Hydridorhodathiaboranes: Synthesis, Characterization,
and Reactivity
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Abstract
The
reaction between pyridine and [8,8-(PPh<sub>3</sub>)<sub>2</sub>-<i>nido</i>-8,7-RhSB<sub>9</sub>H<sub>10</sub>] (<b>1</b>) has given the opportunity to synthesize a new family of
11-vertex hydridorhodathiaboranes that feature boron-bound N-heterocyclic
ligands. To explore the scope of this reaction, <b>1</b> has
been treated with the methylpyridine isomers (picolines) 2-Me-NC<sub>5</sub>H<sub>4</sub>, 3-Me-NC<sub>5</sub>H<sub>4</sub>, and 4-Me-NC<sub>5</sub>H<sub>4</sub>, affording the picoline ligated clusters [8,8,8-(H)(PPh<sub>3</sub>)<sub>2</sub>-9-(L)-<i>nido</i>-8,7-RhSB<sub>9</sub>H<sub>9</sub>], where L = 2-Me-NC<sub>5</sub>H<sub>4</sub> (<b>3</b>), 3-Me-NC<sub>5</sub>H<sub>4</sub> (<b>4</b>), 4-Me-NC<sub>5</sub>H<sub>4</sub> (<b>5</b>). Thermal treatment of these <i>nido</i> clusters leads to dehydrogenation and the formation
of <i>isonido</i>/<i>closo-</i>[1,1-(PPh<sub>3</sub>)<sub>2</sub>-3-(L)-1,2-RhSB<sub>9</sub>H<sub>8</sub>] (<b>9</b>–<b>11</b>). Compounds <b>3</b>–<b>5</b> react with ethylene to form [1,1-(η<sup>2</sup>-C<sub>2</sub>H<sub>4</sub>)(PPh<sub>3</sub>)-3-(L)-1,2-RhSB<sub>9</sub>H<sub>8</sub>] (<b>13</b>–<b>15</b>). Similarly, treatment
of <b>3</b>–<b>5</b> with carbon monoxide produces
[1,1-(CO)(PPh<sub>3</sub>)-3-(L)-1,2-RhSB<sub>9</sub>H<sub>8</sub>] (<b>17</b>–<b>19</b>). These series of η<sup>2</sup>-C<sub>2</sub>H<sub>4</sub> and CO ligated 11-vertex <i>isonido</i>/<i>closo</i>-rhodathiaboranes result from
the substitution of one PPh<sub>3</sub> ligand by ethylene or CO together
with H<sub>2</sub> loss and a concomitant <i>nido</i> to <i>closo</i>/<i>isonido</i> cluster structural transformation.
The reactivity of <b>3</b>–<b>5</b> with propene,
1-hexene, and cyclohexene under a hydrogen atmosphere is also reported
and compared with the reactivity of the pyridine ligated analogue
[8,8,8-(H)(PPh<sub>3</sub>)<sub>2</sub>-9-(NC<sub>5</sub>H<sub>5</sub>)-<i>nido</i>-8,7-RhSB<sub>9</sub>H<sub>9</sub>] (<b>2</b>). Low-temperature NMR studies have allowed the characterization
of intermediates which undergo inter- and intramolecular exchange
processes, depending on the nature of the N-heterocyclic ligand. The
CO ligand enhances the nonrigidity of the cluster, opening mechanisms
of H<sub>2</sub> loss
