title: Unprecedented Variety of Outcomes in the Oxygenation of Dinuclear Alkylzinc Derivatives of an N,N-Coupled Bis(β-diketimine).
abstract: Reactions between O2and organometallics with non-redox-active metal centers have received continuous interest for over 150 years, although significant uncertainties concerning the character and details of the actual mechanism of these reactions persist. Harnessing dinuclear three-coordinate alkylzinc derivatives of an N,N-coupled bis(β-diketimine) proligand (LH2) as a model system, we demonstrate for the first time that a slight modification of the reaction conditions might have a dramatic influence on the oxygenation reaction outcomes, leading to an unprecedented variety of products originating from a single reaction system, that is, partially and fully oxygenated zinc alkoxides, zinc alkylperoxides, and zinc hydroxide compounds. Our studies indicate that accessibility of the three-coordinate zinc center by the O2molecule, coupled with the lower reactivity of Zn-Me vs. Zn-Et units towards dioxygen, are key factors in the oxygenation process, providing a novel tetranuclear methyl(methoxy)zinc {[L][ZnMe][Zn(μ-OMe]}2and zinc ethoxide {[L][Zn(μ-OEt)]2}2. Remarkably, oxygenation of three-coordinate alkylzinc [L][ZnR]2complexes at ambient temperature afforded a unique hydroxide {[L][Zn(μ-OH)]2}2. Oxygenation of the [L][ZnEt]2complex in the presence of 4-methylpyridine (py-Me) at low temperature led to the isolation of a dinuclear zinc ethylperoxide [L][Zn(OOEt)(py-Me)]2, which nicely substantiates the intermediacy of an unstable zinc alkylperoxide in the formation of the subsequent zinc alkoxide and hydroxide compounds. Finally, our investigations provide compelling evidence that a non-redox-active metal center plays a crucial role in the oxygenation process through assisting in single-electron transfer from an M-C bond to an O2molecule. Although the oxygenation of zinc alkyls occurs by radical pathways, the reported results stand in clear contradiction to the widely accepted free-radical chain mechanism.
authors.affiliation: Faculty of Chemistry, Warsaw University of Technology, Noakowskiego 3, 00-664, Warsaw, Poland.
authors.forename: Tomasz
authors.initials: T
authors.lastname: Pietrzak
authors.affiliation: Faculty of Chemistry, Warsaw University of Technology, Noakowskiego 3, 00-664, Warsaw, Poland.
authors.forename: Maciej Damian
authors.initials: MD
authors.lastname: Korzyński
authors.affiliation: Institute of Physical Chemistry, Polish Academy of Science, Kasprzaka 44/52, 01-224, Warsaw, Poland.
authors.forename: Iwona
authors.initials: I
authors.lastname: Justyniak
authors.affiliation: Faculty of Chemistry, Warsaw University of Technology, Noakowskiego 3, 00-664, Warsaw, Poland.
authors.forename: Karolina
authors.initials: K
authors.lastname: Zelga
authors.affiliation: Faculty of Chemistry, Warsaw University of Technology, Noakowskiego 3, 00-664, Warsaw, Poland.
authors.forename: Arkadiusz
authors.initials: A
authors.lastname: Kornowicz
authors.affiliation: Faculty of Chemistry, Warsaw University of Technology, Noakowskiego 3, 00-664, Warsaw, Poland.
authors.forename: Zbigniew
authors.initials: Z
authors.lastname: Ochal
authors.affiliation: Faculty of Chemistry, Warsaw University of Technology, Noakowskiego 3, 00-664, Warsaw, Poland.|Institute of Physical Chemistry, Polish Academy of Science, Kasprzaka 44/52, 01-224, Warsaw, Poland.
authors.forename: Janusz
authors.initials: J
authors.lastname: Lewiński
keywords: alkyls; dioxygen; oxygenation; peroxide; zinc