om5b00163_si_002.xyz (105.9 kB)
Carbon–Hydrogen Bond Activation in Bis(2,6-dimethylbenzenethiolato)tris(trimethylphosphine)ruthenium(II): Ligand Dances and Solvent Transformations
dataset
posted on 2015-07-13, 00:00 authored by Amanda
L. Pitts, Michael B. HallDensity
functional theory (DFT) calculations are used to predict
the mechanism for the intramolecular carbon–hydrogen bond activation
of an ortho methyl group on the RuII(SC6H3Me2-2,6-κ1S)2(PMe3)3 complex to form the cycloruthenated product cis-Ru[SC6H3-(2-CH2)(6-Me)-κ2S2C](PMe3)4 and HSC6H3Me2-2,6 in the presence of PMe3. The DFT calculations also show how changing the solvent from benzene
to methanol prevents C–H activation and results in the unactivated
six-coordinate product Ru(SC6H3Me2-2,6-κ1S)2(PMe3)4 in 100% yield. The reactant was determined to have two plausible
σ-bond metathesis pathways in which to react, one for each of
the two thiolate ligands. The steps in both mechanisms were influenced
by the electronic interactions between the sulfur lone pairs and the
Ru 4d orbitals and the steric repulsion between the methyl groups
on the five ligands in such a way that the methyl group in the SAr
(Ar = SC6H3Me2-2,6) ligand closest
to the Ru pirouettes away to activate the other methyl group. The
equatorial pathway was calculated to be the lower energy mechanism
and, therefore, the dominant pathway for the overall reaction. The
difference between reaction mediums was predicted, by both implicit
and explicit solvation modeling, to be a result of the polarity and
binding of methanol, which transforms the geometry of the reactant
from a less polar distorted trigonal-bipyramidal geometry to a more
polar distorted square-pyramidal geometry. This change in geometry
favors the more rapid addition of a fourth PMe3 ligand
to the more open coordination site, which prevents the C–H
activation.