RESUMO
We report the isolation of a room temperature stable dipyrromethene Cu(O2) complex featuring a side-on O2 coordination. Reactivity studies highlight the unique ability of the dioxygen adduct for both hydrogen-atom abstraction and acid/base chemistry towards phenols, demonstrating that side-on superoxide species can be reactive entities.
RESUMO
Study of the kinetics of intramolecular aryl ether C-O bond cleavage by Ni was facilitated by access to a family of metal complexes supported by diphosphines with pendant aryl-methyl ethers. The nature of the aryl substituents was found to have little effect on the rate of cleavage. In contrast, soluble Lewis acidic additives accelerate the aryl ether cleavage dramatically. The effect of AlMe3 was studied in detail, and showed an increase in rate by several orders of magnitude. Low temperature NMR spectroscopy studies demonstrate quantitative coordination of ether to Al. From the Lewis acid-bound precursor, the activation parameters for ether cleavage are significantly lower. These findings provide a mechanistic basis for milder catalyst design for the activation of strong bonds.
RESUMO
Though numerous catalysts for the dehydrogenation of ammonia borane (AB) are known, those that release >2 equiv of H2 are uncommon. Herein, we report the synthesis of Mo complexes supported by a para-terphenyl diphosphine ligand, 1, displaying metal-arene interactions. Both a Mo(0) N2 complex, 5, and a Mo(II) bis(acetonitrile) complex, 4, exhibit high levels of AB dehydrogenation, releasing over 2.0 equiv of H2. The reaction rate, extent of dehydrogenation, and reaction mechanism vary as a function of the precatalyst oxidation state. Several Mo hydrides (Mo(II)(H)2, [Mo(II)(H)](+), and [Mo(IV)(H)3](+)) relevant to AB chemistry were characterized.
