The complexes [Mn(2-OH(X-sal)pn)] 2 n-(where X ) 5-OCH 3 , H, 5-Cl, 3,5-diCl, or 5-NO 2 and where n ) 0 or 2) are shown to be excellent hydrogen peroxide disproportionation catalysts in acetonitrile. When carried out in an open vessel, the reaction can occur for over 5000 turnovers without an indication of catalyst decomposition. The disproportionation reaction cycles between the [Mn III (2-OH(X-sal)pn)] 2 and the [Mn II (2-OH(X-sal)pn)] 2 2oxidation levels. All derivatives show saturation kinetics with the highest k cat (21.9 ( 0.2 s -1 ) observed for the [Mn III (2-OH(5-Clsal)pn)] 2 dimer and the optimal k cat /K M (990 ( 60 s -1 ‚M -1 ) observed for the [Mn III (2-OHsalpn)] 2 . The first step of the reaction is proposed to be the binding of peroxide to the [Mn III (2-OH(X-sal)pn)] 2 through an alkoxide shift to form a ternary intermediate {[Mn III (2-OH(X-sal)pn)] 2 (H 2 O 2 )}. We propose that the turnoverlimiting step is the oxidation of peroxide from this intermediate. The binding efficiency of the peroxide is dependent on the phenyl-ring substitution with the derivatives donating the most electrons having the highest affinity for the substrate. Studies with isotopically labeled H 2 O 2 indicate that protons are important in the turnover-limiting step of the reaction and that the O-O bond is not cleaved during peroxide oxidation. In a closed vessel, the product dioxygen will oxidize [Mn II (2-OH(5-NO 2 sal)pn)] 2 2to [Mn II/III (2-OH(5-NO 2 sal)pn) 2 ] -, and this species can then be stoichiometrically oxidized by hydrogen peroxide to give [Mn III/IV (2-OH(5-NO 2 sal)pn) 2 (µ 2 -O) 2 ] -. This diµ 2 -oxobridged species is catalytically incompetent; however, addition of hydroxylamine hydrochloride restores catalytic activity. The relationship of this catalytic disproportionation of hydrogen peroxide and inactivation of the catalyst will be used to define a model for similar reactions observed for the Lactobacillus plantarum Mn catalase.Similar to the heme catalases, the manganese catalases disproportionate hydrogen peroxide according to eq 1.These manganese enzymes have been isolated from three different bacteria: Lactobacillus plantarum, 2,3 Thermus thermophilus, 4 and Thermoleophilium album. 5 Through activity studies, 5-7 spectroscopy, 8-11 and X-ray crystallographic structural analysis, 12-14 all three enzymes appear to be very similar.The dinuclear manganese center probably cycles between the Mn II 2 T Mn III 2 oxidation levels during the normal catalytic cycle with at least two proposed mechanisms for the catalytic disproportionation of hydrogen peroxide by the Mn catalases having been presented. 7 Evidence for this cycle has been shown by the identical steady-state kinetics for the oxidized (Mn III 2 ) and reduced (Mn II 2 ) forms of T. thermophilus 6 and by observation of changes in XANES spectra during turnover of the L. plantarum enzyme. 15 Both the L. plantarum 7 and T. thermophilus 6 enzymes exhibit substrate saturation kinetics and show no inhibition by hydrogen peroxide even at high substrate c...

The (N,N-dialkylaminoethyl)cyclopentadienyl group 13 element dichlorides 3 and 4 of the typewith the respective group 13 element trichlorides. The reaction of 3 with LiAlH 4 afforded the cyclopentadienylaluminum dihydride [(Me 2 NCH 2 CH 2 )C 5 H 4 ]AlH 2 (5) in nearly quantitative yield. Treatment of the organogallium dichlorides [ 5), i-Pr (7)} in good yields. The reaction of 6 with LiGaH 4 resulted in the formation of the organogallium dihydride [(Me 2 NCH 2 CH 2 )C 5 H 4 ]GaH 2 (8). The novel compounds 3-5, 7, and 8 were characterized by elemental analysis, NMR spectroscopy, mass spectrometry, and X-ray crystallography. In the solid state and also in solution, all compounds feature a monomeric structure with an intramolecularly coordinated dialkylamino group. The coordinative and electronic saturation of the metal center in these compounds leads to a drastically decreased reactivity toward moisture and air in comparison to nondonorstabilized Cp-group 13 element compounds. The dynamic behavior observed in solution is based on fast haptotropic shifts in a "windshield-wiper" type process. Sufficient volatility makes the organodihydrido compounds 5 and 8 suitable precursors for the deposition of aluminum and gallium, respectively, in the MOCVD process. Ex-situ characterization with sputter auger electron spectroscopy (SAES) provides information about the chemical composition of the aluminum and gallium layers. Irradiation of 5 and 8 in solution is followed by decomposition into the respective metal and into the hydrogen-functionalized ligand [C 5 H 5 (CH 2 CH 2 NMe 2 )].