Diorganoplatinum(ii) complexes with chelating PN ligand 2-(diphenylphosphinoamino)pyridine; synthesis and kinetics of the reaction with MeI

Abstract

New organoplatinum(II) complexes [PtR2(PN)] (PN = 2-(diphenylphosphinoamino)pyridine, R = Me, 1a, or p-MeC6H4, 1b) were synthesized by the reaction of [Pt(p-MeC6H4)2(SMe2)2] or [Me2Pt(μ-SMe2)2PtMe2] with 1 and 2 equiv. of PN, respectively. The reaction of Pt(II) complexes 1 with MeI gave the Pt(IV) complexes [PtR2(PN)MeI] (R = Me; 2a, and p-MeC6H4; 2b). All the complexes were fully characterized using multinuclear (1H, 31P, 13C, and 195Pt) NMR spectroscopy. Density functional theory calculations have been performed to find approximate structures for all described complexes. The platinum(II) complexes have a 5dπ(Pt)-π*(PN) metal-to-ligand charge-transfer band, which was used to easily follow the kinetics of their reactions with MeI. The classical SN2 mechanism was suggested. The rates of the reactions at different temperatures were measured and were consistent with the proposed mechanism, large negative ΔS‡ values were found in each reaction. The PN chelating complexes [PtR2(PN)], 1, reacted almost 100 or 300 times slower with MeI as compared to that of the NN chelating complex [PtR2(bpy)] (bpy = 2,2′-bipyridine) in acetone or benzene, respectively. This was attributed to the π-acceptance through the P ligating atom of PN ligand, which decreases the electron density of Pt(II) in PN chelating complexes.