79121-26-9Relevant articles and documents
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...
Wong, Wah-Hun,Ostovic, Drazen,Bruice, Thomas C.
, p. 3428 - 3436 (2007/10/02)
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.
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
Bruice, Thomas C.,Dicken, C. Michael,Balasubramanian, P. N.,Woon, T. C.,Lu, Fu-Lung
, p. 3436 - 3443 (2007/10/02)
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, ...
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
Dicken, C. Michael,Woon, T. C.,Bruice, Thomas C.
, p. 1636 - 1643 (2007/10/02)
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.
