94890-04-7Relevant articles and documents
Intermediates in the Epoxidation of Alkenes by Cytochrome P-450 Models. 3. Mechanism of Oxygen Transfer from Substituted Oxochromium(V) Porphyrins to Olefinic substrates
Garrison, J. Mark,Bruice, Thomas C.
, p. 191 - 198 (2007/10/02)
Studies were initiated with the following chromium(IV) oxo porphyrin species: chromium(IV) oxide ((TPP)Cr(IV)(O)), chromium(IV) oxide ((Me12TPP)Cr(IV)(O)), chromium(IV) oxide ((Cl8TPP)Cr(IV)(O)), chromium(IV) oxide ((F8TPP)Cr(IV)(O)), and chromium(IV) oxide ((F20TPP)Cr(IV)(O)).Cyclic voltammetric (CH2Cl2, V, SCE) 1e oxidationpotentials for the couples (Porph)Cr(IV)(O)/(Porph)Cr(V)(O)(ClO4) have been determined 12TPP)Cr(IV)(O), 0.825; (Cl8TPP)Cr(IV)(O), 0.895; (F8TPP)Cr(IV)(O), 0.975; (F20TPP)Cr(IV)(O), chemically irreversible>.Standard solutions of (TPP)Cr(V)(O)(ClO4), (Me12TPP)Cr(V)(O)(ClO4), (Cl8TPP)Cr(V)(O)(ClO4), and (F8TPP)Cr(V)(O)(ClO4) were obtained by controlled-potential bulk electrolysis of the corresponding chromium(IV) oxo porphyris, and these solutions were employed in kinetic and product studies of the oxidation of a number of alkenes (CH2Cl2 solvent; 30 deg C).Under the pseudo-first-order condition of >> , the following reactions have been show to take place: (i) (Porph)Cr(V)(O)(ClO4)+alkene --> (Porph)Cr(III)(X)+epoxide (k1); (ii) (Porph)Cr(V)(O)(ClO4)+(Porph)Cr(III)(X) (Porph)Cr(IV)(O)+(Porph)Cr(IV)(X) (k2/k3); and (iii) spontaneous conversion of (Porph)Cr(V)(O) to (Porph)Cr(IV)(O) possibly by oxidation of solvent or supporting electrolyte (k4).The reversibility (k2/k3) of (ii) must be related to the formation of two different chromium(IV) porphyrinspecies, one of which is stabilized by oxo axial ligation ((Porph)Cr(IV)(O)) and one of which is not ((Porph)Cr(IV)(X); where X=Cl(-) or ClO4(-)).This is supported by the observation that the spectrum of (Me12TPP)Cr(IV)(O) remains unchanged in CH2Cl2 solutions of norbornene.Values of the second-order rate constants (k1) for alkene epoxidations were determined by both the slopes of plots of vs the pseudo-first-order rate constants (kobsd) for disappearance of and by computer simulation of the time courses for disappearance and appearance of the species (Porph)Cr(V)(O)(ClO4), (Porph)Cr(III)(X), and (Porph)Cr(IV)(O) according to reactions (i)-(iii).The two methods provided like values of k1.Values of k1 (M-1 s-1), determined from dependence of kobsd on , for reactions with (Me12TPP)Cr(V)(O)(ClO4) are the following: 5.4x1E-2, norbornene; 8.78x1E-4, cis-cyclooctene; 6.82x1E-3, cis-stilbene; and 5.19x1E-13, cyclohexene.With (Cl8TPP)Cr(V)(O)(ClO4) the values of k1 (M-1 s-1) are 9.56x1E-1 for norbornene and 2.13x1E-2 for cis-cyclooctene.Use of computer simulation of...
Oxochromium compounds. 2. Reaction of oxygen with chromium(II) and chromium(III) porphyrins and synthesis of a μ-oxo chromium porphyrin derivative
Liston, David J.,West, Bruce O.
, p. 1568 - 1576 (2008/10/08)
The reaction of oxygen with Cr(II) porphyrin complexes in solution has been found to result in the formation of CrIVO(P) compounds when oxygen is in excess. Solid CrII(P) also react irreversibly with oxygen, and the products dissolve in toluene to form CrIVO(P). The complex (TPP)CrOCr(TPP) has been isolated from the reaction of CrO(TPP) and CrII(TPP) and shown to undergo further reaction with oxygen to give CrO(TPP). The complex shows an IR absorption at 860 cm-1, considered to indicate the presence of the CrOCr linkage, and has μeff = 1.61 μB per Cr at 300 K, indicating substantial antiferromagnetic coupling. Similar μ-oxo complex formation has been demonstrated spectroscopically between other CrO(P)/Cr(P′) combinations where P and P′ may be the same or different. (P)CrOCr(P) complexes can be detected as intermediates in the reaction of CrII(P) with oxygen when the amount of oxygen is restricted. CrIII(P)Cl also reacts with oxygen in chloroform in the presence of HCl to give intermediates that are converted to CrIVO(P) in the presence of basic alumina. A Cr-porphyrin π-cation radical is proposed as the intermediate.
