A Ni(II)-Tri-Phenoxyl Radical Complex

Laurent Benisvy, Chemistry, Bar-Ilan University, Ramat Gan, Israel
Galina Zats, Chemistry, Bar-Ilan University, Ramat Gan, Israel
Ohad Fleker, Chemistry, Bar-Ilan University, Ramat Gan, Israel
Ronit Lavi, Chemistry, Bar-Ilan University, Ramat Gan, Israel
Yossi Gofer, Chemistry, Bar-Ilan University, Ramat Gan, Israel
Galina Romanenko, Tomography Center, Novossibirsk University, Novossibirsk, Russia
Victor Ovcharenko, Tomography Center, Novossibirsk University, Novossibirsk, Russia
Maylis Orio, Laboratoire de Spectrochimie Infrarouge et Raman, Lille University, Villeneuve d'Ascq , France
Dmitry Yufit, Chemistry, Durham University, Durham, UK
Frantisek Hartl, Chemistry, Reading University, Reading, UK

In the last two decades, inspired by the Cu(II)-Tyrosyl radical moiety at the active site of Galactose oxidase (GO)¹, [a fungal enzyme that catalyses a wide range of primary alcohols to their corresponding aldehydes]; chemists have joined efforts to synthesise and characterise persistent transitions metal complexes of phenoxyl radical.² The design of metal phenoxyl radical complexes with desired catalytic and magnetic properties has remained a significant chemical challenge.

Stable phenoxyl radical complexes are rare. Moreover, if a few mono-phenoxyl radical complexes have been isolated; di, and tri-phenoxyl radical complexes are known to be highly unstable and their spectroscopic characterisation requires low temperature experimental set-up.

Herein, we report, using the suitably protected N,O-phenol pyrazole ligand LH,³ the synthesis and characterisation of the bis-NiL₂ square planar complex (1), together with the product of its two-electron oxidation with Ag[SbF₆] (2). Our combined crystallographic, spectrocopic, electrochemical and theoretical studies reveal that 2 contains an unprecedented octahedral Ni(II) dications, [Ni(L^.)₃]^₂₊, bearing three phenoxyl radical ligands. The latter represents the first example of an isolated tris-phenoxyl radical complex, revealing the chemical viabilty of such entities.

Reference:

1. J. W. Wittaker, Chem. Rev., 2003, 103, 2347.

2. F. Thomas, Eu. J. Inorg. Chem., 2007, 2379; C. T. Lyons, T. D. P. Stack, Coord. Chem. Rev., 2013, 257, 528.

3. G. Zats, L. Benisvy, Dalton Trans., 2011, 40, 10889; 2012, 41, 47.


A Ni(II)-Tri-Phenoxyl Radical Complex Laurent Benisvy, Chemistry, Bar-Ilan University, Ramat Gan, Israel Galina Zats, Chemistry, Bar-Ilan University, Ramat Gan, Israel Ohad Fleker, Chemistry, Bar-Ilan University, Ramat Gan, Israel Ronit Lavi, Chemistry, Bar-Ilan University, Ramat Gan, Israel Yossi Gofer, Chemistry, Bar-Ilan University, Ramat Gan, Israel Galina Romanenko, Tomography Center, Novossibirsk University, Novossibirsk, Russia Victor Ovcharenko, Tomography Center, Novossibirsk University, Novossibirsk, Russia Maylis Orio, Laboratoire de Spectrochimie Infrarouge et Raman, Lille University, Villeneuve d'Ascq , France Dmitry Yufit, Chemistry, Durham University, Durham, UK Frantisek Hartl, Chemistry, Reading University, Reading, UK In the last two decades, inspired by the Cu(II)-Tyrosyl radical moiety at the active site of Galactose oxidase (GO)¹, [a fungal enzyme that catalyses a wide range of primary alcohols to their corresponding aldehydes]; chemists have joined efforts to synthesise and characterise persistent transitions metal complexes of phenoxyl radical.² The design of metal phenoxyl radical complexes with desired catalytic and magnetic properties has remained a significant chemical challenge. Stable phenoxyl radical complexes are rare. Moreover, if a few mono-phenoxyl radical complexes have been isolated; di, and tri-phenoxyl radical complexes are known to be highly unstable and their spectroscopic characterisation requires low temperature experimental set-up. Herein, we report, using the suitably protected N,O-phenol pyrazole ligand LH,³ the synthesis and characterisation of the bis-NiL₂ square planar complex (1), together with the product of its two-electron oxidation with Ag[SbF₆] (2). Our combined crystallographic, spectrocopic, electrochemical and theoretical studies reveal that 2 contains an unprecedented octahedral Ni(II) dications, [Ni(L^.)₃]^₂₊, bearing three phenoxyl radical ligands. The latter represents the first example of an isolated tris-phenoxyl radical complex, revealing the chemical viabilty of such entities. Reference: 1. J. W. Wittaker, Chem. Rev., 2003, 103, 2347. 2. F. Thomas, Eu. J. Inorg. Chem., 2007, 2379; C. T. Lyons, T. D. P. Stack, Coord. Chem. Rev., 2013, 257, 528. 3. G. Zats, L. Benisvy, Dalton Trans., 2011, 40, 10889; 2012, 41, 47.

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