A Novel Chiral Ferrocene-Based Amidine/Amidinato Ligand and Its Rhodium Complexes

The N,N‘-bisferrocenyl-substituted chiral formamidine 1 (N,N‘-bis[(S)-2-{(1R)-1-(diphenylphosphino)ethyl}ferrocen-1-yl]formamidine) was prepared from commercially available {(1R)-1-(dimethylamino)ethyl}ferrocene by a multistep procedure in an overall yield of 29%. Deprotonation of 1 followed by
addition of [Rh2Cl2(COD)2] yielded the (formamidinato)rhodium(I) complex 2 [(N,N‘-bis[(S)-2-{(1R)-1-(diphenylphosphino)ethyl}ferrocen-1-yl]formamidinato)rhodium(I)]. Direct reaction of formamidine 1
with [Rh2Cl2(COD)2] led to complex 10 [(κ-N,P-bis[(S)-2-{(1R)-1-(diphenylphosphino)ethyl}ferrocen-1-yl]formamidine)(chloro)(η4-1,5-cyclooctadiene)rhodium(I)], which was converted to 2 upon addition
of base. Oxidative addition of methyl chloride or methyl iodide to 2 yielded the trans adducts 11 [(N,N‘-bis[(S)-2-{(1R)-1-(diphenylphosphino)ethyl}ferrocen-1-yl]formamidinato)(chloro)(methyl)rhodium(III)]
and 12 [(N,N‘-bis[(S)-2-{(1R)-1-(diphenylphosphino)ethyl}ferrocen-1-yl]formamidinato)(iodo)(methyl)rhodium(III)], the configurations of which were determined by means of NMR and, in the case of the
Rh(III) methyl chloride adduct 11, by X-ray analysis.