Associative intraligand substitution of anticancer azolato-bridged compounds without a square-pyramidal intermediate: Formation of a unique tetranuclear, µ3-1,2,3-triazolato-N1,N2,N3-bridged Pt(II) compound

Abstract

The reaction of the anticancer azolato-bridged dinuclear platinum(II) compound [{cis-Pt(NH3)2}2(µ-OH)(µ-1,2,3-triazolato-N1,N2)](NO3)2 (AMTA) in 0.2 M DCl-D2O solution was monitored at 298 K using 1H NMR spectroscopy. Acid hydrolysis of AMTA first provided a dinuclear Pt(II) cationic species [{cis-Pt(NH3)2Cl}2(µ-1,2,3-triazolato-N1,N2)]+ (intermediate A) which then turned into [{cis-Pt(NH3)2Cl}2(µ-1,2,3-triazolato-N1,N3)]+ (intermediate B) by migration of a Pt(II) ion, initially bound to N2, to N3. Hence, intramolecular ligand substitution of N3 for N2 occurred after substitution of two chloride ligands for the hydroxido bridge. Under the reaction conditions, the intermediate A and B were unambiguously detected, and both or either of the intermediate species then dimerized by a substitution of the chlorido ligand by N3 or N2 of a partner molecule to yield an unprecedented tetranuclear Pt(II) compound [{cis-Pt(NH3)2Cl}µ-{cis-Pt(NH3)2}2(µ-1,2,3-triazolato-N2,N3)2-N1,N1′]Cl2(NO3)2 (compound 1), whose 3D structure has been determined by X-ray crystal analysis. The fact that all triazolate nitrogen atoms coordinated to 3 different Pt(II) ions indicates that 1,2,3-triazolate derivatives could be important as a unique tridentate building block for metal-organic framework.