Synthesis and Use in Asymmetric Hydrogenations of Solely Planar Chiral 1,2-Disubstituted and 1,2,3-Trisubstituted Ferrocenyl Diphosphines: A Comparative Study

A total of 12 enantiopure 1,2-disubstituted and 1,2,3-trisubstituted ferrocenyl diphosphines [1-Ph2P-2-R2PCH2-3-R‘-Fc, R = Cy, t-Bu, 3,5-(CH3)2C6H3), R‘ = H, CH3, Ph, 3,5-(CH3)2C6H3)] have been
synthesized, characterized, and tested in asymmetric rhodium- and ruthenium-catalyzed hydrogenations
of four alkenes and two ketones. The performance of these ferrocene derivatives in catalytic hydrogenations
was compared to those of catalysts based on Josiphos, PPF-t-Bu2, and Xyliphos [1-Ph2P-2-R2P(CH3)CH-Fc, R = Cy, t-Bu, 3,5-(CH3)2C6H3)]. Dichloro palladium(II) complexes of Xyliphos and its analogues
lacking the stereogenic center were synthesized as model compounds, and their molecular structures
were studied in solution and, for four complexes, in the solid state. In hydrogenation reactions the
replacement of Xyliphos as the catalyst ligand with its analogues lacking the stereogenic center leads to
changes in product configurations or significant increases or decreases in ee values.