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

Abstract

Treatment of bis(phosphine)platinum(II) carbonate complexes (LL)Pt(CO[sub 3]) (e.g., LL = 1,3-bis(diphenylphosphino)propane) with vicinal diols (i.e., HOCR[sup 1]R[sup 2]CR[sup 3]R[sup 4]OH) gives equilibrium conversion to the corresponding diolate complexes (LL)Pt(OCR[sup 1]R[sup 2]CR[sup 3]R[sup 4]O), 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 10[sup 4]. Corresponding triolate and alditolate complexes were similarly prepared, for which very distinct equilibrium isomeric regioselectivities are observed, favoring complexation of [gamma],[delta]-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) [angstrom], forming five-, six-, and seven-membered rings. Crystal data for PtP[sub 2]O[sub 6]C[sub 33]H[sub 38]-CH[sub 2]Cl[sub 2]: P2[sub 1]2[sub 1]2[sub 1], Z = 4, T = 20 [degree]C, a = 11.225(2) [angstrom], b = 15.875(3) [angstrom], c = 19.964(4) [angstrom], R(F[sub 0]) = 0.058, R[sub w](F[sub o]) = 0.062. 78 refs., 4 figs., 6 tabs.