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Gauging the Redox Non‐Innocence of a Highly Pi‐Acidic Bis‐Tetrazine Pincer Ligand
Author(s) -
Cook Brian J.,
Lord Richard L.,
Chen ChunHsing,
Caulton Kenneth G.
Publication year - 2019
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.201900186
Subject(s) - chemistry , pincer movement , tetrazine , cyclic voltammetry , ligand (biochemistry) , redox , ruthenium , electron paramagnetic resonance , pincer ligand , terpyridine , molecule , medicinal chemistry , amide , photochemistry , crystallography , inorganic chemistry , electrochemistry , metal , organic chemistry , catalysis , biochemistry , receptor , nuclear magnetic resonance , physics , electrode
A 1:1 complex of a 2,6‐ bis ‐tetrazinylpyridine pincer ligand, btzp, with ZnCl 2 is characterized. The molecule is shown to be redox active by cyclic voltammetry and by chemical reduction. The resulting monoanion loses chloride to yield a radical species [Zn(btzp)Cl] whose EPR spectrum is observed. DFT studies show that the electron added upon reduction goes into an orbital primarily comprised of tetrazine nitrogen p π character. The Zn–Cl bonds lengthen but the Zn–N tz bonds shorten upon reduction, in response to taking on amide character. In an alternative approach to evaluating the electron accepting capacity of btzp, the molecule [Ru(btzp)Cl 2 (CO)] has been fully characterized and shows a CO stretching frequency 84 cm – 1 higher than that of its terpyridine analog. This result indicates btzp is strongly electron withdrawing; the CO stretching frequency for [Ru(btzp)Cl 2 (CO)] is among the highest ever observed for a ruthenium(II) monocarbonyl complex. Computational experiments on [Ru(btzp)Cl 2 (L)] test the influence of L on π ‐back donation to btzp.