The palladium(II) bis(iminoxolene) complex (tBuClip)Pd (tBuClipH4 = 4,4'-di-tert-butyl-2,2'-bis(3,5-di-tert-butyl-2-hydroxyphenylamino)biphenyl) reacts with hydrazobenzene to form azobenzene and (tBuClipH2)Pd, where the palladium retains its original oxidation state and coordination sphere, but the ligand is reduced and protonated at nitrogen. Mechanistic data, especially the large isotope effect (kH/kD = 13.6) that varies nonlinearly with the mole fraction of protium in hydrazobenzene, suggest that the reaction takes place by concerted delivery of two hydrogens from the substrate to the complex. Further mechanistic data on reactions with other substrates, and of the nickel and platinum congeners, will be discussed, with particular focus on the question of whether the hydrogens are delivered directly to the nitrogen atoms of the ligands. The doubly oxidized tris(iminoxolene) complex (MeClamp)Ti (MeClampH6 = tris(2-(3',5'-di-tert-butyl-2'-hydroxyphenyl)amino-4-methylphenyl)amine) undergoes similar ligand-centered hydrogenation/dehydrogenation reactions with retention of the metal oxidation state and coordination sphere. The relationship between the reactivity of these complexes and their physical properties, especially their diradical character as judged by optical spectroscopy and variable-temperature NMR spectroscopy, will be explored.

Ligand-centered dehydrogenation reactions of metal bis- and tris-iminoxolenes

251st National Meeting (2016)

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