The dioxomolybdenum(VI) complex [MoO₂Cl₂{p-tolyl(CH₃DAB)}] has been prepared in good yield by reaction of the solvent adduct MoO₂Cl₂(THF)₂ with one equivalent of the bidentate ligand N,N-p-tolyl-2,3-dimethyl-1,4-diazabutadiene. Treatment of the dichloro complex with the Grignard reagent CH₃MgCl gives the dimethyl derivative [MoO₂(CH₃)₂{p-tolyl(CH₃DAB)}]. The complexes are highly active and selective catalysts for the homogeneous epoxidation of cyclooctene using tert-butyl hydroperoxide (TBHP) as the oxidant. In both cases, the initial activity is ca. 175 mol mol⁻¹ _Mo h⁻¹ and cyclooctene oxide is obtained quantitatively within 4 h. It was possible to recover the dimethyl complex at the end of the reaction and reuse it in a second run with only a small decrease in activity. The complexes are also active and selective for the epoxidation of other olefins, such as 1-octene, 2-octene, cyclododecene and (R)-(+)-limonene, with TBHP. The catalytic production of cyclooctene oxide was investigated in detail, varying either the reaction temperature or the initial concentrations of substrate, oxidant and catalyst precursor. Kinetic studies show that the catalyst precursor–oxygen donor complex formation is first-order in TBHP and in the metal complex [MoO₂Cl₂{p-tolyl(CH₃DAB)}]. A specific rate of 3.2 mol⁻¹ dm³ s⁻¹ was found for catalyst formation at 25 °C. Activation parameters for this reaction have also been measured (ΔH^≠ = 48 ± 3 kJ mol⁻¹, ΔS^≠ = −112 ± 10 J mol⁻¹ K⁻¹).

The kinetics of the nitrosation reaction of several substituted sulfonamides and of the denitrosation of the resulting products have been studied. The denitrosation rate is first-order with respect to both the nitroso compound and acid concentration and no effect of added nucleophiles was observed. The denitrosation reaction is general-acid catalysed, with a Brønsted parameter, α_d, of 0.7, which is independent of the substituents on the aromatic ring. Kinetic solvent isotope effects range from k_d H₃O⁺ /k_d D₃O⁺ = 1.20 ± 0.05 to 2.04 ± 0.06 for denitrosation by L₃O⁺ and from k_d ^AH/k_d ^AD = 1.5 ± 0.2 to 2.3 ± 0.3 for denitrosation by dichloroacetic acid, which suggest that a rate-determining proton transfer is involved in this reaction. For nitrosation reaction, the absence of catalysis by nucleophilic anions, the observed general-base catalysis (β_NO = 0.3) and the substituent effects suggest a concerted nitrosation–denitrosation process. The Leffler parameters obtained for N · · · H bond formation (α_nuc = 0.7) as well as for N · · · NO bond breaking (α_lg = 0.17) are in favour of an imbalance in the transition state (α_imbalance = 0.53) with the development of a positive charge on the nitrogen adjacent to the nitroso group.