Impact of Oxidation State on Reactivity and Selectivity Differences between Nickel(III) and Nickel(IV) Alkyl Complexes

Courtney C. Roberts, Nicole M. Camasso, Eric G. Bowes, Melanie S. Sanford

Research output: Contribution to journalArticlepeer-review

9 Scopus citations

Abstract

Described is a systematic comparison of factors impacting the relative rates and selectivities of C(sp3)−C and C(sp3)−O bond-forming reactions at high-valent Ni as a function of oxidation state. Two Ni complexes are compared: a cationic octahedral NiIV complex ligated by tris(pyrazolyl)borate and a cationic octahedral NiIII complex ligated by tris(pyrazolyl)methane. Key features of reactivity/selectivity are revealed: 1) C(sp3)−C(sp2) bond-forming reductive elimination occurs from both centers, but the NiIII complex reacts up to 300-fold faster than the NiIV, 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 NiIV complex exclusively undergoes C(sp3)−OAc bond formation, while the NiIII analogue forms the C(sp3)−C(sp2) coupled product selectively. This difference is rationalized based on the electrophilicity of the respective M−C(sp3) bonds, and thus their relative reactivity towards outer-sphere SN2-type bond-forming reactions.

Original languageEnglish (US)
Pages (from-to)9104-9108
Number of pages5
JournalAngewandte Chemie - International Edition
Volume58
Issue number27
DOIs
StatePublished - Jul 1 2019

Bibliographical note

Funding Information:
This work was supported by the National Science Foundation (CHE-1664961) and the UM Mcubed program. We acknowl- edge Dr. Jeff Kampf for X-ray crystallographic analysis of complexes 1-NiIII+ and 2-NiIV+, and NSF Grant CHE-0840456 for X-ray instrumentation. EGB thanks NSERC for aMichael Smith Foreign Study Supplement (CGS-MSFSS).

Funding Information:
This work was supported by the National Science Foundation (CHE-1664961) and the UM Mcubed program. We acknowledge Dr. Jeff Kampf for X-ray crystallographic analysis of complexes 1-NiIII+ and 2-NiIV+, and NSF Grant CHE-0840456 for X-ray instrumentation. EGB thanks NSERC for a Michael Smith Foreign Study Supplement (CGS-MSFSS).

Publisher Copyright:
© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Keywords

  • C−C coupling
  • kinetics
  • nickel
  • reaction mechanisms
  • structure elucidation

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