FULL PAPER DOI: 10.1002/ejic.201100468 Regiospecific C(naphthyl)–H Bond Activation by Platinum(II) – Isolation, Characterization, Reactivity and TD-DFT Study of the Cycloplatinate Complexes Achintesh Narayan Biswas, [a] Purak Das, [a] Vivek Bagchi, [b] Amitava Choudhury, [c] and Pinaki Bandyopadhyay* [a] Keywords: C–H activation / Cyclometallation / Platinum / Oxidation / Density functional calculations The regiospecific activation of C(naphthyl)–H bonds in a group of naphthylazo-2'-hydroxyarene ligands (H 2 L) has been achieved by platinum(II) compounds under different re- action conditions, and stable cycloplatinates [Pt II L(D)] have been isolated in presence of neutral Lewis bases (D). Struc- tures 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) Introduction Cyclometallation reactions are of considerable interest because of their role in the selective functionalization of C–H bonds [1] and numerous applications of the complexes derived. [2] The topic of C–H bond activation reactions pro- moted by platinum(II) complexes, as a key step in the func- tionalization of small molecules, [3] has undergone a rapid growth. Some representative examples where platinum(II) complexes have been extensively used includes alkane [3,4] and arene [5] functionalization, studies of their thermo- dynamic properties, [6] synthesis of complexes with interest- ing optical properties (luminescence), [7] C–C coupling reac- tions, [2c,8] metallomesogen chemistry [9] and anticancer agents. [10] Since the first report of platinum(II) organome- tallics containing a Pt–C(aryl) bond, [11] the study of cyclo- platination reactions has mainly been confined to the do- main of C(phenyl)–H bond activation. [9,12] Reports on [a] Department of Chemistry, University of North Bengal, Raja Rammohunpur, Siliguri 734013, West Bengal, India Fax: +91-353-2699001 E-mail: pbchem@rediffmail.com [b] Department of Chemistry, Indian Institute of Technology, New Delhi 110016, India [c] Department of Chemistry, Missouri S & T, Rolla, MO 65409, USA Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/ejic.201100468. Eur. J. Inorg. Chem. 2011, 3739–3748 © 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 3739 cycloplatinates with distorted octahedral geometry. In the re- actions with halogens and methyl iodide, trans oxidative ad- dition 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 experi- mental spectra are in very good agreement. C(naphthyl)–H bond activation by platinum(II) are rela- tively few. [13] Moreover, the low electrophilicity of platinum has been found to facilitate the stabilization of higher oxi- dation states, which is reflected in their ability to undergo oxidative addition reactions. A number of studies on oxi- dative addition reaction of platinum(II) compounds having monodentate and bidentate phosphorus or nitrogen ligands have been reported. [14–17] However, cycloplatinate com- pounds have not enjoyed the same popularity. [12e,16,18] This work stems from our interest in the selective acti- vation of different C(naphthyl)–H bonds by transition metal complexes. [19] Herein, selective C(naphthyl)–H bond Scheme 1. Diazene ligands H 2 L 1 –H 2 L 3 .