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Impact of Oxidation State on Reactivity and Selectivity Differences between Nickel(III) and Nickel(IV) Alkyl Complexes
Author(s) -
Roberts Courtney C.,
Camasso Nicole M.,
Bowes Eric G.,
Sanford Melanie S.
Publication year - 2019
Publication title -
angewandte chemie international edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.831
H-Index - 550
eISSN - 1521-3773
pISSN - 1433-7851
DOI - 10.1002/anie.201903638
Subject(s) - chemistry , reactivity (psychology) , nickel , cationic polymerization , selectivity , electrophile , alkyl , medicinal chemistry , dissociation (chemistry) , octahedron , ligand (biochemistry) , oxidation state , outer sphere electron transfer , reductive elimination , metal , stereochemistry , crystallography , catalysis , ion , polymer chemistry , organic chemistry , crystal structure , medicine , biochemistry , alternative medicine , receptor , pathology
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 S N 2‐type bond‐forming reactions.