Thermodynamics of Inter- and Intramolecular Hydrogen Bonding in (Diphosphine)platinum(II) Diolate Complexes and Its Role in Carbohydrate Complexation Regioselectivity

Thermodynamic data are reported for intermolecular hydrogen-bonding association of 1 and 2 equiv of phenol with 1,3-bis(diphenylphosphino)propane](phenylethane-1,2-diolato)platinum(II) ((dppp)Pt(Ped)) in dichloromethane solution: = -7.0 +/- 0.1 kcal/mol, = -7.7 +/- 0.4 kcal/mol, = -11.3 +/- 0.4 eu, and = -17.8 +/- 1.2 eu. For comparison, the thermodynamics for hydrogen bonding of phenol to triphenylphosphine oxide in dichloromethane were also determined: DeltaH degrees = -5.1 +/- 0.3 kcal/mol; DeltaS degrees = -8.8 +/- 1.0 eu. Competitive coordination exchange reactions have been used to determine the apparent intramolecular hydrogen bond strengths in (dppp)Pt(1,2-O,O'-glycerolate) and (dppp)Pt(1,2-O,O'-butane-1,2,4-triolate) in both dichloromethane (DeltaG(313) = -2.05 +/- 0.05 and -2.52 +/- 0.06 kcal/mol, respectively) and pyridine (DeltaG(313) = -0.62 +/- 0.03 and -0.82 +/- 0.03 kcal/mol, respectively). Based on these findings, the role of hydrogen-bonding interactions in determining the regioselectivities of complexation of carbohydrates to diphosphine Pt(II) is discussed.