Ligand Exchange Reaction on a Ru(II)–Pheox Complex as a Mechanistic Study of Catalytic Reactions

A ligand exchange of one of the acetonitrile
ligands of the (acetonitrile)4Ru­(II)–phenyloxazoline
complex (Ru­(II)–Pheox)
by pyridine was demonstrated, and the location of the exchange reaction
was examined by density functional theory (DFT) calculations to study
the mechanism of its catalytic asymmetric reactions. The acetonitrile
was smoothly exchanged with a pyridine to afford the corresponding
(pyridine)­(acetonitrile)3Ru­(II)–Pheox complex with
a trans orientation (C–Ru–N­(pyridine)) in a quantitative
yield, and the complex was analyzed by single-crystal X-ray analysis.
DFT calculations indicated that the most eliminable acetonitrile is
the trans group, which is consistent with the X-ray analysis. The
direction of the ligand exchange is thus determined on the basis of
the energy gap of the ligand elimination instead of the stability
of the metal complex. These results suggested that a reactant in a
Ru–Pheox-catalyzed reaction should approach trans to the C–Ru
bond to generate chirality on the Ru center.