Regiospecific C(naphthyl)-H Bond Activation by Platinum(II) - Isolation, Characterization, Reactivity and TD-DFT Study of the Cycloplatinate Complexes

The regiospecific activation of C(naphthyl)-H bonds in a group of naphthylazo-2'-hydroxyarene ligands (H2L) has been achieved by platinum(II) compounds under different reaction conditions, and stable cycloplatinates [(PtL)-L-II(D)] have been isolated in presence of neutral Lewis bases (D). Structures of the cycloplatinate complexes of platinum(II) have been established by single-crystal X-ray crystallography. The platinum(II) centres are surrounded by a C,N,O-terdentate ligand frame (L) and Lewis base (D) in a distorted square planar fashion. These cycloplatinate species have been found to react with halogens and methyl iodide undergoing metal-centered two electron oxidation affording platinum(IV) cycloplatinates with distorted octahedral geometry. In the reactions with halogens and methyl iodide, trans oxidative addition has been found for [Pt(L)D] (D = 4-picoline), whereas cis addition has been observed for [Pt(L)D] where D is a more sterically demanding triphenylphosphane. Structures of two representative platinum(IV) cycloplatinate species have been determined by single-crystal X-ray crystallography. A time dependent (TD)-DFT study of representative cycloplatinate compounds has been performed. Optical absorption spectra of the cycloplatinate compounds in dichloromethane have been simulated using the TD-DFT method, and the experimental spectra are in very good agreement.