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

New Journal of Chemistry Pub Date: 2009-04-09 DOI: 10.1039/B901262A

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 ((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 (η3-allyl)palladium(II) complex (Rp)-[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 (Rp)-Hdpc, glycoside (Rp)-3, and 12·Me2CO suggested a close structural relationship between dppf and Hdpc.

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