Chelating versus bridging bonding modes of N-substituted bis(diphenylphosphanyl)amine ligands in Pt complexes and Co2Pt clusters

Abstract

N-Substituted dppa ligands Ph₂P–NR–PPh₂ [R = –CH₂CH₂SCH₂C₆H₅ (1), –CH₂CH₂S(CH₂)₅CH₃ (2), –(CH₂)₉CH₃ (3), –C₆H₅ (4)] were used for the synthesis of cis-[PtCl₂{Ph₂PN(R)PPh₂}] complexes [R = –CH₂CH₂SCH₂C₆H₅ (5), –CH₂CH₂S(CH₂)₅CH₃ (6), –(CH₂)₉CH₃ (7), –C₆H₅ (8)] and heterotrinuclear clusters of formula [PtCo₂(CO)₇{Ph₂PN(R)PPh₂}] [R = –CH₂CH₂SCH₂C₆H₅ (9), –CH₂CH₂S(CH₂)₅CH₃ (10), –(CH₂)₉CH₃ (11), –C₆H₅ (12)]. The presence of relatively bulky substituents on N resulted in a higher chelating power of the ligands. The thermodynamic study of the equilibrium between the chelate and the bridged forms of clusters 9–11 showed that the bridged form is favoured by enthalpic factors whereas entropic factors favour chelation. The structures of 5 and 9 were determined by single crystal X-ray diffraction.