Thermodynamics of inter- and intramolecular hydrogen bonding in (disphosphine)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: Delta H-1 degrees = -7.0 +/- 0.1 kcal/mol, Delta H-2 degrees = -7.7 +/- 0.4 kcal/mol, Delta S-1 degrees = -11.3 +/- 0.4 eu, and Delta S-2 degrees -17.8 +/- 1.2 eu. For comparison, the thermodynamics for hydrogen bonding of phenol to triphenylphosphine oxide in dichloromethane were also determined: Delta H degrees = -5.1 +/- 0.3 kcal/mol; Delta S 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 (Delta G(313) = -2.05 +/- 0.05 and -2.52 +/- 0.06 kcal/mol. respectively) and pyridine (Delta G(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.