10.1021/om9807001.s001 Christopher M. Haar Christopher M. Haar Steven P. Nolan Steven P. Nolan William J. Marshall William J. Marshall Kenneth G. Moloy Kenneth G. Moloy Alfred Prock Alfred Prock Warren P. Giering Warren P. Giering Synthetic, Structural, and Solution Thermochemical Studies in the Dimethylbis(phosphine)platinum(II) System. Dichotomy between Structural and Thermodynamic Trends American Chemical Society 1999 phosphine size enthalpic stability scale reaction enthalpy unidentate phosphines Solution Thermochemical Studies cone angles Structural phosphine ligands PEt 3 cone angle 31 P NMR data PMe 2 Ph P 2 PtMe 2 PCy 3 Thermodynamic Trends Reaction enthalpies solution calorimetry P 2 PtMe 2 complexes 1999-01-16 00:00:00 Journal contribution https://acs.figshare.com/articles/journal_contribution/Synthetic_Structural_and_Solution_Thermochemical_Studies_in_the_Dimethylbis_phosphine_platinum_II_System_Dichotomy_between_Structural_and_Thermodynamic_Trends/3783372 Reaction enthalpies of the complex (COD)PtMe<sub>2</sub> (COD = η<sup>4</sup>-1,5-cyclooctadiene) with an extensive series of unidentate phosphines have been measured by solution calorimetry. The molecular structures of <i>cis</i>-P<sub>2</sub>PtMe<sub>2</sub> for P = PEt<sub>3</sub>, PMe<sub>2</sub>Ph, P(pyrrolyl)<sub>3</sub>, and PCy<sub>3</sub> have been determined by single-crystal X-ray diffraction. The relative stabilities of the resulting P<sub>2</sub>PtMe<sub>2</sub> complexes are strongly influenced by the size (cone angle) of the incoming phosphine, with larger cone angles resulting in less thermodynamically stable complexes. Crystallographic and <sup>31</sup>P NMR data, however, do not reflect the enthalpic stability scale and are more closely correlated to the electronic (χ) character of the phosphine ligands. The strength of the Pt−P interaction, as determined from these structural data, is greatest for phosphines with electron-withdrawing substituents, regardless of phosphine size or reaction enthalpy.