OsXCl(phosphine)₂(diamine) and OsXCl(diphosphine)(diamine) (X = Cl, H) Complexes for Ketone Hydrogenation

The osmium complex <i>trans</i>-[OsCl₂(PPh₃)₂(en)] (<b>2</b>) was prepared by reaction of [OsCl₂(PPh₃)₃] (<b>1a</b>) with ethylenediamine (en), whereas the diphosphine derivatives <i>trans</i>-[OsCl₂(dppf)­(NN)] (NN = en (<b>3</b>), bn (<b>4</b>; bn = 1,4-butanediamine)) and <i>trans</i>-[OsCl₂(dpbp)­(en)] (<b>5</b>) were obtained from <b>1a</b>, dppf or dpbp, and the corresponding NN ligand in CH₂Cl₂ or toluene. An X-ray diffraction study has been provided for <b>3</b>. The isolation of the chiral derivatives <i>trans</i>-[OsCl₂(diphosphine)­((<i>R</i>,<i>R</i>)-dpen)] (diphosphine = dppf (<b>6</b>), dpbp (<b>7</b>), (<i>R</i>,<i>R</i>)-skewphos (<b>8</b>)) was achieved by reacting <b>1a</b> with the diphosphine and (<i>R</i>,<i>R</i>)-dpen in toluene. Treatment of the precursor [Os₂Cl₄(P­(<i>m</i>-tolyl)₃)₅] (<b>1b</b>) with en afforded [OsCl₂(P­(<i>m</i>-tolyl)₃)₂(en)] (<b>9</b>), while reaction of <b>1b</b> with dppb and <i>N</i>,<i>N</i>-dmen gave [OsCl₂(dppb)­(<i>N</i>,<i>N</i>-dmen)] (<b>10</b>). The chiral derivatives [OsCl₂(diphosphine)­(NN)] (<b>11</b>–<b>21</b>; diphosphine = (<i>S</i>)-MeObiphep, (<i>R</i>)-MeObiphep, (<i>R</i>)-xylMeObiphep, (<i>R</i>)-binap, (<i>S</i>)-xylbinap, (<i>R</i>)-xylbinap, (<i>R,S</i>)-Josiphos*; NN = en, (<i>R,R</i>)-dpen, (<i>R</i>)-daipen, (<i>R,R</i>)-dppn) were prepared from <b>1b</b> and the corresponding diphosphine and NN ligands in toluene. The monohydride <i>trans</i>-[OsHCl­(P­(<i>m</i>-tolyl)₃)₂(en)] (<b>22</b>) was synthesized by reaction of <b>1b</b> with H₂ (1 atm) in the presence of NEt₃, followed by addition of en in toluene. Similarly, <i>trans</i>-[OsHCl­(dppf)­(en)] (<b>23</b>) was synthesized from <b>1a</b>, H₂, and NEt_3, followed by treatment with dppf and en. Complexes <b>2</b>–<b>5</b>, <b>9</b>, <b>10</b>, <b>22</b>, and <b>23</b> efficiently catalyzed the hydrogenation of acetophenone with H₂ under low pressure (5 atm) at 60–70 °C in ethanol (1–2 mol % of NaOEt) with the ratio S/C = 5000–10000. The chiral derivatives <b>6</b>–<b>8</b> and <b>11</b>–<b>21</b> afforded the asymmetric hydrogenation of acetophenone with up to 90% ee by combining bulky xylyl-substituted MeObiphep or binap-type ligands with (<i>R</i>)-daipen or (<i>R</i>,<i>R</i>)-dpen ligands. Catalytic transfer hydrogenation of acetophenone was observed with <b>3</b>, <b>6</b>, and <b>7</b> (S/C = 2000) in 2-propanol and in the presence of NaO<i>i</i>Pr (2 mol %) at 60–82 °C