Assessment and Application of Density Functional Theory for the Prediction of Structure and Reactivity of Vanadium Complexes

We assess the performance of six
density functionals, each paired
with one of five basis sets (a total of 30 model chemistries) for
the prediction of geometrical parameters in the coordination sphere
of nine vanadium complexes (for a total of 270 structural analyses).
We find that results are generally consistent over the range of functionals
tested and that none fail drastically. For bond lengths, the model
chemistry PBE0/QZVP performed the best overall (having a MAD of only
0.02 Å from experiment) yet PBE0/6-31G* provides nearly identical
results. For bond angles, PBE0 also performed best overall and, when
combined with the 6-31G* basis, produces one of the smallest error
distributions of any model chemistry tested. We subsequently applied
the PBE0/6-31G* model chemistry to understanding the mechanism of
action of a [BIMPY]­VCl3 catalyst in the polymerization
of styrene (Sty) and vinyl acetate (VAc). Our results indicate that
the [BIMPY]­VCl3 catalyst operates through a unique, two-step
reaction pathway: dehalogenation to form a reactive V­(II) intermediate
(a highly favorable process) followed by a potentially reversible
OMRP to control the polymerization of vinyl acetate. Control over
vinyl acetate is facilitated by both the higher reactivity of the
radical species and the participation of the ester group in the trapping
step. In both the Sty and VAc cases we predict relatively poor control
of the polymerization with the vanadium catalyst, which is in good
agreement with our experimental results.