138735-98-5Relevant articles and documents
Kinetics of C-H Bond and Alkene Oxidation by trans-Dioxoruthenium(VI) Porphyrins
Ho, Clare,Leung, Wa-Hung,Che, Chi-Ming
, p. 2933 - 2940 (1991)
A series of VILO2> complexes (H2L = para-substituted tetraphenylporphyrins) have been synthesised and characterized, and the kinetics and mechanism of oxidation of the C-H bond and alkenes investigated.The complexes were selective towards tertiary C-H bonds in saturated alkanes but were almost inactive towards secondary C-H bonds.However, they were reactive towards aromatic hydrocarbons and the second-order rate constants (k2) for the oxidation of ethylbenzene and cumene by (tpp = 5,10,15,20-tetraphenylporphyrinate) were 2.21*10-4 and 3.16*10-4 dm3 mol-1 s-1 respectively.A kinetic isotope effect (kH/kD) of 11.7 was found for the allylic oxidation of cyclohexene by .The major organic products of the oxidation of alkenes in CH2Cl2-MeOH mixtures were epoxides and gave a monomeric product formulated as IV(tpp)O>*EtOH or IV(tpp)(OH)2>*EtOH.Similar reactions with VI(oep)O2> (oep = 2,3,7,8,12,13,17,18-octaethylporphyrinate) gave IV(oep)(OH)>2O> in non-co-ordinating solvents.The observed rate law for alkene oxidation was rate = k2VI>.There exists an almost linear free-energy relationship between log k2 and E1/2 (one-electron oxidation potentials of alkenes) with slope = -1.1 V-1 for the system.Activation parameters have been determined for the oxidation of styrene, norbornene and cyclooctene by VILO2>.Non-linear and U-shaped Hammett plots were observed for the oxidation of substituted styrenes.The mechanism of alkene oxidation is proposed to involve a continuum of transition states, the structures of which may change and be stabilized by different substituents.
