title: Gas-Phase and Computational Study of Identical Nickel- and Palladium-Mediated Organic Transformations Where Mechanisms Proceeding via M(II) or M(IV) Oxidation States Are Determined by Ancillary Ligands.
abstract: Gas-phase studies utilizing ion-molecule reactions, supported by computational chemistry, demonstrate that the reaction of the enolate complexes [(CH2CO2-C,O)M(CH3)](-) (M = Ni (5a), Pd (5b)) with allyl acetate proceed via oxidative addition to give M(IV) species [(CH2CO2-C,O)M(CH3)(η(1)-CH2-CH═CH2)(O2CCH3-O,O')](-) (6) that reductively eliminate 1-butene, to form [(CH2CO2-C,O)M(O2CCH3-O,O')](-) (4). The mechanism contrasts with the M(II)-mediated pathway for the analogous reaction of [(phen)M(CH3)](+) (1a,b) (phen = 1,10-phenanthroline). The different pathways demonstrate the marked effect of electron-rich metal centers in enabling higher oxidation state pathways. Due to the presence of two alkyl groups, the metal-occupied d orbitals (particularly dz(2)) in 5 are considerably destabilized, resulting in more facile oxidative addition; the electron transfer from dz(2) to the C═C π* orbital is the key interaction leading to oxidative addition of allyl acetate to M(II). Upon collision-induced dissociation, 4 undergoes decarboxylation to form 5. These results provide support for the current exploration of roles for Ni(IV) and Pd(IV) in organic synthesis.
authors.affiliation: School of Chemistry, Bio21 Institute of Molecular Science and Biotechnology, University of Melbourne , Parkville, Victoria 3010, Australia.
authors.forename: Krista L
authors.initials: KL
authors.lastname: Vikse
authors.affiliation: School of Chemistry, Bio21 Institute of Molecular Science and Biotechnology, University of Melbourne , Parkville, Victoria 3010, Australia.
authors.forename: George N
authors.initials: GN
authors.lastname: Khairallah
authors.affiliation: School of Chemistry, Bio21 Institute of Molecular Science and Biotechnology, University of Melbourne , Parkville, Victoria 3010, Australia.|Department of Chemistry, Faculty of Science, Central Tehran Branch, Islamic Azad University , Shahrak Gharb, Tehran 1467686831, Iran.|School of Physical Sciences, University of Tasmania , Hobart, Tasmania 7001, Australia.
authors.forename: Alireza
authors.initials: A
authors.lastname: Ariafard
authors.affiliation: School of Physical Sciences, University of Tasmania , Hobart, Tasmania 7001, Australia.
authors.forename: Allan J
authors.initials: AJ
authors.lastname: Canty
authors.affiliation: School of Chemistry, Bio21 Institute of Molecular Science and Biotechnology, University of Melbourne , Parkville, Victoria 3010, Australia.
authors.forename: Richard A J
authors.initials: RA
authors.lastname: O'Hair