Oxidative Addition to Cyclometalated Azobenzene Platinum(II) Complexes: A Route to Octahedral Liquid Crystalline Materials

Abstract

The 4,4‘-disubstituted azobenzene ligands HLa-d react with [(η3-C4H7)Pt(μ-Cl)]2 to give the dinuclear cycloplatinated complexes [(La-d)Pt(μ-Cl)]2, which are easily converted to their mononuclear Pt(II) acetylacetonate derivatives [(La-d)Pt(acac)]. Oxidative addition to the square-planar Pt(II) complexes [(La-d)Pt(acac)] of electrophilic substrates such as I2 or CH3I (RI) eventually led to the corresponding octahedral Pt(IV) [(La-d)Pt(acac)I2] and [(La-d)Pt(acac)(CH3)I] products. Characterization by X-ray crystallography on model complexes [(La)Pt(acac)], [(La)Pt(acac)I2], and [(La)Pt(acac)(CH3)I] has been carried out, showing that the I2 or CH3I ligands are bound to the Pt(IV) center at the apical positions. The presence of two ligands in apical position led to the loss of the short intermolecular Pt- - -Pt distance of 3.311(1) Å observed in the square-planar complex [(La)Pt(acac)]. Thermotropic mesomorphism is observed for both the Pt(II) and Pt(IV) species with clearing temperatures, mainly lower than those of the corresponding organic ligands. These products are the first examples of Pt(IV) octahedral liquid crystalline species and suggest that oxidative addition to appropriate Pt(II) precursors should be a convenient synthetic procedure for new hexacoordinated Pt(IV) mesogenic materials.