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

doi:10.1002/anie.201903638

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

Chemistry (Twin Cities)

Research output: Contribution to journal › Article › peer-review

22 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 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(sp³)−C(sp²) 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(sp³)−OAc bond formation, while the Ni^III 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 S_N2-type bond-forming reactions.

Original language	English (US)
Pages (from-to)	9104-9108
Number of pages	5
Journal	Angewandte Chemie - International Edition
Volume	58
Issue number	27
DOIs	https://doi.org/10.1002/anie.201903638
State	Published - 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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title = "Impact of Oxidation State on Reactivity and Selectivity Differences between Nickel(III) and Nickel(IV) Alkyl Complexes",

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.",

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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: {\textcopyright} 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim",

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T1 - Impact of Oxidation State on Reactivity and Selectivity Differences between Nickel(III) and Nickel(IV) Alkyl Complexes

AU - Roberts, Courtney C.

AU - Camasso, Nicole M.

AU - Bowes, Eric G.

AU - Sanford, Melanie S.

N1 - 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

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N2 - 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.

AB - 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.

KW - C−C coupling

KW - kinetics

KW - nickel

KW - reaction mechanisms

KW - structure elucidation

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

Abstract

Bibliographical note

Keywords

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