The redox chemistry of the series of Pt(II) diimine complexes L2PtMe2 (1; L2 = Ar−NCRCRN−Ar, where Ar/R = 4-MeC6H4/H (a), 4-MeOC6H4/H (b), 4-MeC6H4/Me (c), 4-MeOC6H4/Me (d)), with particular emphasis on the oxidation processes, has been studied in detail.
As seen by cyclic voltammetry, 1a−d undergo two successive, reversible one-electron
reductions at the diimine ligands and an irreversible, metal-centered one-electron oxidation.
The oxidation of 1b has been investigated in some detail. Chemical oxidation of 1b with
Cp2Fe+PF6
- in acetonitrile yields a near 1:1 ratio of the corresponding Pt(II) and Pt(IV)
cations L2Pt(NCMe)Me+ (2b) and fac-L2Pt(NCMe)Me3
+ (3b). Controlled-potential electrolysis
of 1b yields mixtures of 2b and 3b in a 1:1 ratio, as well as the cis,cis (4b) and one cis,trans
(5b) isomer of the dicationic Pt(IV) complexes L2Pt(NCMe)2Me2
2+. The percentage of the
dications 4b and 5b depended on the electrode potential. A mechanism involving methyl
group transfer between two transient Pt(III) intermediates L2PtMe2
•+ is proposed to account
for the generation of 2b and 3b, whereas further oxidation of the Pt(III) species at the
electrode eventually provides 4b and 5b. The X-ray crystal structures of 1b and 3b(OTf-)
have been determined. All Pt−Me bond distances in these two species are essentially
identical, averaging 2.057(1) Å.
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