Steric Effect on the Nucleophilic Reactivity of Nickel(III) Peroxo Complexes

Jalee Kim ^†, Bongki Shin ^†, Hyunjeong Kim ^†, Junhyung Lee ^†, Joongoo Kang ^†, Sachiko Yanagisawa ^§, Takashi Ogura ^§, Hideki Masuda ^⊥, Tomohiro Ozawa ^⊥, and Jaeheung Cho ^*†

^† Department of Emerging Materials Science, DGIST, Daegu 711-873, Korea

^§ Picobiology Institute, Graduate School of Life Science, University of Hyogo, Hyogo 678-1297, Japan

^⊥ Department of Frontier Materials, Graduate School of Engineering, Nagoya Institute of Technology, Nagoya 466-8555, Japan

Inorg. Chem., Article ASAP

DOI: 10.1021/acs.inorgchem.5b00294

Publication Date (Web): June 12, 2015

Copyright © 2015 American Chemical Society

*E-mail: jaeheung@dgist.ac.kr.

http://pubs.acs.org/doi/pdf/10.1021/acs.inorgchem.5b00294 

Synopsis

A set of nickel(III) peroxo complexes, [Ni^III(TBDAP)(O₂)]⁺ and [Ni^III(CHDAP)(O₂)]⁺, were prepared. The spectroscopic characterization clearly shows that the NiO₂ cores are almost identical. However, the different steric properties of the supporting ligands were confirmed by structural characterization. The nucleophilic reactivity of the nickel(III) peroxo complexes was highly dependent on the steric properties of the macrocyclic ligands, with a reactivity order of [Ni^III(TBDAP)(O₂)]⁺ < [Ni^III(CHDAP)(O₂)]⁺.

Abstract

A set of nickel(III) peroxo complexes bearing tetraazamacrocyclic ligands, [Ni^III(TBDAP)(O₂)]⁺ (TBDAP = N,N′-di-tert-butyl-2,11-diaza[3.3](2,6)pyridinophane) and [Ni^III(CHDAP)(O₂)]⁺ (CHDAP = N,N′-dicyclohexyl-2,11-diaza[3.3](2,6)pyridinophane), were prepared by reacting [Ni^II(TBDAP)(NO₃)(H₂O)]⁺ and [Ni^II(CHDAP)(NO₃)]⁺, respectively, with H₂O₂ in the presence of triethylamine. The mononuclear nickel(III) peroxo complexes were fully characterized by various physicochemical methods, such as UV–vis, electrospray ionization mass spectrometry, resonance Raman, electron paramagnetic resonance, and X-ray analysis. The spectroscopic and structural characterization clearly shows that the NiO₂ cores are almost identical where the peroxo ligand is bound in a side-on fashion. However, the different steric properties of the supporting ligands were confirmed by X-ray crystallography, where the CHDAP ligand gives enough space around the Ni core compared to the TBDAP ligand. The nickel(III) peroxo complexes showed reactivity in the oxidation of aldehydes. In the aldehyde deformylation reaction, the nucleophilic reactivity of the nickel(III) peroxo complexes was highly dependent on the steric properties of the macrocyclic ligands, with a reactivity order of [Ni^III(TBDAP)(O₂)]⁺ < [Ni^III(CHDAP)(O₂)]⁺. This result provides fundamental insight into the mechanism of the structure (steric)–reactivity relationship of metal peroxo intermediates.