Syntheses of bispyrazolyl monotriazolyl heteroscorpionate platinum(IV) complexes including an unusual Pt-CH2CH2-Pt bridge

Abstract

Scorpionate ligands provide the benefit of hemilability while minimizing complete dissociation of the ligand. Previous investigations into Tp′PtLnXm complexes [Tp′=hydridotris(3,5-dimethylpyrazolyl)borate] revealed the importance of hemilability as the Tp′ ligand facilitates Pt(II/IV) interconversions. Here we discuss the synthesis and metalation of a series of asymmetric scorpionate ligands bearing two pyrazolyl rings and one triazolyl ring. In addition to utilizing triazole donor arms with differing substituents, we also compare octahedral structures of Pt(IV) complexes with P=O and CH and BH caps at the pole of the facial tridentate umbrella. Oxidation from Pt(II) to Pt(IV) with electrophilic reagents, simple acids and acid chlorides, leads to isomers in some cases, and the binding properties of the various donor arms dictate the stereochemistry of the products. Investigations into the reactivity of heteroscorpionate tridentate ligands bound to platinum(II) led to CCl activation reactions with methylene chloride and 1,2-dichloroethane. Isolation of a dinuclear platinum complex bridged by an ethylene unit produced an unusual proton NMR AA′XX′ pattern in the 1H NMR spectrum due to chirality at each platinum center.