New Ru Complexes Containing the N-Tridentate bpea and Phosphine Ligands: Consequences of Meridional vs Facial Geometry

The synthesis and isolation of the complex cis,fac-[RuIICl2(bpea)(PPh3)] [3; bpea = N,N-bis(2-pyridylmethyl)ethylamine]
and three geometrical isomers of the complex [RuIICl(bpea)(dppe)](BF4) [4; dppe = (1,2-diphenylphosphino)ethane],
trans,fac (4a), cis,fac (4b), and mer(down) (4c), have been described (see Chart for a drawing of their structures).
These complexes have been characterized through analytical, spectroscopic (IR, UV/vis, and 1D and 2D NMR),
and electrochemical (cyclic voltammetry) techniques. In addition, complexes 3, 4a, and 4b have been further
characterized in the solid state through monocrystal X-ray diffraction analysis. The molecular and electronic structures
of isomers 4a, 4b, 4c, and 4d (the mer(up) isomer) have also been studied by means of density functional theory
(DFT) calculations. Furthermore, their low-energy electronic transitions have been simulated using time-dependent
DFT approaches, which have allowed unraveling of their metal-to-ligand charge-transfer nature. Complexes 3 and
4a−c are capable of catalyzing H-transfer types of reactions between alcohols and aromatic ketones such as
acetophenone and 2,2-dimethylpropiophenone (DP). A strong influence of the facial versus meridional geometry in
the bpea ligand coordination mode is observed for these catalytic reactions, with the meridional isomer being much
more active than the facial one. The meridional isomer is even capable of carrying out the H-transfer reaction of
bulky substrates such as DP at room temperature.