Organoplatinum complexes containing bis(diphenylphosphino)amine as ligand: uncommon case of N–H⋯I–Pt hydrogen bonding

Abstract

The complex [PtMe₂(dppa)], 1a, dppa = Ph₂PNHPPh₂, which has previously been prepared as a mixture with the dimeric form [Pt₂Me₄(µ-dppa)₂], was synthesized in pure form by the reaction of [PtCl₂(dppa)] with MeLi. The aryl analogue [Pt(p-MeC₆H₄)₂(dppa)], 1b, was prepared by replacement of SMe₂ in cis-[Pt(p-MeC₆H₄)₂(SMe₂)₂] with dppa. The reaction of the chelate complexes 1 with one equiv. of dppa afforded the complexes [PtR₂(dppa-P)₂], RMe, 2a and R = p-MeC₆H₄2b. The reaction of [PtR₂(dppa)], 1, with neat MeI gave the organoplatinum(IV) complexes [PtR₂MeI(dppa)], RMe, 5a and R = p-MeC₆H₄, 5b. The structure of 5a, determined by X-ray crystallography, indicated that the complex undergoes self-assembly by intermolecular N–H⋯I–Pt hydrogen bonding. MeI was also double oxidatively added to organodiplatinum(II) complex cis,cis-[Me₂Pt(µ-SMe₂)(µ-dppa)PtMe₂], to give diorganoplatinum(IV) complex [Me₃Pt(µ-dppa)(µ-I)₂PtMe₃], 4. The aryl analogue organodiplatinum(II) complex cis,cis-[(p-MeC₆H₄)₂Pt(µ-SMe₂)(µ-dppa)Pt(p-MeC₆H₄)₂], 3b, was prepared by the reaction of cis-[Pt(p-MeC₆H₄)₂(SMe₂)₂] with half equiv. of dppa, but 3b refused to react with MeI, probably because of the steric effects of the aryl ligands. The tetramethyl complex [PtMe₄(dppa)], 6, was prepared either by reaction of 5a with MeLi or by replacement of SMe₂ in [Pt₂Me₈(µ-SMe₂)₂] with dppa. All the complexes were fully characterized in solution by multinuclear NMR (¹H, ¹³C, ³¹P and ¹⁹⁵Pt) methods and their coordination compared with that of the corresponding known dppm complexes.