10.1021/acs.inorgchem.5b01102.s002
Raja Pal
Raja
Pal
Thomas L. Groy
Thomas L.
Groy
Ryan J. Trovitch
Ryan J.
Trovitch
Conversion of Carbon Dioxide to Methanol Using a C–H
Activated Bis(imino)pyridine Molybdenum Hydroboration Catalyst
American Chemical Society
2015
CO 2 reduction
methoxide formation turnover frequency
CO 2 hydroboration
Mo hydroboration catalyst
Ph
CO 2
H 3 COBPin
2PPr
PDI imine substituent
TOF
2015-08-03 00:00:00
Dataset
https://acs.figshare.com/articles/dataset/Conversion_of_Carbon_Dioxide_to_Methanol_Using_a_C_H_Activated_Bis_imino_pyridine_Molybdenum_Hydroboration_Catalyst/2145088
Using
a multistep synthetic pathway, a bis(imino)pyridine (or pyridine diimine,
PDI) molybdenum catalyst for the selective conversion of carbon dioxide
into methanol has been developed. Starting from (<sup>Ph2PPr</sup>PDI)Mo(CO), I<sub>2</sub> addition afforded [(<sup>Ph2PPr</sup>PDI)MoI(CO)][I],
which features a seven-coordinate Mo(II) center. Heating this complex
to 100 °C under vacuum resulted in CO loss and the formation
of [(<sup>Ph2PPr</sup>PDI)MoI][I]. Reduction of [(<sup>Ph2PPr</sup>PDI)MoI][I] in the presence of excess K/Hg yielded (κ<sup>6</sup>-<i>P</i>,<i>N</i>,<i>N</i>,<i>N</i>,<i>C</i>,<i>P</i>-<sup>Ph2PPr</sup>PDI)MoH following methylene group C–H activation at the α-position
of one PDI imine substituent. The addition of CO<sub>2</sub> to (κ<sup>6</sup>-<i>P</i>,<i>N</i>,<i>N</i>,<i>N</i>,<i>C</i>,<i>P</i>-<sup>Ph2PPr</sup>PDI)MoH resulted in facile insertion to generate the respective η<sup>1</sup>-formate complex, (κ<sup>6</sup>-<i>P</i>,<i>N</i>,<i>N</i>,<i>N</i>,<i>C</i>,<i>P</i>-<sup>Ph2PPr</sup>PDI)Mo(OCOH). When low pressures
of CO<sub>2</sub> were added to solutions of (κ<sup>6</sup>-<i>P</i>,<i>N</i>,<i>N</i>,<i>N</i>,<i>C</i>,<i>P</i>-<sup>Ph2PPr</sup>PDI)MoH containing
pinacolborane, the selective formation of H<sub>3</sub>COBPin and
O(BPin)<sub>2</sub> was observed along with precatalyst regeneration.
When HBPin was limited, H<sub>2</sub>C(OBPin)<sub>2</sub> was observed
as an intermediate and (κ<sup>6</sup>-<i>P</i>,<i>N</i>,<i>N</i>,<i>N</i>,<i>C</i>,<i>P</i>-<sup>Ph2PPr</sup>PDI)Mo(OCOH) remained present
throughout CO<sub>2</sub> reduction. The hydroboration of CO<sub>2</sub> to H<sub>3</sub>COBPin was optimized and 97% HBPin utilization by
0.1 mol % (κ<sup>6</sup>-<i>P</i>,<i>N</i>,<i>N</i>,<i>N</i>,<i>C</i>,<i>P</i>-<sup>Ph2PPr</sup>PDI)MoH was demonstrated over 8 h at
90 °C, resulting in a methoxide formation turnover frequency
(TOF) of 40.4 h<sup>–1</sup> (B–H utilization TOF =
121.2 h<sup>–1</sup>). Hydrolysis of the products and distillation
at 65 °C allowed for MeOH isolation. The mechanism of (κ<sup>6</sup>-<i>P</i>,<i>N</i>,<i>N</i>,<i>N</i>,<i>C</i>,<i>P</i>-<sup>Ph2PPr</sup>PDI)MoH mediated CO<sub>2</sub> hydroboration is presented in the
context of these experimental observations. Notably, (κ<sup>6</sup>-<i>P</i>,<i>N</i>,<i>N</i>,<i>N</i>,<i>C</i>,<i>P</i>-<sup>Ph2PPr</sup>PDI)MoH is the first Mo hydroboration catalyst capable of converting
CO<sub>2</sub> to MeOH, and the importance of this study as it relates
to previously described catalysts is discussed.