Preparation, coordination and catalytic use of planar-chiral monocarboxylated dppf analogues

A novel polar dppf derivative possessing only planar chirality, 10,2-bis(diphenylphosphino)ferrocene-1-carboxylic acid (Hdpc), has been synthesised in racemic form and resolved into enantiomers via esters with D-glucose diacetonide ((Rp)- and (Sp)-3). (Rp)-Hdpc was further converted to a series of N-substituted amides that were studied as ligands for Pd-catalysed enantioselective allylic alkylation of racemic (E)-1,3-diphenylprop-2-en-1-yl acetate or ethyl carbonate with malonate esters, showing high activity and good enantioselectivity (er up to 10 : 90). The catalytic results were correlated with the structural data (X-ray diffraction and solution NMR) for (eta(3)-allyl) palladium(II) complex (R-p)-[Pd(eta(3)-1,3-Ph2C3H3){Fe(eta(5)-C5H3-1-(C(O)NHCH2Ph)-2-(PPh2-kappa P))(eta(5)-C5H4PPh2-kappa P)}]ClO4 (16) as a model of the plausible reaction intermediate. A further study into the coordination properties of Hdpc led to isolation of chelate complex [PdCl2(Hdpc-kappa P-2,P')] (12). The crystal structures of rac-Hdpc, methyl ester of (R-p)-Hdpc, glycoside (R-p)-3, and 12 center dot Me2CO suggested a close structural relationship between dppf and Hdpc.