Oxidative addition to cyclometalated azobenzene platinum(II) complexes: A route to octahedral liquid crystalline materials

The 4,4'-disubstituted azobenzene ligands HLa-d react with [(eta(3)-C4H7)Pt (mu-Cl)](2) to give the dinuclear cycloplatinated complexes [(La-d)Pt(mu-Cl )](2), which are easily converted to their mononuclear Pt(II) acetylacetona te derivatives [(La-d)Pt(acac)]. Oxidative addition to the square-planar Pt (II) complexes [(La-d)Pt(acac)] of electrophilic substrates such as I-2 or CH3I (RI) eventually led to the corresponding octahedral Pt(IV)[(La-d)Pt(ac ac)I-2] and [(La-d)Pt(acac)(CH3)I] products. Characterization by X-ray crys tallography on model complexes [(L-a)Pt(acac)], [(L-a)Pt(acac)I-2], and [(L -a)Pt(acac)(CH3)I] has been carried out, showing that the I-2 or CH3I ligan ds 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) Angstrom observed in the square-planar compl ex [(L-a)Pt(acac)]. Thermotropic mesomorphism is observed for both the Pt(I I) and Pt(IV) species with clearing temperatures, mainly lower than those o f 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.