Synthesis and Crystal Structure of Alkynylplatinum(IV) Complex Containing the Terpyridine Ligand

Reaction of square planar [ (C≡CPh)(tpy)]+ (tpy = 2,2′:6′,2′′-terpyridine) with bromine at low temperature provides a general route for the synthesis of octahedral alkynyl(terpyridine)platinum(IV) complex. In this first example of alkynyl(terpyridine)platinum(IV) complex, the alkynyl group is situated in trans position relative to the central nitrogen atom of the terpyridine ligand, and the two bromido ligands are situated in trans positions; an X-ray structural analysis has been completed for trans(Br)-[ Br2(C≡CPh)(tpy)]+. 1. Introduction Platinum(II) terpyridyl complexes with alkynyl ligands have attracted great interest in recent years due to their unique photophysics [1, 2] and their potential applications as photocatalysts for hydrogen evolution [3, 4] and molecular frameworks for light-to-chemical energy conversion [5]. On the other hand, there is a limited range of reported alkynylplatinum(IV) complexes [6–8]: there is no report on alkynylplatinum(IV) complex with terpyridine ligands. Although general oxidizing agents such as halogens and hydrogen peroxide are utilized for oxidation reactions of to centers, halogens are particularly the most useful reagents [9, 10]. However, only one example for oxidation of alkynylplatinum(II) by halogens has been known in [ (Me2bpy)(C≡C-4-tol)2] by iodine to form [ I2(Me2bpy)(C≡C-4-tol)2] [6], due to instability of the -alkynyl bond to halogen-containing oxidants [11]. Therefore, other procedures using 4-nitrophenyl azide and alkynyliodine(III) reagents as oxidants have been explored for oxidation of to [7, 8, 12]. In order to generalize about routes to alkynylplatinum(IV) compounds by halogen-oxidation reaction without Pt-alkynyl bond breaking, we have optimized reaction conditions (the kind of oxidants and temperature) using alkynylplatinum(II) containing the terpyridine ligand as a prototype complex. 2. Materials and Methods All chemicals employed here were used without further purification unless otherwise stated. All solvents purchased for organic synthesis were anhydrous and used without further purification. A Br2–CHCl3 solution was prepared by addition of 12 drops of Br2 to 10？mL of CHCl3 [10]. A Cl2–CHCl3 solution was prepared by a saturated Cl2 gas through 10 mL of CHCl3 for approximately 15？sec [9]. The platinum(II) precursor ([ (C≡CPh)(tpy)]PF6) was prepared in accordance with the published method [2]. 1H NMR spectra were recorded on a JEOL JMN-AL300 spectrometer (25°C) operating at 1H frequency of 300？MHz. ESI-MS data were measured on a Bruker Daltonics micrOTOF equipped with electrospray