10.1021/om500758j.s002
Papri Bhattacharya
Papri
Bhattacharya
Jeanette A. Krause
Jeanette A.
Krause
Hairong Guan
Hairong
Guan
Activation of Dihydrogen and Silanes by Cationic Iron
Bis(phosphinite) Pincer Complexes
American Chemical Society
2014
HBF
BF
HCO 2H
2PO
pincer structure
hydride complexes
electron transfer pathway
iPr 2N
H 2
pincer products
acids CF 3CO
alternative method
H 2.
Ph 3C
iPr 2NEt
basicity order
hydride ligand
CD 3CN results
2014-11-10 00:00:00
Dataset
https://acs.figshare.com/articles/dataset/Activation_of_Dihydrogen_and_Silanes_by_Cationic_Iron_Bis_phosphinite_Pincer_Complexes/2237188
Treatment
of iron POCOP-pincer hydride complexes <i>cis</i>-[2,6-(<sup>i</sup>Pr<sub>2</sub>PO)<sub>2</sub>C<sub>6</sub>H<sub>3</sub>]Fe(H)(PMe<sub>3</sub>)<sub>2</sub> (<b>1-H</b>), [2,6-(<sup>i</sup>Pr<sub>2</sub>PO)<sub>2</sub>C<sub>6</sub>H<sub>3</sub>]Fe(H)(PMe<sub>3</sub>)(CO) (<b>2-H</b>, <i>trans</i> H/CO; <b>2</b>′<b>-H</b>, <i>cis</i> H/CO), and <i>cis</i>-[2,6-(<sup>i</sup>Pr<sub>2</sub>PO)<sub>2</sub>C<sub>6</sub>H<sub>3</sub>]Fe(H)(CO)<sub>2</sub> (<b>3-H</b>) with HBF<sub>4</sub>·Et<sub>2</sub>O in CD<sub>3</sub>CN/THF-<i>d</i><sub>8</sub> results in a rapid evolution of H<sub>2</sub>. Except for the reaction of <b>1-H</b>, which leads to decomposition
of the pincer structure, all other hydrides are converted cleanly
to acetonitrile-trapped cationic complexes. Protonation of these hydrides
with the weaker acids CF<sub>3</sub>CO<sub>2</sub>H and HCO<sub>2</sub>H establishes the basicity order of <b>1-H</b> > <b>2-H</b> > <b>2</b>′<b>-H</b> > <b>3-H</b>, with <b>3-H</b> bearing the least basic hydride ligand. An
alternative method of abstracting hydride by [Ph<sub>3</sub>C]<sup>+</sup>[BF<sub>4</sub>]<sup>−</sup> gives complicated products;
the reaction of <b>2-H</b> generates two pincer products, [HPMe<sub>3</sub>]<sup>+</sup>[BF<sub>4</sub>]<sup>−</sup> and Gomberg’s
dimer, which supports a single electron transfer pathway. Cationic
complexes {[2,6-(<sup>i</sup>Pr<sub>2</sub>PO)<sub>2</sub>C<sub>6</sub>H<sub>3</sub>]Fe(CO)(PMe<sub>3</sub>)(CH<sub>3</sub>CN)}<sup>+</sup>[BF<sub>4</sub>]<sup>−</sup> (<b>2</b><sup><b>+</b></sup><b>-BF</b><sub><b>4</b></sub>, <i>trans</i> CO/CH<sub>3</sub>CN) and <i>cis</i>-{[2,6-(<sup>i</sup>Pr<sub>2</sub>PO)<sub>2</sub>C<sub>6</sub>H<sub>3</sub>]Fe(CO)<sub>2</sub>(CH<sub>3</sub>CN)}<sup>+</sup>[BF<sub>4</sub>]<sup>−</sup> (<b>3</b><sup><b>+</b></sup><b>-BF</b><sub><b>4</b></sub>) are prepared from protonation of <b>2-H</b> (or <b>2</b>′<b>-H</b>) and <b>3-H</b> with
HBF<sub>4</sub>·Et<sub>2</sub>O, respectively. Both compounds
react with H<sub>2</sub> with the aid of <sup>i</sup>Pr<sub>2</sub>NEt to yield neutral hydride complexes and [<sup>i</sup>Pr<sub>2</sub>N(H)Et]<sup>+</sup>[BF<sub>4</sub>]<sup>−</sup>. In addition,
they catalyze the hydrosilylation of benzaldehyde and acetophenone
with (EtO)<sub>3</sub>SiH and show higher catalytic activity than
the neutral hydrides <b>2-H</b>/<b>2</b>′<b>-H</b> and <b>3-H</b>. The mechanism for the formation of <b>2</b><sup><b>+</b></sup><b>-BF</b><sub><b>4</b></sub> and the X-ray structure of <b>2</b><sup><b>+</b></sup><b>-BF</b><sub><b>4</b></sub> are also described.