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

N-Substituted dppa ligands Ph2P - NR - PPh2 [R = - CH2CH2SCH2C6H5 (1), - CH2CH2S(CH2)(5)CH3 (2), -(CH2)(9)CH3 (3), - C6H5 (4)] were used for the synthesis of cis-[PtCl2{Ph2PN(R) PPh2}] complexes [R = - CH2CH2SCH2C6H5 (5), - CH2CH2S(CH2)(5)CH3 (6), -(CH2)(9)CH3 ( 7), - C6H5 (8)] and heterotrinuclear clusters of formula [PtCo2(CO)(7){Ph2PN(R) PPh2}] [R= - CH2CH2SCH2C6H5 ( 9), - CH2CH2S(CH2)(5)CH3 ( 10), -(CH2)(9)CH3 ( 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.