ja505309j_si_002.cif (3.08 MB)
Fine-Tuning the Energy Barrier for Metal-Mediated Dinitrogen NN Bond Cleavage
dataset
posted on 2014-07-16, 00:00 authored by Andrew
J. Keane, Brendan L. Yonke, Masakazu Hirotsu, Peter Y. Zavalij, Lawrence R. SitaExperimental data support a mechanism for NN bond cleavage
within a series of group 5 bimetallic dinitrogen complexes of general
formula, {Cp*M[N(iPr)C(R)N(iPr)]}2(μ-N2) (Cp* = η5-C5Me5) (M = Nb, Ta), that proceeds
in solution through an intramolecular “end-on-bridged”
(μ-η1:η1-N2) to
“side-on-bridged” (μ-η2:η2-N2) isomerization process to quantitatively provide
the corresponding bimetallic bis(μ-nitrido) complexes, {Cp*M[N(iPr)C(R)N(iPr)](μ-N)}2. It is further demonstrated that subtle changes in the steric
and electronic features of the distal R-substituent, where R = Me,
Ph and NMe2, can serve to modulate the magnitude of the
free energy barrier height for NN bond cleavage as assessed
by kinetic studies and experimentally derived activation parameters.
The origin of the contrasting kinetic stability of the first-row congener,
{Cp*V[N(iPr)C(Me)N(iPr)]}2(μ-η1:η1-N2) toward NN bond cleavage is rationalized in
terms of a ground-state electronic structure that favors a significantly
less-reduced μ-N2 fragment.