Reactivity of a half-lantern Pt2(ii,ii) complex with triphenylphosphine: selectivity in a protonation reaction

Abstract

The half-lantern Pt₂(II,II) complex [{Pt(ppy)(μ₂-Spy)}₂], 1, in which ppyH = 2-phenylpyridine and pySH = pyridine-2-thiol, is treated with two equivalents of triphenylphosphine ligand (dissociated Pt–N_Spy bonds) to form complex [Pt(ppy)(η¹-S-Spy)(PPh₃)], 2. This complex can alternatively be obtained directly from the reaction of complex [Pt(ppy)(PPh₃)Cl], 3, with an ethanolic solution of sodium pyridine-2-thiolate. The transphobia effect (T) controls the geometry of complex 2 and spectroscopic data confirms that the phosphine ligand is positioned trans to the nitrogen atom of the cyclometalating fragment (ppy). The solution dynamics of complex 2 was investigated by NMR spectroscopy and it revealed a fluxional behavior in solution. Besides, the protonation reaction conditions for complex 2 revealed the sensitivity of this complex to the anionic group of the acidic species. For instance, reaction of complex 2 with hydrogen chloride that contains a coordinating anion, resulted in a platinum–sulfur bond cleavage and subsequent formation of the corresponding chloride complex 3. In contrast, upon treatment of complex 2 with HPF₆, involving a non-coordinating counter-anion, the pendant nitrogen atom was protonated and complex [Pt(ppy)(η¹-S-Spy^*) (PPh₃)][PF₆], 5, was obtained.