ABSTRACT
Manganese catalysts that activate hydrogen peroxide carry out several different hydrocarbon oxidation reactions with high stereoselectivity. The commonly proposed mechanism for these reactions involves a key manganese(III)-hydroperoxo intermediate, which decays via O-O bond heterolysis to generate a Mn(V)-oxo species that institutes substrate oxidation. Due to the scarcity of characterized MnIII-hydroperoxo complexes, MnIII-alkylperoxo complexes are employed to understand factors that affect the mechanism of the O-O cleavage. Herein, we report a series of novel complexes, including two room-temperature-stable MnIII-alkylperoxo species, supported by a new amide-containing pentadentate ligand (6Medpaq5NO2). We use a combination of spectroscopic methods and density functional theory computations to probe the effects of the electronic changes in the ligand sphere trans to the hydroxo and alkylperoxo units to thermal stability and reactivity. The structural characterizations for both MnII(OTf)(6Medpaq5NO2) and [MnIII(OH)(6Medpaq5NO2)](OTf) were obtained via single-crystal X-ray crystallography. A perturbation to the ligand sphere allowed for a marked increase in reactivity towards an organic substrate, a modest change in the distribution of the O-O cleavage products from homolytic and heterolytic pathways, and little change in thermal stability.
ABSTRACT
We have synthesized and characterized the monomeric diiminophosphinate-stabilized Groupâ 13 metal(I) complexes [Dip LE:], Dip L=Ph2 P(NDip)2 , Dip=2,6-iPr2 C6 H3 ; E=Ga (1), In (2) and Tl (3). In addition, we structurally characterized the dimeric complex [(Dip LGa)2 ], 12 . Similar synthetic attempts using Mes L=Ph2 P(NMes)2 , Mes=2,4,6-Me3 C6 H2 afforded product mixtures from which the mixed oxidation state species [(Mes L)3 Ga4 I3 ] 4 was isolated. [Dip LGa:] 1 is converted with dry air to the gallium(III) oxide species [(Dip LGaO)2 ] 5. Density Functional Theory studies on [Dip LE:] and [(Dip LE)2 ], E=Al-Tl, shed light on the bonding in these compounds and show that the newly formed E-E bonding interactions can be described as weak single σ-bond with no significant π-bonding contribution for E=Al, Ga. A large contribution to the dimer binding enthalpies results from London dispersion forces.
ABSTRACT
Gold nanoparticles are known to be highly versatile oxidation catalysts utilizing molecular oxygen as a feedstock, but the mechanism and species responsible for activating oxygen remain unclear. The reaction between unsupported cationic gold clusters and molecular oxygen has been investigated. The resulting complexes were characterized in the gas phase using IR spectroscopy. A strong red-shift in the observed ν(O-O) stretching frequency indicates the formation of superoxo (O2(-)) moieties. These moieties are seen to form spontaneously in systems, which upon electron transfer attain a closed shell within the spherical jellium model (Au10(+) and Au22(+)), whereas an oxygen induced self-promotion in the activation is observed for other systems (Au4(+), Au12(+), Au21(+)).
ABSTRACT
A powerful oxidant and an unstable isomer of HNO3 , peroxynitrous acid ONOOH is generated by the fast reaction of H2 O2 with HNO2 in acidic medium [Eq. (1)]. If sulfides R2 S are present, ONOOH sulfoxidizes them in minutes. This reaction occurs faster than the decay of ONOOH to HNO3 and allows the fast preparation of sulfoxides with H2 O2 . (1).
ABSTRACT
The environment of the CuI ion in the distal ligand group decides the fate of the reduction of O2 by the two analogues 1 and 2 of the heme a3 CuB center in cytochrome c oxidase. The fourfold coordination by N in 1 favors the CuII oxidation state and leads to a 4 e- -4 H+ reduction and the formation of H2 O under physiological conditions, while with 2 a 2 e- -2 H+ reduction occurs to form the cytotoxic H2 O2 .