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Issue 37, 2017
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Synthesis and redox reactions of bis(verdazyl)palladium complexes

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Abstract

The synthesis and ligand-centered redox chemistry of palladium complexes bearing two potentially bidentate verdazyl ligands is explored. Reaction of 1,5-diisopropyl-3-pyridin-2-yl-6-oxoverdazyl radical 1 with Pd(NCMe)4·2BF4 gives a complex containing two coordinated verdazyl radicals. The structure of this complex consists of one verdazyl bound to Pd in a bidentate mode and the second verdazyl bound in a monodentate fashion through the pyridine substituent; the fourth coordination site is occupied by a solvent molecule (acetonitrile (3) or dimethyl sulfoxide (4)). Two-electron reduction of this complex with decamethylferrocene affords a bis(verdazyl) palladium complex (5) in which both verdazyls have been reduced to their anionic state and are both bound to Pd in bidentate manner. Complex 5 can be independently synthesized by a redox reaction between 1 and Pd2(dba)3. Reduced complex 5 can be re-oxidized to 3 or 4 with AgBF4; in contrast, oxidation with PhICl2 leads to ligand dissociation, ultimately giving radical 1 and a mono(verdazyl)dichloropalladium complex 2. One-electron oxidation using PhICl2 produces a formally “mixed valent” (in ligand) bis(verdazyl)chloropalladium complex (6) with one bidentate verdazyl anion ligand and one monodentate (pyridine-bound) verdazyl radical. Attempted protonation of the verdazyl ligands in complex 5 leads to complete ligand dissociation and protonation of both the tetrazine and pyridine moieties; deprotonation regenerates 5. Subsequent air oxidation of the tetrazane/pyridinium cation (formed as a tetrachloropalladate salt) leads to re-coordination of the verdazyl ligands to give 6 initially, but ultimately produces a combination of free radical 1 and 2.

Graphical abstract: Synthesis and redox reactions of bis(verdazyl)palladium complexes

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Publication details

The article was received on 20 Jul 2017, accepted on 30 Aug 2017 and first published on 01 Sep 2017


Article type: Paper
DOI: 10.1039/C7DT02646C
Citation: Dalton Trans., 2017,46, 12636-12644
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    Synthesis and redox reactions of bis(verdazyl)palladium complexes

    C. A. Sanz, Z. R. McKay, S. W. C. MacLean, B. O. Patrick and R. G. Hicks, Dalton Trans., 2017, 46, 12636
    DOI: 10.1039/C7DT02646C

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