Synthesis, structure, and reactivity of new chiral ferrocenyl pyrazole ligands

Abstract

New chiral ferrocene-based ligands containing an N-phenyl substituted pyrazole unit directly attached to a Cp ring were prepared starting from the common precursor ( R)- N, N-dimethyl-1-[( S)-2-{3-(1-phenyl)-1 H-pyrazolyl}ferrocenyl]ethylamine ( 7a). 7a was obtained in three steps and relatively low yield from the known 1-( R)- N, N-dimethylferrocenylethylamine ( 4). Nucleophilic substitution reactions of the dimethylamino group of 7a using secondary phosphines or pyrazoles led to P, N- and N, N-chelating ligands, respectively, that were used in Pd-catalyzed allylic substitution reactions, affording in part high enantioselectivities. X-ray crystallographic studies of 1-{( R)-1-[( S)-2-{3-(1-phenyl)-1 H-pyrazolyl}ferrocenyl]ethyl}-3,5-dimethyl-1 H-pyrazole ( 9a, C 26H 26FeN 4, a=8.417(7), b=13.268(10), c=20.222(10) Å, orthorhombic, P2 12 12 1 (No. 19), Z=4), the cyclic diferrocenyl derivative ( R,S)-( S,S)- 10 (C 42H 36Fe 2N 4, a=10.312(3), b=12.929(5), c=24.391(8) Å, orthorhombic, P2 12 12 1 (No. 19), Z=4), and the complex [Pd(η 3-C 3H 5)(( R)-( S)- 9b)][PF 6]·CH 2Cl 2 ( 12, C 37H 41F 6FeN 4PPd·CH 2Cl 2, a=13.331(8), b=38.49(2), c=7.601(4) Å, orthorhombic, P2 12 12 1 (No. 19), Z=4), ( R)-( S)- 9b=1-{( R)-1-[( S)-2-{3-(1-phenyl)-1 H-pyrazolyl}ferrocenyl]ethyl}-3-(1-adamantyl)-1 H-pyrazole) have been carried out.