Rhodium and Iridium Complexes with a New Scorpionate Phosphane Ligand

A straightforward synthesis of a new hybrid scorpionate ligand [(allyl)<sub>2</sub>B­(CH<sub>2</sub>PPh<sub>2</sub>)­(Pz)]<sup>−</sup> ([A<sub>2</sub>BPN]<sup>−</sup>) is reported. Coordination to rhodium resulted in square-planar complexes [Rh­(κ<sup>2</sup>-A<sub>2</sub>BPN)­(L)­(L′)] [L = L′ = <sup>1</sup>/<sub>2</sub>cod (1,5-cyclooctadiene), CN<sup><i>t</i></sup>Bu, CO (<b>6</b>); L = CO, L′ = NH<sub>3</sub>, pyridine, PPh<sub>3</sub>, PMe<sub>3</sub>] for which spectroscopic data and the molecular structure of [Rh­(κ<sup>2</sup>-A<sub>2</sub>BPN)­(CO)­PPh<sub>3</sub>] (<b>11</b>) indicate the ligand to be κ<i>N</i>,κ<i>P</i>-bound to rhodium with two dangling free allyl groups. Studies in solution point out that the six-membered Rh–N–N–B–C–P metallacycle undergoes a fast inversion in all of them. The bis­(carbonyl) complex <b>6</b> easily loses a CO group to give [{Rh­(A<sub>2</sub>BPN)­(CO)}<sub>2</sub>], a dinuclear compound in which two mononuclear subunits are brought together by two bridging allyl groups. Coordination to iridium is dominated by a tripodal κ<i>N</i>,κ<i>P</i>,η<sup>2</sup>-CC binding mode in the TBPY-5 complexes [Ir­(κ<sup>3</sup>-A<sub>2</sub>BPN)­(L)­(L′)] [L = L′ = <sup>1</sup>/<sub>2</sub>cod (<b>3</b>), CN<sup><i>t</i></sup>Bu (<b>5</b>), CO (<b>7</b>); L = CO, L′ = PPh<sub>3</sub> (<b>13</b>), PMe<sub>3</sub> (<b>14</b>), H<sub>2</sub>CCH<sub>2</sub>, (<b>17</b>), MeO<sub>2</sub>CCCCO<sub>2</sub>Me (dmad, <b>18</b>)], as confirmed by the single-crystal structure determination of complexes <b>3</b> and <b>18</b>. A fast exchange between the two allyl arms is observed for complexes having L = L′ (<b>3</b>, <b>5</b>, and <b>7</b>), while those having CO and L ligands (<b>14</b>, <b>17</b>, and <b>18</b>) were found to be nonfluxional species. An exception is complex <b>13</b>, which establishes an equilibrium with the SP-4 configuration. Protonation reactions on complexes <b>13</b> and <b>14</b> with HCl yielded the hydride complex [Ir­(κ<sup>2</sup>-A<sub>2</sub>BPN)­(CO)­(Cl)­(H)­PPh<sub>3</sub>] (<b>15</b>) and the <i>C</i>-alkyl compound [Ir­{κ<sup>3</sup>-(allyl)­B­(CH<sub>2</sub>CHCH<sub>3</sub>)­(CH<sub>2</sub>PPh<sub>2</sub>)­(Pz)}­(Cl)­(CO)­PMe<sub>3</sub>] (<b>16</b>), respectively. The bis­(isocyanide) complex <b>5</b> reacts with dmad to form [Ir­(κ<sup>2</sup>-A<sub>2</sub>BPN)­(CN<sup><i>t</i></sup>Bu)<sub>2</sub>(dmad)]. On the whole, the electronic density provided to the metal by the [A<sub>2</sub>BPN]<sup>−</sup> ligand is very sensitive to the coordination mode. The basicity of the new ligand is similar to that of the Tp<sup>Me2</sup> ligand in the κ<i>N</i>,κ<i>P</i> mode but comparable to Tp if coordinated in the κ<i>N</i>,κ<i>P</i>,η<sup>2</sup>-CC mode.