Catalytic Hydrodefluorination of Fluoroarenes Using Ru(IMe<sub>4</sub>)<sub>2</sub>L<sub>2</sub>H<sub>2</sub> (IMe<sub>4</sub> = 1,3,4,5-Tetramethylimidazol-2-ylidene; L<sub>2</sub> = (PPh<sub>3</sub>)<sub>2</sub>, dppe, dppp, dppm) Complexes
journal contribution
posted on 2017-06-02, 20:16 authored by Mateusz K. Cybulski, Jessica E. Nicholls, John P. Lowe, Mary F. Mahon, Michael K. WhittleseyThe all-trans isomer of Ru(IMe<sub>4</sub>)<sub>2</sub>(PPh<sub>3</sub>)<sub>2</sub>H<sub>2</sub> (<b>ttt-4</b>; IMe<sub>4</sub> = 1,3,4,5-tetramethylimidazol-2-ylidene)
reacts with C<sub>6</sub>F<sub>6</sub> at 70 °C to afford the
hydride fluoride complex Ru(IMe<sub>4</sub>)<sub>2</sub>(PPh<sub>3</sub>)<sub>2</sub>HF (<b>ttt</b>-<b>6</b>). At room temperature, <b>ttt</b>-<b>6</b> reacts with Et<sub>3</sub>SiH to give a
mixture of products, one of which is assigned as the silyl trihydride
complex Ru(IMe<sub>4</sub>)<sub>2</sub>(PPh<sub>3</sub>)(SiEt<sub>3</sub>)H<sub>3</sub> (<b>8</b>) by comparison to the isolated
and structurally characterized analogue Ru(IMe<sub>4</sub>)<sub>2</sub>(PPh<sub>3</sub>)(SiPh<sub>3</sub>)H<sub>3</sub> (<b>9</b>).
As <b>ttt-4</b> was re-formed cleanly upon heating <b>ttt</b>-<b>6</b> with Et<sub>3</sub>SiH, it was tested in the catalytic
hydrodefluorination (HDF) of C<sub>6</sub>F<sub>6</sub> (10 mol %,
90 °C), along with <b>9</b>, Ru(IMe<sub>4</sub>)<sub>2</sub>(P-P)HF (P-P = Ph<sub>2</sub>P(CH<sub>2</sub>)<sub>2</sub>PPh<sub>2</sub> (dppe, <b>cct</b>-<b>13</b>), Ph<sub>2</sub>P(CH<sub>2</sub>)<sub>3</sub>PPh<sub>2</sub> (dppp, <b>cct</b>-<b>14</b>), Ph<sub>2</sub>PCH<sub>2</sub>PPh<sub>2</sub> (dppm, <b>cct</b>-<b>15</b>)), Ru(IEt<sub>2</sub>Me<sub>2</sub>)<sub>2</sub>(PPh<sub>3</sub>)<sub>2</sub>HF (<b>cct</b>-<b>7</b>; IEt<sub>2</sub>Me<sub>2</sub> = 1,3-diethyl-4,5-dimethylimidazol-2-ylidene)),
and Ru(IEt<sub>2</sub>Me<sub>2</sub>)<sub>2</sub>(dppe)<sub>2</sub>HF (<b>cct</b>-<b>16</b>) for comparison. Both <b>cct</b>-<b>13</b> and <b>cct</b>-<b>14</b> brought
about near-quantitative conversion to C<sub>6</sub>FH<sub>5</sub> in
24 h, in comparison to ca. 50% conversion with <b>ttt-4</b> in
144 h.
