Planar chiral alkenylferrocene phosphanes: Preparation, structural characterisation and catalytic use in asymmetric allylic alkylation

Planar chiral alkenylferrocene phosphanes, viz. (Sp)-[Fe(η5-C5H3-1-PPh2-2-CHdouble bond; length as m-dashCR2)(η5-C5H5)] (R = H, (Sp)-2; Ph, (Sp)-5) and (Sp)-[Fe(η5-C5H3-1-PPh2-2-(E)-CHdouble bond; length as m-dashCHR)(η5-C5H5)] (R = Ph, (Sp)-3; C(O)CH3, (Sp)-6; and CO2CH2CH3, (Sp)-7) have been prepared by alkenylation of (Sp)-2-(diphenylphosphanyl)ferrocenecarboxaldehyde and tested as ligands for enantioselective palladium-catalysed allylic alkylation of 1,3-diphenyprop-2-en-1-yl acetate with dimethyl malonate. All phosphanylalkenes formed active catalysts. However, the induced enantioselectivity was only poor to moderate [12–43% ee after 20 h at room temperature], with the ee’s and configuration of the preferred product strongly depending on the ligand structure. The catalytic results have been related to solution properties (NMR, ESI MS) and the solid-state structural data (X-ray diffraction) of [Pd(η3-1,3-Ph2C3H3){(Sp)-2-η2:κP}]ClO4 ((Sp)-12), which represent a model of the plausible reaction intermediate.