Regioselective complexation of unprotected carbohydrates by platinum(II): Synthesis, structure, complexation equilibria, and hydrogen-bonding in carbonate-derived bis(phosphine)platinum(II) diolate and alditolate complexes

Article abstract of DOI:10.1021/ja00092a025

Treatment of bis(phosphine)platinum(II) carbonate complexes (LL)Pt(CO₃) (e.g., LL = 1,3-bis(diphenylphosphino)propane) with vicinal diols (i.e., HOCR¹R²CR³R⁴OH) gives equilibrium conversion to the corresponding diolate complexes (LL)Pt(OCR¹R²CR³R⁴O), which are readily isolated in good yield. From competition experiments, relative diol complexation constants were determined as a function of both the diol and the phosphine substituents and found to span a range of over 10⁴. Corresponding triolate and alditolate complexes were similarly prepared, for which very distinct equilibrium isomeric regioselectivities are observed, favoring complexation of γ,δ-threo diols. An X-ray structure of (dppp)Pt(D-mannitolate) shows that the mannitol is bonded to the platinum as its dianion via the oxygens on C3 and C4 to form a 2,5-dioxaplatinacyclopentane chelate ring and that three different strong intramolecular hydrogen-bonding interactions are present between the hydroxyl hydrogens and the metallacycle oxygens (O?O (av) = 2.65(2) A?), forming five-, six-, and seven-membered rings. Crystal data for PtP₂O₆C₃₃H₃₈·CH ₂CI₂: P2₁2₁2₁, Z = 4, T ≈ 20 °C, a = 11.225(2) A?, * = 15.875(3) A?, c = 19.964(4) A?, R(F_o) = 0.058, R^w(F_o) = 0.062.