Electronic and Steric Tuning of an Atropisomeric Disulfoxide Ligand Motif and Its Use in the Rh(I)-Catalyzed Addition Reactions of Boronic Acids to a Wide Range of Acceptors

A novel
chiral disulfoxide ligand pair bearing fluorine atoms at
the 6 and 6′ position of its atropisomeric backbone, (M,S,S)- and (P,S,S)-p-Tol-6F-BIPHESO,
was synthesized. Complexation to a rhodium­(I) precursor gave rise
to μ-Cl- and μ-OH-bridged rhodium dimer complexes incorporating
the new (M,S,S)-p-Tol-6F-BIPHESO ligand, while its sibling (P,S,S)-p-Tol-6F-BIPHESO
was not complexed efficiently to the rhodium precursor. The performance
of this disulfoxide ligand [(M,S,S)-p-Tol-6F-BIPHESO] in catalysis
was tested in both 1,4- and 1,2-addition reactions of arylboronic
acids. We show that addition to both cyclic and acyclic enones as
well as N-tosylarylimines proceeds with high yields
and high enantioselectivities to give the corresponding products.
The synthesis of enantiomerically pure p-Tol-6F-BIPHESO
is straightforward and inexpensive which, together with the high catalytic
performance and wide substrate scope for these addition reactions,
makes it a very attractive alternative to more classical chiral ligand
entities.