TY - JOUR
T1 - Fast catalytic hydroxylation of hydrocarbons with ruthenium porphyrins
AU - Wang, Chuanqing
AU - Shalyaev, Kirill V.
AU - Bonchio, Marcella
AU - Carofiglio, Tommaso
AU - Groves, John Taylor
PY - 2006/6/12
Y1 - 2006/6/12
N2 - Ruthenium porphyrin complexes such as carbonylruthenium(II) tetrakispentafluorophenylporphyrin [RuII(TPFPP)-(CO)] were found to be efficient catalysts for the hydroxylation of alkanes in the presence of 2,6-dichloropyridine N-oxide as the oxidant under mild, nonacidic conditions. Up to 14 800 turnovers (TO) and rates of 800 TO/min were obtained for the hydroxylation of adamantane. The hydroxylation of cis-decalin afforded cis-9-decalol and cis-decalin-9,10-diol, exclusively, thus, excluding a long-lived radicals mechanism. The kinetics of product evolution in a typical catalytic oxygenation showed an initial induction period followed by a fast, apparently zero-order phase with maximum rates and high efficiencies. Deuterium isotope effects (KH/kD) in the range of 4.2-6.4 were found for the hydroxylation of alkanes. A Hammett treatment of the data for the oxidation of para-substituted toluene derivatives showed a linear correlation with a highly negative ρ+ value of -2.0. On the basis-of kinetic and spectroscopic evidence, RuVI(TPFPP)(O)2, Ru II(TPFPP)(CO), and RuIV(TPFPP)Cl2 observed during catalysis were ruled out as candidates for the active catalyst responsible for the high efficiencies and turnover rates in the oxidation reactions. The fastest rates of adamantane hydroxylation with 2,6-dichloropyridine N-oxide were achieved by the reductive activation of RuIV(TPFPP)Cl2 with a zinc amalgam. This redox activation is consistent with the formation of an active Ru(III) intermediate in situ by a one-electron reduction of the Ru(IV) porphyrin. EPR spectra characteristic of Ru(III) have been observed upon the reduction of RuIV(TPFPP)Cl 2 with a zinc amalgam. In the adamantane oxidation mediated with RuIII(TPFPP)(OEt), it was found that, during this process, the Ru(III) porphyrin was gradually converted to a dioxoRu(VI) porphyrin. Concomitant with this conversion, the reaction rates decreased. Catalyst activation was also stimulated by autoxidation of the solvent CH 2Cl2. On the basis of these data, a mechanism is proposed that incorporates a "fast" cycle involving metastable Ru(III) and oxoRu(V) intermediates and a "slow" oxidation cycle, mediated by oxoRu(IV) and trans-dioxoRu(VI) porphyrin complexes.
AB - Ruthenium porphyrin complexes such as carbonylruthenium(II) tetrakispentafluorophenylporphyrin [RuII(TPFPP)-(CO)] were found to be efficient catalysts for the hydroxylation of alkanes in the presence of 2,6-dichloropyridine N-oxide as the oxidant under mild, nonacidic conditions. Up to 14 800 turnovers (TO) and rates of 800 TO/min were obtained for the hydroxylation of adamantane. The hydroxylation of cis-decalin afforded cis-9-decalol and cis-decalin-9,10-diol, exclusively, thus, excluding a long-lived radicals mechanism. The kinetics of product evolution in a typical catalytic oxygenation showed an initial induction period followed by a fast, apparently zero-order phase with maximum rates and high efficiencies. Deuterium isotope effects (KH/kD) in the range of 4.2-6.4 were found for the hydroxylation of alkanes. A Hammett treatment of the data for the oxidation of para-substituted toluene derivatives showed a linear correlation with a highly negative ρ+ value of -2.0. On the basis-of kinetic and spectroscopic evidence, RuVI(TPFPP)(O)2, Ru II(TPFPP)(CO), and RuIV(TPFPP)Cl2 observed during catalysis were ruled out as candidates for the active catalyst responsible for the high efficiencies and turnover rates in the oxidation reactions. The fastest rates of adamantane hydroxylation with 2,6-dichloropyridine N-oxide were achieved by the reductive activation of RuIV(TPFPP)Cl2 with a zinc amalgam. This redox activation is consistent with the formation of an active Ru(III) intermediate in situ by a one-electron reduction of the Ru(IV) porphyrin. EPR spectra characteristic of Ru(III) have been observed upon the reduction of RuIV(TPFPP)Cl 2 with a zinc amalgam. In the adamantane oxidation mediated with RuIII(TPFPP)(OEt), it was found that, during this process, the Ru(III) porphyrin was gradually converted to a dioxoRu(VI) porphyrin. Concomitant with this conversion, the reaction rates decreased. Catalyst activation was also stimulated by autoxidation of the solvent CH 2Cl2. On the basis of these data, a mechanism is proposed that incorporates a "fast" cycle involving metastable Ru(III) and oxoRu(V) intermediates and a "slow" oxidation cycle, mediated by oxoRu(IV) and trans-dioxoRu(VI) porphyrin complexes.
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U2 - 10.1021/ic0520566
DO - 10.1021/ic0520566
M3 - Article
C2 - 16749842
AN - SCOPUS:33745630936
SN - 0020-1669
VL - 45
SP - 4769
EP - 4782
JO - Inorganic Chemistry
JF - Inorganic Chemistry
IS - 12
ER -