Molecular
and Silica-Supported Molybdenum Alkyne Metathesis
Catalysts: Influence of Electronics and Dynamics on Activity Revealed
by Kinetics, Solid-State NMR, and Chemical Shift Analysis
Deven
P. Estes
Christopher P. Gordon
Alexey Fedorov
Wei-Chih Liao
Henrike Ehrhorn
Celine Bittner
Manuel Luca Zier
Dirk Bockfeld
Ka Wing Chan
Odile Eisenstein
Christophe Raynaud
Matthias Tamm
Christophe Copéret
10.1021/jacs.7b09934.s003
https://acs.figshare.com/articles/dataset/Molecular_and_Silica-Supported_Molybdenum_Alkyne_Metathesis_Catalysts_Influence_of_Electronics_and_Dynamics_on_Activity_Revealed_by_Kinetics_Solid-State_NMR_and_Chemical_Shift_Analysis/5615716
Molybdenum-based
molecular alkylidyne complexes of the type [MesCMo{OC(CH<sub>3</sub>)<sub>3–<i>x</i></sub>(CF<sub>3</sub>)<sub><i>x</i></sub>}<sub>3</sub>] (<b>MoF</b><sub><b>0</b></sub>, <i>x</i> = 0; <b>MoF</b><sub><b>3</b></sub>, <i>x</i> = 1; <b>MoF</b><sub><b>6</b></sub>, <i>x</i> = 2; <b>MoF</b><sub><b>9</b></sub>, <i>x</i> = 3; Mes = 2,4,6-trimethylphenyl)
and their silica-supported analogues are prepared and characterized
at the molecular level, in particular by solid-state NMR, and their
alkyne metathesis catalytic activity is evaluated. The <sup>13</sup>C NMR chemical shift of the alkylidyne carbon increases with increasing
number of fluorine atoms on the alkoxide ligands for both molecular
and supported catalysts but with more shielded values for the supported
complexes. The activity of these catalysts increases in the order <b>MoF</b><sub><b>0</b></sub> < <b>MoF</b><sub><b>3</b></sub> < <b>MoF</b><sub><b>6</b></sub> before
sharply decreasing for <b>MoF</b><sub><b>9</b></sub>,
with a similar effect for the supported systems (<b>MoF</b><sub><b>0</b></sub> ≈ <b>MoF</b><sub><b>9</b></sub> < <b>MoF</b><sub><b>6</b></sub> < <b>MoF</b><sub><b>3</b></sub>). This is consistent with the
different kinetic behavior (zeroth order in alkyne for <b>MoF</b><sub><b>9</b></sub> derivatives instead of first order for
the others) and the isolation of stable metallacyclobutadiene intermediates
of <b>MoF</b><sub><b>9</b></sub> for both molecular and
supported species. Detailed solid-state NMR analysis of molecular
and silica-supported metal alkylidyne catalysts coupled with DFT/ZORA
calculations rationalize the NMR spectroscopic signatures and discernible
activity trends at the frontier orbital level: (1) increasing the
number of fluorine atoms lowers the energy of the π*(MC)
orbital, explaining the more deshielded chemical shift values; it
also leads to an increased electrophilicity and higher reactivity
for catalysts up to <b>MoF</b><sub><b>6</b></sub>, prior
to a sharp decrease in reactivity for <b>MoF</b><sub><b>9</b></sub> due to the formation of stable metallacyclobutadiene intermediates;
(2) the silica-supported catalysts are less active than their molecular
analogues because they are less electrophilic and dynamic, as revealed
by their <sup>13</sup>C NMR chemical shift tensors.
2017-10-30 00:00:00
MoF 9 derivatives
13 C NMR chemical shift tensors
MoF 9
MoF 3
MoF 6
deshielded chemical shift values
metallacyclobutadiene intermediates
alkylidyne carbon increases
order MoF 0
Chemical Shift Analysis Molybdenum-based
NMR spectroscopic signatures
DFT
CF
silica-supported metal alkylidyne catalysts
13 C NMR chemical shift
Silica-Supported Molybdenum Alkyne Metathesis Catalysts
fluorine atoms