Generation and Reactivity of a One-Electron-Oxidized Manganese(V) Imido Complex with a Tetraamido Macrocyclic Ligand.

The synthesis and X-ray structure of a new manganese(V) mesitylimido complex with a tetraamido macrocyclic ligand (TAML), [MnV (TAML)(N-Mes)]- (1), are reported. Compound 1 is oxidized by [(p-BrC6 H4 )3 N]+. [SbCl6 ]- and the resulting MnVI species readily undergoes H-atom transfer and nitrene transfer reactions.

Synergistic effects of CH3CO2H and Ca2+ on C-H bond activation by MnO4.

The activation of metal-oxo species with Lewis acids is of current interest. In this work, the effects of a weak Brønsted acid such as CH3CO2H and a weak Lewis acid such as Ca2+ on C-H bond activation by KMnO4 have been investigated. Although MnO4 - is rather non-basic (pK a of MnO3(OH) = -2.25), it can be activated by AcOH or Ca2+ to oxidize cyclohexane at room temperature to give cyclohexanone as the major product. A synergistic effect occurs when both AcOH and Ca2+ are present; the relative rates for the oxidation of cyclohexane by MnO4 -/AcOH, MnO4 -/Ca2+ and MnO4 -/AcOH/Ca2+ are 1 : 73 : 198. DFT calculations show that in the active intermediate of MnO4 -/AcOH/Ca2+, MnO4 - is H-bonded to 3 AcOH molecules, while Ca2+ is bonded to 3 AcOH molecules as well as to an oxo ligand of MnO4 -. Our results also suggest that these synergistic activating effects of a weak Brønsted acid and a weak Lewis acid should be applicable to a variety of metal-oxo species.

Cooperative activating effects of metal ion and Brønsted acid on a metal oxo species.

Metal oxo (M[double bond, length as m-dash]O) complexes are common oxidants in chemical and biological systems. The use of Lewis acids to activate metal oxo species has attracted great interest in recent years, especially after the discovery of the CaMn4O5 cluster in the oxygen-evolving centre of photosystem II. Strong Lewis acids such as Sc3+ and BF3, as well as strong Brønsted acids such as H2SO4 and CF3SO3H, are commonly used to activate metal oxo species. In this work, we demonstrate that relatively weak Lewis acids such as Ca2+ and other group 2 metal ions, as well as weak Brønsted acids such as CH3CO2H, can readily activate the stable RuO4 - complex towards the oxidation of alkanes. Notably, the use of Ca2+ and CH3CO2H together produces a remarkable cooperative effect on RuO4 -, resulting in a much more efficient oxidant. DFT calculations show that Ca2+ and CH3CO2H can bind to two oxo ligands to form a chelate ring. This results in substantial lowering of the barrier for hydrogen atom abstraction from cyclohexane.

If cytology of Warthin tumor is accurate, can management be conservative?

We conducted a retrospective study to assess the accuracy of fine-needle aspiration cytology (FNAC) in the diagnosis of Warthin tumor and to evaluate the subsequent risk of conservative nonsurgical management. We reviewed the records of 75 patients (76 tumors) with a parotid mass that had been diagnosed as a Warthin tumor by FNAC. This patient population was made up of 64 men and 11 women, aged 46 to 93 years (mean: 67). Of the 76 tumors, 40 were treated with surgical excision and 36 with conservative measures. Histology of the 40 excised parotid masses revealed that 38 (95%) were indeed Warthin tumors, 1 (2.5%) was a low-grade adenocarcinoma, and 1 was benign-not otherwise specified. None of the 36 tumors underwent malignant transformation either clinically or on repeat FNAC (if performed) during a follow-up of 4 to 120 months (mean: 55.5 ± 32.2). We conclude that conservative management of Warthin tumors confidently diagnosed on FNAC may be an option for patients who are unwilling or unable to undergo surgical excision.

FeCl3-activated oxidation of alkanes by [Os(N)O3]-.

Although the ion [Os(VIII)(N)(O)(3)](-) is a stable species and is not known to act as an oxidant for organic substrates, it is readily activated by FeCl(3) in CH(2)Cl(2)/CH(3)CO(2)H to oxidize alkanes efficiently at room temperature. The oxidation can be made catalytic by using 2,6-dichloropyridine N-oxide as the terminal oxidant. The active intermediates in stoichiometric and catalytic oxidation are proposed to be [(O)(3)Os(VIII)N-Fe(III)] and [Cl(4)(O)Os(VIII)N-Fe(III)], respectively.