Synthesis and Small Molecule Reactivity of <i>trans</i>-Dihydride Isomers of Ru(NHC)<sub>2</sub>(PPh<sub>3</sub>)<sub>2</sub>H<sub>2</sub> (NHC = N‑Heterocyclic Carbene)
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Abstract
Addition of IMe<sub>4</sub> (1,3,4,5-tetramethylimidazol-2-ylidene)
to Ru(PPh<sub>3</sub>)<sub>3</sub>HCl (in the presence
of H<sub>2</sub>) or Ru(PPh<sub>3</sub>)<sub>4</sub>H<sub>2</sub> gave the all-trans isomer of Ru(IMe<sub>4</sub>)<sub>2</sub>(PPh<sub>3</sub>)<sub>2</sub>H<sub>2</sub> (<b>1a</b>), whereas 1,3-diethyl-4,5-dimethylimidazol-2-ylidene (IEt<sub>2</sub>Me<sub>2</sub>) reacted with Ru(PPh<sub>3</sub>)<sub>4</sub>H<sub>2</sub> to form <i>cis</i>,<i>cis</i>,<i>trans</i>-Ru(IEt<sub>2</sub>Me<sub>2</sub>)<sub>2</sub>(PPh<sub>3</sub>)<sub>2</sub>H<sub>2</sub> (<b>2b</b>). H/D exchange of <b>1a</b> with C<sub>6</sub>D<sub>6</sub> (elevated temperature) or D<sub>2</sub> (room
temperature) gave Ru(IMe<sub>4</sub>)<sub>2</sub>(PPh<sub>3</sub>)<sub>2</sub>HD (<b>1a-HD</b>) and Ru(IMe<sub>4</sub>)<sub>2</sub>(PPh<sub>3</sub>)<sub>2</sub>D<sub>2</sub> (<b>1a-D</b><sub><b>2</b></sub>). CO reacted
with <b>1a</b> to give a mixture of Ru(IMe<sub>4</sub>)<sub>2</sub>(PPh<sub>3</sub>)(CO)H<sub>2</sub> (<b>3</b>) and Ru(IMe<sub>4</sub>)<sub>2</sub>(CO)<sub>3</sub> (<b>4</b>); <b>2b</b> reacted in a similar manner,
although more slowly, allowing isolation of the monocarbonyl species
Ru(IEt<sub>2</sub>Me<sub>2</sub>)<sub>2</sub>(PPh<sub>3</sub>)(CO)H<sub>2</sub> (<b>5</b>). Insertion
of CO<sub>2</sub> into one of the Ru–H bonds of <b>1a</b> and <b>2b</b> generated mixtures of major and minor isomers
of the κ<sup>2</sup>-formate complexes Ru(IMe<sub>4</sub>)<sub>2</sub>(PPh<sub>3</sub>)(OCHO)H (<b>7</b>/<b>8</b>) and Ru(IEt<sub>2</sub>Me<sub>2</sub>)<sub>2</sub>(PPh<sub>3</sub>)(OCHO)H (<b>9</b>/<b>10</b>). The hydridic
nature of <b>1a</b> and <b>2b</b> was apparent by their
reactivity toward MeI, which gave [Ru(IMe<sub>4</sub>)<sub>2</sub>(PPh<sub>3</sub>)<sub>2</sub>H]I (<b>11</b>), Ru(IEt<sub>2</sub>Me<sub>2</sub>)<sub>2</sub>(PPh<sub>3</sub>)HI
(<b>12</b>), [Ru(IEt<sub>2</sub>Me<sub>2</sub>)<sub>2</sub>(PPh<sub>3</sub>)<sub>2</sub>H]I (<b>13</b>), and Ru(IEt<sub>2</sub>Me<sub>2</sub>)(PPh<sub>3</sub>)<sub>2</sub>HI (<b>14</b>). Complexes <b>1a</b>, <b>2b</b>, <b>5</b>, <b>9</b>, <b>11</b>, <b>13</b>, and <b>14</b> were structurally characterized
