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

The chiral ferrocene derivative ( R , R p )‐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(η 5 ‐C 5 Me 5 )} 2 ] with 1 gives [RhCl 2 (η 5 ‐C 5 Me 5 )( 1 ‐κ P )] ( 9 ) containing P‐monodentate 1 , which undergoes smooth conversion to the (phosphanylalkyl)ferrocenecarboxylato complex [RhCl(η 5 ‐C 5 Me 5 ){Fe(η 5 ‐C 5 H 5 )(η 5 ‐C 5 H 3 ‐1‐CH(Me)PPh 2 ‐2‐COO‐κ 2 O , P }] ( 10 ) upon treatment with silica gel or alumina. Yet another O , P ‐chelate complex,[Rh{Fe(η 5 ‐C 5 H 5 )(η 5 ‐C 5 H 3 ‐1‐CH(Me)PPh 2 ‐2‐COO‐κ 2 O , P }(CO)(PCy 3 )] ( 11 ; Cy = cyclohexyl) is obtained directly by an acid‐base reaction between the acetylacetonato complex [Rh(acac)(CO)(PCy 3 )] and 1 . Amide 6 reacts with [{Pd(μ‐Cl)(η 3 ‐C 3 H 5 )} 2 ] to give the expected phosphane complex [PdCl(η 3 ‐C 3 H 5 )( 6 ‐κ P )] ( 12 ), while the replacement of the cyclooctadiene (cod) ligand in [PdCl(Me)(cod)] affords the chelate complex [PdCl(Me)( 6 ‐κ 2 O,P )] ( 13 ). All compounds are characterised by spectroscopic methods and the solid‐state structures of 5 , 9 , 11 , 13 , ( R , S p )‐2‐[1‐(diphenylphosphoryl)ethyl]‐1‐[ N ‐( R )‐(1‐phenylethyl)carbamoyl]ferrocene [( R )‐ 8 ; phosphane oxide from ( R )‐ 7 ], and the synthetic precursors ( R , S p )‐1‐bromo‐2‐[1‐(diphenylphosphanyl)ethyl]ferrocene ( 2 ) and ( R , S p )‐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)