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

Abstract

A novel polar dppf derivative possessing only planar chirality, 1′,2-bis(diphenylphosphino)-ferrocene-1-carboxylic acid (Hdpc), has been synthesised in racemic form and resolved into enantiomers via esters with D-glucose diacetonide ((R_p)- and (S_p)-3). (R_p)-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 (η³-allyl)palladium(II) complex (R_p)-[Pd(η³-1,3-Ph₂C₃H₃){Fe(η⁵-C₅H₃-1-(C(O)NHCH₂Ph)-2-(PPh₂-κP))(η⁵-C₅H₄PPh₂-κP)}]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-κ²P,P′)] (12). The crystal structures of rac-Hdpc, methyl ester of (R_p)-Hdpc, glycoside (R_p)-3, and 12·Me₂CO suggested a close structural relationship between dppf and Hdpc.