Reversibly reducible cis-dichloroplatinum(II) and cis-dichloropalladium(II) complexes of bis(1-methylimidazol-2-yl)glyoxal

Complexes cis-MCl2(big), big = bis(1-methylimidazol-2-yl)glyoxal, M = Pt, Pd, were prepared and characterized through electrochemistry, spectroscopy, and for M = Pt, by X-ray structure analysis. The seven-membered chelate ring formed through N,N ' coordination of the ligand big shows a boat conformation in agreement with density functional theory (DFT) calculation results. No significant intermolecular interactions were observed for the platinum compound. Both the Pd-II and Pt-II complexes undergo reversible one-electron reduction in CH2Cl2/0.1 M Bu4NPF6; the reduced palladium compound disintegrates above -30 degrees C. Electron paramagnetic resonance (EPR), UV-vis, and IR spectroelectrochemistry studies were employed to study the monoanions. The anion radical complex [cis-PtCl2(big)](center dot-) exhibits a well-resolved EPR spectrum with small but well-detectable g anisotropy and an isotropic Pt-195 hyperfine coupling of 12.2 G. DFT calculations confirm the spin concentration in the alpha-semidione part of the radical complex with small delocalization to the bis(imidazolyl)metal section. The results show that EPR and electroactive moieties can be linked to the cis-dichloroplatinum(II) group via imidazole coordination.