Synthesis, Coordination and Catalytic Utility of Novel Phosphanyl–ferrocenecarboxylic Ligands Combining Planar and Central Chirality

Abstract

AbstractThe chiral ferrocene derivative (R,Rp)‐2‐[1‐(diphenylphosphanyl)ethyl]ferrocenecarboxylic acid (1) is prepared together with selected derivatives resulting from modification at the phosphane moiety [P‐oxide (5) and P‐sulfide (4)] and the carboxyl group {amides bearing benzyl (6) and (R)‐ or (S)‐1‐phenylethyl substituents [(R)‐7 and (S)‐7] at the amide nitrogen atom}. Acid 1 and amide 6 are studied as ligands in rhodium and palladium complexes. Bridge cleavage of the dimer [{Rh(μ‐Cl)Cl(η5‐C5Me5)}2] with 1 gives [RhCl2(η5‐C5Me5)(1‐κP)] (9) containing P‐monodentate 1, which undergoes smooth conversion to the (phosphanylalkyl)ferrocenecarboxylato complex [RhCl(η5‐C5Me5){Fe(η5‐C5H5)(η5‐C5H3‐1‐CH(Me)PPh2‐2‐COO‐κ2O,P}] (10) upon treatment with silica gel or alumina. Yet another O,P‐chelate complex,[Rh{Fe(η5‐C5H5)(η5‐C5H3‐1‐CH(Me)PPh2‐2‐COO‐κ2O,P}(CO)(PCy3)] (11; Cy = cyclohexyl) is obtained directly by an acid‐base reaction between the acetylacetonato complex [Rh(acac)(CO)(PCy3)] and 1. Amide 6 reacts with [{Pd(μ‐Cl)(η3‐C3H5)}2] to give the expected phosphane complex [PdCl(η3‐C3H5)(6‐κP)] (12), while the replacement of the cyclooctadiene (cod) ligand in [PdCl(Me)(cod)] affords the chelate complex [PdCl(Me)(6‐κ2O,P)] (13). All compounds are characterised by spectroscopic methods and the solid‐state structures of 5, 9, 11, 13, (R,Sp)‐2‐[1‐(diphenylphosphoryl)ethyl]‐1‐[N‐(R)‐(1‐phenylethyl)carbamoyl]ferrocene [(R)‐8; phosphane oxide from (R)‐7], and the synthetic precursors (R,Sp)‐1‐bromo‐2‐[1‐(diphenylphosphanyl)ethyl]ferrocene (2) and (R,Sp)‐1‐bromo‐2‐[1‐(diphenylthiophosphoryl)ethyl]ferrocene (3) determined by single‐crystal X‐ray diffraction. The catalytic properties of 1 and the amides are probed in enanatioselective rhodium‐catalysed hydrogenation and palladium‐catalysed asymmetric allylic alkylation. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)