Po-Kam Lo

Lewis acid-activated oxidation of alcohols by permanganate

The oxidation of alcohols by KMnO(4) is greatly accelerated by various Lewis acids. Notably the rate is increased by 4 orders of magnitude in the presence of Ca(2+). The mechanisms of the oxidation of CH(3)OH and PhCH(OH)CH(3) by MnO(4)(-) and BF(3)·MnO(4)(-) have also been studied computationally by the DFT method.

Functionalization of Alkynes by a (Salen)ruthenium(VI) Nitrido Complex

Exploring new reactivity of metal nitrides is of great interest because it can give insights to N2 fixation chemistry and provide new methods for nitrogenation of organic substrates. In this work, reaction of a (salen)ruthenium(VI) nitrido complex with various alkynes results in the formation of novel (salen)ruthenium(III) imine complexes. Kinetic and computational studies suggest that the reactions go through an initial ruthenium(IV) aziro intermediate, followed by addition of nucleophiles to give the (salen)ruthenium(III) imine complexes. These unprecedented reactions provide a new pathway for nitrogenation of alkynes based on a metal nitride.

Ca2+-Induced Oxygen Generation by FeO42- at pH 9-10

Although FeO4(2-) (ferrate(IV)) is a very strong oxidant that readily oxidizes water in acidic medium, at pH 9-10 it is relatively stable (<2 % decomposition after 1 h at 298 K). However, FeO4(2-) is readily activated by Ca(2+) at pH 9-10 to generate O2. The reaction has the following rate law: d[O2]/dt=kCa [Ca(2+) ][FeO4(2-)](2). (18)O-labeling experiments show that both O atoms in O2 come from FeO4(2-). These results together with DFT calculations suggest that the function of Ca(2+) is to facilitate O-O coupling between two FeO4 (2-) ions by bridging them together. Similar activating effects are also observed with Mg(2+) and Sr(2+).

Highly Selective and Efficient Ring Hydroxylation of Alkylbenzenes with Hydrogen Peroxide and an Osmium(VI) Nitrido Catalyst

The OsVI nitrido complex, OsVI (N)(quin)2 (OTs) (1, quin=2-quinaldinate, OTs=tosylate), is a highly selective and efficient catalyst for the ring hydroxylation of alkylbenzenes with H2 O2 at room temperature. Oxidation of various alkylbenzenes occurs with ring/chain oxidation ratios ranging from 96.7/3.3 to 99.9/0.1, and total product yields from 93 % to 98 %. Moreover, turnover numbers up to 6360, 5670, and 3880 can be achieved for the oxidation of p-xylene, ethylbenzene, and mesitylene, respectively. Density functional theory calculations suggest that the active intermediate is an OsVIII nitrido oxo species.

Oxidation of hydroquinones by a (salen)ruthenium(VI) nitrido complex

Hydroquinone is readily oxidized by a (salen)ruthenium(vi) nitrido complex in the presence of pyridine to give benzoquinone. Experimental and computational studies suggest that the reaction occurs via a novel mechanism that involves an initial electrophilic attack at the aromatic ring of the hydroquinone by the nitrido ligand.

Mechanism of Water Oxidation by Ferrate(VI) at pH 7 - 9

The kinetics of water oxidation by K2 FeO4 has been reinvestigated by UV/Vis spectrophotometry from pH 7-9 in 0.2 m phosphate buffer. The rate of reaction was found to be second-order in both [FeO4 2- ] and [H+ ]. These results are consistent with a proposed mechanism in which the first step involves the initial equilibrium protonation of FeO4 2- to give FeO3 (OH)- , which then undergoes rate-limiting O-O bond formation. Analysis of the O2 isotopic composition for the reaction in H2 18 O suggests that the predominant pathway for water oxidation by ferrate is intramolecular O-O coupling. DFT calculations have also been performed, which support the proposed mechanism.

Proton-Coupled O-Atom Transfer in the Oxidation of HSO3– by the Ruthenium Oxo Complex trans-[RuVI(TMC)(O)2]2+ (TMC = 1,4,8,11-Tetramethyl-1,4,8,11-tetraazacyclotetradecane)

We have previously reported that the oxidation of SO32- to SO42- by a trans-dioxoruthenium(VI) complex, [RuVI(TMC)(O)2)]2+ (RuVI; TMC = 1,4,8,11-tetramethyl-1,4,8,11-tetraazcyclotetradecane) in aqueous solutions occurs via an O-atom transfer mechanism. In this work, we have reinvestigated the effects of the pH on the oxidation of SIV by RuVI in more detail in order to obtain kinetic data for the HSO3- pathway. The HSO3- pathway exhibits a deuterium isotope effect of 17.4, which indicates that O-H bond breaking occurs in the rate-limiting step. Density functional theory calculations have been performed that suggest that the oxidation of HSO3- by RuVI may occur via a concerted or stepwise proton-coupled O-atom transfer mechanism.