Impact of Oxidation State on Reactivity and Selectivity Differences between Nickel(III) and Nickel(IV) Alkyl Complexes. (24th May 2019)

• Record Type: Journal Article
• Authors: Roberts, Courtney C.; Camasso, Nicole M.; Bowes, Eric G.; Sanford, Melanie S.
• Is Part Of: Angewandte Chemie. Volume 131:Number 27(2019)
• Page Start: 9202
• Page End: 9206
• Publication Date: 2019-05-24
• Subjects: C-C-Kupplung -- Nickel -- Reaktionskinetik -- Reaktionsmechanismen -- Strukturaufklärung; Chemistry -- Periodicals; 540
• DOI: 10.1002/ange.201903638
• Languages: English
• ISSNs: 0044-8249

Abstract

Abstract: Described is a systematic comparison of factors impacting the relative rates and selectivities of C(sp 3 )−C and C(sp 3 )−O bond‐forming reactions at high‐valent Ni as a function of oxidation state. Two Ni complexes are compared: a cationic octahedral Ni IV complex ligated by tris(pyrazolyl)borate and a cationic octahedral Ni III complex ligated by tris(pyrazolyl)methane. Key features of reactivity/selectivity are revealed: 1) C(sp 3 )−C(sp 2 ) bond‐forming reductive elimination occurs from both centers, but the Ni III complex reacts up to 300‐fold faster than the Ni IV, depending on the reaction conditions. The relative reactivity is proposed to derive from ligand dissociation kinetics, which vary as a function of oxidation state and the presence/absence of visible light. 2) Upon the addition of acetate (AcO − ), the Ni IV complex exclusively undergoes C(sp 3 )−OAc bond formation, while the Ni III analogue forms the C(sp 3 )−C(sp 2 ) coupled product selectively. This difference is rationalized based on the electrophilicity of the respective M−C(sp 3 ) bonds, and thus their relative reactivity towards outer‐sphere SN 2‐type bond‐forming reactions. Abstract : Ein systematischer Vergleich von Faktoren, die die relativen Reaktionsgeschwindigkeiten und Selektivitäten von C(sp 3 )‐C‐ und C(sp 3 )‐O‐Kupplungen an hochvalenten Ni‐Zentren in Abhängigkeit vom Oxidationszustand (Ni III oder Ni IV ) beeinflussen, wird beschrieben. Zwei Ni‐Komplexe werden verglichen: ein kationischer oktaedrischer Ni IV ‐Komplex mit einem Tris(pyrazolyl)borat‐Liganden und ein kationischer oktaedrischer Ni III ‐Komplex mit einem Tris(pyrazolyl)methan‐Liganden.