Gas-Phase and Computational Study of Identical Nickel- and Palladium-Mediated Organic Transformations Where Mechanisms Proceeding via MII or MIV Oxidation States Are Determined by Ancillary Ligands

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• 作者：Krista L. Vikse ; George N. Khairallah ; Alireza Ariafard ; Allan J. Canty ; Richard A. J. O鈥橦air
• 刊名：Journal of the American Chemical Society
• 出版年：2015
• 出版时间：October 28, 2015
• 年：2015
• 卷：137
• 期：42
• 页码：13588-13593
• 全文大小：401K
• ISSN：1520-5126

文摘

Gas-phase studies utilizing ion鈥搈olecule reactions, supported by computational chemistry, demonstrate that the reaction of the enolate complexes [(CHb>2b>COb>2b>鈥?i>C,O)M(CHb>3b>)]^{鈭?/sup> (M = Ni (<b>5ab>), Pd (<b>5bb>)) with allyl acetate proceed via oxidative addition to give MIV species [(CHb>2b>COb>2b>鈥?i>C,O)M(CHb>3b>)(畏1-CHb>2b>鈥擟H鈺怌Hb>2b>)(Ob>2b>CCHb>3b>鈥?i>O,O鈥?]鈭?/sup> (<b>6b>) that reductively eliminate 1-butene, to form [(CHb>2b>COb>2b>鈥?i>C,O)M(Ob>2b>CCHb>3b>鈥?i>O,O鈥?]鈭?/sup> (<b>4b>). The mechanism contrasts with the MII-mediated pathway for the analogous reaction of [(phen)M(CHb>3b>)]+ (<b>1a,bb>) (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 db>zb>2) in <b>5b> are considerably destabilized, resulting in more facile oxidative addition; the electron transfer from db>zb>2 to the C鈺怌 蟺* orbital is the key interaction leading to oxidative addition of allyl acetate to MII. Upon collision-induced dissociation, <b>4b> undergoes decarboxylation to form <b>5b>. These results provide support for the current exploration of roles for NiIV and PdIV in organic synthesis.}