10.1021/acs.organomet.0c00156.s001
Lara Cancela
Lara
Cancela
Miguel A. Esteruelas
Miguel A.
Esteruelas
Ana M. López
Ana M.
López
Montserrat Oliván
Montserrat
Oliván
Enrique Oñate
Enrique
Oñate
Ainhoa San-Torcuato
Ainhoa
San-Torcuato
Andrea Vélez
Andrea
Vélez
Osmium- and Iridium-Promoted C–H Bond Activation
of 2,2′-Bipyridines and Related Heterocycles: Kinetic and Thermodynamic
Preferences
American Chemical Society
2020
BF
benzimidazolium tetrafluoroborate
OsH 6
imidazolium tetrafluoroborate yields
Thermodynamic Preferences
iridium-pentahydride IrH 5
Related Heterocycles
deuteride counterpart OsD 6
bond
C py
P i Pr 3
C NHC
reactivity pattern
substrates pyridyl-benzimidazolium
metalated carbon atom
2020-05-22 22:30:32
Journal contribution
https://acs.figshare.com/articles/journal_contribution/Osmium-_and_Iridium-Promoted_C_H_Bond_Activation_of_2_2_-Bipyridines_and_Related_Heterocycles_Kinetic_and_Thermodynamic_Preferences/12361028
The <i>d</i><sup>2</sup>-hexahydride complex OsH<sub>6</sub>(P<sup>i</sup>Pr<sub>3</sub>)<sub>2</sub> (<b>1</b>)
promotes the activation of C–H bonds of 2,2′-bipyridines
and related heterocycles. The study of the same reactions with the
deuteride counterpart OsD<sub>6</sub>(P<sup>i</sup>Pr<sub>3</sub>)<sub>2</sub> (<b>1</b>-<i>d</i>) reveals that the activation
of the C–H bonds situated in the sterically less hindered positions
is kinetically preferred. However, the isolated products are the result
of the thermodynamic control of the reactions. Thus, reactions of <b>1</b> with 2,2′-bipyridine, 6-phenyl-2,2′-bipyridine,
and 6-methyl-2,2′-bipyridine give the “rollover cyclometalation”
products OsH<sub>3</sub>{κ<sup>2</sup>-<i>C</i>,<i>N</i>-[C<sub>5</sub>(R)H<sub>2</sub>N-py]}(P<sup>i</sup>Pr<sub>3</sub>)<sub>2</sub> (R = H (<b>2</b>), Ph (<b>3</b>),
Me (<b>4</b>)), whereas 3,5-dimethyl-6-phenyl-2,2′-bipyridine
affords OsH<sub>2</sub>{κ<sup>3</sup>-<i>C</i>,<i>N</i>,<i>C</i>-[C<sub>5</sub>H<sub>3</sub>N-(Me)<sub>2</sub>py-C<sub>5</sub>H<sub>4</sub>]}(P<sup>i</sup>Pr<sub>3</sub>)<sub>2</sub> (<b>5</b>), containing a dianionic C,N,C-pincer
ligand. The behavior of substrates pyridyl-benzimidazolium and -imidazolium
is similar. Reaction of <b>1</b> with 3-methyl-1-(6-phenylpyridin-2-yl)-1<i>H</i>-benzimidazolium tetrafluoroborate leads to OsH<sub>3</sub>{κ<sup>2</sup>-<i>C</i>,<i>C</i>-[MeBzim-C<sub>5</sub>(Ph)H<sub>2</sub>N]}(P<sup>i</sup>Pr<sub>3</sub>)<sub>2</sub> (<b>6</b>), bearing an anionic C<sub>py</sub>,C<sub>NHC</sub>-chelate. On the other hand, 3-methyl-1-(6-phenylpyridin-2-yl)-1<i>H</i>-imidazolium tetrafluoroborate yields [OsH<sub>2</sub>{κ<sup>3</sup>-<i>C</i>,<i>N</i>,<i>C</i>-(MeIm-py-C<sub>6</sub>H<sub>4</sub>)}(P<sup>i</sup>Pr<sub>3</sub>)<sub>2</sub>]BF<sub>4</sub> (<b>7</b>), containing a monoanionic C,N,C-pincer with
a NHC-unit coordinated in an abnormal fashion. The reactivity pattern
of these substrates is also observed with the <i>d</i><sup>4</sup>-iridium-pentahydride IrH<sub>5</sub>(P<sup>i</sup>Pr<sub>3</sub>)<sub>2</sub> (<b>8</b>), which has generated IrH<sub>2</sub>{κ<sup>2</sup>-<i>C</i>,<i>N</i>-[C<sub>5</sub>(R)H<sub>2</sub>N-py]}(P<sup>i</sup>Pr<sub>3</sub>)<sub>2</sub> (R = H, (<b>9</b>), Ph (<b>10</b>)) and
IrH{κ<sup>3</sup>-<i>C</i>,<i>N</i>,<i>C</i>-[C<sub>5</sub>H<sub>3</sub>N-(Me<sub>2</sub>)py-C<sub>5</sub>H<sub>4</sub>]}(P<sup>i</sup>Pr<sub>3</sub>)<sub>2</sub> (<b>11</b>). The osmium(IV)–carbon bonds display a higher degree
of covalency than the iridium(III)–carbon bonds. In contrast
to <b>2</b>, the metalated carbon atom of <b>9</b> undergoes
the addition of a proton of methanol to give [IrH<sub>2</sub>{κ<sup>2</sup>-<i>N</i>,<i>N</i>-(bipy)}(P<sup>i</sup>Pr<sub>3</sub>)<sub>2</sub>]BF<sub>4</sub> (<b>12</b>).