engleski

DFT study of the ammonia N-H bond activation by dicyclopalladated azobenzene complex

Metal-mediated ammonia N–H bond activation is extensively studied as the first step in catalytic transformation of inexpensive ammonia into more precious N-containing compounds. Ammonia activation is usually hindered by the strong ammonia N–H bond and, in case of late-transition metals, preferential formation of ammine Werner-like adducts over amido complexes comprising the amido (NH2) group. Recently, a reversible N–H bond activation of gaseous ammonia has been achieved using a solid dicyclopalladated azobenzene, [Pd2Cl2(L-2H)(O-DMF)2], as well as by its reaction in ammonia-rich DMSO solution, Scheme 1 [2]. Spectroscopic monitoring of the reaction by in situ solid-state Raman method as well as by UV-vis spectroscopy in DMSO solution showed a stepwise activation yielding the first dipalladated amido complex with a PdII-(μ-NH2)-PdII bridge, [Pd2(μ-NH2)(L-2H)(NH3)3]Cl, via a stable diammine dicyclopalladated intermediate [Pd2Cl2(L-2H)2(NH3)2]. Here we describe a computational study that has supplemented the experimental data in elucidation of the mechanism of the presented heterolytic N-H bond activation by the dicyclopalladated azobenzene. DFT calculations support the stepwise mechanism assisted by exogenous ammonia that consists of ammonia coordination, chloride elimination and ammonia-assisted cleavage of the ammonia N-H bond by palladium.

DFT ; UV-vis kinetics ; N-H bond activation ; dicyclopalladated azobenzene ; mechanism

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