The catalysis of the decomposition of p-cyano-N,N-dimethylaniline N-oxide (NO) with meso-(tetraphenylporphinato)iron(III) chloride IIICl> has been studied at 25 deg C in CH2Cl2 with i = 5.0E-4 to 8.0E-3 M > IIICl>i = 3.0E-5 to 5.0E-4 M.The iron(III) porphyrin catalyst was shown to be unaltered in catalytic efficiency to 120 turnovers (the highest examined).The influence of O2 and the purity of solvent upon the kinetics of the reactions and products obtained have been assessed.In the absence of an oxidizable substrate, NO gives way to the following products: p-cyano-N,N-dimethylaniline (DA), 52percent yield; p-cyano-N-methylaniline (MA), 25percent yield; N-formyl-p-cyano-N-methylaniline (FA), 4percent yield; p-cyanoaniline (A), 2percent yield; N,N'-dimethyl-N,N'-bis(p-cyanophenyl)hydrazine (H), 12percent yield; N,N'-bis(p-cyanophenyl-N-methylmethylenediamine (MD), 6percent yield; and CH2O, 11percent yield.The major portion of the products (i.e., DA, MA, H and MD) absorb appreciably at 320 nm where absorbance by (TPP)FeIIICl is minimal.The formation of products was followed spectrophotometrically at 320 nm and by HPLC at 280 and 320 nm.Both means were found to be in quantitative agreement.Spectral monitoring of the increase in A320 showed that the first-order decomposition of the N-oxide was independent of i but increases with an increase in IIICl>i.The appearance of DA, MA, FA, MD, and CH2O also followed the first-order rate law, while the formation of the products H and A are characterized by a lag period followed by a constantly accelerated formation ending abruptly with the consumption of the N-oxide.Of the various products, only A exhibited inhibition of the kinetics for decomposition of N-oxide by (TPP)FeIIICl.At the concentration formed in the kinetic experiment, however, A is not inhibiting.The rate constant for "oxygen" transfer from NO to (TPP)FeIIICl to form IV=O>+. was determined by trapping this species with 2,4,6-tri-tert-butylphenol (TBPH).In the presence of TBPH trap, DA is formed in 100percent yield, showing that the other decomposition products of the N-oxide arise via stepwise oxidation of DA by IV=O>+..An intermolecular deuterium kinetic isotope effect of unity was obtained by comparison of the initial rate contants for the reactions of p-NCC6H4N+(CH3)2O-/p-NCC6H4N+(CD3)2O-.A discriminatory intramolecular deuterium isotope effect of 4.5 was observed when p-NCC6H4N+(CH3)(CD3)O- was used and the formation of p-NCC6H4NH(CD3)/p-NCC6H4NH(CH3) was monitored.The isotope effects are in agreement with the finding that rate-determining oxygen transfer from NO to (TPP)FeIIICl is followed by demethylation of DA.A variety of alkenes and cyclohexane are shown to compete with DA as substrates.With these, the yields of epoxidation and/or hydroxylation products are comparable to those reported previously when iodosylbenzene was used as the oxygen source under similar conditions.The stereospecifity seen with iodosylbenzene is also evidenced with NO.At 1.0 M 2,3-dimeth...
- Dicken, C. Michael,Lu, Fu-Lung,Nee, Michael W.,Bruice, Thomas C.
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p. 5776 - 5789
(2007/10/02)
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- Photobenzidine Rearrangements. 7. Disproportionation and Recombination of N-Methylarylamino Radicals in the Photodecomposition of 1,4-Bis(p-cyanophenyl)-1,4-dimethyl-2-tetrazene and Other 2-Tetrazenes
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The photochemical decomposition of 1,4-bis(p-cyanophenyl)-1,4-dimethyl-2-tetrazene (1c) in 1,2-dimethoxyethane (DME) was studied in detail.It was deduced that N-methyl-p-cyanoanilino radicals are formed and undergo three reactions: recombination into 1,2-bis(p-cyanophenyl)-1,2-dimethylhydrazine (2c, 21 percent), disproportionation (70 percent) into N-methyl-p-cyanoaniline (3c) and N-methylene-p-cyanoaniline (4c), and hydrogen atom abstraction (7 percent).A small amount of a p-semidine is thought to be formed also.These deductions were made from quantitative high-pressure LC measurements of yields of 2c, 3c, p-cyanoaniline (5c), and formaldehyde, the last two products arising from hydrolysis of 4c.Quantitative measurement of the conversion of 4c into 3c by hydrogenation and by trapping of radicals with butyl mercaptan was also used.Approximately 10 percent of 2e is formed in a solvent cage.Disproportionation also appears to occur within the cage.Less detailed studies were carried out with 1,4-diphenyl-1,4-dimethyl-2-tetrazene (1d) and 1,4-bis(p-bromophenyl)-1,4-dimethyl-2-tetrazene (1e).Decomposition of 1d led to 40 percent of N,N'-dimethyldiphenylhydrazine (2d, 10 percent in cage) and 40 percent of disproportionation products.The remaining 20 percent of the 1d is thought to form a p-semidine (N,N'-dimethyl-N-phenyl-1,4-benzenediamine) and the dibenzocarbazole related to it.Radicals from the decomposition of 1e led to 37 percent of 1,2-bis(p-bromophenyl)-1,2-dimethylhydrazine (2e, 10 percent in cage), 47 percent of disproportionation, and 16 percent of hydrogen abstraction.
- Bae, Dong Hak,Shine, Henry J.
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p. 4700 - 4704
(2007/10/02)
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