Flat vs. Folded Chelate Rings in cis-PtIIa2 (a = NH3, a2 = en, a2 = 2, 2′-bpy) Complexes of Twofold Substituted Diazine Ligands

Abstract

Acid-base and ligating properties of three bis(substituted)pyrazine (pz) and pyrimidine (pym) ligands (pyrazine-2, 5-dicarboxylic acid, 2, 5-pzdcH2, 2, 3-bis(pyridine-2-yl)pyrazine, 2, 3-bppz, pyrimidine-4, 6-dicarboxylic acid, 4, 6-pmdcH 2) toward cis-Pt IIa 2 (a = NH 3, a 2 = en, a 2 = 2, 2'-bpy) have been studied. Combinations of pz-N/pym-N with donor atoms of the substituents lead to 5-membered platinum chelates, but exclusive N, N-coordination through the pyridyl substituents of 2, 3-bppz can lead to a 7-membered platinum chelate with a characteristic L-shape of the resulting cation. It is observed for Pt II(2, 2'-bpy), yet not for Pt II(en), and is a consequence of differences in sterical interactions between the 2, 3-bppz ligand and the coligands of Pt II. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.